JP2001250540A - Negative electrode material for nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alloy powder as a negative electrode material for a nonaqueous electrolyte secondary battery, having a capacity higher than that of a conventional carbonaceous negative electrode material, and to provide an improved cycle life. SOLUTION: The alloy powder, containing a phase of an element (for example, Si) having Li storage ability and a phase consisting of an intermetallic compound of this element is produced in an oxygen concentration reduced atmosphere with quench coagulation method. If required, the alloy powder is subjected to heat treatment in one of the following conditions (1)-(3), so that the thickness of a surface oxidized layer is 5 nm or less and/or the atomic ratio of oxygen/element (a) in the most outside surface layer portion of the surface oxidized layer is 0.35 or less: (1) heat treatment in an inactive gas atmosphere at an oxygen concentration of 500 ppm or less, (2) heat treatment in a vacuum of 10 Pa or less, and (3) heat treatment in an inactive gas containing a 0.5 vol.% or more hydrogen gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode material for a non-aqueous electrolyte secondary battery capable of inserting and extracting a large amount of an alkali metal such as Li. The non-aqueous electrolyte secondary battery referred to in the present invention includes a battery using a non-aqueous electrolyte in which a supporting electrolyte is dissolved in an organic solvent and a non-aqueous electrolyte such as a polymer electrolyte or a gel electrolyte.

[0002]

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

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

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

To increase the capacity, there has been a proposal to use an element such as Al, which can reversibly occlude and release Li by forming an intermetallic compound, as a negative electrode material.
Cracks occur due to the volume change associated with the release, resulting in pulverization. Therefore, in a secondary battery using this negative electrode material, as the charge / discharge cycle progresses, the capacity rapidly decreases, and the cycle life becomes short.

As a countermeasure to prevent the negative electrode material from being pulverized due to the volume change, Al, Li, Si,
It has been proposed to add B or the like to increase the lattice constant of the Al material in advance (JP-A-3-280363). However, the effect is insufficient and the cycle life cannot be sufficiently improved.

[0007] In addition, although proposals have been made to occlude and release Li between lattices of other intermetallic compounds of silicides (JP-A-7-240201, JP-A-9-63651, etc.), all of them are large. It was not effective.

Further, although there have been proposals for various negative electrode materials for nonaqueous electrolyte secondary batteries and negative electrodes provided with the materials, there has been no proposal for a manufacturing method for maximizing the performance of the materials.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a method for storing and storing Li.
The amount released is large, so the charge / discharge capacity when used as a negative electrode material of a non-aqueous electrolyte secondary battery is large, and the capacity decrease due to repeated charge / discharge is small,
An object of the present invention is to provide a negative electrode material for a non-aqueous electrolyte secondary battery, which has an excellent cycle life. Another object of the present invention is to provide a method for producing a negative electrode material in which a nonaqueous electrolyte secondary battery provided with a negative electrode composed of the negative electrode material exhibits the best performance.

[0010]

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

However, as in the case of Al, the negative electrode material made of Si has a large volume change due to the occlusion and release of Li, so that it is easy to pulverize due to cracking. For this reason, the capacity is significantly reduced due to the charge / discharge cycle, and the cycle life is extremely shortened. Thus, almost no attempt has been made to use Si as a negative electrode material.

The present inventors have paid attention to the characteristic of an extremely high theoretical capacity of a negative electrode material made of Si, and have repeatedly studied to improve the cycle life thereof. As a result, it is possible to prevent pulverization due to volume expansion and contraction. In addition to taking measures,
Since the oxide film (surface oxide layer) inevitably existing on the surface of the negative electrode material has a great influence on the charge / discharge characteristics, it has been found that it is necessary to take measures against this point.

Specifically, during charge / discharge, a reaction inhibition film mainly composed of Li—Si—O bonds is formed on the alloy surface, and this film has an irreversible electric capacity (electricity required for charging). (The amount of electricity that is not discharged inside). Therefore, as the thickness of the reaction inhibition film increases, the degree of inhibition of the occlusion and release of Li also increases, and the discharge capacity decreases significantly and the cycle life decreases.

To prevent the adverse effect of the reaction inhibition film,
It is effective to control the thickness of the surface oxide layer of the negative electrode material to a certain value or less, and more preferably to control the oxygen concentration of the outermost layer of the surface oxide layer to a certain value or less, thereby inhibiting the reaction accompanying charge / discharge. Film formation is suppressed, cycle life,
It has been found that electrode characteristics such as irreversible electric capacity and charge / discharge efficiency in initial charge / discharge can be improved, and the present invention has been achieved.

