JP4794972B2 - Non-aqueous electrolyte secondary battery negative electrode and non-aqueous electrolyte secondary battery including the same - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery having a high capacity and a long life, and more particularly to improvement of a negative electrode for a non-aqueous electrolyte secondary battery.

  Many researches and developments have been made using metallic lithium capable of realizing a high energy density at a high voltage as a negative electrode of a nonaqueous electrolyte secondary battery. Currently, lithium ion batteries that use a graphite material that reversibly occludes and releases lithium and has excellent cycle life and safety as a negative electrode have been put into practical use.

  However, in a battery using a graphite material as a negative electrode, the achieved practical capacity of graphite is about 350 mAh / g, which is quite close to the theoretical capacity of graphite material (372 mAh / g). Therefore, as long as a graphite material is used for the negative electrode, future dramatic capacity improvement cannot be expected. On the other hand, the capacity required for a non-aqueous electrolyte secondary battery serving as an energy source tends to increase as the functionality of portable devices increases. Therefore, in order to realize a further increase in capacity, a negative electrode material having a capacity higher than that of graphite is required.

  At present, an alloy material (alloy forming material) containing silicon or tin is attracting attention as a material that provides high capacity. Metal elements such as silicon and tin can occlude and release lithium ions electrochemically, and can be charged and discharged with a much larger capacity than graphite materials. For example, silicon is known to have a theoretical discharge capacity of 4199 mAh / g, which is 11 times higher than that of graphite.

  On the other hand, the alloy material forms lithium alloys such as lithium-silicon and lithium-tin when occludes lithium. The formation of a lithium alloy involves a very large expansion based on changes in the crystal structure of the alloy. For example, the volume of silicon expands theoretically by a factor of 4.1 by charging lithium to the maximum. Therefore, the active material, that is, the alloy material is peeled off from the current collector of the negative electrode, the electric conduction is lost, and battery characteristics, particularly high rate discharge characteristics and charge / discharge cycle characteristics are deteriorated. In the case of graphite, since the intercalation reaction in which lithium is inserted between graphite layers is used, the volume of graphite expands only 1.1 times.

  Many attempts have been made to use a combination of graphite and an alloy material from the viewpoint of alleviating the above expansion and obtaining a high capacity. However, when graphite and an alloy material are simply mixed, the alloy material expands in a non-uniform direction within the electrode plate, so that the surrounding graphite moves under stress, leading to peeling. As a result, similarly to the negative electrode using the alloy material alone, the electron conductivity is lowered, and the high rate discharge characteristics and charge / discharge cycle characteristics of the battery are lowered.

  In Patent Document 1, the ratio of the silicon compound particle size RSi to the carbon material particle size Rc: By controlling RSi / Rc to 1 or less, the influence of the greatly expanding alloy material is alleviated and the battery characteristics are improved. Proposals have been made. However, even if the influence of the expansion of the alloy is mitigated by controlling the particle size, the current collection deterioration due to cracking of the alloy particles cannot be suppressed. Further, cracking of the alloy particles occurs every charge / discharge cycle, and the surface area of the alloy material increases, so that a side reaction of film formation on the alloy surface becomes a problem. Therefore, the proposal of Patent Document 1 is not suitable for practical use.

In Patent Document 2, it is proposed to embed metal particles or metal oxide particles capable of electrochemically reacting with Li in carbon particles. In this proposal, the metal particles or metal oxide particles are fixed to the surface of the carbon particles, thereby suppressing separation due to expansion. In this case, a high effect can be obtained in the initial charge / discharge cycle, but the metal particles or the metal oxide particles are eventually detached from the carbon particles by repeated expansion and contraction. As a result, the expansion coefficient of the negative electrode increases, and peeling occurs across the entire electrode plate.
JP 2000-357515 A JP 2000-243396 A

  As described above, the combined use of an alloy material and a graphite material has been widely studied from the viewpoint of using a high-capacity alloy material as a negative electrode material, but both proposals are sufficiently affected by the uneven expansion of the alloy material. It has not been reduced. In other words, in the case of the conventional proposal, the disconnection of the electrical continuity between the particles in the negative electrode and the separation of the alloy material and the graphite material from the current collector occur, eventually resulting in a decrease in the electronic conductivity of the negative electrode and the battery characteristics. descend.

  In view of the above, the present invention provides battery characteristics associated with expansion of an alloy material as described above when an alloy material containing Si and electrochemically occluding and releasing Li and a graphite material are used as active materials. The purpose is to suppress the decrease.

  That is, the present invention includes at least one alloy material capable of electrochemically inserting and extracting Li and graphite, and the alloy material includes an A phase mainly composed of Si, and at least one transition metal element. A ratio of the A phase to the total weight of the A phase and the B phase, including at least one of the A phase and the B phase including a B phase composed of an intermetallic compound with Si. However, it is more than 40% by weight and 95% by weight or less, and the ratio of graphite to the total weight of the alloy material and graphite is 50% by weight or more and 95% by weight or less. .

The alloy material is preferably present in the gap formed by the graphite particles.
The maximum particle size of the alloy material is desirably 10 μm or less.
It is desirable that at least a part of the alloy material is bonded to the graphite surface via a binder.
The ratio of the average particle size Ralloy of the alloy material to the average particle size Rgraphite of graphite: Ralloy / Rgraphite is preferably in the range of 0.15 to 0.90.
The negative electrode of the present invention can further contain a conductive additive. The specific surface area of the conductive additive is desirably 10 m ² / g or more.

The conductive aid is desirably carbon fiber having an aspect ratio of 10 or more. It is desirable that at least one end of the carbon fiber is attached or bonded to the alloy material, or attached or bonded to graphite.
It is particularly preferable that at least a part of the carbon fiber has one end attached to or bonded to the alloy material and the other end attached to or bonded to the graphite.
The carbon fiber can be obtained by heating at least one of the alloy material and graphite under a hydrocarbon stream.
The ratio of the conductive additive to the total weight of the alloy material, graphite, and conductive additive is desirably 10% by weight or less.

  The present invention is also a nonaqueous electrolyte secondary battery composed of a positive electrode capable of electrochemically inserting and extracting Li, the negative electrode described above, and a nonaqueous electrolytic solution, wherein the negative electrode includes Li electrochemically. The alloy material includes at least one kind of occluding and releasing alloy material and graphite, and the alloy material includes an A phase mainly composed of Si and a B phase composed of an intermetallic compound of at least one transition metal element and Si. And at least one of the A phase and the B phase is composed of a microcrystalline or amorphous region, and the proportion of the A phase in the total weight of the A phase and the B phase is more than 40 wt% and not more than 95 wt% The ratio of graphite to the total weight of the alloy material and graphite relates to a non-aqueous electrolyte secondary battery having a weight ratio of 50 wt% or more and 95 wt% or less.

