JP2004095469A - Negative electrode material for nonaqueous electrolyte secondary battery and manufacturing method of same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode material and a manufacturing method of the same having high discharge capacity and discharge/charge efficiency, an excellent cycle life, and stable performance by improving the cycle life of the negative electrode material for a nonaqueous electrolyte secondary battery having an active material phase (a phase reversely reacting with Li) of high capacity such as Si and Sn, and an inactive phase (for example, CoSi<SB>2</SB>). <P>SOLUTION: This manufacturing method conducts mechanical grinding processing (crushing and granulation by grinding) of the negative electrode material obtained by quenching from molten metal with a ball mill type device (an attritor, vibrating ball mill, planetary ball mill or the like), or conducts the mechanical grinding processing of mixture of fine powder of the active material phase and the inactive phase. A contained rate of the active material phase does not change before and after the processing. The active material phase of the negative electrode material subjected to the mechanical grinding processing is fined, and a peak strength of at least one active material phase becomes not more than 50 % of the peak strength before the mechanical grinding processing in an X-ray diffraction pattern. <P>COPYRIGHT: (C)2004,JPO

Description

【００６７】
表１からわかるように、本発明の第１の方法に従って、好ましくは急冷鋳造材をＭＧ処理することによって、高い放電容量を維持したまま、充放電効率と特にサイクル寿命を大きく改善することができ、放電容量と充放電効率が高く、サイクル寿命も良好な負極材料が得られることがわかる。表からわかるように、ピーク強度比が５０％以下になるまでＭＧ処理を行うと、充放電効率とサイクル寿命がいずれも９０％以上と良好になる。原料粉末の鋳造時の冷却速度が速く、活物質相のサイズが小さいほど、短いＭＧ処理時間でピーク強度比を５０％以下にすることができる。ピーク強度比を小さい負極材料を得るには、ロッドミルやボールミルより、アトライター、振動ボールミル、遊星ボールミルを使用する方が効率的である。
【００６８】
原料粉末を冷却速度が１０^２℃／ｓｅｃ未満の通常のインゴット鋳造法により調製した場合には、ピーク強度比が５０％以下の負極材料を得るのに非常に長いＭＧ処理時間が必要となるが、そのように長時間かけてピーク強度比を５０％以下にすれば、原料が急冷材である場合と遜色のない負極特性の結果が得られた。
【００６９】
（実施例２）
本例は、本発明に係る第２の方法による非水電解質二次電池用負極材料の製造を例示する。
【００７０】
活物質相となるＳｉ金属の試薬を乳鉢で粉砕し、分級して、平均粒径の異なる活物質相の粉末を得た。別に、不活性相となるＣｏＳｉ_２を、単ロール急冷法または通常のインゴット鋳造法で鋳造し、乳鉢で粉砕し、分級して、平均粒径約３０μｍの不活性相の粉末を得た。
【００７１】
活物質相のＳｉ粉末と不活性相のＣｏＳｉ_２粉末各１種類ずつを、実施例１と同様にＣｏ−６０％Ｓｉとなる割合で混合し、この混合粉末を実施例１と同様にアトライターを用いてＭＧ処理し、活物質相と不活性相とを有する負極材料の粉末を得た。
【００７２】
比較のために、上記と同様に調製したＳｉ粉末　（−６３μｍに分級、平均粒径１５μｍ）　とＣｏ粉末　（試薬を分級したもの、平均粒径約１５μｍ）　をＣｏ−６０％Ｓｉとなる割合で混合し、この混合粉末をアトライターを用いてメカニカルアロイング　（ＭＡ）　処理し、処理中に不活性相のＣｏＳｉ_２を生成させて、活物質相と不活性相とを有する負極材料を得た。処理条件はＭＧ法と同様であり、処理はアルゴン雰囲気中で行った。
【００７３】
上記２種類の方法で得られた負極材料の電極特性、ピーク強度比　（原料混合粉末のＸ線回折パターンとの比較）　、酸素濃度を実施例１と同様に調べた結果を表２にまとめて示す。また、ＭＧ処理またはＭＡ処理の前後での放電容量を調べた結果も、処理後の負極材料の充放電効率およびサイクル寿命の結果と共に、表２に併記する。
【００７４】
【表２】

【００７５】
表２からわかるように、本発明に従って活物質相のＳｉ粉末と不活性相のＣｏＳｉ_２粉末との混合物をＭＧ処理して得た負極材料は、この処理の前後で活物質相（Ｓｉ）の含有量が実質的に変化せず　（放電容量が実質的に変化しないことで確認）　、放電容量、充放電効率、サイクル寿命のどれもが非常に良好であった。
【００７６】
一方、同組成の負極材料の構成元素であるＳｉ粉末とＣｏ粉末をＭＡ処理して、処理中に不活性相を生成させる方法では、活物質であるＳｉの合金化が完全には進行していない分、放電容量は高いものの、不活性相によるサイクル寿命の改善が不十分で、処理時間を１００　時間と非常に長くしてもサイクル寿命を良好な水準まで改善することができなかった。また、負極材料の酸素濃度が高いため、充放電効率も低くなった。さらに、ＭＡ法では、処理時間によって活物質相のＳｉ含有量が変化するため放電容量の変化が大きく、安定した容量の負極材料を得ることが困難であることもわかる。
【００７７】
なお、ＭＡ法の処理時間０の例からわかるように、活物質相のＳｉ相が不活性相に包囲されず、また微分散していない状態で存在していると、サイクル寿命は５％と著しく低い。本発明では、第１および第２の方法のいずれでも、このＳｉの示す低いサイクル寿命を９０％以上にまで高めることが可能である。
【００７８】
【発明の効果】
本発明によれば、現行の実用リチウムイオン二次電池の負極材料である炭素材料より高容量で、充放電効率とサイクル寿命に優れ、性能が安定した非水電解質二次電池用負極材料を比較的低コストで供給することが可能となり、非水電解質二次電池の小型化、高性能化を可能にする。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a negative electrode material for a non-aqueous electrolyte secondary battery capable of storing and releasing a large amount and reversibly of an alkali metal such as Li, and a method for producing the negative electrode material. Non-aqueous electrolyte secondary batteries include batteries using a liquid non-aqueous electrolyte in which a supporting electrolyte is dissolved in an organic solvent, and batteries using a solid-state non-aqueous electrolyte such as a polymer electrolyte or a gel electrolyte.
