WO2007015508A1 - Alloy for negative electrode of lithium secondary battery - Google Patents

Abstract

A melt is obtained by melting two or more metal materials including an element, such as Si and Sn, capable of absorbing and desorbing Li element, and another metal material including Cu and the like. The thus-obtained melt is cooled and solidified at a rate of more than 2 × 103 ˚C/sec and not more than 104 ˚C/sec by strip casting, and then pulverized and classified, thereby obtaining an alloy powder having an average grain size of 0.1-50 μm. A negative electrode for secondary batteries is obtained by arranging this alloy powder and a conductive material on a collector in the form of a layer by using a binder. By using such a negative electrode, there can be obtained a lithium secondary battery having high charge/discharge capacity and excellent cycle characteristics.

Description

 Specification

 Alloy for lithium secondary battery negative electrode

 Technical field

 The present invention relates to a lithium secondary battery negative electrode alloy having a large charge / discharge capacity and excellent cycle characteristics, a method for producing a lithium storage alloy, and a lithium secondary battery using the alloy. Background art

 [0002] Lithium secondary batteries are frequently used in portable electronic devices and the like as high-tech energy density batteries. In order to extend the driving time of this portable electronic device, power saving of elements and the like is being promoted. However, multifunctionalization is progressing at a pace exceeding power saving, power consumption is increasing, and it is becoming difficult to sufficiently lengthen the driving time.

 Therefore, in order to increase the drive time of electronic equipment and realize multi-function, there is a need for higher capacity and smaller size of secondary batteries.

 [0003] Carbon is usually used as a negative electrode material for lithium secondary batteries. However, carbon cannot theoretically occlude more Li than the composition of LiC, and its theoretical capacity is 372

 6

 mAhZg. Therefore, the use of non-carbon materials such as alloys having a large theoretical capacity as the negative electrode material for lithium secondary batteries has been studied.

 [0004] Si, Al, Sn, Ge, Sb, etc. have been studied as elements having a large theoretical capacity! In particular, Si has a theoretical capacity of 200 mAhZg, and is expected to surpass 3900 mAhZg of metallic lithium, which is attractive for reducing the size and capacity of batteries.

 [0005] However, these non-carbon materials expand and contract greatly due to structural changes when lithium ions are inserted and extracted. Since the surface force of non-carbon materials is gradually occluded into the interior, the material breaks down due to the difference in volume between the surface and the interior, producing fine powder. This fine powder generation breaks the electrical contact between the non-carbon materials and increases the internal resistance.

[0006] Patent Document 1 discloses a negative electrode material having a structure mainly composed of a Li storage phase oc (eg, coexistence of S 相 and Sn phase) and an intermetallic compound or a phase β also having a solid solution force. Yes. This negative electrode material is assembled so that 13 becomes the primary crystal upon solidification, and then α and j8 precipitate as eutectic. The melt of the raw material selected for composition is rapidly solidified by the atomization method, roll quenching method, etc. It is described that it is obtained by The alloy shown as an example of actual manufacture has a thickness of 20 μm and an alloy structure with a size of several nm. Patent Document 1: JP 2001-297757 A

 [0007] Patent Document 2 includes a layer containing Sn as a constituent element and MA (note that MA is La, Ce, Pr, Nd, Mg, Si, Ca, Ga, Y, Zr, Nb, Ag, In) And a negative electrode including an alloy having a unit cell made of a composite layered structure having a layer including a layer including a constituent element as a constituent element selected from the group consisting of Hf and Pb. This alloy is described as being obtained by cooling at a rate of 100 ° CZ seconds to 2000 ° CZ seconds, preferably 300 ° CZ seconds to 1300 ° CZ seconds, by a strip casting method. The thickness of the resulting alloy is 10 μm or more and 50 μm or less.

 Patent Document 2: Japanese Patent Laid-Open No. 2006-120324

 [0008] Patent Document 3 includes a mixture of particles containing a carbon atom capable of inserting and desorbing lithium ions or a compound containing Z and tin atoms, and a vapor grown carbon fiber. A negative electrode material has been proposed. This negative electrode material is an attempt to relieve the volume expansion of the particles by a composite with fibrous carbon.

 Patent Document 3: Japanese Patent Application Laid-Open No. 2004-178922

 [0009] In Patent Document 4, there is a solid solution force formed in a non-equilibrium state between an element A alloying with an alkali metal or alkaline earth metal and an element B not alloying with an alkali metal or alkaline earth metal. It describes battery active materials that occlude and release alkali metals or alkaline earth metals.

 Patent Document 4: Japanese Patent Laid-Open No. 2002-075350

[0010] Further, Patent Document 5 discloses a negative electrode material made of Si alloy powder containing Si and one or more of Cu, Ni and Co as constituent elements. This Si alloy powder is synthesized by a single roll method or an atomizing method, and includes an intermetallic compound phase containing Si and at least one of the group consisting of Cu, Ni and Co as constituent elements. , S It is described that it has a eutectic phase including a phase i and a primary crystal phase of Si dispersed in the eutectic phase.