  According to the present invention, in a negative electrode using a combination of an alloy material and a graphite material, it is possible to suppress a decrease in battery characteristics due to expansion of the alloy material, thereby realizing a high capacity non-aqueous electrolyte secondary battery with excellent cycle characteristics. it can.

  The alloy material capable of electrochemically inserting and extracting Li according to the present invention has characteristics different from those of conventional alloy materials. The alloy material according to the present invention includes an A phase mainly composed of Si and a B phase composed of an intermetallic compound of a transition metal element and Si. This alloy material is not only moderated in expansion, but also suppresses a decrease in electronic conductivity of the negative electrode accompanying expansion and contraction. Therefore, the negative electrode for a non-aqueous electrolyte secondary battery of the present invention containing this alloy material and graphite gives a battery with high capacity and excellent cycle characteristics.

  The A phase is a phase responsible for insertion and extraction of Li, and is a phase that can electrochemically react with Li. The A phase may be a phase mainly composed of Si, but is preferably a phase composed of Si alone. When the A phase is composed of Si alone, the amount of Li absorbed and released by the alloy material per unit weight or unit volume can be made extremely large. However, since Si simple substance is a semiconductor, it has poor electronic conductivity. Therefore, it is effective to add a trace amount of additive elements such as phosphorus (P), hydrogen (H), etc., or transition metal elements to the A phase up to about 5% by weight.

The B phase is composed of an intermetallic compound of a transition metal element and Si. The intermetallic compound containing Si has a high affinity with the A phase, and cracks at the interface between the A phase and the B phase hardly occur. In addition, the B phase has higher electron conductivity and higher hardness than the Si single phase. Therefore, the B phase works to supplement the low electronic conductivity of the A phase and to maintain the shape of the alloy particles against the expansion stress. There may be a plurality of B phases. That is, two or more types of intermetallic compounds having different compositions may exist as the B phase. For example, MSi ₂ and MSi (M is a transition metal) may be present in the alloy material particles. Further, intermetallic compounds containing different transition metal elements, for example, M ¹ Si ₂ and M ² Si ₂ (M ¹ and M ² are different transition metals) may exist in the alloy material particles.

  The transition metal element is preferably at least one selected from the group consisting of Ti, Zr, Ni, Co, Mn, Fe and Cu, and particularly preferably at least one selected from the group consisting of Ti and Zr. These element silicides have higher electronic conductivity and higher hardness than silicides of other elements.

  The A phase and / or the B phase are composed of microcrystalline or amorphous regions. When a crystalline alloy material is used, the alloy particles are liable to crack with the occlusion of Li, and the current collecting property of the negative electrode is rapidly reduced, resulting in a deterioration in battery characteristics. On the other hand, when a microcrystalline or amorphous alloy material is used, cracking of the alloy particles due to expansion accompanying the occlusion of Li hardly occurs.

  In the present invention, an alloy material having a crystal grain (crystallite) diameter of 50 nm or less is defined as a microcrystal. If the alloy material has a microcrystalline region, one or more peaks that are not sharp but can be obtained with a half-value width are observed in the diffraction spectrum of alloy particles obtained by X-ray diffraction measurement. The The diameter of the crystal grain (crystallite) of the alloy material is obtained by calculating the half width of the peak with the highest intensity in the diffraction spectrum of the alloy particle obtained by X-ray diffraction measurement. It can be calculated from

  On the other hand, when the alloy material has an amorphous region, a broad halo pattern in which the half width cannot be recognized in the range of 2θ = 15 to 40 ° of the diffraction spectrum of the alloy particle obtained by X-ray diffraction measurement. Is observed.

The proportion of the A phase in the total weight of the A phase and the B phase is more than 40% by weight and 95% by weight or less. By increasing the proportion of the A phase to more than 40% by weight, a high capacity can be effectively achieved. In addition, by making the ratio of the A phase 95% by weight or less, the low electron conductivity of the A phase can be supplemented and the effect of maintaining the shape of the alloy material particles can be maintained high. It becomes easy to make it amorphous. From the viewpoint of prominent these effects, the ratio of the A phase to the total weight of the A phase and the B phase is preferably 65% by weight or more and 85% by weight or less, and 70% by weight or more and 80% by weight or less. It is particularly preferred.
On the other hand, if the proportion of the A phase exceeds 95% by weight, it becomes difficult to make the alloy material particles microcrystalline or amorphous, which is not suitable for the present invention. On the other hand, if the proportion of the A phase is less than 40% by weight, the capacity is lower than that of a battery using conventional graphite as a negative electrode, which is not suitable for the present invention.

  The content of Si contained in the alloy material according to the present invention is preferably 60% by weight or more. When the proportion of Si in the whole alloy is 60% by weight or more, when the transition metal occupying the balance and Si form an intermetallic compound (silicide), the proportion of the A phase exceeds 40% by weight, and the effect Therefore, it is possible to realize a high capacity.

  The negative electrode of the present invention includes the above alloy material and graphite. From the viewpoint of exerting both the alloy material and graphite in a well-balanced manner, the ratio of graphite to the total weight of the alloy material and graphite is 50% by weight or more and 95% by weight or less, and 65% by weight or more and 85% by weight. % Or less is preferable. When the amount of graphite is less than 50% by weight, the amount of graphite in contact with the alloy material decreases, and the number of contact points between the alloy materials increases. For this reason, voids are easily generated inside the negative electrode due to the expansion of the alloy material, and the expansion of the entire negative electrode is increased. On the other hand, when the amount of graphite is more than 95% by weight, the contribution of the alloy material to the capacity becomes extremely small, and only a capacity comparable to that of the negative electrode using only graphite can be obtained.

  The graphite used in the present invention may be any graphite material as long as it can generally be used for a non-aqueous electrolyte secondary battery. For example, natural graphite such as flaky graphite and artificial graphite produced by various methods can be used.

  The average particle size of graphite is preferably 5 μm or more and 50 μm or less, and more preferably 7 μm or more and 25 μm or less. If the average particle diameter of graphite becomes too fine, the ability to follow deformation increases, and the adverse effect on the electrode plate due to expansion of the alloy material is alleviated, but the specific surface area of graphite itself increases. From the viewpoint of suppressing side reactions between graphite and electrolyte, reducing the film formed on the graphite surface, and limiting the irreversible capacity of the negative electrode to a small amount, the average particle size of graphite should be 5 μm or more, and the ratio of graphite itself It is desirable not to increase the surface area too much. Further, when the average particle diameter of graphite is larger than 50 μm, irregularities are easily formed on the negative electrode surface, and voids in the negative electrode are increased, making it difficult to collect current to the alloy in the negative electrode. From the viewpoint of obtaining a negative electrode having excellent current collecting properties, it is desirable that the average particle size of graphite is 50 μm or less.

