WO2014080902A1

WO2014080902A1 - Negative electrode for electric device and electric device using same

Info

Publication number: WO2014080902A1
Application number: PCT/JP2013/081156
Authority: WO
Inventors: 貴志真田; 渡邉　学; 文博三木; 健介山本; 千葉　啓貴
Original assignee: 日産自動車株式会社
Priority date: 2012-11-22
Filing date: 2013-11-19
Publication date: 2014-05-30
Also published as: JP2016027529A

Abstract

[Problem] To provide a negative electrode for an electric device such as an Li-ion secondary cell, said negative electrode maintaining high cycle characteristics and having well-balanced characteristics including high initial capacity. [Solution] A negative electrode for an electric device, having a collector and having an electrode layer including a negative electrode active substance, a conductive assistant, and a binder that are arranged on the surface of the collector. The negative electrode for an electric device is characterized by: the negative electrode active substance including an alloy indicated by formula (1) (in the formula (1), M is at least one metal selected from a group comprising C, Nb, and a combination of same, A is unavoidable impurities, x, y, z, and a indicate values in percent by mass, 0<x<100, 0<y<100, 0<z<100, 0≤a<0.5, and x+y+z+a=100); and the elastic elongation of the collector being at least 1.30%.

Description

Negative electrode for electric device and electric device using the same

The present invention relates to a negative electrode for an electric device and an electric device using the same. The negative electrode for an electric device and the electric device using the same according to the present invention are used as, for example, a driving power source or an auxiliary power source for a motor of a vehicle such as an electric vehicle, a fuel cell vehicle, and a hybrid electric vehicle as a secondary battery or a capacitor. It is done.

In recent years, in order to cope with air pollution and global warming, reduction of the amount of carbon dioxide has been strongly desired. In the automobile industry, there is a great expectation for reducing carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV). Electric devices such as secondary batteries for motor drive that hold the key to their practical application. Is being actively developed.

As a secondary battery for driving a motor, it is required to have extremely high output characteristics and high energy as compared with a consumer lithium ion secondary battery used for a mobile phone, a notebook personal computer or the like. Therefore, lithium ion secondary batteries having the highest theoretical energy among all the batteries are attracting attention, and are currently being developed rapidly.

Generally, a lithium ion secondary battery includes a positive electrode in which a positive electrode active material or the like is applied to both surfaces of a positive electrode current collector using a binder, and a negative electrode in which a negative electrode active material or the like is applied to both surfaces of a negative electrode current collector using a binder. However, it has the structure connected through an electrolyte layer and accommodated in a battery case.

Conventionally, carbon / graphite-based materials that are advantageous in terms of charge / discharge cycle life and cost have been used for negative electrodes of lithium ion secondary batteries. However, since carbon / graphite-based negative electrode materials are charged / discharged by occlusion / release of lithium ions into / from graphite crystals, the charge / discharge capacity of the theoretical capacity 372 mAh / g or more obtained from LiC ₆ which is the maximum lithium-introduced compound. There is a disadvantage that cannot be obtained. For this reason, it is difficult to obtain a capacity and energy density that satisfy the practical use level of the vehicle application with the carbon / graphite negative electrode material.

On the other hand, a battery using a material that is alloyed with Li for the negative electrode is expected as a negative electrode material for vehicle use because the energy density is improved as compared with a conventional carbon / graphite negative electrode material. For example, the Si material absorbs and releases _4.4 mol of lithium ions per mol as shown in the following reaction formula (A) in charge and discharge, and the theoretical capacity is 2100 mAh / in Li ₂₂ Si ₅ (= Li _4.4 Si). g. Furthermore, when calculated per Si weight, it has an initial capacity of 3200 mAh / g.

However, a lithium ion secondary battery using a material that is alloyed with Li for the negative electrode has a large expansion and contraction in the negative electrode during charge and discharge. For example, when Li ions are occluded, the volume expansion is about 1.2 times in graphite materials, whereas in Si materials, when Si and Li are alloyed, transition from the amorphous state to the crystalline state causes a large volume change. (Approximately 4 times), there was a problem of reducing the cycle life of the electrode. In the case of the Si negative electrode active material, the capacity and the cycle durability are in a trade-off relationship, and there is a problem that it is difficult to improve the high cycle durability while exhibiting a high capacity.

In order to solve such a problem, a negative electrode active material for a lithium ion secondary battery including an amorphous alloy having the formula: Si _x M _y Al _z has been proposed (see, for example, Patent Document 1). Here, x, y, and z in the formula represent atomic percentage values, and x + y + z = 100, x ≧ 55, y <22, z> 0, M represents Mn, Mo, Nb, W, Ta, Fe, Cu, It is a metal composed of at least one of Ti, V, Cr, Ni, Co, Zr, and Y. In the invention described in Patent Document 1, paragraph “0018” describes that, by minimizing the content of metal M, a good cycle life is exhibited in addition to high capacity.

Special table 2009-517850

However, in the case of a lithium ion secondary battery using a negative electrode having an amorphous alloy having the formula described in Patent Document 1; Si _x M _y Al _z , although it is said that good cycle characteristics can be exhibited, The initial capacity was not sufficient. In addition, the cycle characteristics were not sufficient.

Therefore, an object of the present invention is to provide a negative electrode for an electric device such as a Li ion secondary battery that maintains a high cycle characteristic and has a high initial capacity and a well-balanced characteristic.

The present inventors have conducted intensive research to solve the above problems. As a result, it has been found that the above problem can be solved by using a predetermined ternary Si alloy as a negative electrode active material and using a negative electrode current collector having a predetermined elastic elongation, and to complete the present invention. It came.

That is, the present invention relates to a negative electrode for an electric device having a current collector and an electrode layer including a negative electrode active material, a conductive additive, and a binder disposed on the surface of the current collector. At this time, the negative electrode active material has the following formula (1):

An elastic elongation of the current collector is 1.30% or more. In this case, in the above formula (1), M is at least one metal selected from the group consisting of C, Nb, and combinations thereof. A is an inevitable impurity. Furthermore, x, y, z, and a represent mass% values, where 0 <x <100, 0 <y <100, 0 <z <100, and 0 ≦ a <0.5. , X + y + z + a = 100.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view schematically showing an outline of a laminated flat non-bipolar lithium ion secondary battery which is a typical embodiment of an electric device according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view schematically showing the appearance of a stacked flat lithium ion secondary battery that is a representative embodiment of an electric device according to the present invention. The discharge capacity (mAhg) of the first cycle of the battery using each sample (sample numbers 1 to 33) performed in Reference Example A of the invention was plotted according to the color of the capacity (with light and shade). FIG. 3 is a composition diagram of a Si—Al—C ternary alloy. The discharge capacity retention rate (%) at the 50th cycle of the battery using each sample (sample numbers 1 to 33) performed in Reference Example A of the present invention is color-coded according to the magnitude of the discharge capacity retention rate (light / dark) 2 is a composition diagram of a plotted Si—Al—C ternary alloy. FIG. 4 is a drawing in which the composition range of the Si—Al—C ternary alloy composition of FIG. 3 is color-coded (with shading) surrounded by the composition range of the Si—Al—C alloy sample of Reference Example A. Here, Si + Al + C (all units are wt% / 100) = 1.00, 0.36 ≦ Si (wt% / 100) <1.00, and 0 <Al (wt% / 100 ) <0.64 and 0 <C (wt% / 100) <0.64. FIG. 5 is a drawing in which a preferred composition range of the Si—Al—C alloy sample of Reference Example A is color-coded (shaded) with the composition diagram of the Si—Al—C ternary alloy of FIG. . Here, Si + Al + C (all units are wt% / 100) = 1.00, 0.36 ≦ Si (wt% / 100) ≦ 0.80, and 0.10 ≦ Al (wt%). /100)≦0.56 and 0.03 ≦ C (wt% / 100) ≦ 0.37. In the composition diagram of the Si—Al—C ternary alloy in FIG. 4, a more preferable composition range of the Si—Al—C alloy sample of Reference Example A is color-coded (shaded) and enclosed. is there. Here, Si + Al + C (all units are wt% / 100) = 1.00, 0.41 ≦ Si (wt% / 100) ≦ 0.71, and 0.10 ≦ Al (wt%). /100)≦0.56 and 0.03 ≦ C (wt% / 100) ≦ 0.29. In the composition diagram of the Si—Al—C ternary alloy in FIG. 4, the particularly preferred composition range of the Si—Al—C alloy sample of Reference Example A is color-coded (with shading) and enclosed. is there. Here, Si + Al + C (all units are wt% / 100) = 1.00, 0.41 ≦ Si (wt% / 100) ≦ 0.71, and 0.15 ≦ Al (wt%). /100)≦0.56 and 0.03 ≦ C (wt% / 100) ≦ 0.29. In the composition diagram of the Si—Al—C ternary alloy of FIG. 4, among the Si—Al—C alloy sample of Reference Example A, a particularly preferred composition range is color-coded (shaded) and enclosed. is there. Here, Si + Al + C (all units are wt% / 100) = 1.00, 0.43 ≦ Si (wt% / 100) ≦ 0.61, and 0.20 ≦ Al (wt%). /100)≦0.54 and 0.03 ≦ C (wt% / 100) ≦ 0.29. Evaluation cell (CR 2032 type coin cell) using an evaluation electrode using the Si (58 wt%)-Al (38 wt%)-C (4 wt%) alloy obtained in Sample 7 of Reference Example A of the present invention as a negative electrode active material 1) All the charge / discharge curves from 1 to 50 cycles in FIG. FIG. 11 is a plot of each example in the composition diagram of the Si—Al—Nb ternary alloy, 0.27 <Si (mass% / 100) <1.00, 0.00 <Al (mass% / 100) <0.73, 0.00 <Nb (mass% / 100) <0.58. FIG. 12 is a plot of each example in the composition diagram of the Si—Al—Nb ternary alloy, 0.47 <Si (mass% / 100) <0.95, 0.02 <Al (mass% / 100) <0.48, 0.01 <Nb (mass% / 100) <0.23. FIG. 13 is a plot of each example in the composition diagram of the Si—Al—Nb ternary alloy, 0.61 <Si (mass% / 100) <0.84, 0.02 <Al (mass% / 100) <0.25, 0.02 <Nb (mass% / 100) <0.23, or 0.47 <Si (mass% / 100) <0.56, 0.33 <Al (mass) % / 100) <0.48, 0.01 <Nb (mass% / 100) <0.16. In an Example, it is drawing which represents the relationship between the elastic elongation of a negative electrode electrical power collector, and the improvement rate of the discharge capacity maintenance factor of a battery.