According to the present invention, there is provided an alloy powder comprising at least one phase of an element a capable of reversibly combining and dissociating with Li and a phase of an intermetallic compound containing at least one of said elements. And the thickness of the surface oxide layer of this alloy powder is 5
a negative electrode material for a non-aqueous electrolyte secondary battery, wherein the atomic ratio of oxygen / element a at the outermost layer portion of the surface oxide layer of the alloy powder is 0.35 or less. .

Although the method for producing the negative electrode material for a non-aqueous electrolyte secondary battery of the present invention is not particularly limited, it can be produced by utilizing heat treatment. In that case, the compound is reversibly combined with Li
At a temperature lower than the solidus temperature of the alloy, a powder of an alloy containing at least one phase of element a that can be dissociated and a phase of an intermetallic compound containing at least one element a is added to
A method characterized by applying one or more heat treatments of (1) to (3) can be adopted: (1) heat treatment in an inert gas atmosphere having an oxygen concentration of 500 ppm or less; (2) ) Heat treatment in a vacuum of 10 Pa or less; and (3) heat treatment in an inert gas containing 0.5 vol% or more of hydrogen gas.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION A negative electrode material of a non-aqueous electrolyte secondary battery of the present invention comprises a phase of one or more elements a capable of reversibly combining and dissociating with Li (hereinafter referred to as A phase), And a phase of an intermetallic compound containing at least one element a (hereinafter referred to as a B phase).

The A phase that can be combined and dissociated with Li is the main Li storage phase. The B phase of the intermetallic compound has a remarkably small Li storage capacity or no Li storage capacity as compared with the A phase. However, the presence of this B phase in contact with the A phase leads to
The phase change (expansion / shrinkage) of the phase A upon release is restrained by the phase B, which is restrained and cracking and pulverization of the alloy powder are prevented, so that the cycle life is remarkably improved.

Examples of the element a constituting the A phase, which can be reversibly combined and dissociated with Li, include C, Si, Ge, S
n, Pb, P, Al and the like. Of these, Si, Al, and Sn having a large Li storage amount are preferable, and Si is particularly preferable. In the following description, the A phase is the Si phase (the element a is the S phase).
i) will be described as an example, where the element a is other L
The same applies in principle when the element is an occlusion element.

The type of the phase (B phase) of the intermetallic compound containing at least one kind of the element a is not particularly limited. If the B phase has no or a very small Li storage capacity in principle, the A phase can be restricted to a volume change. However, when the B phase is separated from the A phase, the effect of this constraint is lost. Therefore, the B phase is an intermetallic compound phase containing the element a constituting the A phase so that the B phase can be strongly bonded to the A phase during solidification. This intermetallic compound is composed of an element a and one or more elements b selected from Group 2 (IIA), transition, Group 13 (IIIB) and Group 14 (IVB) elements of the periodic table. It is preferably an intermetallic compound.

Examples of the element b constituting the intermetallic compound (B phase) are as follows: Group 2 elements: Be, Mg, Ca, Sr, Ba, Ra; Transition elements: Sc, Ti, V, Cr , Mn, Fe, Co, Ni, Zn, Y,
Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, lanthanoid
(La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, T
m, Yb, Lu), Hf, Ta, W, Re, Os, Ir, Pr, Au, Hg,
Actinoids (Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk,
Cf, Es, Fm, Md, No, Lr); Group 13 elements: B, Al, Ga, In, Tl; Group 14 elements: C, Si, Ge, Sn, Pb.

Among the above elements, preferred are Mg for Group 2 elements; Ti, V, Cr, Mn, Fe, Co, Ni, and Z for transition elements.
n, and rare earth elements (particularly lanthanides such as Nd); 13
A group 14 element is Al; a group 14 element is C, Si, Ge, Sn, and Pb.

The alloy powder used as a negative electrode material in the present invention preferably has a structure composed of only A phase, which is the main Li storage phase, and B phase, which is the phase of the intermetallic compound of the A phase element. , And other phases may coexist.