  Usually, a negative electrode for a non-aqueous electrolyte secondary battery includes a current collector made of a metal foil and a negative electrode mixture layer supported on both surfaces thereof. Accordingly, the particle size of the graphite or alloy material may be set to be smaller than the thickness per one side of the negative electrode mixture layer.

  The alloy material is preferably present in the gap formed by the graphite particles. In FIG. 1, the cross-sectional photograph of an example of the negative electrode of this invention is shown. The negative electrode in FIG. 1 includes a current collector 1 and a mixture layer supported on one surface thereof. The mixture layer is composed of graphite particles 3 having a large particle diameter and alloy particles 2 arranged so as to fill the voids. In addition, there are appropriate voids around the alloy particles 2. By adopting such a structure, when the alloy particles 2 expand, the expansion can be relaxed, and current collection at the time of expansion also becomes easy. In addition, according to the above structure, the electrolyte can sufficiently spread around the alloy material, and high rate discharge characteristics and charge / discharge cycle characteristics can be improved.

  From the viewpoint of easily obtaining the structure shown in FIG. 1, the maximum particle size of the alloy material is preferably 10 μm or less, and more preferably 5 μm or less. When the maximum particle size of the alloy material is larger than 10 μm, the ratio of the alloy particles entering between the graphite particles decreases, and the ratio of the alloy material that aggregates increases. When the alloy material is agglomerated, when the alloy particles expand, they may push each other and cause excessive expansion in the negative electrode.

Moreover, it is desirable that at least a part of the alloy material is bonded to the graphite surface via a binder. Such a structure is excellent in terms of alleviating excessive expansion and maintaining current collecting properties. By having such a structure, even if the alloy material repeatedly expands and contracts, the alloy material tends to exist stably in the voids formed between the graphite particles. As a result, excessive expansion of the negative electrode mixture layer is suppressed. Furthermore, current collection can always be ensured by fixing the alloy material to the surface of the graphite particles.
In order to obtain such a structure, it is desirable to use a technique in which graphite and a binder are mixed and then an alloy material is added and further mixed. Since there are almost no functional groups on the graphite surface, the affinity with the binder is low. Therefore, it is desirable to mix graphite and a binder in advance while applying a strong stirring force or stress. On the other hand, the surface of the alloy material is generally covered with an oxide or the like, and has high affinity with the binder. Therefore, the above structure can be obtained only by mixing the alloy material with the mixture of graphite and binder.

  From the viewpoint of easily obtaining the structure as shown in FIG. 1, the ratio of the average particle diameter Ralloy of the alloy material to the average particle diameter Rgraphite of graphite: Ralloy / Rgraphite may be in the range of 0.15 to 0.90. desirable. For example, when the average particle diameter Rgraphite of graphite is 18 μm, the preferable average particle diameter Ralloy of the alloy material is in the range of 2.7 μm to 16.2 μm. However, as described above, it is more desirable that the maximum particle size of the alloy material is 10 μm or less. Therefore, the optimum range of Ralloy is 2.7 μm or more and 10 μm or less.

  When Ralloy / Rgraphite is less than 0.15, a large number of alloy particles are more likely to be sandwiched in the voids between the graphite particles, so that when the alloy particles expand, they press each other and generate a relatively large expansion in the negative electrode. There are things to do. On the other hand, when Ralloy / Rgraphite is larger than 0.9, the graphite particles and the alloy particles have substantially the same size, so that the voids inside the negative electrode for relaxing the expansion of the alloy particles are reduced. The most preferable range of Ralloy / Rgraphite is 0.2 to 0.4, and in this range, the ability to relax the expansion of the alloy material is the highest.

  The negative electrode can further contain a conductive additive. The conductive additive is added mainly to improve the current collection efficiency from the alloy material. Therefore, it is preferable that the conductive additive is mainly present in the vicinity of the alloy particles.

The specific surface area of the conductive additive is desirably 10 m ² / g or more. Although it is possible to improve the current collection efficiency even with a conductive auxiliary material having a specific surface area of less than 10 m ² / g, from the viewpoint of obtaining the effect of improving the current collection efficiency with a small amount, the specific surface area is 10 m ² / g or more. It is desirable to use a conductive aid.
As the conductive aid, for example, carbon black is preferable, and acetylene black is particularly preferable. Carbon fibers having an aspect ratio of 10 or more are also suitable as a conductive additive. In particular, the carbon fiber contributes to maintaining the current collecting property between the particles of the alloy material or between the alloy material and graphite.

  It is desirable that at least one end of the carbon fiber is attached to the surface of the alloy material or graphite, and it is particularly desirable that the carbon fiber is bonded (for example, chemically bonded) to the surface of the alloy material or graphite. This stabilizes the transfer of electrons via the carbon fiber even while the alloy material is expanding or contracting. As a result, current collection is improved. It is particularly desirable that one end of the carbon fiber is attached or bonded to the alloy material and the other end is attached or bonded to the graphite present in the vicinity. When the carbon fiber is bonded to both the alloy material and graphite, the alloy material is more strongly fixed to the graphite surface. Therefore, the effect of reducing the expansion of the negative electrode is enhanced.

  As the carbon fiber, vapor grown carbon fiber (VGCF) or carbon nanotube can be used. For example, carbon fiber can be imparted to the negative electrode as a conductive additive by kneading at least one of the alloy material and graphite and carbon fiber together with a binder. In addition, the carbon fiber can be grown on the surface of the alloy material or graphite by heating at least one of the alloy material and graphite in a hydrocarbon stream. The heating atmosphere is desirably a reducing atmosphere. As the hydrocarbon, for example, methane, ethane, ethylene, acetylene, or the like can be used. 400-800 degreeC is suitable for heating temperature. Carbon monoxide may be used instead of hydrocarbon. When the heating temperature is lower than 400 ° C., carbon fibers are hardly formed, and sufficient conductivity may not be imparted to the negative electrode. Conversely, when the heating temperature is higher than 800 ° C., highly conductive carbon fibers are produced, but the crystallization of the alloy material proceeds, and the electrode characteristics may deteriorate.