As described above, the present invention is characterized in that a predetermined ternary Si alloy is used as a negative electrode active material and a negative electrode current collector having a predetermined elastic elongation is used.

According to the present invention, by using a specific Si alloy as the negative electrode active material, the amorphous-crystal phase transition when Si and Li are alloyed can be suppressed, and the cycle characteristics of the battery can be improved. Furthermore, in the negative electrode using the specific Si alloy described above, by using a current collector having a predetermined elastic elongation, the volume change of the negative electrode active material layer due to the expansion / contraction of the negative electrode active material accompanying charge / discharge of the battery Following this, the current collector can be elastically deformed. Therefore, plastic deformation of the current collector hardly occurs, distortion of the negative electrode active material layer due to plastic deformation of the current collector can be reduced, and a uniform inter-electrode distance from the positive electrode can be maintained. As a result, an electric device having high capacity and high cycle durability can be obtained.

Hereinafter, embodiments of an anode for an electric device of the present invention and an electric device using the same will be described with reference to the drawings. However, the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following modes. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

Hereinafter, a basic configuration of an electric device to which the negative electrode for an electric device of the present invention can be applied will be described with reference to the drawings. In the present embodiment, a lithium ion secondary battery will be described as an example of an electric device. In the present invention, the “electrode layer” means a mixture layer containing a negative electrode active material, a conductive additive, and a binder, but may be referred to as a “negative electrode active material layer” in the description of this specification. Similarly, the electrode layer on the positive electrode side is also referred to as a “positive electrode active material layer”.

First, in a negative electrode for a lithium ion secondary battery, which is a typical embodiment of the negative electrode for an electric device according to the present invention, and a lithium ion secondary battery using the same, the voltage of the cell (single cell layer) is large. High energy density and high power density can be achieved. Therefore, the lithium ion secondary battery using the negative electrode for the lithium ion secondary battery of the present embodiment is excellent as a vehicle driving power source or an auxiliary power source. As a result, it can be suitably used as a lithium ion secondary battery for a vehicle driving power source or the like. In addition to this, the present invention can be sufficiently applied to lithium ion secondary batteries for portable devices such as mobile phones.

That is, the lithium ion secondary battery that is the subject of the present embodiment only needs to use the negative electrode for the lithium ion secondary battery of the present embodiment described below. It should not be restricted.

For example, when the lithium ion secondary battery is distinguished by form / structure, it can be applied to any conventionally known form / structure such as a stacked (flat) battery or a wound (cylindrical) battery. Is. By adopting a stacked (flat) battery structure, long-term reliability can be secured by a sealing technique such as simple thermocompression bonding, which is advantageous in terms of cost and workability.

Moreover, when viewed in terms of electrical connection form (electrode structure) in a lithium ion secondary battery, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries. Is.

When distinguished by the type of electrolyte layer in the lithium ion secondary battery, a solution electrolyte type battery using a solution electrolyte such as a nonaqueous electrolyte solution for the electrolyte layer, a polymer battery using a polymer electrolyte for the electrolyte layer, etc. It can be applied to any conventionally known electrolyte layer type. The polymer battery is further divided into a gel electrolyte type battery using a polymer gel electrolyte (also simply referred to as a gel electrolyte) and a solid polymer (all solid) type battery using a polymer solid electrolyte (also simply referred to as a polymer electrolyte). It is done.

Therefore, in the following description, the non-bipolar (internal parallel connection type) lithium ion secondary battery using the negative electrode for the lithium ion secondary battery of this embodiment will be described very simply with reference to the drawings. However, the technical scope of the lithium ion secondary battery of the present embodiment should not be limited to these.

<Overall battery structure>
FIG. 1 schematically shows the overall structure of a flat (stacked) lithium ion secondary battery (hereinafter also simply referred to as “stacked battery”), which is a typical embodiment of the electrical device of the present invention. FIG.

As shown in FIG. 1, the stacked battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminate sheet 29 that is an exterior body. . Here, in the power generation element 21, the positive electrode in which the positive electrode active material layer 13 is disposed on both surfaces of the positive electrode current collector 11, the electrolyte layer 17, and the negative electrode active material layer 15 is disposed on both surfaces of the negative electrode current collector 12. It has a configuration in which a negative electrode is laminated. Specifically, the negative electrode, the electrolyte layer, and the positive electrode are laminated in this order so that one positive electrode active material layer 13 and the negative electrode active material layer 15 adjacent thereto face each other with the electrolyte layer 17 therebetween. .

Thereby, the adjacent positive electrode, electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked battery 10 shown in FIG. 1 has a configuration in which a plurality of single battery layers 19 are stacked and electrically connected in parallel. The positive electrode current collector 13 on the outermost layer located on both outermost layers of the power generating element 21 is provided with the positive electrode active material layer 13 only on one side, but the active material layer may be provided on both sides. . That is, instead of using a current collector dedicated to the outermost layer provided with an active material layer only on one side, a current collector having an active material layer on both sides may be used as it is as an outermost current collector. Further, by reversing the arrangement of the positive electrode and the negative electrode as compared with FIG. 1, the outermost negative electrode current collector is positioned on both outermost layers of the power generation element 21, and one side of the outermost negative electrode current collector or A negative electrode active material layer may be disposed on both sides.

The positive electrode current collector 11 and the negative electrode current collector 12 are attached to a positive electrode current collector plate 25 and a negative electrode current collector plate 27 that are electrically connected to the respective electrodes (positive electrode and negative electrode), and are sandwiched between end portions of the laminate sheet 29. Thus, it has a structure led out of the laminate sheet 29. The positive electrode current collector plate 25 and the negative electrode current collector plate 27 are ultrasonically welded to the positive electrode current collector 11 and the negative electrode current collector 12 of each electrode via a positive electrode lead and a negative electrode lead (not shown), respectively, as necessary. Or resistance welding or the like.

The lithium ion secondary battery described above is characterized by a negative electrode. Hereinafter, main components of the battery including the negative electrode will be described.

<Positive electrode>
[Positive electrode active material layer]
The positive electrode active material layer 13 includes a positive electrode active material, and further includes other additives as necessary.

(Positive electrode active material)
Examples of the positive electrode active material include lithium-transition metal composite oxides, lithium-transition metal phosphate compounds, lithium-transition metal sulfate compounds, solid solution systems, ternary systems, NiMn systems, NiCo systems, and spinel Mn systems. It is done.

Examples of the lithium-transition metal composite oxide include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni, Mn, Co) O ₂ , Li (Li, Ni, Mn, Co) O ₂ , LiFePO ₄ and Examples include those in which some of these transition metals are substituted with other elements.

The solid solution system includes xLiMO ₂ · (1-x) Li ₂ NO ₃ (0 <x <1, M is one or more transition metals having an average oxidation state of 3+, and N is an average oxidation state of 4+), LiRO _2- LiMn ₂ O ₄ (R = transition metal elements such as Ni, Mn, Co, and Fe).

Examples of the ternary system include nickel / cobalt / manganese (composite) cathode materials.

Examples of the NiMn system include LiNi _0.5 Mn _1.5 O ₄ .

Examples of the NiCo system include Li (NiCo) O ₂ .

Examples of the spinel Mn system include LiMn ₂ O ₄ .

In some cases, two or more positive electrode active materials may be used in combination. Preferably, from the viewpoint of capacity and output characteristics, a lithium-transition metal composite oxide is used as the positive electrode active material. Of course, positive electrode active materials other than those described above may be used. When the optimum particle size is different for expressing the unique effect of each active material, the optimum particle size may be blended and used for expressing each unique effect. It is not always necessary to make the particle diameter uniform.

The average particle diameter of the positive electrode active material contained in the positive electrode active material layer 13 is not particularly limited, but is preferably 1 to 30 μm and more preferably 5 to 20 μm from the viewpoint of increasing the output. In the present specification, the “particle diameter” refers to the outline of the active material particles (observation surface) observed using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). It means the maximum distance among any two points. In this specification, the value of “average particle diameter” is the value of particles observed in several to several tens of fields using observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The value calculated as the average value of the particle diameter shall be adopted. The particle diameters and average particle diameters of other components can be defined in the same manner.

The positive electrode (positive electrode active material layer) can be applied by any one of a kneading method, a sputtering method, a vapor deposition method, a CVD method, a PVD method, an ion plating method, and a thermal spraying method in addition to a method of applying (coating) a normal slurry. Can be formed.

<Positive electrode current collector>
The positive electrode current collector 11 is made of a conductive material. The size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used.

There is no particular limitation on the thickness of the current collector. The thickness of the current collector is usually about 1 to 100 μm.

The shape of the current collector is not particularly limited. In the laminated battery 10 shown in FIG. 1, in addition to the current collector foil, a mesh shape (such as an expanded grid) can be used.

There are no particular restrictions on the materials that make up the current collector. For example, a metal or a resin in which a conductive filler is added to a conductive polymer material or a non-conductive polymer material can be employed.

Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient.

Also, examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxadiazole. Since such a conductive polymer material has sufficient conductivity without adding a conductive filler, it is advantageous in terms of facilitating the manufacturing process or reducing the weight of the current collector.

Non-conductive polymer materials include, for example, polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA) , Polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or polystyrene (PS). Such a non-conductive polymer material may have excellent potential resistance or solvent resistance.

A conductive filler may be added to the conductive polymer material or the non-conductive polymer material as necessary. In particular, when the resin used as the base material of the current collector is made of only a non-conductive polymer, a conductive filler is inevitably necessary to impart conductivity to the resin.

The conductive filler can be used without particular limitation as long as it has a conductivity. For example, metals, conductive carbon, etc. are mentioned as a material excellent in electroconductivity, electric potential resistance, or lithium ion barrier | blocking property. The metal is not particularly limited, but at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb, and K, or these metals It is preferable to contain an alloy or metal oxide containing. Moreover, there is no restriction | limiting in particular as electroconductive carbon. Preferably, it includes at least one selected from the group consisting of acetylene black, vulcan, black pearl, carbon nanofiber, ketjen black, carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene.

The amount of the conductive filler added is not particularly limited as long as it is an amount capable of imparting sufficient conductivity to the current collector, and is generally about 5 to 35% by mass.

<Negative electrode>
The negative electrode of the present embodiment includes a current collector and an electrode layer including a specific negative electrode active material, a conductive additive, and a binder disposed on the surface of the current collector, and the current collector has an elastic elongation. 1. It is characterized by being 30% or more.

[Negative electrode active material layer]
The negative electrode active material layer 15 includes a negative electrode active material, and further includes other additives as necessary.