The negative electrode material for a non-aqueous electrolyte secondary battery of the present invention comprises an alloy powder containing the above-mentioned A phase and B phase, and the surface oxide layer of this alloy powder has a thickness of 5 nm (= 50 °) or less; Preferably, the atomic ratio of O / Si (oxygen / element a) in the outermost layer of the surface oxide layer of this alloy powder is 0.35 or less.
The reason for limiting the surface oxide layer of the alloy powder in this way will be described below.

The thickness of the surface oxide layer : As the thickness of the Li-Si-O-based reaction inhibiting film formed on the surface of the alloy powder by the reaction of oxygen with Li and Si increases, the movement of Li ions accompanying charge / discharge increases. It becomes difficult and the charge / discharge characteristics deteriorate. If the surface oxide layer, which is the oxygen-enriched layer on the surface of the alloy powder, is thick, the oxygen and Li, Si
Reacts, and the above-mentioned reaction inhibiting film grows and becomes thicker, so that the charge / discharge characteristics are rapidly lowered and the cycle life is shortened.

However, if the thickness of the surface oxide layer serving as an oxygen supply source is smaller than 5 nm, oxygen is not supplied sufficiently, so that the Li—Si—O-based reaction inhibition film formed by the reaction of oxygen with Li and Si is not formed. Growth can be suppressed, and a decrease in cycle life due to rapid deterioration of charge / discharge characteristics can be prevented. The thickness of this surface oxide layer is preferably 3 nm or less.

O / Si atomic ratio of the outermost layer of the surface oxide layer :
The oxygen concentration in the surface oxide layer of the alloy powder is usually not constant throughout the oxide layer, but exhibits a concentration gradient that is highest on the outer surface of the powder and decreases toward the inside. Therefore, when the oxygen concentration in the outermost layer portion of the surface oxide layer is high, oxygen sufficient for forming a Li-Si-O-based reaction inhibition film is supplied from the surface oxide film,
As the cycle is repeated, the reaction inhibition film grows,
Discharge characteristics deteriorate, resulting in a decrease in cycle life. As a result of examination from this point, if the oxygen concentration in the outermost layer portion of the surface oxide layer is 0.35 or less in O / Si atomic ratio, oxygen required for growing the reaction inhibition film is not sufficiently supplied, and the cycle life is shortened. I found that it could be improved. Desirably, the O / Si atomic ratio is 0.25 or less.

In the present invention, the thickness of the surface oxide layer means
When the alloy powder is quantitatively analyzed for oxygen in the depth direction from the surface, it means the thickness of the portion until the oxygen concentration becomes constant. The O / Si atomic ratio of the outermost layer is the O / Si atomic ratio determined by a surface analyzer. Even if the element a is an element other than Si, the value of the atomic ratio of O / element a indicating the oxygen concentration in the outermost layer may be the same as when a is Si.

The non-aqueous electrolyte secondary battery negative electrode material of the present invention comprises:
It can be produced by melting the alloy raw material, solidifying the obtained molten alloy, and pulverizing as necessary. As a solidification method, it is preferable to employ a rapid solidification method so as to obtain a structure in which an A phase which is a Li storage phase and a B phase which is an intermetallic compound phase for restraining a change in volume are finely mixed. . Preferred quenching and solidifying methods include atomizing, particularly gas atomizing, rotating electrode, and roll quenching.
(Both single and twin rolls are possible), and centrifugal casting. Since a powdery alloy is obtained by the atomizing method or the rotating electrode method, pulverization may not be necessary in some cases. Since a flaky alloy is obtained by the roll quenching method or the centrifugal casting method, the alloy is pulverized and powdered.

The alloy raw material to be melted is adjusted so that the element of the Li storage phase (A phase) is in excess of the phase of the intermetallic compound (B phase). For example, in the NiSi binary intermetallic compound since it is NiSi ₂ and NiSi, composition corresponding to NiSi _2: selecting the composition of the raw material so that (Si about 49 wt%) of Si-rich. Thereby, a Si phase and an intermetallic compound phase (NiSi phase and / or NiSi ₂ phase) precipitate during solidification. In some alloy systems, the intermetallic compound phase and the Li storage phase may form a eutectic. As long as the Li storage phase and the intermetallic compound phase are present, the precipitation form of each phase is not particularly limited.

According to the present invention, as described above, an alloy powder having a thin surface oxide layer and / or a low oxygen concentration in the surface layer is manufactured, so that oxygen can be dissolved in the alloy even when the alloy material is melted. It is advantageous to suppress as far as possible. In that sense, the oxygen content in the melting atmosphere gas of the alloy raw material is set to 500
It is preferable to limit to ppm or less. Desirably, the oxygen content is less than 100 ppm.