 Patent Document 5: Japanese Unexamined Patent Application Publication No. 2004-362895

 Disclosure of the invention

 Problems to be solved by the invention

[0011] However, according to the study by the present inventors, the non-carbon materials described in Patent Documents 1 to 5 described above have undergone material destruction due to volume change, and still produce fine powder, resulting in cycle characteristics. Oh! I was still satisfied with my strength.

 An object of the present invention is to provide a lithium secondary battery negative electrode alloy having a large charge / discharge capacity and excellent cycle characteristics, a method for producing a lithium storage alloy, and a lithium secondary battery.

 Means for solving the problem

 [0012] In order to achieve the above object, the present inventors have studied a method for producing an alloy composed of an element having the ability to occlude and release lithium element, and as a result, have found an element that has the ability to occlude and release Li element. Phase A containing as a main component and Phase B containing another element as a main component capable of occluding and releasing Li element, and the larger one of the above phases, phase A is a specific size When an alloy having a thickness is used as a negative electrode material for a lithium secondary battery, a large volume change does not occur, the generation of fine powder is almost eliminated, and a lithium secondary battery having a large charge / discharge capacity and excellent cycle characteristics can be obtained. I found out. The present invention has been completed as a result of further studies based on this finding.

 That is, the present invention includes the following.

 (1) It has a phase A containing an element capable of occluding and releasing Li element as a main constituent and a phase B containing another element capable of occluding and releasing a Li element as a main constituent.

An alloy for negative electrodes of lithium secondary batteries, in which the larger phase A of the above phases is 0.05 m to 20 m.

 (2) The lithium secondary battery negative electrode alloy according to (1), wherein one of phase A and phase B forms a dispersed phase, and the other phase forms a continuous phase.

(3) The mass ratio of the main constituent element of phase A to the main constituent element of phase B is 20/80 The alloy for negative electrodes of lithium secondary batteries according to (1) or (2), which is ˜80Z20.

 (4) Element of the main component of the phase and the elemental force of the main component of the phase The group force consisting of Sn, Si, Ge, Pb, Al, and In is also an element selected from (1) to (3) The alloy for a lithium secondary battery negative electrode according to any one of the above.

[0014] (5) having a phase containing Si element as a main component and a phase containing Sn element as a main component, and the larger phase A among the above phases is 0.05 m to 20 m The size of lithium secondary battery negative electrode alloy.

 (6) At least one of the phase containing Si element as the main constituent or the phase containing Sn element as the main constituent constitutes the dispersed phase and the other phase constitutes the continuous phase (5 The alloy for negative electrodes for lithium secondary batteries described in 1).

 (7) The mass ratio of Si element to Sn element (SiZSn =) force is 0Ζ80 to 80Ζ20. The alloy for negative electrodes for lithium secondary batteries according to (5) or (6).

 (8) Ti, V, Co, Ni, Cu, Mo, Ru, Rh, Pd, Pt, Be, Nd, W, Au, Ag, and Ga. The alloy for lithium secondary battery negative electrode according to any one of 4) to (7).

 (9) Group force including B, C, N, 0, S, and P forces Further including at least one element selected from (4) to (8) For a lithium secondary battery negative electrode according to any one of (4) to (8) alloy.

 (10) Ti, V, Co, Ni, Cu, Mo, Ru, Rh, Pd, Pt, Be, Nd, W, Au, Ag, and at least one element that can also be selected as a group force, and B, and B, Group force consisting of C, N, 0, S and P Total force of at least one element selected 0.1% or more and less than 35% by weight of the total (4) to (9) An alloy for a negative electrode of a lithium secondary battery as described in 1.

 (11) The alloy for negative electrodes of lithium secondary batteries according to any one of (1) to (10), wherein the average particle size (d50) is within the range of 0.1 111 to 50 111.

[0015] (12) Two or more metal materials each containing an element capable of occluding and releasing Li element are melted to obtain a molten metal, and the molten metal is melted at 2 X 10 ³ ° C / second by the strip casting method. A method for producing a lithium storage alloy, comprising a step of cooling and solidifying at a rate of more than 10 ⁴ ° CZ seconds.

(13) In the strip cast method, the molten metal is striped and brought into contact with the cooling roll (12) A method for producing a lithium storage alloy as described in 1. above.

 (14) Elemental force capable of occluding and releasing Li element Sn, Si, Ge, Pb, Al and In force Group force The selected element (12) or (13) Production method.

[15] (15) A metal material containing a Sn element and a metal material containing a Si element are melted to obtain a molten metal, and the molten metal is obtained by a strip casting method for more than 2 × 10 ³ ° CZ seconds and 10 ⁴ ° CZ. A method for producing a lithium storage alloy, comprising a step of cooling and solidifying at a rate of seconds or less.