(Negative electrode active material)
The negative electrode active material includes a predetermined alloy.

Alloy In this embodiment, the alloy is represented by the following chemical formula (1).

In the above formula (1), M is at least one metal selected from the group consisting of C, Nb, and combinations thereof. A is an inevitable impurity. Furthermore, x, y, z, and a represent mass% values, where 0 <x <100, 0 <y <100, 0 <z <100, and 0 ≦ a <0.5. , X + y + z + a = 100. In the present specification, the “inevitable impurity” means an Si alloy that is present in a raw material or inevitably mixed in a manufacturing process. The inevitable impurities are originally unnecessary impurities, but are a very small amount and do not affect the characteristics of the Si alloy.

In the present embodiment, the first additive element Al and the second additive element M (at least one metal selected from the group consisting of C, Nb, and combinations thereof) are selected as the negative electrode active material. Thus, the cycle life can be improved by suppressing the phase transition of the amorphous-crystal during the Li alloying. This also makes the capacity higher than that of a conventional negative electrode active material, for example, a carbon-based negative electrode active material.

Here, in the case of Li alloying, the amorphous-crystal phase transition is suppressed because, in the Si material, when Si and Li are alloyed, the amorphous state transitions to the crystalline state, causing a large volume change (about 4 times). For this reason, the particles themselves are broken and the function as the active material is lost. Therefore, by suppressing the amorphous-crystal phase transition, it is possible to suppress the collapse of the particles themselves, maintain the function as the active material (high capacity), and improve the cycle life. By selecting the first and second additive elements, a Si alloy negative electrode active material having a high capacity and high cycle durability can be provided.

As described above, M is at least one metal selected from the group consisting of C, Nb, and combinations thereof. Therefore, hereinafter, Si _x Al _y C _z A _a and Si _x Al _y Nb _z A _a Si alloys will be described.

Si _x Al _y C _z _{A a}
As described above, the Si _x Al _y C _z A _a is selected from Al as the first additive element and C as the second additive element, so that an amorphous-crystalline phase can be formed during Li alloying. The cycle life can be improved by suppressing the transition. This also makes the capacity higher than that of a conventional negative electrode active material, for example, a carbon-based negative electrode active material.

In the above alloy composition, x, y, and z are represented by the following formula (1):

It is preferable to satisfy.

Specifically, when the composition ratio of the Si—Al—C alloy is within the range surrounded by the thick solid line in FIG. 5 (inside the triangle), the composition ratio is extremely high that cannot be realized with an existing carbon-based negative electrode active material. High capacity can be realized. Similarly, even if compared with the existing Sn-based alloy negative electrode active material, the initial capacity is higher (initial capacity 1113 mAh / g or more), the capacity can be increased, and high initial charge / discharge efficiency (94% or more) can be realized. Further, regarding the cycle durability that is in a trade-off relationship with the increase in capacity, when compared with the Sn-based negative electrode active material having a high capacity but poor cycle durability and the multi-component alloy negative electrode active material described in Patent Document 1, Can provide an excellent Si alloy negative electrode active material capable of realizing remarkably excellent cycle durability.

In one embodiment, the x, y, and z are represented by the following formula (2):

It is further preferable to satisfy As described above, when the composition ratio of the first additive element Al to the second additive element C and the high-capacity element Si is within the appropriate range as defined above, the Si alloy negative electrode active material having better characteristics can be obtained. Can provide material. Specifically, even when the composition ratio of the Si—Al—C alloy is within the range surrounded by the thick solid line in FIG. 6 (inside the hexagon in FIG. 6), it cannot be realized with the existing carbon-based negative electrode active material. A much higher capacity can be achieved. Similarly, even if compared with the existing Sn-based alloy negative electrode active material, the initial capacity is higher (initial capacity 1113 mAh / g or more), the capacity can be increased, and high initial charge / discharge efficiency (94% or more) can be realized. In particular, in this case, the composition range in which samples 1 to 18 of Reference Example A were specifically high in initial capacity, increased in capacity, and achieved high initial charge / discharge efficiency was selected (= thick solid line in FIG. 6). A hexagon enclosed). Further, regarding the cycle durability that is in a trade-off relationship with the increase in capacity, when compared with the Sn-based negative electrode active material having a high capacity but poor cycle durability and the multi-component alloy negative electrode active material described in Patent Document 1, Can provide an excellent Si alloy negative electrode capable of realizing excellent cycle durability.

In one embodiment, the x, y, and z are represented by the following formula (3):

Even more preferably. As described above, when the composition ratio of the first additive element Al to the second additive element C and the high-capacity element Si is within the appropriate range as defined above, the Si alloy negative electrode active material having better characteristics can be obtained. Can provide material. Specifically, even when the composition ratio of the Si—Al—C alloy is within the range surrounded by the thick solid line in FIG. 7 (inside the hexagon in FIG. 7), it cannot be realized with the existing carbon-based negative electrode active material. A much higher capacity can be achieved. Similarly, even when compared with the existing Sn-based alloy negative electrode active material, the initial capacity is higher (initial capacity 1133 mAh / g or more), the capacity can be increased, and high initial charge / discharge efficiency (94% or more) can be realized. Further, regarding the cycle durability that is in a trade-off relationship with the increase in capacity, when compared with the Sn-based negative electrode active material having a high capacity but poor cycle durability and the multi-component alloy negative electrode active material described in Patent Document 1, Can realize extremely excellent cycle durability. Specifically, it is possible to realize a high discharge capacity maintenance rate of 64% or more at the 50th cycle. In particular, in this case, among the samples 1 to 18 of Reference Example A, only the composition range in which the initial capacity is specifically high, the capacity can be increased, the initial charge / discharge efficiency is high, and the cycle durability can be realized in a balanced manner. It is selected (= hexagon surrounded by a thick solid line in FIG. 7). Thereby, a high performance Si alloy negative electrode active material can be provided (refer to Table 1 and FIGS. 3, 4, and 7).

In one embodiment, the x, y, and z are represented by the following formula (4):

It is particularly preferable to satisfy In this embodiment, the Si alloy negative electrode having particularly good characteristics when the composition ratio of Al as the first additive element, C as the second additive element, and the high-capacity element Si is within the appropriate range specified above. An active material can be provided. Specifically, even when the composition ratio of the Si—Al—C alloy is within the range surrounded by the thick solid line in FIG. 8 (inside the small hexagon), it is not possible with the existing carbon-based negative electrode active material. High capacity can be realized. Similarly, even when compared with the existing Sn-based alloy negative electrode active material, the initial capacity is higher (initial capacity 1133 mAh / g or more), the capacity can be increased, and high initial charge / discharge efficiency (94% or more) can be realized. Further, regarding the cycle durability that is in a trade-off relationship with the increase in capacity, when compared with the Sn-based negative electrode active material having a high capacity but poor cycle durability and the multi-component alloy negative electrode active material described in Patent Document 1, Can realize extremely excellent cycle durability. Specifically, a high discharge capacity retention ratio of 74% or more at the 50th cycle can be realized. In other words, in this case, among the samples 1 to 18 of Reference Example A, the composition range in which the initial capacity is high and the capacity can be increased, the initial charge / discharge efficiency is high, and the cycle durability can be realized in a very balanced manner. Selected (small hexagon surrounded by thick solid line in FIG. 8). Thereby, a higher performance Si alloy negative electrode active material can be provided (refer to Table 1 and FIGS. 3, 4, and 8).

In one embodiment, the x, y, and z are represented by the following formula (5):

It is particularly preferable to satisfy the above. In the present embodiment, the Si alloy negative electrode having the best characteristics when the composition ratio of the first additive element Al and the second additive element C, and the high-capacity element Si is within the appropriate range specified above. An active material can be provided. Specifically, when the composition ratio of the Si—Al—C alloy is within the range surrounded by the thick solid line in FIG. 9 (inside the smallest hexagon), it cannot be realized with the existing carbon-based negative electrode active material. A much higher capacity can be achieved. Similarly, even if compared with the existing Sn-based alloy negative electrode active material, the initial capacity is higher (initial capacity 1192 mAh / g or more), the capacity can be increased, and high initial charge / discharge efficiency (97% or more) can be realized. Further, regarding the cycle durability that is in a trade-off relationship with the increase in capacity, when compared with the Sn-based negative electrode active material having a high capacity but poor cycle durability and the multi-component alloy negative electrode active material described in Patent Document 1, Can realize extremely excellent cycle durability. Specifically, an even higher discharge capacity retention rate of 81% or more at the 50th cycle can be realized. That is, in this case, among the samples 1 to 18 of Reference Example A, the initial capacity is higher and the capacity can be increased, the initial charge / discharge efficiency is higher, and a higher cycle durability can be realized in the most balanced manner ( (Best mode) only (= the smallest hexagon surrounded by the thick solid line in FIG. 9). Thereby, a very high performance Si alloy negative electrode active material can be provided (refer to Table 1 and FIGS. 3, 4 and 9). On the other hand, in _a ternary alloy represented by the composition formula Si _x Al _y C _z (A _a ), _a binary alloy that does not contain any one of the metal elements added to Si (y = 0 Si—C alloy) In addition, it is difficult to realize high initial charge / discharge efficiency and high cycle characteristics with Si and Al (Z = 0) and Si alone. Therefore, the initial charge / discharge efficiency is not sufficient, and the cycle characteristics deteriorate (deteriorate), so that the initial capacity can be increased and the capacity can be increased as described above, the initial charge / discharge efficiency is higher, and the cycle durability is higher. Cannot be realized in the most balanced manner.