[0002]
[Prior art]
With the spread of portable devices, demand for high-capacity non-aqueous electrolyte secondary batteries has increased, and further higher capacities have been demanded.
[0003]
The non-aqueous electrolyte secondary battery currently in practical use is a lithium ion secondary battery using a carbon material for the negative electrode. However, in the case of graphite, the maximum theoretical capacity of graphite is as low as 372 mAh / g. Therefore, there is a limit in increasing the capacity.
[0004]
If the negative electrode is composed of metal Li, the capacity can be increased by a factor of 10 or more as compared with the carbon material, but there is a risk that the metal Li will precipitate in a dendrite form on the negative electrode during charging, break through the separator, and cause a short circuit. Therefore, metal Li cannot be used for the negative electrode of a practical battery from the viewpoint of battery safety.
[0005]
Al, Si, Sn, and their intermetallic compounds, whose theoretical capacity is as high as Li, have been proposed as a new high capacity negative electrode material replacing metal Li. However, these materials have a large capacity and a large expansion and contraction due to charge / discharge instead of high capacity. Therefore, a non-aqueous electrolyte secondary battery using these materials for the negative electrode has a large decrease in capacity due to charge / discharge cycles, and has a remarkably short cycle life.
[0006]
In order to solve this, it has been studied to make the active material phase ultrafine by alloying with an inert element using a mechanical alloying (MA) method. When the active material phase is miniaturized and the periphery of the fine active material phase is surrounded by the inactive phase, a change in volume of the active material phase during charging and discharging is suppressed, and the cycle life is improved.
[0007]
[Problems to be solved by the invention]
However, in an alloy manufactured by the MA method, an active material phase and an inactive phase are generated by an alloying reaction between elements, so that the amount of the active material phase changes in a reaction process. That is, since the amount of the generated active material phase is very sensitive to the progress of the reaction, it is difficult to produce a negative electrode material having a stable capacity. As a result, the non-aqueous electrolyte secondary battery has a problem of a large variation in capacity, which is a problem for a practical battery, and the cycle life is not sufficiently improved. Further, when alloying is performed using pure powder of an element as a raw material, there is a problem that the oxygen concentration of the resulting alloy increases, the irreversible capacity of the negative electrode material increases, and the charge / discharge efficiency decreases. Further, fine elemental powder used in the MA method is expensive.
[0008]
The present invention provides a large amount of occlusion / release of Li (or other alkali metal), and therefore a large charge / discharge capacity when used as a negative electrode material of a non-aqueous electrolyte secondary battery, and repetition of charge / discharge. It is an object of the present invention to provide a stable high-performance negative electrode material for a non-aqueous electrolyte secondary battery and a method for producing the same, which have a small capacity reduction, a very excellent cycle life, a high charge-discharge efficiency, and a small variation in characteristics. .
[0009]
[Means for Solving the Problems]
The present inventor uses a mixture of fine powders of elemental elements constituting the negative electrode material as a raw material, and does not use the MA method of alloying by mixing, granulating, and pulverizing, but collapses and forms by compressing and crushing the prealloyed raw material. It has been found that when the active material phase is made ultra-fine by treatment using a mechanical grinding (MG) method (mechanical grinding treatment) in which grains are repeated, the above-described problems of the MA method can be avoided and the above object can be achieved. .
[0010]
According to the present invention, one or more active material phases composed of one or more elements capable of reversibly reacting with Li, and one or more active material phases selected from a group IIA element, a transition element, a group IIIB element, and a group IVB element of the long period type periodic table are provided. And at least one inert phase composed of at least one element, and a negative electrode material for a non-aqueous electrolyte secondary battery manufactured through mechanical grinding having at least an X-ray diffraction pattern of the negative electrode material. A negative electrode material for a non-aqueous electrolyte secondary battery is provided, wherein the peak intensity of one active material phase is 50% or less of the peak intensity before grinding.