 (16) Ti, V, Co, Ni, Cu, Mo, Ru, Rh, Pd, Pt, Be, Nd, W, Au, Ag, and Ga group force that further includes at least one element selected from the molten metal The method for producing a lithium storage alloy according to any one of (14) and (15).

 (17) The method for producing a lithium storage alloy according to any one of (14) to (16), wherein the molten metal further includes at least one element selected from a group force including B, C, N, 0, S, and P forces. .

 (18) Ti, V, Co, Ni, Cu, Mo, Ru, Rh, Pd, Pt, Be, Nd, W, Au, Ag, and at least one element that can also be selected as a group force, and B, and B, Group force consisting of C, N, 0, S and P Total power of at least one element selected 0.1% or more and less than 35% by weight of the total molten metal (14) to (17) The manufacturing method of lithium occlusion alloy of description.

(19) The method for producing a lithium storage alloy according to any one of (12) to (18), wherein the solidified product obtained by the strip casting method is a flake having an average thickness exceeding 50 μm and not exceeding 300 μm.

 (20) Average particle size (d50) The method according to any one of (12) to (19), further comprising a step of grinding and Z or classification so as to be within a range of 0.1 μπι to 50 / ζ m. Manufacturing method of lithium storage alloy.

 (21) A lithium secondary battery using the lithium secondary battery negative electrode alloy according to any one of (1) to (11).

 [0018] In the present specification, when "more than x" and "y or less" are indicated, the boundary values X and y are included. “Less than χ” and “greater than y” indicate that the boundary values X and y are not included. The boundary values X and y in the range indicated by “x to y” are included in the range.

The invention's effect [0019] The lithium secondary battery negative electrode alloy of the present invention does not cause a large volume change even when lithium ions are occluded and Z or released, and hardly generates fine powder.

 By using the powder of the lithium secondary battery negative electrode alloy of the present invention as a negative electrode material for a lithium secondary battery, a lithium secondary battery excellent in charge / discharge characteristics and cycle characteristics can be obtained.

 Brief Description of Drawings

FIG. 1 is a diagram showing an example of a cross-sectional structure of an alloy according to the present invention.

 FIG. 2 is an enlarged view of FIG.

 FIG. 3 is a top view schematically showing an example of a single roll rapid solidification method (strip casting method).

 4 is a side view of the apparatus shown in FIG.

 FIG. 5 is a perspective view of the apparatus shown in FIG. 3.

 Explanation of symbols

[0021] 1: Crucible

 2: Tundish

 3: Cooling roll

 4: Collection box

 5: Molten metal

 C: Alloy flake

 6: Roll surface (solidified surface)

 9: Free surface

 BEST MODE FOR CARRYING OUT THE INVENTION

[Alloy for negative electrode of lithium secondary battery]

 The lithium secondary battery negative electrode alloy of the present invention is composed mainly of phase A containing an element capable of occluding and releasing Li element as a main component and another element capable of occluding and releasing Li element. Phase B included as a component, and the larger phase A of the above phases has a size of 0.05 m to 20 μm.

[0023] An element capable of occluding and releasing Li element (hereinafter simply referred to as "Li occluding element") is there. ) Include, for example, Sn, Si, Ge, Pb, Al, In and the like. The present invention is characterized by having at least two phases containing this Li storage element as a main constituent. For example, a phase containing Si element as a main constituent, a phase containing Sn element as a main constituent, a phase containing Si element as a main constituent, a phase containing A1 element as a main constituent, and a Si element as a main constituent There are combinations such as a phase containing Ge and a phase containing Ge as a main constituent. In the present invention, a combination of a phase containing Si element as a main constituent and a phase containing Sn element as a main constituent is particularly suitable. That is, a lithium secondary battery negative alloy preferable in the present invention has a phase containing Si element as a main constituent and a phase containing Sn element as a main constituent, and the larger phase of the above phases. A has a size of 0.05 m to 20 m.

 [0024] When Li is occluded into an element that has the ability to occlude and release Li, it is represented by the chemical formula LiM (where M is the Li occlusion element) o X is The force that depends on the amount of Li stored In the present invention, when the maximum amount of Li is stored, X is greater than 0.01, more than 6 / J, and preferably less than 0.9 to 4.1. More preferably, it is more preferably a force of 0.24-0.5 1! / ,.

 [0025] The alloy for the negative electrode of the lithium secondary battery is preferably one in which either phase A or phase B forms a dispersed phase and the other phase forms a continuous phase. FIG. 1 and FIG. 2 show an example of an electron micrograph image of a flake of the alloy of the present invention having a phase A containing Si element as a main constituent and a phase B containing Sn element as a main constituent. The central part in Fig. 1 and the right half in Fig. 2 are images of slice C. The white part is phase B and the gray part is phase A. The left end of the flake C shown in Fig. 1 and Fig. 2 is the solidified surface 6 formed by contact with the roll described later, and the right end of the flake shown in Fig. 1 is the free side on the opposite side of the roll contact surface Surface 9 is.