Specifically, the negative electrode active material, in the production state (uncharged state), a ternary amorphous alloy represented by _{_{_{Si x Al y C z (A}}} a) having an appropriate composition ratio described above. And in the lithium ion secondary battery using the negative electrode active material of this embodiment, even when Si and Li are alloyed by charging / discharging, it is possible to suppress the transition from the amorphous state to the crystalline state and cause a large volume change. It has remarkable characteristics that can be achieved. Since patents in other ternary and quaternary alloys represented by Document 1 Si _x M _y Al _z, is still high cycle characteristics, in particular difficult to maintain a high discharge capacity retention ratio at 50th cycle As a result, a great problem arises in that the cycle characteristics rapidly deteriorate (deteriorate). That is, in the ternary and quaternary alloys of Patent Document 1, the initial capacity (discharge capacity at the first cycle) is much higher than the existing carbon-based negative electrode active material (theoretical capacity 372 mAh / g). The capacity is higher than that of the Sn-based negative electrode active material (theoretical capacity is about 600 to 700 mAh / g). However, the cycle characteristics are very poor and sufficient when compared with the discharge capacity retention ratio (about 60%) of the 50th cycle of the Sn-based negative electrode active material that can be increased in capacity to about 600 to 700 mAh / g. There wasn't. That is, the balance between the increase in capacity and the cycle durability, which are in a trade-off relationship, is poor and cannot be put into practical use. Specifically, the quaternary alloy of Si ₆₂ Al ₁₈ Fe ₁₆ Zr _{4 in} Example 1 of Patent Document 1 has an initial capacity as high as about 1150 mAh / g from FIG. 2, but only 5 to 6 cycles. It is shown that the later circulation capacity is already only about 1090 mAh / g. That is, in Example 1 of Patent Document 1, the discharge capacity maintenance rate at the 5th to 6th cycles has already been greatly reduced to about 95%, and the discharge capacity maintenance rate has decreased by about 1% every cycle. Is shown. From this, it is presumed that at the 50th cycle, the discharge capacity retention rate decreases by approximately 50% (= the discharge capacity retention rate decreases by approximately 50%). Similarly, in the ternary alloy of Si ₅₅ Al _29.3 Fe _15.7 of Example 2, the initial capacity is as high as about 1430 mAh / g from FIG. 4, but the circulation capacity after only 5 to 6 cycles is It has already been shown that it has already greatly decreased to about 1300 mAh / g. That is, in Example 2 of Patent Document 1, the discharge capacity maintenance rate at the 5th to 6th cycles has already rapidly decreased to about 90%, and the discharge capacity maintenance rate has decreased by about 2% for each cycle. Is shown. From this, it is presumed that at the 50th cycle, the discharge capacity maintenance rate is reduced by almost 100% (= the discharge capacity maintenance rate is reduced to almost 0%). In the quaternary alloy of Si ₆₀ Al ₂₀ Fe ₁₂ Ti ₈ of Example 3 and the quaternary alloy of Si ₆₂ Al ₁₆ Fe ₁₄ Ti ₈ of Example 4, there is no description of the initial capacity. It is shown that the circulating capacity after ˜6 cycles has already become a low value of 700 to 1200 mAh / g. The discharge capacity retention rate at the 5th to 6th cycles in Example 3 of Patent Document 1 is about the same as or less than that of Examples 1 and 2, and the discharge capacity retention rate at the 50th cycle also decreases by about 50% to 100% (= It is presumed that the discharge capacity retention rate is reduced to approximately 50% to 0%). In addition, since the alloy composition of patent document 1 is described by atomic ratio, when converted into mass ratio like this embodiment, about 20 mass% of Fe is contained in the Example, and it becomes a 1st addition element. It can be said that the alloy composition is disclosed.

For this reason, batteries using these binary alloys or ternary or quaternary alloys described in Patent Document 1 have cycle characteristics that satisfy a practical level in fields where cycle durability is strongly required, such as in vehicles. There are problems in its reliability and safety, such as insufficient availability, making it difficult to put it to practical use. On the other hand, in the negative electrode active material using a ternary alloy represented by the present embodiment _{_{_{Si x Al y C z (A}}} a), has a high discharge capacity maintenance ratio of the 50th cycle as high cycle characteristics (FIG. 7 To 9). Furthermore, the initial capacity (discharge capacity at the first cycle) is also significantly higher than that of the existing carbon-based negative electrode active material, and is equal to or higher than that of the existing Sn-based negative electrode active material (see Table 1 and FIG. 3). A negative electrode active material having high initial charge / discharge efficiency and exhibiting well-balanced characteristics can be provided. In other words, in addition to the increase in capacity and cycle durability that have not been realized due to the trade-off relationship between the existing carbon-based and Sn-based negative electrode active materials and the ternary and quaternary alloys described in Patent Document 1, further initial The present inventors have found a negative electrode active material using an alloy that can achieve charge / discharge efficiency in a high-order and well-balanced manner. Specifically, two types of Al and C are selected from the group consisting of one or two or more additive element species in which there are very various combinations, and a specific composition of these additive element species and high-capacity element Si is selected. It has been found that the intended purpose can be achieved by selecting the ratio (composition range). As a result, it is excellent in that it can provide a lithium ion secondary battery that has a higher initial capacity, a higher capacity, a higher initial charge / discharge efficiency, and a higher balance in cycle durability.

Will be described in more detail below the anode active material _{_{_{_{Si x Al y C z A a}}}} .

(1) About the total mass% value of the alloy As the total mass% value of the alloy having the composition formula Si _x Al _y C _z A _a , x + y + z + a = 100 (where x, y, z, and a Represents mass% value). That is, it must be made of a Si—Al—C ternary alloy. In other words, it can be said that a binary alloy, a ternary alloy having another composition, or a quaternary or higher alloy to which another metal is added is not included. However, the above inevitable impurity A may be included. Incidentally, the negative electrode active material layer 15 of the present embodiment, a combination of at least one composition formula Si _x Al _y C _z _{A a} may be contained the alloy having two or more different the alloy compositions May be used.

(2) a mass% value of Si in the alloy having the above composition formula _Si x _Al y _C z _{A a} for mass percentage of Si in the alloy, the range of x is preferably 36 ≦ x <100 More preferably, 36 ≦ x ≦ 80, still more preferably 41 ≦ x ≦ 71, and particularly preferably 43 ≦ x ≦ 61. The higher the mass percentage value (x value) of the high-capacity element Si in the alloy, the higher the capacity, and if it is in the range of 36 ≦ x <100, it cannot be realized with existing carbon-based negative electrode active materials. This is because an extremely high capacity can be realized. Similarly, even when compared with the Sn-based negative electrode active material, a higher capacity alloy can be obtained (see FIG. 5). Furthermore, if it is in the range of 36 ≦ x <100, the discharge capacity retention rate (cycle durability) at the 50th cycle is also excellent.

Preferably, the mass% value (x value) of the high-capacity element Si in the alloy preferably maintains a high cycle characteristic (a high discharge capacity retention rate at the 50th cycle) while maintaining a high balance between the initial capacity and the high charge / discharge efficiency. The range of 36 ≦ x ≦ 80 is desirable from the viewpoint of providing the negative electrode active material shown. In addition, when the composition ratio of Al as the first additive element and C in the second additive element is appropriate, good characteristics (high capacity and cycle that are in a trade-off relationship with existing alloy negative electrode active materials) It is possible to realize a Si alloy negative electrode active material having durability and characteristics excellent in charge / discharge efficiency. That is, the higher the mass% value (x value) of the high-capacity element Si in the alloy, the higher the capacity, but the cycle durability tends to decrease. However, if it is within the range of 36 ≦ x ≦ 80 It is preferable in that a high charge / discharge efficiency and a high discharge capacity retention ratio can be realized together with an increase in capacity.

More preferably, the mass% value (x value) of the high-capacity element Si in the alloy exhibits a high balance between the high initial capacity and the high charge / discharge efficiency while maintaining higher cycle characteristics (higher discharge capacity retention ratio). From the viewpoint of providing a negative electrode active material, the range of 41 ≦ x ≦ 71 is more desirable. In addition, when the ratio of Al as the first additive element and C of the second additive element described later is more appropriate, a Si alloy negative electrode active material having better characteristics can be provided (Table 1 and FIG. (Refer to 7 and 8 thick internal lines) That is, if 41 ≦ x ≦ 71, which is a more preferable range, the capacity is increased (1113 mAh / g or more, particularly 1133 mA / g or more), and the charge / discharge efficiency (94% or more) is high. It is more excellent in that a high discharge capacity retention ratio (64% or more, particularly 74% or more) can be realized (internal reference surrounded by a thick solid line in Table 1, FIG. 7 and FIG. 8).

The mass% value (x value) of the high-capacity element Si in the alloy is particularly preferably a balance between high initial capacity and high charge / discharge efficiency while maintaining particularly high cycle characteristics (particularly high discharge capacity retention). From the viewpoint of providing a negative electrode active material, the range of 43 ≦ x ≦ 61 is particularly desirable. In addition, a high-performance Si alloy negative electrode active material having the best characteristics can be provided when the ratio of Al, which is the first additive element, and C of the second additive element, which will be described later, is more appropriate (Table 1). 1 and the internal reference surrounded by the thick solid line in FIG. 9). That is, in the particularly preferred range of 43 ≦ x ≦ 61, the capacity is high (1192 mAh / g or more), high charge / discharge efficiency (97% or more), and particularly high discharge capacity maintenance ratio (81 in the 50th cycle) (81 % Or more) can be maintained (internal reference enclosed by a thick solid line in Table 1 and FIG. 9). On the other hand, the composition formula _{_{_{_{Si x Al y C z (A}}}} a) in compared with the ternary alloy represented binary not containing one of the additive metal element to high capacity element Si (Al, C) High initial charge / discharge efficiency and high cycle characteristics cannot be realized with the alloys of the series (y = 0 Si—C alloy or z = 0 Si—Al alloy). In particular, the high initial charge / discharge efficiency and the high discharge capacity maintenance ratio at the 50th cycle cannot be sufficiently maintained, the initial charge / discharge efficiency is not sufficient, and the cycle characteristics are deteriorated (deteriorated). Therefore, in addition to the high capacity as described above, a particularly high discharge capacity maintenance rate at the 50th cycle cannot be realized in a most balanced manner with high charge / discharge efficiency. Further, when x = 100 (in the case of pure Si containing no added metal elements Al and C to Si), capacity and cycle durability are in a trade-off relationship, and high cycle durability is exhibited while exhibiting high capacity. It is extremely difficult to improve. That is, since it is only a high-capacity element Si, it has the highest capacity, but on the other hand, the deterioration as a negative electrode active material is remarkable due to the expansion and contraction phenomenon of Si accompanying charging and discharging, and the worst and extremely low discharge capacity maintenance Only rate is obtained. Therefore, in addition to the high capacity as described above, a particularly high discharge capacity maintenance rate at the 50th cycle cannot be realized in a most balanced manner with high charge / discharge efficiency.

Here, in the case of x ≧ 41, especially x ≧ 43, the content ratio (balance) of Si material having an initial capacity of 3200 mAh / g, Al as the first additive element, and C as the second additive element is optimal. (See the range surrounded by the thick solid line in FIGS. 7 to 9). Therefore, it is excellent in that the most favorable characteristics can be expressed and the increase in capacity at the vehicle application level can be stably and safely maintained over a long period of time. On the other hand, when x ≦ 71, particularly x ≦ 61, the high content Si material having an initial capacity of 3200 mAh / g and the content ratio (balance) of the first additive element Al and the second additive element C are optimal. (See the range surrounded by the thick solid line in FIGS. 7 to 9). Therefore, when alloying Si and Li, the amorphous-crystal phase transition can be remarkably suppressed, and the cycle life and charge / discharge efficiency can be greatly improved. That is, it is possible to realize a discharge capacity maintenance ratio of 50th cycle of 64% or more, particularly 74% or more, and particularly 81% or more. Further, the initial charge / discharge efficiency of 94% or more, particularly 97% or more can be realized. However, even if x is outside the above optimal range (41 ≦ x ≦ 71, particularly 43 ≦ x ≦ 61), it is within a range where the above-described operational effects can be effectively expressed. Needless to say, it is included in the technical scope (scope of rights) of the present invention.