  From the viewpoint of suppressing a decrease in discharge capacity and an increase in irreversible capacity due to side reactions, the ratio of the conductive additive to the total weight of the alloy material, graphite, and conductive additive is desirably 10% by weight or less, It is further desirable that the amount be 5 wt% or less.

  The negative electrode includes a binder for fixing the graphite material, the alloy material, and the like to each other and fixing the mixture layer to the current collector. As the binder, a material that is electrochemically inactive with respect to Li in the working potential range of the negative electrode and does not affect other substances as much as possible is selected. For example, styrene-butadiene copolymer rubber, polyacrylic acid, polyethylene, polyurethane, polymethyl methacrylate, polyvinylidene fluoride, polytetrafluoroethylene, carboxymethylcellulose, methylcellulose and the like are suitable as the binder. These may be used alone or in combination. The amount of the binder added is preferably as large as possible from the viewpoint of maintaining the structure of the mixture layer, but is preferably as small as possible from the viewpoint of improving battery capacity and improving discharge characteristics.

  When the negative electrode of the present invention is composed of a current collector made of a metal foil and a negative electrode mixture layer supported on both surfaces thereof, it is desirable to use a copper foil or a copper alloy foil as the current collector. In the case of a copper alloy foil, the copper content is preferably 90% by weight or more. From the viewpoint of improving the strength or flexibility of the current collector, it is effective to include an element such as P, Ag, or Cr in the current collector.

  The thickness of the current collector is preferably 6 μm or more and 40 μm or less. A current collector having a thickness of less than 6 μm is difficult to handle, and it is difficult to maintain the strength required for the current collector, and the current collector may be broken or wrinkled by expansion and contraction of the mixture layer. On the other hand, when the current collector is thicker than 40 μm, the volume ratio of the current collector to the battery becomes large, which is disadvantageous in terms of capacity depending on the type of battery. Also, thick current collectors are difficult to handle, such as difficult to bend.

  The negative electrode mixture layer is made of a mixture of an alloy material, graphite, a binder, and the like, and includes other additives such as a conductive additive as necessary. The thickness of the negative electrode mixture layer is generally from 10 μm to 100 μm, and often from 50 μm to 100 μm per side of the current collector. Although the thickness of the mixture layer may be thinner than 10 μm, it is necessary to consider that the volume ratio of the current collector in the negative electrode does not become too large. Moreover, although the thickness of the mixture layer may be thicker than 100 μm, the high-rate discharge characteristics may be deteriorated because the electrolyte solution hardly penetrates to the vicinity of the current collector.

Density of the negative electrode mixture layer is preferably in the discharged state is ^{0.8g / cm 3 ~2g / cm 3} . The porosity of the negative electrode mixture layer is desirably 70% or less. The porosity is calculated by (measured density of negative electrode mixture layer) / (true density of negative electrode mixture layer) × 100 (%). The true density of the negative electrode mixture layer is calculated from the true density and mixing ratio of each negative electrode material (alloy material, graphite, binder, etc.).

The non-aqueous electrolyte secondary battery of the present invention includes the above-described negative electrode, a positive electrode capable of electrochemically inserting and extracting Li, and a non-aqueous electrolyte.
If a positive electrode is proposed as a positive electrode of a nonaqueous electrolyte secondary battery, it can be used without limitation. The manufacturing method of the positive electrode may be performed as usual. For example, a positive electrode active material, a conductive agent such as carbon black, and a binder such as polyvinylidene fluoride are mixed in a liquid phase, and the obtained paste is applied onto a positive electrode current collector made of Al or the like. The positive electrode is obtained by drying and rolling.

Any positive electrode active material can be used without particular limitation as long as it is proposed as a positive electrode active material for a non-aqueous electrolyte secondary battery, but a lithium-containing transition metal compound is preferred. Representative examples of the lithium-containing transition metal compound include, but are not limited to, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , and LiMnO ₂ . A compound obtained by substituting a transition metal element of the above compound with a different metal element is also preferably used. For _{example, LiCo 1-x Mg x O} 2, LiNi 1-y Co y O 2, LiNi 1-yz Co y Mn z O 2 (x, y, z are all integers), and the like.

Any non-aqueous electrolyte can be used without particular limitation as long as it is proposed as an electrolyte for a non-aqueous electrolyte secondary battery. However, an electrolyte composed of a non-aqueous solvent and a lithium salt soluble therein can be used. preferable. As the non-aqueous solvent, a mixed solvent of cyclic carbonates such as ethylene carbonate and propylene carbonate and chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate is generally used. Furthermore, γ-butyl lactone, dimethoxyethane, or the like may be mixed in a non-aqueous solvent. Examples of the lithium salt include inorganic lithium fluoride and a lithium imide compound. Examples of the former include LiPF ₆ and LiBF ₄ , and examples of the latter include LiN (CF ₃ SO ₂ ) ₃ . Furthermore, LiClO ₄ , LiCF ₃ SO _3, or the like may be mixed in the lithium salt. The non-aqueous electrolyte may be a gel electrolyte or a solid electrolyte.

  In order to prevent an internal short circuit between the positive electrode and the negative electrode, a separator is installed between them. As the material of the separator, any material can be used as long as it allows a non-aqueous electrolyte to pass through appropriately and prevents the contact between the positive electrode and the negative electrode. A microporous film made of polyethylene, polypropylene, or the like is generally used for the nonaqueous electrolyte secondary battery, and the thickness is generally 10 μm or more and 30 μm or less.

  The present invention can be applied to non-aqueous electrolyte secondary batteries having various shapes such as a cylindrical shape, a flat shape, a coin shape, and a square shape, and the shape of the battery is not particularly limited. INDUSTRIAL APPLICABILITY The present invention can be applied to batteries of various sealing forms, including batteries that contain power generation elements such as electrodes and electrolytes in metal battery cans and laminated film cases. Is not particularly limited.

  Next, the present invention will be specifically described based on examples and comparative examples. However, the following examples illustrate preferred modes of the present invention, and the present invention is not limited to the following examples. Absent.

Example 1
In Examples and Comparative Examples, negative electrodes and cylindrical batteries were produced in the following manner, and their cycle life and discharge capacity were evaluated.
(1) Production of Alloy Material Metal Ti (purity 99.9%, particle size 100-150 μm) and metal Si (purity 99.9%, average particle size 3 μm) are in a weight ratio of Ti: Si = 9. 2: Weighed and mixed to 90.8.