It is preferable that the coagulation atmosphere is also a vacuum or an inert gas atmosphere, and its oxygen content is reduced as much as possible. Further, when the pulverization is performed, it is preferable that the pulverization atmosphere is also an inert gas atmosphere having a low oxygen content.

When an alloy is manufactured by such rapid solidification, the obtained alloy may be subjected to a heat treatment in order to remove lattice distortion. The heat treatment is performed at a temperature lower than the solidus temperature of the alloy so that no melting of the alloy occurs during the heat treatment. A preferred heat treatment temperature is higher than the solidus temperature.
The temperature is 100 ° C. or higher, more preferably 200 ° C. or higher. Thereby, coarsening of the structure during the heat treatment can be suppressed to a minimum.

During the heat treatment, the surface of the alloy powder is oxidized, and the thickness of the surface oxide layer increases, and / or the oxygen concentration in the outermost layer increases, whereby the thickness and / or the thickness of the above-described surface oxide layer increase. Alternatively, there is a possibility that the oxygen concentration in the outermost layer portion is deviated. To prevent this, heat treatment is performed under the conditions that satisfy any of the following (1) to (3) to minimize the oxidation of the surface of the alloy powder as much as possible, and in some cases, the oxide layer that has already been formed And the oxygen concentration in the surface layer can be reduced.

(1) Inert gas atmosphere When the heat treatment is performed in an inert gas atmosphere, the heat treatment step is performed in an inert gas atmosphere having an oxygen concentration of 500 ppm or less in the atmosphere to reduce the thickness of the oxide layer by 5%. nm or less. This oxygen concentration is preferably at most 100 ppm, more preferably at most 50 ppm.

(2) Vacuum Atmosphere When the heat treatment is performed in a vacuum atmosphere, the heat treatment is performed under a high vacuum at a pressure of 10 Pa or less. The pressure is preferably 1 Pa or less.

(3) Hydrogen-containing heat treatment atmosphere To prevent surface oxidation, it is effective to perform heat treatment in a reducing atmosphere. For this purpose, heat treatment is performed in an inert gas atmosphere containing 0.5 vol% or more of hydrogen gas. If the hydrogen gas concentration is lower than this, it is substantially the same as the inert gas alone, so the oxygen concentration needs to be reduced as in (1). The hydrogen gas concentration is preferably set to 1.0 vol% or more. The upper limit of the hydrogen gas concentration is not particularly specified, but considering the danger of explosion, it is not preferable to make the concentration higher than 10 vol%. Any one of the heat treatments (1) to (3) may be carried out, but two or three heat treatments may be carried out in combination.

In order to further reduce the surface oxidation of the alloy powder during the heat treatment, an alloy material containing an easily oxidizable element which is easily oxidized by the alloy may be provided in the heat treatment furnace as an oxygen getter. Thereby, the oxygen getter preferentially reacts with oxygen to capture oxygen, so that the oxygen concentration in the furnace is reduced, and the suppression of surface oxidation of the alloy powder produced in the present invention becomes more effective. When the alloy powder contains a Si phase, it is desirable to use, as the easily oxidizable material, a Ti or Zr metal having a lower free energy of oxide formation than Si, or an alloy of these metals.

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

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

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

When a carbonaceous material is compounded in the negative electrode, it is preferable to use the carbon material in an amount of 5% by weight or more and 80% by weight or less with respect to the negative electrode material of the present invention. If the amount is less than 5 wt%, sufficient conductivity cannot be provided, and if it exceeds 80 wt%, the capacity of the negative electrode decreases. More preferred blending amount is 20wt
% Or more and 50 wt% or less.

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

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

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

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

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

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

[0049]

【Example】

Example 1 An alloy powder having the composition shown in Tables 1 and 2 was
It was produced by a gas atomizing method as described below. In the alloy compositions shown in Tables 1 and 2, the Li storage phase is Si, and the intermetallic compound phase precipitated during solidification is Ni.
In -52Si NiSi + NiSi _2, the _{Co-54Si CoSi 2, Ti-} 60
It is TiSi _{2 for} Si and VSi ₂ for V-59Si.