Further, it is disclosed in the above-mentioned embodiment of Patent Document 1 that the degradation of cycle characteristics due to a considerable capacity reduction is already exhibited in only about 5 to 6 cycles. That is, in the example of Patent Document 1, the discharge capacity maintenance rate at the 5th to 6th cycles has already been reduced to 90 to 95%, and the discharge capacity maintenance rate at the 50th cycle has been reduced to almost 50 to 0%. It will be. On the other hand, in the present embodiment, the combination of the first additive element Al and the second additive element C to Si is mutually complementary, so to speak, many trials and errors, and various combinations of additive (metal or nonmetal) elements. It was possible to select through an excessive experiment. And by combining the content of the high-capacity Si material within the optimum range shown above in the combination, the reduction in the discharge capacity maintenance ratio and the initial charge / discharge efficiency at the 50th cycle is greatly reduced along with the increase in capacity. It is also excellent in that it can be done. That is, when Si and Li are alloyed, the crystal is crystallized from an amorphous state by a particularly remarkable synergistic effect (effect) due to the optimum range of the first additive element Al and the second additive element C mutually complementary to the Al. The transition to the state can be suppressed, and a large volume change can be prevented. Furthermore, it is excellent also in that the high cycle durability of the electrode can be improved while showing a high capacity.

(3) About the mass% value of Al in the alloy The range of y that is the mass% value of Al in the alloy having the composition formula Si _x Al _y C _z A _a is preferably 0 <y <64, More preferably, 10 ≦ y ≦ 56, still more preferably 15 ≦ y ≦ 56, and particularly preferably 20 ≦ y ≦ 54. This is because if the numerical value of the mass percentage (y value) of the first additive element Al in which the capacity as an electrode does not decrease even if the concentration of C in the alloy increases, the value of C Due to the synergistic characteristics of Al and Al, the amorphous-crystal phase transition of the high-capacity Si material can be effectively suppressed. As a result, the initial capacity is high, the capacity can be increased, the initial charge / discharge efficiency is high, and an effect excellent in cycle life (cycle durability) can be exhibited. Specifically, a high initial capacity of 1113 mAh / g or higher, particularly 1133 mAh / g or higher, particularly 1192 mAh / g or higher, can exhibit a high initial charge / discharge efficiency of 94% or higher, particularly 97% or higher. Further, a high discharge capacity retention rate at the 50th cycle of 64% or more, particularly 74% or more, particularly 81% or more can be exhibited (see Table 1, FIGS. 7 to 9). In addition, the content x value of the high-capacity Si material can be maintained at a certain value (36 ≦ x <100), and the capacity can be increased significantly, which cannot be realized with existing carbon-based negative electrode active materials. realizable. Similarly, even when compared with the existing Sn-based alloy negative electrode active material, a higher capacity alloy can be obtained.

The mass% value (y value) of the first additive element Al in the alloy is preferably 10 from the viewpoint of providing a negative electrode active material that exhibits a high balance between high cycle characteristics and high initial capacity and high initial charge / discharge efficiency. A range of ≦ y ≦ 56 is desirable. During Li alloying, the capacity of the second additive element C, which suppresses the amorphous-crystal phase transition and improves the cycle life, and the negative electrode active material (negative electrode) does not decrease even when the concentration of the second additive element increases. Selection of the first additive element Al is extremely important and useful in the present embodiment. With such first and second additive elements, a known ternary alloy, a quaternary or higher alloy such as Patent Document 1, and a binary alloy such as a Si—C alloy or Si—Al alloy can be used. It was found that there was a significant difference in action and effect. When the content ratio of the first additive element Al (and the second additive element C mutually complementary with Al) is appropriate, the Si alloy negative electrode active material having good characteristics is obtained (Table 1 and FIG. 7). (See composition range surrounded by thick solid line). That is, if the numerical value of the mass% value (y value) of the first additive element Al in the alloy is 10 ≦ y ≦ 56 in the preferred range, due to the synergistic effect (mutual complementary characteristics) with the second additive element C, When alloying, the effect of suppressing the amorphous-crystal phase transition and improving the cycle life can be effectively expressed. As a result, the initial capacity is high, the capacity can be increased, the initial charge / discharge efficiency is high, and an effect excellent in cycle life (cycle durability) can be exhibited. Specifically, an excellent effect of a high initial charge / discharge efficiency of 94% or more can be exhibited at a high initial capacity of 1113 mAh / g or more, particularly 1133 mAh / g or more. Further, an excellent effect of a high discharge capacity retention rate of 64% or more at the 50th cycle can be exhibited (see Table 1 and FIG. 7). In this case, among the samples 1 to 18 of Reference Example A, the composition range in which the capacity can be increased and high initial charge / discharge efficiency and cycle life (cycle durability) can be realized (particularly with respect to the Al content, 10 ≦ y ≦ 56) is selected (the hexagon surrounded by the thick solid line in FIG. 7). By selecting 10 ≦ y ≦ 56 for the composition range, particularly the Al content, existing high-capacity Sn-based negative electrode active materials and patent documents can be obtained by a synergistic effect (mutual complementary characteristics) with the second additive element C. Compared with the multi-component alloy negative electrode active material described in No. 1, it is possible to realize a cycle durability that is remarkably excellent. As a result, it is possible to provide a Si alloy negative electrode active material that realizes a discharge capacity retention rate of 64% or more at the 50th cycle (see Table 1 and the composition range surrounded by a thick solid line in FIG. 7).

The mass% value (y value) of the first additive element Al in the alloy is particularly preferably 15 from the viewpoint of providing a negative electrode active material having a higher balance between high cycle characteristics and high initial capacity and initial charge / discharge efficiency. A range of ≦ y ≦ 56 is desirable. When the content ratio of the first additive element Al, which can exhibit the effect of suppressing the amorphous-crystal phase transition and improving the cycle life due to the synergistic effect (mutual complementary characteristics) with C during Li alloying, is more appropriate This is because a Si alloy negative electrode active material having even better characteristics can be provided. That is, in the particularly preferred range of 15 ≦ y ≦ 56, it is possible to suppress the amorphous-crystal phase transition when alloying due to a synergistic effect with C (mutual complementarity). As a result, the initial capacity is high, the capacity can be increased, the initial charge / discharge efficiency is high, and an effect excellent in cycle life (cycle durability) can be exhibited. Specifically, an excellent effect of high initial charge / discharge efficiency of 94% or more can be exhibited at a high initial capacity of 1133 mAh / g or more. Further, an excellent effect of a high discharge capacity retention ratio of 74% or more at the 50th cycle can be exhibited (see Table 1 and FIG. 8). Particularly in this case, among the samples 1 to 18 of Reference Example A, the composition range (especially containing Al) can achieve higher capacity, and can realize higher initial charge / discharge efficiency and better cycle life (cycle durability). Regarding the amount, 15 ≦ y ≦ 56) is selected. That is, the composition range is inside a small hexagon surrounded by a thick solid line in FIG. By selecting 15 ≦ y ≦ 56 for the composition range, particularly the Al content, the synergistic effect with C increases the capacity, as well as the existing high capacity Sn-based negative electrode active materials and the multiple elements described in Patent Document 1. Compared with the negative electrode-based alloy negative electrode active material, it is possible to realize remarkably excellent cycle durability. As a result, a well-balanced Si alloy negative electrode active material that realizes a discharge capacity retention ratio of 64% or more at the 50th cycle can be provided.

The mass% value (y value) of the first additive element Al in the alloy is particularly preferable from the viewpoint of providing a negative electrode active material that exhibits the best balance between higher cycle characteristics and higher initial capacity and higher initial charge / discharge efficiency. A range of 20 ≦ y ≦ 54 is desirable. In the case of Li alloying, when the content ratio of the first additive element Al, which has the effect of suppressing the amorphous-crystal phase transition and improving the cycle life by the synergistic effect with C (mutual complementary characteristics), is most appropriate In addition, the Si alloy negative electrode active material having the best characteristics can be provided. That is, in the particularly preferred range of 20 ≦ y ≦ 54, the amorphous-crystal phase transition can be more effectively suppressed during alloying due to a synergistic effect with C (mutual complementarity). As a result, the initial capacity is high, the capacity can be increased, the initial charge / discharge efficiency is high, and an effect excellent in cycle life (cycle durability) can be exhibited. Specifically, an excellent effect of high initial charge / discharge efficiency of 97% or higher can be exhibited at a high initial capacity of 1192 mAh / g or higher. Furthermore, the outstanding effect of the high discharge capacity maintenance factor 81% or more in 50th cycle can also be expressed (refer Table 1, FIG. 9). Particularly in this case, among the samples 1 to 18 of Reference Example A, the composition range (especially containing Al) can achieve higher capacity, and can realize higher initial charge / discharge efficiency and better cycle life (cycle durability). Regarding the amount, 20 ≦ y ≦ 54) is selected. That is, the composition range within the smallest hexagon surrounded by the thick solid line in FIG. By selecting 20 ≦ y ≦ 54 with respect to the composition range, particularly the Al content, a synergistic effect with C can increase the capacity, as well as the existing high capacity Sn-based negative electrode active material and Patent Document 1 Even when compared with the multi-component alloy negative electrode active material, it is possible to provide a well-balanced Si alloy negative electrode active material that realizes excellent cycle durability and initial charge / discharge efficiency. On the other hand, the composition formula _{_{_{_{Si x Al y C z (A}}}} a) adding a metal element of the ternary system to the Si alloy represented by (Al, C) 2 ternary alloy does not contain one of (especially, High cycle characteristics and charge / discharge efficiency cannot be maintained with a Y—Si—C alloy). In particular, the high discharge capacity maintenance rate and the high initial charge / discharge efficiency at the 50th cycle cannot be maintained, and the initial charge / discharge efficiency is reduced or the cycle characteristics are deteriorated (deteriorated). Therefore, it has not been possible to provide a Si alloy negative electrode active material that achieves the best balance between the above-described excellent cycle durability and high initial capacity and charge / discharge efficiency.