 [0026] As shown in FIGS. 1 and 2, the lithium secondary battery negative electrode alloy of the present invention has a network, dendritic or marbling state around phase A (gray part) and phase B (white part). The expanded phase structure has the relationship of phase A size> phase size.

The size of the larger phase A is 0.05 μm to 20 μm, preferably 0.2 μm to 8 m, more preferably 0.5 μm to 8 μm, particularly preferably 0. 8 μm to 2 μm. Big When the size of phase A is in this range, a lithium secondary battery having stable charge / discharge characteristics can be obtained.

 Note that the size of phase A is larger in the electron micrograph of the alloy flakes as shown in Fig. 1 by dividing the line parallel to both sides of the flakes with 1Z4, 1/2, and Each of them is drawn at a position corresponding to 3Z4, and the number of phases B with the smaller size intersecting the line segment is obtained. The length of the line segment is divided by the number of phase B, and the thickness of the flake is 1Z4, 1 It was expressed as the average value of the calculated values at positions corresponding to / 2, and 3Z4.

[0027] As shown in Fig. 1 and Fig. 2, the phase A is often included in a shape that is short in the direction parallel to the roll surface that is long in the thickness direction of the thin piece. Phase A has a minor axis diameter of preferably 0.05 to 20 μm and a major axis diameter of preferably 0.05 to 300 μm. Although it is not particularly limited by the ratio of the major axis diameter to the minor axis diameter (major axis diameter Z minor axis diameter), it is preferably 1 to 6 000, and more preferably 1 to 30. The minor axis diameter of phase B is usually smaller than the minor axis diameter of phase A.

 [0028] The mass ratio of the main constituent element of phase A to the main constituent element of phase B is not particularly limited. Preferably, it is 20 or 80 to 80/20, more preferably 30/70 ~ 70/30

[0029] The lithium secondary battery negative electrode alloy of the present invention may contain other elements in addition to an element capable of occluding and releasing Li elements.

 Preferred elements that may be included include Ti, V, Co, Ni, Cu, Mo, Ru, Rh, Pd, Pt, Be, Nd, W, Au, Ag, Ga, etc. 1 type or 2 types or more may be contained. These elements are considered to play a role of connecting Phase A and Phase B described above.

 [0030] In addition, elements that are inevitably included in the alloy manufacturing process may be included in the lithium secondary battery negative electrode alloy of the present invention. Examples include B, C, N, 0, S, P, and Al. When Al is used as the Li storage element, the A1 element is not included in the unavoidable element. When Al is used as the Li storage element, the Al element is included in the unavoidable element.

[0031] In the lithium secondary battery negative electrode alloy of the present invention, other elements than the element capable of occluding and releasing Li elements, that is, Ti, V, Co, Ni, Cu, Mo, Ru, Rh, Pd, At least one element selected from the group consisting of Pt, Be, Nd, W, Au, Ag, and Ga, and at least one element selected from the group force that also includes B, C, N, 0, S, and P forces. The total amount is preferably 0.1% by mass or more and less than 35% by mass, more preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 5% by mass. It is particularly preferred that it is less than or equal to%.

 [0032] The lithium secondary battery negative electrode alloy of the present invention has an average particle size (d50) in order to increase the contact area with lithium ions to an appropriate size and to facilitate the formation of a negative electrode. 0.1 m to 50 μm is preferable 1 m to: LO / zm is more preferable. The average particle size (d50) is a 50% cumulative particle size in a volume-based particle size distribution. The average particle size can be measured with a laser diffraction particle size distribution analyzer.

 [0033] The lithium secondary battery negative electrode alloy of the present invention is not particularly limited as long as it is a production method capable of forming the above phase structure. Alloy fabrication methods include strip casting with a single roll, ribbon production by ultra-quenching, centrifugal casting with molten metal droplets attached to the mold, rotating electrode method, water atomization method, gas atomization method, etc. Can be mentioned. However, according to previous studies by the present inventors, it has been found that an alloy for a lithium secondary battery negative electrode having the phase structure defined in the present invention can be obtained by the production method described below.

 [Production Method of Lithium Storage Alloy]

A method for producing a lithium storage alloy (lithium secondary battery negative electrode alloy) according to the present invention comprises obtaining a molten metal by melting two or more metal materials containing an element capable of inserting and extracting Li element, and stripping the molten metal. It includes a step of cooling and solidifying by a casting method at a rate exceeding 2 X 10 ³ ° CZ seconds and not exceeding 10 ⁴ ° CZ seconds.