A raw material having a predetermined composition is melted at a high frequency in an argon atmosphere to form a molten metal. After the molten metal is poured into a tundish, a fine stream of the molten metal is formed through pores provided at the bottom of the tundish. The powder was atomized by spraying a high-pressure atomizing gas. Argon gas was used as the spray gas. After cooling to room temperature, the alloy powder was taken out, and a part of the alloy powder was subjected to a heat treatment in an argon gas atmosphere. Tables 1 and 2 also show the oxygen concentration in the melting atmosphere and the heat treatment atmosphere and the heat treatment conditions.

In order to determine the thickness of the surface oxide layer of the obtained alloy powder and the O / Si atomic ratio of the outermost layer, this alloy powder was analyzed using a micro Auger apparatus under the following conditions.

First, the O / Si atomic ratio was calculated from the results of the quantitative analysis of the surface. Further, quantitative analysis of oxygen in the depth direction was performed while performing Ar sputtering, and the depth until the oxygen concentration became constant was defined as the thickness of the surface oxide layer.

Separately, the characteristics of these alloy powders as negative electrode materials were evaluated as follows. 63 μm of each alloy powder
A powder having an average particle size of 30 μm, obtained by classification with a sieve, is used. 10 wt% of polyvinylidene fluoride as a binder and 10 wt% of N-methylpyrrolidone as a solvent are added to the powder.
Added and mixed. Next, carbon material (acetylene black) powder was added as conductive powder in an amount of 10% by weight of the mixture, and kneaded to form a uniform slurry. This slurry was applied to an electrolytic copper foil having a thickness of 30 μm, dried, rolled and consolidated, and then punched out using a punch having a diameter of 13 mm to obtain a disk member, which was used as a negative electrode. The thickness of the negative electrode material layer on the copper foil was about 100 μm.

The performance of the negative electrode as a single 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 solution in which LiPF ₆ as a supporting electrolyte was dissolved at a concentration of 1 M in a 1: 1 mixed solvent of ethylene carbonate and dimethoxyethane. The measurement was performed at 25 ° C., and charging and discharging were performed using a device capable of maintaining an inert atmosphere such as a glove box under the condition that the dew point of the atmosphere was about −70 ° C.

First, the battery is charged by 1/10 charge (condition 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 of the negative electrode 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. This charge / discharge cycle was repeated, and the discharge capacity at the 300th cycle was measured. The discharge capacity is
It is expressed in units of mAh / cc (cc is calculated from the volume of the negative electrode plate, the area of the negative electrode plate and the thickness of the negative electrode material layer).

From the measured values of the discharge capacities, the cycle life and charge / discharge efficiency were calculated as follows. (a) Cycle life Cycle life (%) = (discharge capacity at 300th cycle) / (discharge capacity at 1st cycle) x 100 where discharge capacity at 1st cycle is the first charge, then discharge The discharge capacity at the time of doing. Also, 300
The discharge capacity at the cycle refers to the discharge capacity at the time of performing the 300th charge and discharging. This cycle life is 80%
Above is good.

(B) Charging / Discharging Efficiency The battery is completely discharged before measuring the charging / discharging efficiency, and charging and discharging are continuously performed in the subsequent cycle according to the above conditions. The amount of discharged electricity and the amount of charged electricity at that time are measured, and the charge / discharge efficiency is calculated by the following equation. Charge / discharge efficiency (%) = (discharged electricity / charged electricity immediately before discharge) × 100 In this example, the charge and discharge efficiencies at the first and third cycles were measured. The charge / discharge efficiency in the first cycle indicates the degree of initial activation. If the charge / discharge efficiency is high, the capacity is higher than the initial one, and the charge / discharge repeated operation for activating the battery becomes unnecessary or reduced. can do.

Table 1 shows that several samples having different values of the thickness of the surface oxide layer by the surface analysis described above are shown.
The results of alloy composition, thickness of surface oxide layer, and negative electrode characteristics (discharge capacity, charge / discharge efficiency, cycle life) are shown.

[0059]

[Table 1]

From Table 1, it can be seen that the alloy powder having a surface oxide layer thickness of more than 5 nm has a lower discharge capacity than the alloy powder having the same composition and a surface oxide layer thickness of 5 nm or less, and also has the first cycle. Low charge and discharge efficiency. That is, a part of the charged electricity cannot be taken out during discharging. There is also a problem that the cycle life is lower than 80%.

The alloy powder having a surface oxide layer having a thickness of 5 nm or less has a high charge / discharge efficiency of 70% or more in the first cycle and a high cycle life of 80% or more. An alloy powder having a surface oxide layer thickness of 3 nm or less has a very high charge and discharge efficiency of 90% or more in the first cycle and a cycle life of 90% or more.
% Or more has good characteristics.