  3.5 kg of this mixed powder is weighed and put into a vibration mill device (FV-20, manufactured by Chuo Kako Co., Ltd.), and a stainless steel ball (diameter 2 cm) occupies 70% by volume of the mill device content. I put it in. After the inside of the container was evacuated, Ar (purity 99.999%, Japanese oxygen) was introduced so that the pressure became 1 atm. The operating conditions of the mill device were an amplitude of 8 mm and a rotation speed of 1200 rpm. Under these conditions, mechanical alloying operation was performed for 80 hours.

  When the Ti—Si alloy obtained by the above operation was collected and the particle size distribution was examined, it was found to have a wide particle size distribution of 0.5 μm to 80 μm. By classifying the Ti—Si alloy with a sieve (10 μm mesh size), an alloy material (hereinafter referred to as alloy a) having a maximum particle size of 10 μm and an average particle size of 8 μm was obtained.

When the alloy a was analyzed by X-ray diffraction measurement, an XRD profile as shown in FIG. 2 was obtained. As can be seen from FIG. 2, the alloy a is a microcrystalline alloy material, and the crystal grain size (crystallite) calculated from the half-value width of the peak with the highest intensity based on Scherrer's formula was 10 nm. It was.
Here, the maximum peak was observed in the vicinity of 2θ = 28 to 29 °, and the half width of the peak was 0.5. The half width was calculated from FIG. 3 obtained by subtracting the background from FIG.

From the results of the X-ray diffraction measurement, it was estimated that the Si a phase (A phase) and TiSi ₂ phase (B phase) exist in the alloy a. Assuming that only these two phases are present in the alloy a and calculating the abundance ratio of the Si simple phase and the TiSi ₂ phase, it was found that Si: TiSi ₂ = 80: 20 (weight ratio).

When the cross section of the alloy a was observed with a transmission electron microscope (TEM), an Si region composed of an amorphous region, crystal grains having a particle size of about 10 nm (crystallites), and crystal grains having a particle size of about 15 to 20 nm ( It has been found that there are TiSi ₂ phases having crystallites).

(2) Production of Negative Electrode Alloy a obtained above and graphite were mixed at a weight ratio shown in Table 1. 5 parts by weight of polyacrylic acid (molecular weight 150,000, manufactured by Wako Pure Chemical Industries, Ltd.) is added as a binder to a total of 100 parts by weight of alloy a and graphite, and sufficiently kneaded with pure water. Thus, a negative electrode mixture paste was obtained. At that time, the whole amount of the alloy a and 2.5 parts by weight of polyacrylic acid were kneaded until uniform, and then graphite and the remaining polyacrylic acid were added and kneaded. Here, scaly graphite (KS-44) having an average particle diameter of 20 μm manufactured by Timcal Corporation was used as graphite.

The negative electrode mixture paste was applied to both sides of a current collector made of an electrolytic copper foil (manufactured by Furukawa Circuit Foil Co., Ltd.) having a thickness of 10 μm, dried and rolled. As a result, a negative electrode comprising a current collector and a negative electrode mixture layer carried on both surfaces thereof was obtained.
When the cross section of the obtained negative electrode was observed with a scanning electron microscope (SEM), it was confirmed that a structure substantially the same as that in FIG. 1 was formed. The density of the negative electrode mixture layer was 1.3 to 1.4 g / cm ³ , and the porosity of the negative electrode mixture layer was 40 to 45%.

(3) Production of positive electrode LiCoO ₂ which is a positive electrode active material was synthesized by mixing Li ₂ CO ₃ and CoCO ₃ at a predetermined molar ratio and heating at 950 ° C., and this was made into a size of 45 μm or less. What was classified was used. To 100 parts by weight of the positive electrode active material, 5 parts by weight of acetylene black as a conductive agent, 4 parts by weight of polyvinylidene fluoride as a binder, and an appropriate amount of N-methyl-2-pyrrolidone as a dispersion medium are added and mixed thoroughly. A positive electrode mixture paste was obtained.
The positive electrode mixture paste was applied to both sides of a current collector made of an aluminum foil having a thickness of 15 μm (manufactured by Showa Denko KK), dried and rolled. As a result, a positive electrode comprising a current collector and a positive electrode mixture layer carried on both surfaces thereof was obtained.

(4) Production of Cylindrical Battery A cylindrical lithium ion secondary battery as shown in FIG. 4 was produced.
The positive electrode 35 and the negative electrode 36 were each cut into a predetermined size. One end of an aluminum positive electrode lead 35a was connected to the positive electrode current collector. One end of a nickel negative electrode lead 36a was connected to the negative electrode current collector. Thereafter, the positive electrode 35 and the negative electrode 36 were wound through a separator 37 made of a polyethylene resin microporous film having a width wider than both electrode plates and a thickness of 20 μm, thereby constituting an electrode plate group. The outer surface of the electrode plate group was interposed with a separator 37. An upper insulating ring 38 a and a lower insulating ring 38 b are arranged above and below the electrode plate group, respectively, and accommodated in the inner space of the battery can 31. Next, a non-aqueous electrolyte was poured into the battery can and impregnated into the electrode plate group. The other end of the positive electrode lead 35a was welded to the back surface of the sealing plate 32 having the insulating packing 33 disposed on the periphery. The other end of the negative electrode lead 36a was welded to the inner bottom surface of the battery can. Finally, the opening of the battery can 31 was closed with a sealing plate 32. Thus, cylindrical lithium ion secondary batteries (batteries 1 to 9) were completed. Among the batteries 1 to 9, the batteries 1 to 6 are examples, and the batteries 7 to 9 are comparative examples.
As the non-aqueous electrolyte, a solution obtained by dissolving lithium hexafluorophosphate at a concentration of 1 mol / L in a mixed non-aqueous solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 1: 1 was used.

(5) Battery evaluation <i> Discharge capacity In a constant temperature bath set at 20 ° C., constant current charging of a cylindrical battery was performed at a charging current of 0.2 C (1 C is a 1 hour rate current) and a battery voltage of 4. This was performed until the voltage reached 05 V, and then constant voltage charging was performed at 4.05 V until the current value reached 0.01 C. Thereafter, the cylindrical battery was discharged at a current of 0.2 C until the battery voltage reached 2.5V. The discharge capacity at this time is shown in Table 1.

<Ii> Cycle life In a thermostat set to 20 ° C., the charge / discharge cycle of the battery after measuring the discharge capacity was repeated under the following conditions.
Constant charging current is performed until the battery voltage reaches 4.05 V at a charging current of 1 C, and then constant voltage charging is performed at 4.05 V until the current value reaches 0.05 C. Thereafter, the cylindrical battery is discharged. The operation performed until the battery voltage became 2.5 V with a current of 1 C was repeated. And the ratio of the discharge capacity of the 100th cycle with respect to the discharge capacity of the 2nd cycle was calculated | required in percentage, and it was set as the capacity | capacitance maintenance factor (%). The results are shown in Table 1. The closer the capacity retention rate is to 100%, the better the cycle life.