[0011]
The present invention also provides one or more active material phases composed of one or more elements capable of reversibly reacting with Li, and one or more active material phases selected from a group IIA element, a transition element, a group IIIB element, and a group IVB element of the long period periodic table. And a method for producing a negative electrode material for a non-aqueous electrolyte secondary battery having at least one inert phase composed of at least one element selected from the group consisting of:
[0012]
The first method is characterized by subjecting a solid cast from a molten negative electrode material to a mechanical grinding treatment.
Another second production method comprises subjecting a mixture of an active material phase and an inactive phase to mechanical grinding treatment, wherein the content of the active material phase does not substantially change before and after this treatment. I do.
[0013]
In any method, the mechanical grinding treatment is preferably performed using a ball-shaped grinding medium, and the peak intensity of at least one active material phase in the X-ray diffraction pattern of the negative electrode material is the peak intensity before the treatment. It is preferably performed until 50% or less.
[0014]
In the first method, an anode material having both an active material phase and an inactive phase, preferably cast by quenching, is treated by the MG method to ultrafine the structure. Although the structure of the negative electrode material obtained by quenching has been refined to some extent, refinement of the structure by quenching alone is not enough to improve the cycle life. Needs to be further miniaturized. Therefore, the active material phase is made ultra-fine by treating it with the MG method to make the structure ultra-fine.
[0015]
In the first method, it is preferable to rapidly cool the negative electrode material from the molten metal and to refine the structure in advance before the treatment by the MG method, in order to efficiently perform ultrafine refinement of the structure by the MG method in a short time. If the treatment by the MG method is performed for a long time, rapid cooling during casting is not always necessary.
[0016]
In the second method, an inert phase and an active material phase are separately prepared, and the mixture is treated by the MG method. In this case, the size of the particles of each phase in the mixture is the size of the phase. Therefore, regarding the active material phase, since the active material phase can be refined before the treatment by finely pulverizing the particles, there is no need to control the structure by the cooling rate as in the first method. The inert phase having a size of about 5 mm or less is sufficient for improving the cycle characteristics, and need not always be powdered before being treated by the MG method.
[0017]
In the present invention, a negative electrode material having an ultrafine structure generally indicates that the size (average minor axis diameter) of the active material phase is 100 nm or less. The size of the active material phase is preferably 50 nm or less, more preferably 30 nm or less.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
The negative electrode material for a non-aqueous electrolyte secondary battery of the present invention comprises one or more active material phases composed of one or more elements capable of reversibly reacting with Li, a group IIA element of a long period type periodic table, a transition element, It has one or more inert phases composed of one or more elements selected from the group IIIB elements and the group IVB elements, and at least the active material phase is miniaturized to an extent sufficient to improve the cycle life. An inert phase means a phase that does not show substantial reactivity with Li, and may be slightly reactive.
[0019]
Examples of elements that can form a reversible reaction with Li, which constitute the active material phase, are Si, Ge, Sn, Pb, Al, P, Ga, In, and Zn. The active material phase can be composed of one or more of these elements or their alloys. In the present invention, “alloy” is meant to include intermetallic compounds.
[0020]
Desirable active material phases include high capacity Si and / or Sn. That is, the desired active material phase is at least one selected from Si metal, Si alloy (eg, Si—P, Si—Ge), Sn metal, and Sn alloy (eg, Sn—Cu). The alloy may be an intermetallic compound as described above.
[0021]
Examples of one or more elements selected from Group IIA, transition, Group IIIB and Group IVB elements of the Long Periodic Table constituting the inert phase are as follows:
Group IIA elements: Be, Mg, Ca, Sr, Ba, Ra;
Transition elements: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, lanthanoid, actinoid;
Group IIIB elements: B, Al, Ga, Ub, Tl;
Group IVA elements: C, Si, Ge, Sn, Pb.
[0022]
The inert phase is at least one element selected from Mg, Ca, Ba, Ti, V, Cr, W, Mn, Fe, Co, Ni, and Cu, and an alloy containing them (as described above, It is desirable to be comprised from. When the inert phase is composed of an alloy, the alloy can be an alloy of the element constituting the active material phase and another element selected from the above. For example, when the active material phase is composed of Si, the inactive phase is an alloy of Si and another element (eg, CoSi ₂ ).
[0023]
The negative electrode material for a non-aqueous electrolyte secondary battery according to the present invention is a material having one or more active material phases and one or more inactive phases, which has been subjected to mechanical grinding (MG) treatment. In the X-ray diffraction pattern, the peak intensity of at least one active material phase is not more than 50% of the peak intensity before the MG treatment.