[0035] (Melt preparation process)

 The molten metal preparation step is an alloy raw material, that is, the above-mentioned Li storage element, for example, an element selected from the group consisting of Sn, Si, Ge, Pb, Al and In, preferably two metal materials containing Si element and Sn element This is a step of melting the above to obtain a molten metal.

In addition, the molten metal that contains two or more metallic materials containing Li storage elements contains Element, for example, Ti, V, Co, Ni, Cu, Mo, Ru, Rh, Pd, Pt, Be, Nd, W, Au, Ag, and Ga , C, N, 0, S and at least one element selected from the group force consisting of P and P may be melted.

 These metal materials may be mixed in advance and melted in the melt, or one metal material may be melted and another metal material may be poured into the melt to melt.

 [0036] The ratio of the Li storage element is not particularly limited, but the mass specific force between the main constituent element of phase A and the main constituent element of phase B is preferably 20 / 80-80 / 20, more preferably Is used at a rate of 30/70 to 70Z30.

 The ratio of elements other than Li storage elements is preferably 0.1% by mass or more and less than 35% by mass of the whole alloy, more preferably 0.1% by mass or more and 10% by mass or less. It is particularly preferably 0.5% by mass or more and 5% by mass or less.

 [0037] The metal material is melted by heating to a temperature equal to or higher than the melting point. The heating temperature is usually 1200 ° C to 1800 ° C. In addition, it is preferable to perform melting in an inert gas atmosphere or a vacuum at a pressure of 0. IMPa (atmospheric pressure) to 0.2 MPa. Examples of the inert gas include Ar and He.

 Heating reduces impurities in the metal material, such as metal oxides, and increases the purity of the alloy. Therefore, if the heating temperature is too low, the above-described reduction reaction may not proceed sufficiently and the purity of the alloy may be lowered. On the other hand, if the heating temperature is too high, the amount of evaporation of the metal element increases, making it difficult to adjust to the desired composition.

 [0038] (Coagulation process)

 The solidification step is a step in which the molten metal obtained in the previous molten metal preparation step is rapidly solidified to produce an alloy. Examples of the rapid solidification method include a strip casting method, a new centrifugal forging method using a tundish that also has a rotating disk force, a centrifugal forging method, and the like, but the strip casting method is used in the production method of the present invention.

[0039] In the present invention, the cooling rate in the solidification step is at least 2 X 10 ³ ° C / sec and at most 10 ⁴ ° C / sec, preferably at least 3 X in the range from the temperature of the molten metal to 600 ° C. 10 ³ ° C / second to 10 ⁴ ° CZ second, more preferably 3 X 10 ³ ° CZ second to 8 X 10 ³ ° CZ second.

By adjusting to such a cooling rate, it is possible to control the magnitude of the aforementioned phase A. it can. If the cooling rate is too slow, the size of phase A will be greater than 20 / zm. If the cooling rate is too fast, the size of phase A will be too small.

FIGS. 3 to 5 are diagrams for explaining the strip casting method, FIG. 3 is a top view of an example of an apparatus used for the strip casting method, and FIG. 4 is a side view of the example of the apparatus shown in FIG. FIG. 5 is a perspective view of the apparatus example shown in FIG.

[0041] The apparatus shown in the figure includes a crucible 1, a tundish 2, a cooling roll 3, and a collection container 4.

 In this apparatus, the alloy raw material is melted in the crucible 1 and a molten metal 5 is generated. The generated molten metal 5 is poured through a tundish 2 onto a cylindrical cooling roll 3 that rotates in a predetermined direction (counterclockwise direction in the drawing).

 The tundish 2 is a device including a rectifying mechanism and a slag removing mechanism.

 The cooling roll 3 is a roll cooled by water cooling or the like. The molten metal 5 in contact with the roll is rapidly solidified to produce an alloy. The cooling speed of the molten metal 5 can be controlled by the peripheral speed of the cooling roll 3, the amount of molten metal poured onto the cooling roll 3, and the like. The chill roll is usually made of a material that has good thermal conductivity and is easily available, such as copper or a copper alloy. Depending on the material of the cooling hole 3 and its surface condition, metal tends to adhere to the surface, so a cleaning device is installed if necessary.

 As shown in FIG. 3 or FIG. 5, the molten metal is preferably poured out from the slit-shaped mouth (rectifying mechanism) of the tundish 2 in a strip shape and brought into contact with the cooling roll. When the molten metal is brought into contact with the strip, the strip-shaped alloy flakes C are easily formed.

[0042] The produced alloy is peeled off from the cooling roll 3 by centrifugal force, jumps out in the direction of the arrow 8, becomes a flake C, and is collected in the collection container 4. In the present invention, it is preferable to control the thickness of the alloy flake C (solidified material) to be more than 50 μm and not more than 300 μm by controlling the amount of pouring on the cooling roll 3 or the like. More preferably, it is 80 μm or more and 210 μm or less. If the alloy flakes are too thin, the solidification rate will increase excessively and the size of phase A may become too small. Also, if the thickness of the alloy flakes is too thick, the solidification rate decreases and the size of phase A may become too large.