<< Comparative Example 1 >>
In the production of the negative electrode, a cylindrical lithium ion secondary battery (battery 10) was produced in the same manner as in Example 1 except that only the graphite was used without using the alloy a. The binder (polyacrylic acid) was added in an amount of 5 parts by weight per 100 parts by weight of graphite.

<< Comparative Example 2 >>
In the production of the negative electrode, graphite is not used but only alloy a is used, and 10 parts by weight of acetylene black (DENKA BLACK manufactured by Denki Kagaku Kogyo Co., Ltd.) having a specific surface area of 70 m ² / g is used as a conductive additive. A cylindrical lithium ion secondary battery (battery 11) was produced in the same manner as in Example 1 except for the addition. The binder (polyacrylic acid) was added in an amount of 5 parts by weight per 100 parts by weight of the alloy a.
The batteries of Comparative Examples 1 and 2 were evaluated in the same manner as in Example 1. The results are shown in Table 2.

In Example 1, in the case of the batteries 1 to 6 using the negative electrode in which the ratio of the graphite to the total weight of the alloy a and the graphite is 50% by weight to 95% by weight, the capacity is particularly improved as compared with the comparative example 1. And it turns out that a cycle life improves compared with the comparative example 2.
Moreover, when the batteries of Comparative Examples 1 and 2 were disassembled after 100 cycles and the degree of expansion was evaluated, 1.1 times in Comparative Example 1 and 3 in Comparative Example 2 compared to the thickness of the negative electrode before charging and discharging. It had expanded twice. On the other hand, for example, when the battery 3 of Example 1 was disassembled after 100 cycles and the degree of expansion was evaluated, expansion of about 1.5 times was confirmed. That is, it was found that the batteries of the examples were able to suppress expansion due to the alloy while maintaining a high capacity.

Example 2
In preparation of the negative electrode, the mixing weight ratio of graphite (KS-44 manufactured by Timcal) and Ti—Si alloy (alloy a) was fixed at 80:20, and the total of alloy a and graphite (KS-44) was 100. The above-mentioned acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd., specific surface area 70 m ² / g) or specific surface area of 14 m ² / weight per part by weight as a conductive additive in the proportions (parts by weight) shown in Table 3. g of graphite (KS4 manufactured by Timcal) was added, and 5 parts by weight of polyacrylic acid was added as a binder.
Except for the above, a cylindrical lithium ion secondary battery (batteries 12 to 20) was produced in the same manner as in Example 1. At that time, the total amount of the alloy a, 3 parts by weight of polyacrylic acid, and a predetermined addition amount of acetylene black or KS4 are kneaded until uniform, and then graphite (KS-44) and the remaining polyacrylic acid are mixed. Added and kneaded.
The batteries 12 to 20 of Example 2 were evaluated in the same manner as in Example 1. The results are shown in Table 3.

In the battery of this example, since the negative electrode contained acetylene black or KS4 as a conductive additive, the characteristics were improved, and the cycle life was particularly improved. Further, even when the conductive additive was added in a small amount of about 2 parts by weight, the capacity increased as compared with the case where the conductive additive was not added (battery 3 of Example 1).
When the cross-section of the negative electrode of this example was observed with an SEM, it was found that an appropriate amount of conductive additive was disposed around the particles of the alloy a. It is considered that the conductivity of the negative electrode is sufficiently ensured by such an arrangement of the conductive aid, and as a result, the capacity of the alloy a is maximized.

Example 3
<I> Battery 21
A Ti—Si alloy having a wide particle size distribution of 0.5 μm to 80 μm obtained by the same operation as in Example 1 is passed through a first sieve (45 μm mesh size) to remove particles larger than 45 μm, and then a second Particles smaller than 20 μm were removed by passing through a sieve (20 μm mesh size) to obtain an alloy material (hereinafter referred to as alloy b) having a particle size distribution of 20 to 45 μm and an average particle size of 32 μm.
A cylindrical lithium ion secondary battery (battery 21) was produced in the same manner as the battery 3 of Example 1 except that the alloy b was used.

<Ii> Battery 22
A Ti—Si alloy having a wide particle size distribution of 0.5 μm to 80 μm obtained by the same operation as in Example 1 was passed through a first sieve (20 μm mesh size) to remove large particles, and then a second sieve ( Small particles were removed through a 10 μm mesh size) to obtain an alloy material (hereinafter referred to as alloy c) having a particle size distribution of 10 to 20 μm and an average particle size of 13 μm.
A cylindrical lithium ion secondary battery (battery 22) was produced in the same manner as the battery 3 of Example 1 except that the alloy c was used.

<Iii> Battery 23
An alloy having a maximum particle size of 10 μm and an average particle size of 8 μm is obtained by classifying a Ti—Si alloy having a wide particle size distribution of 0.5 μm to 80 μm obtained by the same operation as in Example 1 with a sieve (10 μm mesh size). A material (hereinafter referred to as alloy d) was obtained.
A cylindrical lithium ion secondary battery (battery 23) was produced in the same manner as the battery 3 of Example 1 except that the alloy d was used.
The batteries 21 to 23 in Example 3 were evaluated in the same manner as in Example 1. The results are shown in Table 4.

In the battery of this example, the initial capacity is large, but the charge / discharge cycle characteristics tend to be low. In particular, in the case of the battery 21 and the battery 22, even when compared with the comparative example 2, the result was bad. When the cross section of the negative electrode used in these batteries 21 to 22 was observed with an SEM, it was found that the graphite particles and the alloy particles were present in an aggregated state and did not have the structure shown in FIG. did.
When the battery 21 and the battery 22 were disassembled after 100 cycles and the negative electrode was observed, most of the mixture was peeled off and it was difficult to contact the current collector. Furthermore, wrinkles and cracks were observed at the ends of the current collector. It is considered that the current collector was deformed by the expansion stress of the alloy material, resulting in defects such as wrinkles and cutting. Moreover, in Example 23, peeling of the mixture was confirmed in part.