[0024]
The peak intensity ratio of the active material phase after the MG treatment to that before the MG treatment is a measure of the ultrafineness of the active material phase by the MG treatment. If the peak intensity ratio is higher than 50%, the ultrafineness of the active material phase is reduced. It is insufficient, and the effect of improving the cycle life cannot be sufficiently achieved. This peak intensity ratio is preferably 40% or less.
[0025]
The ratio between the active material phase and the inactive phase in the negative electrode material is not particularly limited. Generally, the cycle life increases as the number of inert phases increases, but the capacity tends to decrease. The inert phase may be present in such a ratio that a required cycle life is obtained. In the present invention, the active material phase is made ultrafine by being subjected to the treatment by the MG method, so that the effect of improving the cycle life by the inactive phase is more effectively exhibited. As a result, it is possible to sufficiently improve the cycle life even if the ratio of the inactive phase is smaller than in the conventional case, so that a negative electrode material having a high capacity and a sufficient cycle life can be obtained.
[0026]
In the first method for producing a negative electrode material for a nonaqueous electrolyte secondary battery according to the present invention, first, the negative electrode material having the active material phase and the inactive phase described above is cast. For example, the active material phase is a Si phase, and the inactive phase is a Si—Co intermetallic compound (eg, CoSi ₂ ) Phase, a mixture of Si and Co blended so as to be more Si-rich than the composition of the intermetallic compound is charged into a melting furnace and heated and melted to obtain a molten metal made of a Si-Co alloy. The relative proportion between the active material phase and the inactive phase that precipitates during cooling from the molten metal is determined by the degree of Si richness, that is, the raw material composition. Such conditions can be easily set from the equilibrium diagram.
[0027]
When the raw material contains an easily oxidizable element, the heating atmosphere is an inert gas or a vacuum. However, since there are some compositions which are not so affected by the atmosphere, the atmosphere adjustment is not necessarily required. The heating method includes high-frequency induction heating, arc melting, plasma melting, resistance heating, and the like, and any method may be used. In melting, it is important to form a compositionally uniform molten metal.
[0028]
The molten alloy is preferably 1 × 10 ² Casting is performed by quenching at a cooling rate of at least ° C / sec to obtain a solid of the negative electrode material. During cooling, the active material phase (eg, Si) and the inert phase (eg, CoSi) ₂ ) Is deposited to obtain a negative electrode material having a structure containing an active material phase and an inactive phase. However, by rapidly cooling, the structure of the obtained material is refined to some extent. The cooling rate is more preferably 1 × 10 ³ C / sec or more. Cooling rate is 1 × 10 ² When the temperature is lower than ° C./sec, a very long processing time is required particularly in the next MG processing performed to improve the cycle life.
[0029]
Cooling rate is 1 × 10 ² As typical casting methods at a temperature of at least ° C / sec, there are a gas atomizing method, a roll quenching method, and a flat plate casting method, and the cooling rate generally becomes lower in this order.
In the gas atomizing method, the molten metal in the tundish flows out of the pores at the bottom of the tundish to be trickle, and this is mixed with Ar, N ₂ , He or the like is sprayed with a high-pressure inert gas to pulverize the molten metal and solidify it in a powder form, thereby obtaining a spherical powder.
[0030]
The roll quenching method is a method in which a molten metal is dropped on a single roll or twin rolls rotating at a high speed, or pulled up by a roll to obtain a thin cast piece. The obtained thin slab is ground to an appropriate size.
[0031]
The flat plate casting method is a method of casting a molten metal into a flat mold so as to reduce the thickness of the ingot, and the cooling rate is higher than that of the block ingot. The obtained flat ingot is ground to an appropriate size.
[0032]
The rapid casting method is not limited to the above method. Rotating electrode method, liquid atomizing method, melt spinning method, etc. ² There are methods that can be cast at a cooling rate of at least ° C / sec, and these methods can also be adopted.
[0033]
The usual ingot casting method in which a molten metal is poured into a refractory or metal mold and cooled to obtain a block-shaped ingot generally has a cooling rate of 10%. ¹ ° C / sec, 1 × 10 ² Since the temperature does not reach C / sec, it is not a preferable method to be employed in the first method of the present invention. However, it is not impossible to produce the negative electrode material of the present invention by performing the MG treatment for a very long time.
[0034]
A negative electrode material having a fine structure including an active material phase and an inactive phase is pulverized to an appropriate size, if necessary, and then subjected to MG treatment to make the structure ultrafine. The size of the negative electrode material to be subjected to the MG treatment is preferably 5 mm or less in average particle size, more preferably 1 mm or less, and even more preferably 500 μm or less.
[0035]
The MG (mechanical grinding) treatment is a treatment in which a compressive force and a shearing force are applied to particles of a material to be treated, and the particles are repeatedly disintegrated and granulated while being crushed. As a result, the original structure is destroyed, and particles having a structure in which the phase existing before the treatment is ultrafinely dispersed on the order of nanometers are formed. However, the type and content of the active material phase constituting the ultrafine structure are substantially the same as before the treatment, and no new phase is formed by the treatment. The fact that the type and content of the active material phase do not substantially change by the MG treatment means that the discharge capacity of the negative electrode material before and after the MG treatment is substantially the same (change rate is within 5%, preferably within 1%). Can be confirmed. Due to the characteristics of this MG treatment, the negative electrode material of the present invention shows a stable discharge capacity. In this point, it is different from the MA method (mechanical alloying method) in which the alloying reaction between elements occurs and the content of the active material phase changes by the treatment.