[0043] The flakes C recovered in the recovery container 4 are taken out after being cooled to room temperature in the same container. . Note that it is preferable to provide a cooling mechanism, a heat insulation mechanism, or the like in the recovery container 4 to control the cooling rate of the alloy flakes C in the container. Thus, by controlling the cooling rate at the time of cooling to room temperature after cooling to 600 ° C. by the cooling roll 3, the uniformity of the alloy structure can be further improved.

 [0044] (Crushing and Z or classification process)

 In order to use the lithium storage alloy obtained in the above process as a negative electrode material for a lithium secondary battery, the particle size of the alloy is adjusted. The particle size can be adjusted by a known pulverization method and / or classification method without particular limitation depending on the method. Examples of the pulverizing means include a hammer mill, a jaw crusher, a collision type pulverizer, a ball mill, an attritor, and a jet mill. In particular, the jet mill can be pulverized by colliding with the alloy itself coarsely pulverized with high-pressure nitrogen or high-pressure argon, so it can produce fine powder with very little contamination and high purity. The structure is preferable because a powder with less acidity on the powder surface can be produced.

 [0045] Further, when the alloy is pulverized, a composite of the alloy and carbon can be obtained by adding a carbon material such as graphite powder or carbon fiber. This composite is suitable as a negative electrode material. Examples of the classification method include an airflow classification method and a sieving method.

 The alloy powder may oxidize and burn if left in air. Therefore, it is preferable to store the alloy powder in ethylene carbonate or propylene carbonate for safe storage.

 [Lithium secondary battery]

 The lithium secondary battery of the present invention uses the above-mentioned alloy for negative electrodes of lithium secondary batteries. Specifically, the lithium storage alloy powder is used as an active material for a negative electrode of a lithium secondary battery. As described above, the lithium storage alloy powder preferably has an average particle size (d50) in the range of 0.1 / ζ πι to 50 / ζ πι, and an average particle size in the range of l to 10 / zm. Is more preferable, especially about 1 to 5 μm.

 [0047] The negative electrode of a lithium secondary battery is usually obtained by laminating an active material and a conductive material on a current collector with a binder.

[0048] Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, and styrene butadiene. For example, Yen Rubber. The binder is dissolved or dispersed in a solvent such as N-methylpyrrolidone, xylene, or water, and is suitable for mixing with active materials.

[0049] As the conductive material, a carbon-based conductive aid is usually used. The current collector is a foil, a punching metal, a net, or the like made of a known material such as copper, aluminum, stainless steel, nickel, or an alloy thereof. It is also possible to use a surface roughened by etching or the like.

 [0050] In order to laminate the active material and the conductive material on the current collector, a known method can be employed. For example, there is a method of kneading the lithium storage alloy, a conductive material, and a binder, preparing a slurry-like coating agent, applying the coating agent to a current collector, drying, and pressing.

 Examples of means for kneading the alloy, the conductive material, and the binder include a ribbon mixer, a screw-type mixer, a planetary mixer, and a universal mixer.

 Examples of means for applying the coating agent to the current collector include a doctor blade and a bar coater. A roll press machine or the like is usually used for press force after coating.

 [0051] A lithium secondary battery is obtained by placing the above-described negative electrode and positive electrode in a container containing an electrolyte so as to face each other with a separator interposed therebetween and sealing.

 The positive electrode, separator, and electrolyte used in the lithium secondary battery of the present invention may be those normally used in lithium secondary batteries. Examples of the positive electrode include those formed of lithium cobaltate, lithium nickelate, lithium manganate, and complex oxides or mixtures thereof. Examples of the separator include a microporous film nonwoven fabric made of polyethylene or polypropylene.

 [0052] Examples of the electrolyte include known Li salts such as LiPF, LiBF, and Liimide salt. Electrolyte

 6 4

 Usually used after being dissolved in a solvent. Examples of the solvent for dissolving the electrolyte include known solvents such as jetyl carbonate, ethylene carbonate, and propylene carbonate. The dissolution concentration of the electrolyte is not particularly limited, and is usually about 1 mol Z liter.

 [0053] Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples.

[0054] Examples In a crucible with a double structure of carbon and alumina, put 210g of metal tin (2N (purity 99%)), 455g of metal silicon (4N (purity 99.99%)) and 35g of electrolytic copper, The molten metal was prepared by heating to 1400 ° C in argon in an induction furnace. This molten metal was rectified into a strip shape and brought into contact with a cooling roll using a device for strip casting having a configuration as shown in FIGS. 3 to 5, and rapidly cooled and solidified to obtain an alloy flake. The peripheral speed of the copper cooling roll was 1.0 mZs, the thickness of the alloy flakes was 300 μm, and the cooling rate from the molten metal temperature to 600 ° C was 3000 ° CZ seconds.