Table 2 shows that the alloy composition, the thickness of the surface oxide layer, and the thickness of the outermost layer portion of some samples having different values of the O / Si atomic ratio of the outermost layer portion of the surface oxide layer by the surface analysis described above. 2 shows the results of the O / Si atomic ratio and the characteristics of the negative electrode (discharge capacity, charge / discharge efficiency, cycle life).

[0063]

[Table 2]

The following can be seen from Table 2: The alloy powder having an O / Si atomic ratio of 0.35 or less at the outermost layer of the surface oxide layer has a higher discharge capacity and higher charge / discharge efficiency in the first cycle. Also, the cycle life is improved to 85% or more. When the atomic ratio is 0.25 or less, the charge / discharge efficiency and the cycle life are further improved.

[0065]

Example 2 An alloy having a composition shown in Table 3 was prepared by a single roll quenching method from a molten metal, and the obtained ribbon-like alloy was pulverized and classified with a 60 μm sieve to obtain an alloy powder having an average particle diameter of 30 μm. Obtained. Each of these processing atmospheres was an argon gas atmosphere. Table 3 shows the oxygen concentration in the melting atmosphere.

The obtained alloy powder was heat-treated under various conditions shown in Table 3. The heat treatment of some alloy powders was performed by installing an easily oxidizable material as an oxygen getter in a heat treatment furnace.
The thickness of the surface oxide layer and the negative electrode properties of the heat-treated alloy powder were investigated in the same manner as in Example 1, and the results are also shown in Table 3.

[0067]

[Table 3]

Table 3 shows that the heat treatment atmosphere is an inert gas atmosphere having an oxygen concentration of 500 ppm or less, a high vacuum of 10 Pa or less, or an inert gas atmosphere.
When the reducing gas is mixed with a hydrogen gas of 0.5 vol% or more, oxidation of the alloy powder surface during the heat treatment is prevented, the thickness of the surface oxide layer can be controlled to 5 nm or less, and a good cycle life can be obtained. . Further, when an oxygen getter made of an easily oxidizable material such as Zr or Ti powder is provided in the heat treatment atmosphere, the thickness of the oxide layer can be further reduced without using a reducing gas, and the cycle life can be further improved. .

[0069]

According to the present invention, it is possible to obtain a negative electrode material for a non-aqueous electrolyte secondary battery having a very high discharge capacity and a cycle life of 80% or more as compared with a conventional atmosphere material made of a carbon material. It is expected to contribute to improving the performance of non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries.

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Noriyuki Nego 1-8 Fuso-cho, Amagasaki City, Hyogo Prefecture Within Sumitomo Metal Industries, Ltd. Electronics Technology Research Laboratory (72) Inventor Yukiteru Takeshita 1-8 Fuso-cho, Amagasaki City, Hyogo Prefecture No. Sumitomo Metal Industries, Ltd. Electronics Technology Research Laboratory (72) Inventor Motoharu Kobiga 1-8 Fuso-cho, Amagasaki City, Hyogo Prefecture Sumitomo Metal Industries, Ltd. Electronics Technology Research Laboratory (72) Inventor Koji Yonemura Fuso, Amagasaki City, Hyogo Prefecture No. 1-8, Sumitomo Metal Industries, Ltd.Electronic Technology Research Laboratories (72) Inventor Yoshiaki Nitta 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Haruna Shimamura Kadoma, Osaka Pref. 1006 Kadoma Matsushita Electric Industrial Co., Ltd. F-term (reference) 5H029 AJ05 AK03 AL01 AL11 AM03 AM04 AM05 AM07 DJ12 DJ16 HJ02 HJ04 5H050 AA07 BA17 CA07 CA08 CA09 CB01 CB02 DA03 FA12 FA18 HA02 HA04 HA12

Claims (2)

[Claims] 1. An alloy powder comprising at least one phase of an element a capable of reversibly combining and dissociating with Li and a phase of an intermetallic compound containing at least one element a. A negative electrode material for a non-aqueous electrolyte secondary battery, wherein the thickness of the surface oxide layer of the powder is 5 nm or less. 2. The negative electrode material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the atomic ratio of oxygen / element a at the outermost layer portion of the surface oxide layer of the alloy powder is 0.35 or less.