[0036]
On the other hand, the structure is not broken by mere pulverization, so that the particles after pulverization retain the structure before pulverization. That is, in the pulverization, only the particle diameter is reduced, and the structure is not made fine. MG processing, in which the tissue is rubbed and broken during processing and the tissue is ultra-fine, differs from grinding in this regard.
[0037]
The MG treatment can be performed by any pulverizer capable of crushing the material. Among them, a pulverizer using a ball-shaped pulverizing medium, that is, a ball mill type pulverizer, has a simple structure, that the balls of the pulverizing medium can be easily obtained from various materials, and that the pulverizing medium is used at the contact point between the balls. This method has advantages such as the fact that the grinding proceeds uniformly in a very large number of places due to the occurrence of the grinding (this is particularly important from the viewpoint of high uniformity of the reaction and, therefore, the stability of the product). Particularly suitable for use in the invention. Above all, not only the grinding cylinder is simply rotated, but also a vibrating ball mill that increases the grinding energy by applying vibration, an attritor that forcibly agitates the ball and the ball of the grinding medium with a rod, and the grinding energy with the rotational force and centrifugal force And a planetary ball mill with an increased
[0038]
Japanese Patent Application Laid-Open No. Hei 10-223221 describes that a rapidly solidified amorphous or low crystalline negative electrode material is pulverized by a sample mill. In this case, since the material obtained by quenching has already become amorphous or low-crystalline, it is unlikely that the structure will be further refined by pulverization. Instead, the crushing is merely performed for the purpose of pulverizing the quenched material.
[0039]
The time of the MG treatment can be determined using the peak intensity of at least one active material phase in the X-ray diffraction pattern of the negative electrode material as an index. That is, the peak intensity of the active material phase gradually decreases as the MG processing is continued because the active material phase becomes ultrafine or the crystal structure is disordered by the MG treatment. Performing the MG treatment until the ratio of the peak intensity after the treatment to the peak intensity of the active material phase before the treatment (hereinafter, simply referred to as peak intensity ratio) becomes 50% or less maintains the high capacity of the negative electrode material. As it is, the cycle life can be remarkably improved, so that it has been found preferable. The processing time required to reduce the peak intensity ratio to 50% or less in the MG processing tends to be shorter as the structure of the negative electrode material to be processed is finer (that is, as the cooling rate during casting is higher).
[0040]
The MG treatment is preferably performed in an atmosphere of an inert gas such as argon in order to prevent oxidation of the material during the treatment. However, as in the case of casting, some materials are not easily oxidized. When the active material phase contains Si and / or Sn, the oxygen concentration of the material after the MG treatment is preferably 2.5% by mass or less, more preferably 2.0% by mass or less. If the oxygen concentration exceeds 2.5% by mass, the irreversible capacity becomes large, and the charge / discharge efficiency is significantly reduced.
[0041]
Even in ball milling of the same material as in the MG method, the mechanical alloying (MA) method, in which the element itself is used as a raw material and an alloying reaction occurs between the elements during the processing, is performed in an inert gas atmosphere. However, since the raw material is usually a fine powder (to promote the alloying reaction) and the oxygen concentration is high, the amount of oxygen in the negative electrode material obtained after the treatment tends to be high, and the charge / discharge efficiency is low. Become.
[0042]
In the second method for producing a negative electrode material for a nonaqueous electrolyte secondary battery according to the present invention, a mixture of an active material phase material and an inactive phase material is subjected to MG treatment. Unlike the MA method, in the MG method, no alloying reaction occurs between the active material phase and the inactive phase, so that the type and content of the existing phase do not substantially change before and after the treatment. However, as a result of the MG treatment, the material of the active material phase and the material of the inactive phase are repeatedly crushed and repeatedly disintegrated and granulated. A negative electrode material containing an active material phase and an inactive phase in one particle is obtained. As in the first method, the content of the active material phase does not change during processing, so that the discharge capacity of the obtained negative electrode material is stabilized.
[0043]
In the second method, since the material of the active material phase and the material of the inactive phase used for the MG processing are constituent units of each phase before the MG processing, the material of the active material phase that needs to be ultra-fine is finely powdered. By doing so, it is possible to obtain a negative electrode material in which the active material phase is further refined during the MG treatment and the active material phase has an ultrafine structure. If the inert phase is about 5 mm or less as described above, it is sufficient to improve the cycle life. Therefore, unlike the first method, the material to be subjected to MG processing does not need to have a fine quenched structure. The material of the active material phase and the material of the inert phase may be prepared, for example, by pulverizing a usual ingot casting material. Of course, a rapid solidification method such as atomization may be employed.