Here, when y ≧ 10, particularly y ≧ 15, and especially y ≧ 20, the high-capacity Si material having the initial capacity of 3200 mAh / g, the first additive element Al, and the further second additive element C The content ratio (balance) can be in an optimum range (see the range surrounded by the thick solid line in FIGS. 7 to 9). Therefore, even if the C concentration that can suppress the amorphous-crystal phase transition, which is a characteristic of Al, increases, the capacity decrease as the negative electrode active material (negative electrode) is effectively suppressed. Life (especially discharge capacity maintenance rate) and charge / discharge efficiency can be significantly improved. As a result, the negative electrode active material (negative electrode) is excellent in that it can exhibit the best characteristics and can maintain a high capacity at the vehicle application level stably and safely over a long period of time. On the other hand, in the case of y ≦ 56, particularly y ≦ 54, the content ratio of the high-capacity Si material having an initial capacity of about 3200 mAh / g, the first additive element Al, and the second additive element C ( (Balance) can be an optimum range (see the range surrounded by a thick solid line in FIGS. 7 to 9). Therefore, when alloying Si and Li, the amorphous-crystal phase transition can be remarkably suppressed, and the cycle life (particularly the discharge capacity retention rate) and charge / discharge efficiency can be greatly improved along with the increase in capacity. . That is, a high initial capacity of 1133 mAh / g or more, particularly 1192 mAh / g or more can be realized, and a high initial charge / discharge efficiency of 94% or more, particularly 97% or more can be realized. Further, a high discharge capacity retention ratio of 64% or more, particularly 74% or more, particularly 81% or more can be realized at the 50th cycle. However, even if y is outside the above optimal range (10 ≦ y ≦ 56, especially 15 ≦ y ≦ 56, and in particular, 20 ≦ y ≦ 54), the above-described effects of the present embodiment are effectively expressed. Needless to say, it is included in the technical scope (right range) of the present invention as long as it can be performed.

Further, it is disclosed in the above-mentioned embodiment of Patent Document 1 that the degradation of cycle characteristics due to a considerable capacity reduction is already exhibited in only about 5 to 6 cycles. That is, in the example of Patent Document 1, the discharge capacity maintenance rate at the 5th to 6th cycles has already been reduced to 90 to 95%, and the discharge capacity maintenance rate at the 50th cycle has been reduced to almost 50 to 0%. It will be. On the other hand, in this embodiment, the combination of the first additive element Al and the second additive element C to the high-capacity Si material has a mutually complementary relationship, so to speak, many trials and errors, and various additions (metal or non-additional). It can be selected through an excessive experiment with a combination of (metal) elements (only one combination). And in that combination, by further making the Al content within the optimum range shown above, it is possible to greatly reduce the reduction in the discharge capacity maintenance ratio and the initial charge / discharge efficiency at the 50th cycle as well as the increase in capacity. Are better. That is, when Si and Li are alloyed, the crystal is crystallized from the amorphous state by a particularly remarkable synergistic effect (effect) due to the optimum range of the first additive element Al (and the second additive element C mutually complementary to Al). Transition to the state can be suppressed, and a large volume change can be prevented. Furthermore, it is also excellent in that the high cycle durability of the electrode can be improved while exhibiting high capacity and high charge / discharge efficiency.

(4) the range of z is the mass percent of C in the alloy with C mass% The above composition formula for values _Si x _Al y _C z _{A a} of the alloy is preferably 0 <z <64, More preferably, 3 ≦ z ≦ 37, and further preferably 3 ≦ z ≦ 29. This is because, if the numerical value of the mass% value (z value) of the second additive element species C in the alloy is in the range of 0 <z <64, the high capacity Si due to the characteristics of C and the synergistic characteristics with Al. The amorphous-crystal phase transition of the material can be effectively suppressed. As a result, an effect excellent in cycle life (cycle durability), in particular, a high discharge capacity retention ratio (64% or more, particularly 74% or more, particularly 81% or more) at the 50th cycle can be exhibited (FIG. 7). To 9). Moreover, the effect excellent in the initial stage charge / discharge efficiency (94% or more, especially 97% or more) can be expressed (refer Table 1). In addition, the value x of the content of the high-capacity Si material can be maintained at a certain value (36 ≦ x <100), and a high capacity that cannot be realized with an existing carbon-based negative electrode active material can be realized. . Similarly, an alloy having a higher capacity (initial capacity 1113 mAh / g or more, particularly 1133 mAh / g or more, especially 1192 mAh / g or more) can be obtained even when compared with existing Sn-based negative electrode active materials (Table 1 and FIG. 5-8).

Preferably, the mass% value (z value) of the second additive element C in the alloy maintains a high cycle characteristic (a high discharge capacity retention ratio at the 50th cycle), and a balance between a high initial capacity and a high initial charge / discharge efficiency. From the viewpoint of providing a well-shown negative electrode active material, a range of 3 ≦ z ≦ 37 is desirable. To provide a Si alloy negative electrode active material having good characteristics when the content ratio of C having an effect of suppressing the amorphous-crystal phase transition and improving the cycle life is appropriate at the time of forming the Li alloy. (See the composition range surrounded by the thick solid line in Table 1 and FIG. 6). That is, if the value of the mass% (z value) of the second additive element C in the alloy is 3 ≦ z ≦ 37, which is a preferable range, the amorphous-crystal phase transition is suppressed during alloying and the cycle life is reduced. It is preferable at the point which can effectively express the effect which improves. In this case, the composition range (especially with respect to the C content) in which high capacity (1113 mAh / g or more) and high initial charge / discharge efficiency (94% or more) could be realized with Samples 1 to 18 of Reference Example A. (3 ≦ z ≦ 37) is selected (a hexagon surrounded by a thick solid line in FIG. 6). By selecting 3 ≦ z ≦ 37 with respect to the composition range, particularly the C content, the initial charge / discharge efficiency is higher than that of the existing Sn-based negative electrode active material and the multi-component alloy negative electrode active material described in Patent Document 1. And Si alloy negative electrode active material realizing cycle durability.

Particularly preferably as the mass% value (z value) of the second additive element C in the alloy, the initial capacity and the initial charge / discharge efficiency are also maintained while maintaining higher cycle characteristics (high discharge capacity retention rate at the 50th cycle). The range of 3 ≦ z ≦ 29 is desirable from the viewpoint of providing a negative electrode active material exhibiting the highest balance of high characteristics. When the content ratio of the second additive element C having the effect of suppressing the amorphous-crystal phase transition and improving the cycle life is most appropriate during the Li alloying, the Si alloy negative electrode active material having the best characteristics is most suitable. Substances can be provided (see Table 1 and Figures 7-9). That is, in the particularly preferable range of 3 ≦ z ≦ 29, when alloying, the effect of suppressing the amorphous-crystal phase transition and improving the initial capacity, initial charge / discharge efficiency, and cycle life is more effectively exhibited. be able to. As a result, a high initial capacity of 1133 mAh / g or more, particularly 1192 mAh / g or more can be realized, and a high initial charge / discharge efficiency of 94% or more, particularly 97% or more can be realized. Further, a high discharge capacity retention ratio of 64% or more, particularly 74% or more, particularly 81% or more can be realized at the 50th cycle (see Table 1 and FIGS. 7 to 9). In particular, in this case, among the samples 1 to 18 of Reference Example A, the composition range (particularly C) that can achieve higher capacity, higher initial charge / discharge efficiency, and higher discharge capacity retention ratio at the 50th cycle. With respect to the content, 3 ≦ z ≦ 29) was selected (hexagons surrounded by thick solid lines in FIGS. 7 to 9). By selecting 3 ≦ z ≦ 29 for the above composition range, particularly C content, with excellent cycle durability compared to the Sn-based negative electrode active material and the multi-component alloy negative electrode active material described in Patent Document 1, It is possible to provide a Si alloy negative electrode active material that achieves the most balanced characteristics with high initial capacity and charge / discharge efficiency. On the other hand, the composition formula _{_{_{_{Si x Al y C z (A}}}} a) adding a metal element to Si respect ternary alloy represented by (Al, C) 2 ternary alloy does not contain one of ( In particular, high cycle characteristics and charging / discharging efficiency cannot be realized with a Si—Al alloy with z = 0. In particular, the high discharge capacity maintenance rate and the high initial charge / discharge efficiency at the 50th cycle cannot be maintained, and the initial charge / discharge efficiency is reduced or the cycle characteristics are deteriorated (deteriorated). Therefore, it has not been possible to provide a Si alloy negative electrode active material that achieves the best balance between the above-described excellent cycle durability and high initial capacity and charge / discharge efficiency.

Here, when z ≧ 3 (C content is 3% by mass or more), the content ratio of the high-capacity Si material having the initial capacity of 3200 mAh / g and the first additive element Al and the second additive element C (Balance) can be in an optimal range (see the range surrounded by the thick solid line in FIGS. 7 to 9). Therefore, it effectively suppresses the amorphous-crystal phase transition of the Si material, which is a characteristic of C (and also a synergistic characteristic with Al), increases the capacity, as well as the cycle life (especially the discharge capacity maintenance rate) and charge. Discharge efficiency can be significantly improved. As a result, the negative electrode active material (negative electrode) is excellent in that it can exhibit better characteristics and can maintain a high capacity at the vehicle application level stably and safely over a long period of time. On the other hand, when z ≦ 29 (C content is 29 mass% or less), a high-capacity Si material having an initial capacity (theoretical capacity) of about 3200 mAh / g, the first additive element Al, and the second additive element The content ratio (balance) of C can be in an optimum range (see the range surrounded by the thick solid line in FIGS. 7 to 9). Therefore, when alloying Si and Li, the amorphous-crystal phase transition can be remarkably suppressed, and the cycle life can be greatly improved. That is, a high initial capacity of 1133 mAh / g or more, particularly 1192 mAh / g or more can be realized, and a high initial charge / discharge efficiency of 94% or more, particularly 97% or more can be realized. Further, a high discharge capacity retention ratio of 64% or more, particularly 74% or more, particularly 81% or more can be realized at the 50th cycle. However, even if z is outside the above optimal range (3 ≦ z ≦ 29), it is within the technical scope of the present invention as long as the effects of the above-described embodiment can be effectively expressed. Needless to say, it is included in the scope of rights.