 [0055] The obtained alloy flakes were crushed in an alumina mortar and powdered, and X-ray diffraction measurement was performed. Diffraction peaks corresponding to Sn metal and Si metal were observed. In addition, when the cross-section of the alloy was observed with a scanning electron microscope (Hitachi S-530), the structure of the alloy was observed using a backscattered electron image. Two phases were observed, one containing mainly Si and the other containing Sn. It was. As shown in Fig. 1 and Fig. 2, around phase A (gray part) mainly containing Si element, phase B (white part) mainly containing Sn element develops in a network, dendritic or marbling. It was. In the cross-sectional photograph, draw a line segment at the position of 1Z4, 1/2, 3Z4 with respect to the thickness of the alloy flakes parallel to the roll surface, count the intersection of this line segment and phase B, and length of the line segment When the average value of the values obtained by dividing the number by the number of intersections was calculated, the size of phase A was about 8 μm.

[0056] (Evaluation of battery characteristics)

 The alloy flakes were wet crushed with isopropanol using an attritor to obtain an alloy powder having an average particle size of 1.3 m.

 To 1 part by mass of the above-mentioned alloy powder, 0.2 part by mass of acetylene black (manufactured by Denki Kagaku) and 0.1 part by mass of polyfluorinated vinylidene indder (manufactured by Kureha Chemical) are added, An appropriate amount of redone was added as a solvent and kneaded with a planetary mixer to obtain a stock solution. This stock solution was adjusted to a viscosity suitable for coating, applied to a high-purity copper foil with a doctor blade at a thickness of about 100 μm, and vacuum-dried to obtain a negative electrode material.

 The negative electrode material was punched into a disk shape having a diameter of 18 mm, pressed between super steel press plates, and dried again with a vacuum dryer at 120 ° C. for 12 hours to obtain a negative electrode.

A metal lithium foil was punched into a disk shape having a diameter of 18 mm to obtain a positive electrode. In addition, a separator was obtained by punching a polypropylene microporous film into a disk with a diameter of 19 mm. It was.

 In a propylene screw-in lidded cell, the negative electrode, separator, and positive electrode were stacked in this order. An electrolyte solution prepared by dissolving LiPF in a mixed solution of ethylene carbonate and jetyl carbonate at a concentration of 1 mol and liter is poured into a cell, sealed with a lid, and evaluated.

 6

 A lithium secondary battery for charging was obtained.

 [0057] (Charge / discharge cycle test)

A constant current charge was performed from the rest potential to 0.002 V, a current density of 0.2 mAZcm ² , and then a constant voltage charge until the current value dropped to 25 A. Then, constant voltage discharge was performed at 0.2 mA / cm ² and cut off at 1.5 V. This operation was one cycle, and a total of 50 cycles were performed.

 [0058] This example was repeated three times. The size of phase A mainly containing Si element of the alloy obtained in the example, the value of X, the capacity of the evaluation lithium secondary battery obtained using the alloy at the time of 1 cycle, at the time of 50 cycles Table 1 shows the capacity retention and capacity retention rate for one cycle at 50 cycles.

 [0059] Comparative Example

 In a crucible having a double structure of carbon and alumina, 210 g of metal tin (2N), 455 g of metal silicon (4N), and 35 g of electrolytic copper were placed, and heated to 1400 ° C in argon in a high frequency induction furnace. A molten metal was prepared by heating. This molten metal was poured into an iron book mold with an interval of 30 mm to obtain an alloy lump.

 [0060] The obtained alloy lump was pulverized with an alumina mortar and subjected to X-ray diffraction measurement. Diffraction peaks corresponding to Sn metal and Si metal were observed. In addition, when the cross-section of the alloy was observed with a scanning electron microscope (Hitachi S-530), the structure of the alloy was observed using a backscattered electron image. Admitted. The larger phase A is 55 μm in size.

 [0061] The alloy lump was wet pulverized with isopropanol using an attritor to obtain an alloy powder having an average particle size of 1.5 µm.

This comparative example was repeated three times. The size of the phase A mainly containing Si element of the alloy obtained in the comparative example, the value of X, and the lithium secondary battery for evaluation obtained using the alloy in one cycle The capacity, the capacity at 50 cycles, and the capacity retention for one cycle at 50 cycles were determined in the same manner as in the example. The results are shown in Table 1.

[0062] As shown in Table 1, when the alloy obtained in the present invention (Example) was used as a negative electrode, compared with a sample prepared from a book mold forging (Comparative Example) It can be seen that the decrease in capacity is suppressed to a small extent, and the decrease in capacity due to alloy particle collapse is alleviated.