[0044]
When the active material phase used in the second method is a fine powder, a negative electrode material having an ultrafine structure can be obtained in a short MG treatment time. The average particle size of the material of the active material phase is preferably 20 μm or less, more preferably 10 μm or less, and most preferably 5 μm or less. The particle size of the material of the inert phase has little effect on the characteristics of the negative electrode material, and the average particle size is preferably 5 mm or less, more preferably 1 mm or less.
[0045]
The MG treatment comprises mixing a mixture of at least one active material phase material and at least one inert phase material in place of the cast negative electrode material having the active material phase and the inert phase used in the first method. Except for its use, it may be implemented as described for the first method. Also in this case, it is preferable to perform the MG treatment until the ratio of the same peak intensity of the material after the treatment to the peak intensity of the active material phase in the X-ray diffraction pattern of the mixture before the MG treatment becomes 50% or less.
[0046]
From the negative electrode material according to the present invention, a negative electrode for a non-aqueous electrolyte secondary battery can be produced according to a conventional method. For example, a negative electrode mixture is prepared by mixing a suitable binder into a powdered negative electrode material and, if necessary, mixing an appropriate conductive powder to improve conductivity. A solvent for dissolving the binder is added to the negative electrode mixture, and if necessary, sufficiently stirred using a homogenizer and glass beads to form a slurry. This slurry is applied to an electrode substrate (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 to obtain a non-aqueous electrolyte secondary battery. A negative electrode is obtained.
[0047]
As the binder, water-insoluble resins such as PVDF (polyvinylidene fluoride), PMMA (polymethyl methacrylate), PTFE (polytetrafluoroethylene), and styrene-butadiene rubber (however, used for non-aqueous electrolyte of batteries) And water-soluble resins such as CMC (carboxymethylcellulose) and PVA (polyvinyl alcohol). As the solvent, an organic solvent such as NMP (N-methylpyrrolidone) or DMF (dimethylformamide) or water is used depending on the binder.
[0048]
As the conductive powder, any of a carbon material (eg, carbon black, graphite) and a metal (eg, Ni) can be used, but a carbon material is preferable. Since the carbon 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. The preferred carbon material is acetylene black.
[0049]
A non-aqueous electrolyte secondary battery is manufactured using the negative electrode manufactured as described above. 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. However, it is theoretically applicable to other non-aqueous electrolyte secondary batteries.
[0050]
The non-aqueous electrolyte secondary battery has a basic structure including a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte. As the negative electrode, the one produced according to the present invention as described above is used, and as the other positive electrode, separator and electrolyte, conventionally known ones or materials to be developed in the future may be appropriately used.
[0051]
【Example】
(Example 1)
This example illustrates the production of a negative electrode material for a non-aqueous electrolyte secondary battery by the first method according to the present invention. In the following examples, the percentages related to the composition are% by mass.
[0052]
A molten metal having the composition shown in Table 1 was cast by a gas atomizing method, a single-roll quenching method, a flat casting method, or a normal casting method. Except for the gas atomizing method, the molten metal was pulverized into a powder form by a mortar, and inert with the active material phase. A raw material powder having a phase was obtained.
[0053]
The cooling rate of each casting method was as follows.
Gas atomizing method (abbreviated as AT):
Ar gas: 1 × 10 ⁵ ° C / sec,
Single roll quenching method (abbreviated as SC): 5 × 10 ⁴ ° C / sec,
Flat plate casting method (abbreviated as flat plate): 2 × 10 ² ° C / sec,
Ingot casting method (abbreviated as IT): 5 ° C./sec.
[0054]
The cross section of the obtained raw material powder was observed by SEM, and the size of the active material phase was examined. As for the active material phase, 10 randomly selected per visual field were observed, and the minor axis diameter of each was measured. This measurement was performed for five visual fields, and their average value (average minor axis diameter of the active material phase) was defined as the size of the active material phase.
[0055]
This raw material powder was sieved to −63 μm, and 80 g of the sieved powder was subjected to MG treatment under an argon atmosphere at atmospheric pressure using any of the following crushers to obtain a negative electrode material:
Attritor (abbreviated as A): 250 rpm,
Ball mill (abbreviated as B): 200 rpm,
Vibration ball mill (abbreviated as V): frequency 40 Hz,
Planetary ball mill (abbreviated as P): rotation / revolution speed 60/60 rpm,
Rod mill (abbreviated as R): rotation speed 200 rpm. .
[0056]
The balls used in the attritor (A), ball mill (B), vibrating ball mill (O) and planetary ball mill (S) using the ball as a grinding medium were all 3/8 inch in diameter.
[0057]
X-ray diffraction patterns of the obtained negative electrode material powder (that is, powder after MG processing) and raw material powder (that is, powder before MG processing) were measured using CuKα radiation, and the peak intensity ratio of the active material phase was determined. It was determined by the following equation:
Peak intensity ratio = peak intensity after MG processing / peak intensity before MG processing × 100.
[0058]
Further, the oxygen concentration of the negative electrode material obtained by the MG treatment was measured by an active gas carrier melting infrared absorption method.