<< Comparative Example 3 >>
The Ti—Si alloy (alloy a) used in Example 1 was introduced into an electric furnace, and heat treatment was performed at 1000 ° C. for 3 hours under vacuum. As a result, the alloy a was changed to an alloy material with high crystallinity (hereinafter, alloy e). The alloy e was analyzed by X-ray diffraction measurement, and the grain size of the crystal grain (crystallite) calculated from the half-value width of the peak with the highest intensity based on the Scherrer equation was 1 μm. However, the particle size distribution of the alloy e remained the same as that of the alloy a and did not change. Therefore, the average particle diameter of the alloy e remained at 8 μm and the maximum particle diameter remained at 10 μm.
A cylindrical lithium ion secondary battery (battery 24) was produced in the same manner as the battery 3 of Example 1 except that the alloy e was used, and the same evaluation as in Example 1 was performed. The results are shown in Table 5.

  The battery 24 has a high capacity but low charge / discharge cycle characteristics. When the battery 24 was disassembled after 100 cycles and the negative electrode was observed, the alloy particles were further pulverized into submicron-sized particles. This is thought to be because the Si crystal phase enlarged by the heat treatment was expanded and destroyed by the insertion of Li.

Example 4
In the production of the alloy material, except that Zr, Ni, Co, Mn, Fe or Cu (all of which purity is 99.9% and particle size is 100 to 150 μm) is used as the transition metal M instead of the metal Ti. The alloy material was manufactured by the synthesis method similar to 1. The obtained alloy material was passed through the same sieve as in Example 1 to obtain a maximum particle size of 8 μm and an average particle size of 5 μm. Hereinafter, alloy materials using Zr, Ni, Co, Mn, Fe, and Cu are referred to as alloys f, g, h, i, j, and k, respectively.

When the alloys f to k were analyzed by X-ray diffraction measurement, an XRD profile as shown in FIG. 2 was obtained, and it was found that the alloys were microcrystalline alloy materials. Moreover, the grain size of the crystal grains (crystallites) calculated from the half-value width of the peak with the highest intensity based on Scherrer's formula was in the range of 9 to 25 nm.
From the result of the X-ray diffraction measurement, it was estimated that Si single phase (A phase) and MSi ₂ phase (B phase) existed in the alloys f to k. Assuming that only these two phases exist in the alloys f to k and calculating the abundance ratio of the Si simple substance phase and the MSi ₂ phase, the weight ratio of Si: MSi ₂ was as shown in Table 6. (Si phase: 65-83 wt%).

  A cylindrical lithium ion secondary battery (batteries 25 to 30) was produced in the same manner as the battery 3 of Example 1 except that the alloys f to k were used, and the same evaluation as in Example 1 was performed. The results are shown in Table 6.

  From the results of the batteries 25 to 30, it was found that a battery having both a high capacity and a long life can be obtained by using any alloy material. The alloy materials that showed particularly good charge / discharge cycle characteristics were Ti—Si alloy (alloy a) and Zr—Si alloy (alloy f). It is assumed that these materials have higher electron conductivity of the alloy powder itself than other alloy materials, and as a result, good charge / discharge cycle characteristics are obtained without being affected by expansion.

Example 5
Ti-Si alloys having a wide particle size distribution of 0.5 μm to 80 μm obtained by the same operation as in Example 1 are classified using various sieves, and the average particle size is 2 μm, 5 μm, or 7 μm, and the maximum An alloy material having a particle size of 10 μm or less was obtained.
On the other hand, graphite (KS-44) was also crushed and classified by sieving to obtain a graphite material having an average particle size of 8 μm, 13 μm, 16 μm, or 20 μm (untreated).
Cylindrical lithium ions in the same manner as the battery 3 of Example 1, except that the above alloy materials and graphite materials were mixed in the combinations shown in Table 7 at a ratio of graphite: alloy = 80: 20 (weight ratio). Secondary batteries (batteries 31 to 38) were produced and evaluated in the same manner as in Example 1. Table 7 shows the results together with the ratio of the average particle diameter Ralloy of the alloy material and the average particle diameter Rgraphite of the graphite: Ralloy / Rgraphite.

In the battery 36 and the battery 38, the cycle life was relatively low. In the battery 36 and the battery 38, the Ralloy / Rgraphite value is lower than 0.15. When the negative electrode cross section of these batteries was observed with an SEM, a plurality of alloy particles formed aggregates while being sandwiched between graphite particles. Therefore, when the battery after 100 cycles was disassembled and the negative electrode was observed, a part of the negative electrode mixture was peeled from the current collector.
On the other hand, when the Ralloy / Rgraphite value was in the range of 0.15 to 0.9, high capacity and good cycle life were obtained. Further, when the Ralloy / Rgraphite value was in the range of 0.2 to 0.4, a long life was obtained particularly at a high capacity. Observation of the negative electrode cross section of these batteries revealed that the alloy particles were uniformly dispersed among the graphite particles, and the structure as shown in FIG. 1 was confirmed.

Example 6
Similar to the batteries 1 to 6 of Example 1, alloy a and graphite (KS-44) were used in the weight ratios shown in Table 8. Further, 5 parts by weight of polyacrylic acid (molecular weight: 150,000, manufactured by Wako Pure Chemical Industries, Ltd.) was used as a binder with respect to a total of 100 parts by weight of alloy a and graphite. However, graphite and polyacrylic acid were kneaded in advance together with the total amount of pure water. Thereafter, an alloy a was added to a mixture of graphite, polyacrylic acid and pure water, and further kneaded to obtain a negative electrode mixture paste. A negative electrode was obtained in the same manner as in Example 1 except that this paste was used.

When the cross section of the obtained negative electrode was observed by SEM, it was confirmed that a structure substantially similar to that shown in FIG. 1 was formed. Furthermore, it was confirmed that the graphite surface and the alloy a were adhered at a plurality of contacts. The density of the negative electrode mixture layer was 1.3 g / cm ³ , and the porosity of the negative electrode mixture layer was 45%.
Cylindrical lithium ion batteries (batteries 39 to 44) were produced in the same manner as in Example 1 using the obtained negative electrode. Evaluation similar to Example 1 was performed about the batteries 39-44. The results are shown in Table 8.

  The batteries 39 to 44 have a small capacity but a high cycle characteristic as compared with the batteries 1 to 6 of Example 1. When these batteries were disassembled and evaluated after evaluation, the expansion of the negative electrode was as low as 1.3 to 1.4 times. In addition, in the battery 4 and the battery 42, SEM observation of the negative electrode after decomposition was performed. As a result, a part of the mixture surface of the negative electrode of the battery 4 was swollen. On the other hand, the battery 42 maintained a substantially smooth surface. In the battery of Example 6, since the alloy material was fixed on the graphite surface via the binder, it is considered that excessive expansion was suppressed.