[0063] [Table 1] Table 1

* SC method: Strip cast method

 BM method: Book mold method

Claims

The scope of the claims  [1] having phase A containing an element capable of occluding and releasing Li as a main constituent and phase B containing another element capable of occluding and releasing a Li element as a main constituent An alloy for a lithium secondary battery negative electrode, wherein the larger one of the phases, the larger phase A is 0.05 μm to 20 μm.  [2] The lithium secondary battery negative electrode alloy according to claim 1, wherein one of phase A and phase B forms a dispersed phase, and the other phase forms a continuous phase. [3] The mass ratio of the main constituent element of phase A to the main constituent element of phase B is 20Z80 ~ 8 The lithium secondary battery negative electrode alloy according to claim 1 or 2, wherein the alloy is 0 to 20. [4] The element of the main component of the phase and the elemental force of the main component of the phase are elements for which the group force consisting of Sn, Si, Ge, Pb, Al and In is also selected. The alloy for lithium secondary battery negative electrode according to 1. [5] having a phase containing Si element as a main constituent and a phase containing Sn element as a main constituent, and the larger phase A of the above phases is 0.05 μm to 20 μm The size of the lithium secondary battery negative electrode alloy.  [6] One of a phase containing Si element as a main component or a phase containing Sn element as a main component, wherein one phase forms a dispersed phase and the other phase forms a continuous phase Item 5. The lithium secondary battery negative electrode alloy according to Item 5. [7] The mass ratio (SiZSn =) force of Si element and Sn element is ¾0Ζ80 ~ 80Ζ20, 6. The lithium secondary battery negative electrode alloy according to 6. [8] A group force including Ti, V, Co, Ni, Cu, Mo, Ru, Rh, Pd, Pt, Be, Nd, W, Au, Ag, and Ga forces. Claim that further includes at least one element selected Item 8. The alloy for a lithium secondary battery negative electrode according to any one of Items 4 to 7. [9] The lithium secondary battery negative electrode alloy according to any one of claims 4 to 8, further comprising at least one element selected from a group force including B, C, N, 0, S, and P forces. [10] Group force consisting of Ti, V, Co, Ni, Cu, Mo, Ru, Rh, Pd, Pt, Be, Nd, W, Au, Ag, and Ga forces At least one element selected, and B, Total mass force of at least one element selected from the group consisting of C, N, 0, S, and P force 0.1 mass% or more and less than 35 mass% of the total An alloy for a lithium secondary battery negative electrode according to any one of claims 4 to 9. [11] The lithium secondary battery negative electrode alloy according to any one of [1] to [10], wherein the average particle size (d50) is in the range of 0.1111 to 50111. [12] Two or more metal materials each containing an element capable of occluding and releasing Li elements are melted to obtain a molten metal, and this molten metal exceeds 2 X 10 ³ ° C / second by strip casting. ^A method for producing a lithium storage alloy, comprising a step of cooling and solidifying at a rate of ⁴ ° CZ seconds or less.  13. The method for producing a lithium storage alloy according to claim 12, wherein in the strip casting method, the molten metal is formed into a strip shape and brought into contact with a cooling roll. [14] The elemental force capable of occluding and releasing Li element The group power consisting of Sn, Si, Ge, Pb, Al, and In. The production of the lithium-occlusion alloy according to claim 12 or 13, which is an element selected. Method. [15] A metal material containing Sn element and a metal material containing Si element are melted to obtain a molten metal, and the molten metal is obtained by a strip casting method at a speed of 2 X 10 ³ ° CZ seconds or more and 10 ⁴ ° CZ seconds or less. A method for producing a lithium storage alloy, comprising a step of cooling and solidifying the material. [16] At least one element selected from the group force including Ti, V, Co, Ni, Cu, Mo, Ru, Rh, Pd, Pt, Be, Nd, W, Au, Ag, and Ga force is further added to the molten metal. The method for producing a lithium storage alloy according to any one of claims 14 and 15. [17] The method for producing a lithium storage alloy according to any one of [14] to [16], further comprising at least one element selected from a group force including B, C, N, 0, S, and P forces in the molten metal. [18] Group force consisting of Ti, V, Co, Ni, Cu, Mo, Ru, Rh, Pd, Pt, Be, Nd, W, Au, Ag, and Ga forces At least one element selected, and B, The total amount of at least one element selected from the group consisting of C, N, 0, S, and P force is 0.1 mass% or more and less than 35 mass% of the entire molten metal. The manufacturing method of lithium occlusion alloy of description. [19] The method for producing a lithium storage alloy according to any one of [12] to [18], wherein the solidified product obtained by the strip casting method is a flake having an average thickness exceeding 50 μm and not exceeding 300 μm. [20] Average particle size (d50) 0.1 μπι ～ 50 / ζ m so as to be within the range The method for producing a lithium storage alloy according to any one of claims 12 to 19, further comprising a step of:  [21] A lithium secondary battery using the lithium secondary battery negative electrode alloy according to any one of claims 1 to 11.