The electrode characteristics of the negative electrode material were examined by the following method.
[0059]
The powder of the negative electrode material was classified into −63 μm (average diameter 10 μm), 9 parts by mass of polyvinylidene fluoride as a binder, 10 parts by mass of a solvent N-methylpyrrolidone, and 10 parts by mass of a conductive agent with respect to 100 parts by mass of the negative electrode material. 9 parts by mass of carbon (acetylene black) was added and kneaded to prepare a uniform slurry. This slurry was applied to a copper foil having a thickness of 30 μm, dried and roll-rolled, and then punched with a die to a diameter of 13 mm to produce a negative electrode. The thickness of the negative electrode layer on the copper foil was about 100 μm.
[0060]
The performance of a single electrode of the negative electrode was evaluated using a so-called three-electrode cell using Li metal for the counter electrode and the reference electrode. The electrolyte used was a supporting electrolyte LiPF in a 1: 1 mixed solvent of ethylene carbonate and dimethoxyethane. ₆ Was used at a concentration of 1M. The measurement was performed at 25 ° C., and the measurement was performed using an apparatus capable of maintaining an inert atmosphere such as a glove box under the condition that the atmosphere dew point was about −70 ° C.
[0061]
First, charging is performed by 1 / 10C charging (a current value such that the battery is fully charged in 10 hours) until the potential of the negative electrode becomes 0 V with respect to the potential of the reference electrode. The discharge was performed until the potential became 2 V, and the discharge capacity in the first cycle at this time was defined as the discharge capacity of the negative electrode using the negative electrode material.
[0062]
Further, as shown in the following equation, the ratio of the discharge capacity to the charge capacity in the first cycle was determined as the charge / discharge efficiency. Charge / discharge efficiency is a measure of the small irreversible capacity:
Charge / discharge efficiency (%) = discharge capacity / charge capacity × 100.
[0063]
The charge / discharge was repeated under the above conditions, the discharge capacity at the 300th cycle was measured, and the cycle life was calculated from the following equation:
Cycle life (%) = discharge capacity at 300th cycle / discharge capacity at 1st cycle × 100.
[0064]
Both the charge and discharge efficiency and the cycle life are good if they are 90% or more, and particularly good if they are 95% or more.
The discharge capacity is represented by a capacity per volume, that is, a unit of mAh / cc (cc is calculated by the volume of the negative electrode plate, the area of the negative electrode plate and the thickness of the negative electrode material layer).
[0065]
The test results were obtained from the composition of the negative electrode material, the apparatus used for the casting method and the MG treatment, the peak intensity ratio of the active material phase, the oxygen concentration of the negative electrode material, the types of the active material phase and the inactive phase, and the active material in the raw material powder. It is shown in Table 1 together with the phase size (average minor axis diameter). In Table 1, the example in which the MG time is 0 means the result with the raw material powder not subjected to MG, and all are comparative examples.
[0066]
[Table 1]

[0067]
As can be seen from Table 1, by subjecting the quenched cast material to MG treatment, preferably according to the first method of the present invention, the charge and discharge efficiency and especially the cycle life can be greatly improved while maintaining a high discharge capacity. It can be seen that a negative electrode material having high discharge capacity and charge / discharge efficiency and good cycle life can be obtained. As can be seen from the table, when the MG treatment is performed until the peak intensity ratio becomes 50% or less, both the charge / discharge efficiency and the cycle life become 90% or more. As the cooling rate during the casting of the raw material powder is higher and the size of the active material phase is smaller, the peak intensity ratio can be reduced to 50% or less in a shorter MG processing time. In order to obtain a negative electrode material having a small peak intensity ratio, it is more efficient to use an attritor, a vibrating ball mill, or a planetary ball mill than a rod mill or a ball mill.
[0068]
Cooling rate of raw material powder is 10 ² When prepared by a usual ingot casting method at a temperature of less than 50 ° C./sec, a very long MG treatment time is required to obtain a negative electrode material having a peak intensity ratio of 50% or less, but such a long time is required. When the peak intensity ratio was set to 50% or less, the result of the negative electrode characteristics was obtained, which was comparable to the case where the raw material was a quenched material.
[0069]
(Example 2)
This example illustrates the production of a negative electrode material for a non-aqueous electrolyte secondary battery by the second method according to the present invention.
[0070]
The Si metal reagent serving as the active material phase was pulverized in a mortar and classified to obtain powders of active material phases having different average particle diameters. Separately, CoSi which becomes an inert phase ₂ Was cast by a single roll quenching method or a usual ingot casting method, crushed in a mortar, and classified to obtain an inert phase powder having an average particle size of about 30 μm.
[0071]
Active material phase Si powder and inert phase CoSi ₂ One kind of each powder was mixed at a proportion of Co-60% Si as in Example 1, and the mixed powder was subjected to MG treatment using an attritor as in Example 1 to obtain an active material phase and an inert material. A negative electrode material powder having a phase was obtained.