Example 7
(Battery 45)
The battery of Example 1 except that 3 parts by weight of VGCF (manufactured by Showa Denko KK, average length 20 μm, aspect ratio 500) is further added as a carbon fiber to 100 parts by weight of the alloy a and graphite. Similarly to 4, a negative electrode was produced. Using this negative electrode, a battery 45 was produced in the same manner as in Example 1.

(Battery 46)
Alloy a was placed on a SiO ₂ boat and placed in a tubular furnace. The inside of the furnace was maintained at a vacuum degree of 3.0 × 10 ⁻¹ Pa. In a vacuum furnace, methane was circulated at a flow rate of 10 sccm together with a mixed gas of helium and hydrogen. In this state, the alloy a was heated at 500 ° C. for 30 minutes. As a result, carbon fibers having an aspect ratio of about 20 to 100 could be grown on the surface of the alloy a. The amount of carbon fiber produced was 6 parts by weight per 100 parts by weight of alloy a. A negative electrode was prepared in the same manner as the battery 4 of Example 1 except that the composite material of the alloy a and carbon fiber thus obtained was used instead of the alloy a, and the negative electrode was used in the same manner as in Example 1. Thus, a battery battery 46 was produced.

(Battery 47)
Graphite and alloy a were mixed at a weight ratio of graphite: alloy a = 70: 30, and composited with a mechanofusion apparatus (manufactured by Hosokawa Micron Corporation). When the obtained composite material was observed by SEM, it was found that the graphite surface was covered with the alloy a. The average particle size of the composite material was about 28 μm. Carbon fibers were deposited on the surface of the composite material under the same conditions as in the battery 48 except that this composite material was used instead of the alloy a. According to SEM observation, the aspect ratio of the carbon fiber was about 20 to 100, and a part of the carbon fiber was adhered not only to the surface of the alloy a but also to the surface of graphite. The amount of carbon fiber produced was 6 parts by weight per 100 parts by weight of alloy a. A negative electrode was produced in the same manner as the battery 4 of Example 1 except that the composite material of alloy a, graphite, and carbon fiber thus obtained was used in place of the alloy a and graphite, and the negative electrode was used. In the same manner as in Example 1, a battery battery 47 was produced.
The batteries 45 to 47 were evaluated in the same manner as in Example 1. The results are shown in Table 9.

  As shown in Table 9, the batteries 45 to 47 all had improved charge / discharge cycle characteristics compared to the battery 4. That is, mixing of the carbon fiber into the negative electrode was effective in improving charge / discharge cycle characteristics. Further, when the carbon fiber was bonded to the alloy material or graphite, the charge / discharge cycle characteristics were greatly improved. This is thought to be due to the improvement in current collection.

  The negative electrode for a non-aqueous electrolyte secondary battery of the present invention provides an excellent non-aqueous electrolyte secondary battery having both high capacity and good charge / discharge cycle characteristics. The present invention can be applied to all forms of non-aqueous electrolyte secondary batteries. For example, the present invention has not only the cylindrical shape mentioned in the embodiment but also a coin shape, a square shape, a flat shape, etc. The present invention can also be applied to a battery having an electrode plate group structure such as a mold or a stacked type. The nonaqueous electrolyte secondary battery of the present invention is useful as a main power source for mobile communication devices, portable electronic devices and the like.

It is a cross-sectional photograph (1000-times multiplication factor) of an example of the negative electrode of this invention. 3 is an XRD profile of a Ti—Si alloy according to the present invention. FIG. 3 is a diagram in which a background is subtracted from the XRD profile of FIG. 2. It is a longitudinal cross-sectional view of the cylindrical battery produced in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Current collector 2 Alloy particle 3 Graphite particle 31 Battery can 32 Sealing plate 33 Insulation packing 35 Positive electrode 35a Positive electrode lead 36 Negative electrode 36a Negative electrode lead 37 Separator 38a Upper insulating ring 38b Lower insulating ring

Claims (11)

Including at least one alloy material capable of electrochemically inserting and extracting Li and graphite;
The alloy material includes an A phase mainly composed of Si, and a B phase composed of an intermetallic compound of at least one transition metal element and Si,
At least one of the A phase and the B phase is composed of a microcrystalline or amorphous region;
The proportion of the A phase in the total weight of the A phase and the B phase is more than 40% by weight and 95% by weight or less,
The negative electrode for a non-aqueous electrolyte secondary battery, wherein a ratio of the graphite to a total weight of the alloy material and the graphite is 50% by weight or more and 95% by weight or less.   The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the alloy material is present in a gap formed by the graphite particles.   The negative electrode for a nonaqueous electrolyte secondary battery according to claim 2, wherein the alloy material has a maximum particle size of 10 μm or less.   The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1, further comprising a binder, wherein at least a part of the alloy material is adhered to the graphite surface via the binder.   The ratio of the average particle diameter Ralloy of the alloy material to the average particle diameter Rgraphite of the graphite: Ralloy / Rgraphite is in the range of 0.15 to 0.90. Negative electrode. The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1, further comprising a conductive additive, wherein the specific surface area of the conductive additive is 10 m ² / g or more.   The non-aqueous electrolyte secondary battery according to claim 6, wherein the conductive additive is a carbon fiber having an aspect ratio of 10 or more, and at least one end of the carbon fiber is attached or bonded to the alloy material. Negative electrode.   The non-aqueous electrolyte secondary battery according to claim 7, wherein at least a part of the carbon fiber has one end attached or bonded to the alloy material and the other end attached or bonded to the graphite. Negative electrode.   The negative electrode for a nonaqueous electrolyte secondary battery according to claim 8, wherein the carbon fiber is obtained by heating at least one of the alloy material and the graphite in a hydrocarbon stream.   The negative electrode for a nonaqueous electrolyte secondary battery according to claim 6, wherein a ratio of the conductive additive to a total weight of the alloy material, the graphite, and the conductive additive is 10% by weight or less. In a non-aqueous electrolyte secondary battery composed of a positive electrode, a negative electrode, and a non-aqueous electrolyte capable of electrochemically inserting and extracting Li,
The negative electrode includes at least one alloy material capable of electrochemically inserting and extracting Li and graphite.
The at least one alloy material includes an A phase mainly composed of Si, and a B phase composed of an intermetallic compound of at least one transition metal element and Si,
At least one of the A phase and the B phase is composed of a microcrystalline or amorphous region;
The proportion of the A phase in the total weight of the A phase and the B phase is more than 40% by weight and 95% by weight or less,
The ratio of the said graphite to the total weight of the said alloy material and the said graphite is a nonaqueous electrolyte secondary battery which is 50 to 95 weight%.