Further, it is disclosed in the above-mentioned embodiment of Patent Document 1 that the degradation of cycle characteristics due to a considerable capacity reduction is already exhibited in only about 5 to 6 cycles. That is, in the example of Patent Document 1, the discharge capacity maintenance rate at the 5th to 6th cycles has already been reduced to 90 to 95%, and the discharge capacity maintenance rate at the 50th cycle has been reduced to almost 50 to 0%. It will be. On the other hand, in the present embodiment, the combination of the first additive element Al and the second additive element C to the high-capacity Si material is mutually complementary, so to speak, many trials and errors and various additions (metal or nonmetal). It can be selected through an excessive experiment with combinations of elemental species (only one combination). And in the combination, if the content of C is further in the optimum range shown above, it is also excellent in that the decrease in the discharge capacity maintenance rate at the 50th cycle can be greatly reduced. That is, when Si and Li are alloyed, the crystalline state is changed from an amorphous state by a particularly remarkable synergistic effect (effect) due to the optimum range of the first additive element Al and further the second additive element C mutually complementary to Al. Can be prevented and a large volume change can be prevented. Furthermore, it is excellent in that the high cycle durability and the initial charge / discharge efficiency of the electrode can be improved while showing a high capacity (see Table 1 and FIGS. 7 to 9).

(5) Range of a a weight percent of A in the alloy having the above composition formula _Si x _Al y _C z _{A a} for mass% value of A in the alloy is 0 ≦ a <0.5, More preferably, 0 <x <0.1. As described above, A is present in the raw material in the Si alloy or is inevitably mixed in the manufacturing process, and is originally unnecessary, but it is a trace amount and affects the characteristics of the Si alloy. Therefore, it is allowed to be contained in the alloy.

Si _x Al _y Nb _z _{A a}
As described above, the Si _x Al _y C _z A _a is selected from Al as the first additive element and Nb as the second additive element. The cycle life can be improved by suppressing the transition. This also makes the capacity higher than that of a conventional negative electrode active material, for example, a carbon-based negative electrode active material.

In the composition of the alloy, 27 <x <100, 0 <y <73, and preferably 0 <z <58. This numerical range corresponds to the range indicated by the symbol A in FIG. Such a negative electrode active material can exhibit excellent cycle characteristics while maintaining a high discharge capacity as compared with a carbon-based negative electrode active material having a charge / discharge capacity of about 300 mAh / g. It is suitably used for a negative electrode. As a result, it can be suitably used as a lithium-ion secondary battery for vehicle drive power or auxiliary power. In addition to this, the present invention can be sufficiently applied to lithium ion secondary batteries for portable devices such as mobile phones.

More specifically, when the negative electrode active material is used for a negative electrode for a lithium ion secondary battery, the alloy absorbs lithium ions during charge / discharge of the battery and releases lithium ions during discharge. The negative electrode active material is a Si alloy negative electrode active material, and includes a first additive element that suppresses amorphous-crystal phase transition and improves cycle life when alloyed with lithium by charging. It contains some Al, and further contains Nb as a second additive element that makes it difficult to reduce the capacity as an electrode even if the concentration of the first additive element increases. As a result, high capacity and high cycle durability can be exhibited, and further high charge / discharge efficiency can be exhibited in the initial stage.

At this time, in the negative electrode active material made of a Si—Al—Nb-based alloy, if the x exceeds 27, a sufficient initial capacity can be obtained. If x is less than 100, cycle characteristics improved over conventional pure silicon can be obtained. In addition, when y exceeds 0, cycle characteristics improved over pure silicon are obtained, and when y is less than 73, the silicon content is relatively high, so that the initial capacity is the existing capacity. There is a tendency to be improved as compared with the negative electrode active material. When z exceeds 0, cycle characteristics improved over pure silicon are obtained, and when z is less than 58, the silicon content is relatively high, so that the initial capacity is less than the existing negative electrode active capacity. There is a tendency to improve compared to substances.

Further, from the viewpoint of exhibiting more excellent cycle characteristics, 47 <x <95, 2 <y <48, and 1 <z <23 are preferable. This numerical range corresponds to the range indicated by the symbol B in FIG.

Further, from the viewpoint of further exhibiting excellent cycle characteristics, 61 <x <84, 2 <y <25, and 2 <z <23 are preferable. This numerical range corresponds to the range indicated by the symbol C in FIG.

Further, 47 <x <56, 33 <y <48, and 1 <z <16 are also preferable from the viewpoint that even better cycle characteristics can be exhibited. This numerical range corresponds to the range indicated by the symbol D in FIG.

Note that, as described above, A is an impurity (unavoidable impurity) other than the above three components derived from the raw materials and the manufacturing method. The a is 0 ≦ a <0.5, and more preferably 0 ≦ a <0.1.

(Average particle diameter of Si alloy)
The average particle diameter of the Si alloy is not particularly limited as long as it is approximately the same as the average particle diameter of the negative electrode active material contained in the existing negative electrode active material layer 15. From the viewpoint of higher output, it is preferably in the range of 1 to 20 μm. However, it is not limited at all to the above range, and it goes without saying that it may be outside the above range as long as the effects of the present embodiment can be effectively expressed. The shape of the Si alloy is not particularly limited, and may be spherical, elliptical, cylindrical, polygonal, flaky, indeterminate, or the like.

(Alloy manufacturing method)
As a method for producing an alloy having a composition formula Si _x Al _y M _z _{A a} according to the present embodiment is not limited in particular, it can be prepared by utilizing the manufacturing various known. That is, since there is almost no difference in the alloy state and characteristics depending on the production method, various production methods can be applied.

Specifically, for example, a mechanical alloy method, an arc plasma melting method, or the like can be used as a method for producing a particle form of an alloy having the composition formula Si _x Al _y M _z A _a .

In the method of manufacturing in the form of the above particles, a slurry can be prepared by adding a binder, a conductive additive and a viscosity adjusting solvent to the particles, and a slurry electrode can be formed using the slurry. Therefore, it is excellent in that it is easy to mass-produce (mass production) and to be practically used as an actual battery electrode.

(Negative electrode current collector)
The negative electrode current collector 12 is made of a conductive material. The size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used.

The shape of the current collector is not particularly limited. In the stacked battery 10 shown in FIG. 1, in addition to the current collector foil, a mesh shape (expanded grid or the like) can be used. In this embodiment, it is desirable to use the current collector foil.

Specifically, examples of the metal include copper, aluminum, nickel, iron, stainless steel, titanium, and alloys thereof. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. From the viewpoints of electron conductivity, battery operating potential, and adhesion of the negative electrode active material by sputtering to the current collector, copper can be preferably used as described later.

The negative electrode of this embodiment is characterized in that the elastic elongation in the planar direction of the current collector is 1.30% or more. Here, the elastic elongation (%) of the current collector is the ratio (%) of the size of the elastic elongation up to the proportional limit in the tensile direction to the original size.

By applying a specific ternary Si alloy as the negative electrode active material, the negative electrode of the present embodiment can obtain a high initial discharge capacity similar to that of the Si negative electrode, and at the same time, amorphous when Si and Li are alloyed. -The effect of suppressing the phase transition of the crystal and improving the cycle life can be obtained.

However, when a battery is manufactured using a negative electrode in which a negative electrode active material layer having the above specific ternary Si alloy together with a binder and a conductive auxiliary agent is applied on the negative electrode current collector, the negative electrode accompanies charging / discharging of the battery. The active material may expand and contract. Along with this, the volume of the negative electrode active material layer changes, and stress acts on the current collector that is in close contact with the negative electrode active material layer. At this time, if the current collector cannot follow the volume change of the negative electrode active material layer, the current collector is plastically deformed, and the current collector is wrinkled. When wrinkles occur in the current collector, the negative electrode active material layer is distorted, and the distance between the electrodes and the positive electrode becomes non-uniform, so that Li reactivity may be reduced or electrode concentration may occur. Furthermore, there is a possibility that the current collector is cracked or broken due to plastic deformation of the current collector, or that the negative electrode active material layer is directly broken. As a result, the discharge capacity of the battery is reduced.

The negative electrode of the present embodiment solves such a problem, and by using a negative electrode having an elastic elongation of 1.30% or more, the negative electrode active material layer due to expansion / contraction of the negative electrode active material due to charge / discharge is used. The current collector can elastically follow the volume change. Therefore, wrinkles that can be caused by stress acting on the current collector that is in close contact with the negative electrode active material layer can be suppressed, so that distortion of the negative electrode active material layer or breakage of the negative electrode active material layer or current collector can be prevented. Can be prevented. As a result, the distance between the electrodes and the positive electrode is kept uniform. Furthermore, side reactions are less likely to occur. Therefore, a high discharge capacity can be obtained. Furthermore, even if charging / discharging is repeated, plastic deformation of the current collector hardly occurs, so that cycle durability can be improved.

In addition, if the current collector has an elastic elongation of 1.30% or more, even if the elasticity of the negative electrode active material layer is lost due to expansion / contraction of the negative electrode active material due to charge / discharge, Since it adheres to the negative electrode active material layer and elastically deforms, a decrease in capacity and a decrease in cycle durability can be minimized.

The elastic elongation of the current collector used in the negative electrode of this embodiment is preferably 1.40% or more. If the elastic elongation of the current collector is 1.40% or more, it is easier to follow in view of the degree of volume change accompanying charging / discharging of the negative electrode active material used in the present embodiment. Therefore, the improvement rate of the discharge capacity maintenance rate is high, and the cycle characteristics can be further improved. Further, when the elastic elongation of the current collector is 1.50% or more, a higher effect can be obtained when the negative electrode active material of the present embodiment is used.

Since the larger the elastic elongation of the current collector is, the more the volume change of the negative electrode active material layer can be elastically followed, the upper limit value of the elastic elongation is not particularly limited.

The negative electrode active material used in the present embodiment has a large volume change due to charge / discharge compared with a carbon material such as graphite, but using the current collector as described above can suppress plastic deformation of the current collector. It is possible to suppress the distortion of the negative electrode active material layer and the decrease in the discharge capacity due to this. However, when pure Si is used as the negative electrode active material, the volume change associated with charge / discharge is even greater, so even using the current collector as described above, the volume change of the negative electrode active material layer cannot be sufficiently followed. It may be difficult to prevent a decrease in capacity. In the case of the active material of the ternary Si alloy used in the present embodiment, the elastic elongation of the current collector may be 1.30% or more, and a battery having excellent discharge capacity and cycle characteristics can be obtained (see FIG. 14). ).

In this specification, the elastic elongation (%) of the current collector is a value measured according to the tensile test method of JIS K 6251 (2010). The elastic elongation (%) of the current collector is a value measured at 25 ° C.

The current collector in the present embodiment preferably has a tensile strength of 150 N / mm ² or more. If the tensile strength is 150 N / mm ² or more, the effect of preventing breakage of the current collector is high.