[0072]
For comparison, Si powder (classified to −63 μm, average particle size of 15 μm) and Co powder (classified reagent, average particle size of about 15 μm) prepared in the same manner as above were mixed at a ratio of Co-60% Si. The mixed powder is subjected to mechanical alloying (MA) treatment using an attritor, and an inert phase of CoSi is treated during the treatment. ₂ Was produced to obtain a negative electrode material having an active material phase and an inactive phase. The processing conditions were the same as in the MG method, and the processing was performed in an argon atmosphere.
[0073]
Table 2 summarizes the results obtained by examining the electrode characteristics, peak intensity ratio (comparison with the X-ray diffraction pattern of the raw material mixed powder), and oxygen concentration of the negative electrode material obtained by the above two methods in the same manner as in Example 1. Show. Table 2 also shows the results of examining the discharge capacity before and after the MG treatment or the MA treatment, together with the results of the charge / discharge efficiency and cycle life of the negative electrode material after the treatment.
[0074]
[Table 2]

[0075]
As can be seen from Table 2, the active material phase Si powder and the inactive phase CoSi ₂ The negative electrode material obtained by performing the MG treatment on the mixture with the powder has substantially no change in the content of the active material phase (Si) before and after the treatment (confirmed by substantially no change in the discharge capacity). The discharge capacity, charge / discharge efficiency, and cycle life were all very good.
[0076]
On the other hand, in the method in which the Si powder and the Co powder, which are the constituent elements of the negative electrode material having the same composition, are subjected to MA treatment to generate an inactive phase during the treatment, alloying of the active material, Si, has completely progressed. For this reason, although the discharge capacity was high, the cycle life was not sufficiently improved by the inactive phase, and the cycle life could not be improved to a satisfactory level even when the treatment time was as long as 100 hours. Further, since the oxygen concentration of the negative electrode material was high, the charge / discharge efficiency was low. Furthermore, in the MA method, since the Si content of the active material phase changes depending on the treatment time, the change in discharge capacity is large, and it can be seen that it is difficult to obtain a negative electrode material having a stable capacity.
[0077]
As can be seen from the example of the processing time 0 in the MA method, when the Si phase of the active material phase is not surrounded by the inactive phase and exists in a state of not being finely dispersed, the cycle life is 5%. Remarkably low. In the present invention, it is possible to increase the low cycle life exhibited by Si to 90% or more by any of the first and second methods.
[0078]
【The invention's effect】
According to the present invention, a negative electrode material for a non-aqueous electrolyte secondary battery having higher capacity, superior charge / discharge efficiency and cycle life, and more stable performance than a carbon material which is a negative electrode material of a current practical lithium ion secondary battery is compared. The non-aqueous electrolyte secondary battery can be supplied at extremely low cost, and the size and performance of the non-aqueous electrolyte secondary battery can be reduced.

Claims (6)

One or more active material phases composed of one or more elements capable of reversibly reacting with Li, and one or more active elements selected from a group IIA, a transition element, a group IIIB, and a group IVB in the long-term periodic table. A negative electrode material for a non-aqueous electrolyte secondary battery, which has been subjected to mechanical grinding and has at least one inert phase composed of an element, wherein at least one active material phase peak is present in an X-ray diffraction pattern of the negative electrode material. A negative electrode material for a non-aqueous electrolyte secondary battery, wherein the strength is 50% or less of the peak strength before the mechanical grinding treatment. One or more active material phases composed of one or more elements capable of reversibly reacting with Li, and one or more active elements selected from a group IIA, a transition element, a group IIIB, and a group IVB in the long-term periodic table. A method for producing a negative electrode material for a non-aqueous electrolyte secondary battery having at least one inert phase composed of an element, comprising subjecting a solid cast from a molten metal of the negative electrode material to mechanical grinding treatment. And a method for producing a negative electrode material for a non-aqueous electrolyte secondary battery. 3. The method for producing a negative electrode material for a non-aqueous electrolyte secondary battery according to claim 2, wherein the solid is obtained by quenching a molten metal of the negative electrode material at a rate of 1 × 10 ² ° C./sec or more. One or more active material phases composed of one or more elements capable of reversibly reacting with Li, and one or more active elements selected from a group IIA, a transition element, a group IIIB, and a group IVB in the long-term periodic table. A method for producing a negative electrode material for a non-aqueous electrolyte secondary battery having one or more inert phases composed of elements, and comprising mechanically grinding a mixture of an active material phase and an inert phase, A method for producing a negative electrode material for a non-aqueous electrolyte secondary battery, wherein the content of the active material phase does not substantially change before and after this treatment. The method for producing a negative electrode material for a non-aqueous electrolyte secondary battery according to any one of claims 2 to 4, wherein the mechanical grinding treatment is performed using a ball-shaped grinding medium. The method according to any one of claims 2 to 5, wherein the mechanical grinding treatment is performed until the peak intensity of at least one active material phase in the X-ray diffraction pattern of the negative electrode material becomes 50% or less of the peak intensity before the treatment. A method for producing a negative electrode material for a water electrolyte secondary battery.