In addition, in this specification, the value measured according to the tensile test method of JISK6251 (2010) shall be used for the tensile strength (N / mm < ² >) of a collector. The tensile strength (N / mm ² ) of the current collector is a value when measured at 25 ° C.

As long as the elastic collector has an elastic elongation of 1.30% or more, the material constituting the current collector is not particularly limited as described above, preferably copper, aluminum, nickel, iron, stainless steel. Metals such as titanium and cobalt, or alloys of these metals can be used.

Among the above metals, a metal foil using copper, nickel, stainless steel, or an alloy obtained by adding another metal to these metals has mechanical strength, adhesion to the active material layer, chemical stability, and battery reaction. It is preferable from the viewpoint of electrochemical stability at electric potential, conductivity, cost and the like. In particular, copper or a copper alloy is particularly preferable for the reason of the standard redox potential.

As the copper foil, a rolled copper foil (a copper foil obtained by a rolling method) or an electrolytic copper foil (a copper foil obtained by an electrolytic method) can be used. As for the copper alloy foil, either an electrolytic copper alloy foil or a rolled copper alloy foil can be used. In the negative electrode of this embodiment, it is preferable to use a rolled copper foil or a rolled copper alloy foil because of its high tensile strength and excellent flexibility.

As the copper alloy, an alloy obtained by adding an element such as Zr, Cr, Zn, or Sn to copper can be preferably used. Such an alloy has a higher elastic modulus than pure copper, and easily follows the volume change of the negative electrode active material layer, so that plastic deformation hardly occurs. For this reason, the current collector is unlikely to be wrinkled or broken. Further, an alloy obtained by adding an element such as Zr, Cr, Zn, or Sn to copper can improve heat resistance as compared with pure copper. In particular, if the alloy has a softening point higher than the heat treatment temperature (about 300 ° C.) when the slurry containing the negative electrode active material is applied to the current collector and dried in the negative electrode manufacturing process, the heat treatment It is preferable because elasticity can be maintained later. Among them, an alloy added with Cr, Zn, and Sn is preferable for the reason of maintaining elasticity after the heat treatment. These alloy elements may be used alone or in combination of two or more. The total content of these alloy elements is, for example, 0.01 to 0.9% by mass, preferably 0.03 to 0.9% by mass, and more preferably 0.3 to 0.9% by mass. % By mass. If the content of the alloy element is 0.03% by mass or more, it is suitable for the reason of maintaining elasticity after the heat treatment.

The method for obtaining a current collector having an elastic elongation of 1.30% or more is not particularly limited. When the current collector of the present embodiment is made of a metal foil, the mechanical characteristics can be changed by heating, cooling, pressure, and impurity element addition. In addition, you may use the commercially available metal foil which has said elongation.

The thickness of the current collector of the negative electrode is not particularly limited, but in the negative electrode of this embodiment, it is preferably 5 to 15 μm, and more preferably 5 to 10 μm. A thickness of the negative electrode current collector of 5 μm or more is preferable because sufficient mechanical strength can be obtained. In addition, if the thickness of the negative electrode current collector is 15 μm or less, it is preferable in terms of thinning the battery.

It should be noted that the current collector for the bipolar electrode may be the same as the current collector for the negative electrode. In particular, it is desirable to use one having resistance to the positive electrode potential and the negative electrode potential.

(Requirements common to positive and negative electrodes)
Hereinafter, the requirements common to the positive electrode and the negative electrode will be described.

The positive electrode active material layer 13 and the negative electrode active material layer 15 include a binder, a conductive additive, an electrolyte salt (lithium salt), an ion conductive polymer, and the like.

The binder used for the binder active material layer is not particularly limited, and examples thereof include the following materials. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile (PEN), polyacrylonitrile, polyimide, polyamide, polyamideimide, cellulose, carboxymethylcellulose (CMC), ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene / butadiene Rubber (SBR), isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and hydrogenated product thereof, styrene / isoprene / styrene block copolymer and Thermoplastic polymers such as hydrogenated products, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene hexafluoropropylene Copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene Fluororesin such as copolymer (ECTFE), polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluorine Rubber (VDF-HFP-TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-teto Fluoroethylene fluoro rubber (VDF-PFP-TFE fluoro rubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluoro rubber (VDF-PFMVE-TFE fluoro rubber), vinylidene fluoride-chlorotrifluoroethylene Vinylidene fluoride-based fluororubbers such as epoxy-based fluororubbers (VDF-CTFE-based fluororubbers), and epoxy resins. Among these, polyvinylidene fluoride, polyimide, styrene / butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, polyamide, and polyamideimide are more preferable. These suitable binders are excellent in heat resistance, have a very wide potential window, are stable at both the positive electrode potential and the negative electrode potential, and can be used for the active material layer. These binders may be used alone or in combination of two.

The amount of the binder contained in the active material layer is not particularly limited as long as it is an amount capable of binding the active material, but is preferably 0.5 to 15% by mass with respect to the active material layer. More preferably, it is 1 to 10% by mass.

Conductive auxiliary agent A conductive auxiliary agent means the additive mix | blended in order to improve the electroconductivity of a positive electrode active material layer or a negative electrode active material layer. Examples of the conductive assistant include carbon materials such as carbon black such as acetylene black, graphite, and vapor grown carbon fiber. When the active material layer contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

Moreover, the conductive binder having the functions of the conductive assistant and the binder may be used in place of the conductive assistant and the binder, or may be used in combination with one or both of the conductive assistant and the binder. . Commercially available TAB-2 (manufactured by Hosen Co., Ltd.) can be used as the conductive binder.

The content of the conductive additive mixed into the active material layer is in the range of 1% by mass or more, more preferably 3% by mass or more, and further preferably 5% by mass or more with respect to the total amount of the active material layer. In addition, the content of the conductive additive mixed in the active material layer is 15% by mass or less, more preferably 10% by mass or less, and further preferably 7% by mass or less with respect to the total amount of the active material layer. is there. By defining the compounding ratio (content) of the conductive auxiliary agent in the positive electrode active material layer within the above range, the electronic conductivity of the active material itself is low and the electrode resistance can be reduced by the amount of the conductive auxiliary agent. Is done. That is, it is possible to sufficiently ensure the electronic conductivity without hindering the electrode reaction, to suppress the decrease in the energy density due to the decrease in the electrode density, and to improve the energy density due to the increase in the electrode density. .

Electrolyte salt (lithium salt)
Examples of the electrolyte salt (lithium salt) include Li (C ₂ F ₅ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO _{3 and the} like.

Ion conductive polymer Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

The compounding ratio of the components contained in the negative electrode active material layer in the case of using the positive electrode active material layer and the alloy in the form of particles of (5) (ii) above is not particularly limited. The mixing ratio can be adjusted by appropriately referring to known knowledge about the non-aqueous solvent secondary battery.

The thickness of each active material layer (active material layer on one side of the current collector) is not particularly limited, and conventionally known knowledge about the battery can be appropriately referred to. As an example, the thickness of each active material layer is usually about 1 to 500 μm, preferably 2 to 100 μm, taking into consideration the intended use of the battery (emphasis on output, energy, etc.) and ion conductivity.

<Electrolyte layer>
A liquid electrolyte or a polymer electrolyte can be used as the electrolyte constituting the electrolyte layer 17.

The liquid electrolyte has a form in which a lithium salt (electrolyte salt) is dissolved in an organic solvent. Examples of the organic solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), Examples include carbonates such as methylpropyl carbonate (MPC).

As the lithium _{_{_{_{salt, Li (CF 3 SO 2)}}}} 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiAsF 6, LiTaF 6, LiClO 4, LiCF 3 SO 3 , etc. A compound that can be added to the active material layer of the electrode can be employed.

On the other hand, polymer electrolytes are classified into gel electrolytes containing an electrolytic solution and intrinsic polymer electrolytes not containing an electrolytic solution.

The gel electrolyte has a configuration in which the above liquid electrolyte (electrolytic solution) is injected into a matrix polymer made of an ion conductive polymer. The use of a gel polymer electrolyte as the electrolyte is superior in that the fluidity of the electrolyte is lost and it is easy to block ion conduction between the layers.

Examples of the ion conductive polymer used as the matrix polymer include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. In such polyalkylene oxide polymers, electrolyte salts such as lithium salts can be well dissolved.

The ratio of the liquid electrolyte (electrolytic solution) in the gel electrolyte is not particularly limited, but is preferably about several mass% to 98 mass% from the viewpoint of ionic conductivity. In the present embodiment, the gel electrolyte having a large amount of electrolytic solution having a ratio of the electrolytic solution of 70% by mass or more is particularly effective.

When the electrolyte layer is composed of a liquid electrolyte, a gel electrolyte, or an intrinsic polymer electrolyte, a separator may be used for the electrolyte layer. Specific examples of the separator (including non-woven fabric) include a microporous film made of polyolefin such as polyethylene and polypropylene, a porous flat plate, and a non-woven fabric.

The intrinsic polymer electrolyte has a structure in which a supporting salt (lithium salt) is dissolved in the above matrix polymer, and does not contain an organic solvent that is a plasticizer. Therefore, when the electrolyte layer is composed of an intrinsic polymer electrolyte, there is no fear of liquid leakage from the battery, and the reliability of the battery can be improved.

The matrix polymer of the gel electrolyte or the intrinsic polymer electrolyte can express excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte using an appropriate polymerization initiator. A polymerization treatment may be performed.

<Current collector plate and lead>
A current collecting plate may be used for the purpose of taking out the current outside the battery. The current collector plate is electrically connected to the current collector and the lead, and is taken out of the laminate sheet that is a battery exterior material.

The material constituting the current collector plate is not particularly limited, and a known highly conductive material conventionally used as a current collector plate for a lithium ion secondary battery can be used. As a constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable, and aluminum is more preferable from the viewpoint of light weight, corrosion resistance, and high conductivity. Copper or the like is preferable. Note that the same material may be used for the positive electrode current collector plate and the negative electrode current collector plate, or different materials may be used.

∙ Use positive terminal lead and negative terminal lead as required. As the material of the positive terminal lead and the negative terminal lead, a terminal lead used in a known lithium ion secondary battery can be used. It should be noted that the part taken out from the battery outer packaging material 29 has a heat insulating property so as not to affect the product (for example, automobile parts, particularly electronic devices) by contacting with peripheral devices or wiring and causing leakage. It is preferable to coat with a heat shrinkable tube or the like.

<Battery exterior material>
As the battery exterior material 29, a known metal can case can be used, and a bag-like case using a laminate film containing aluminum that can cover the power generation element can be used. For example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used as the laminate film, but the laminate film is not limited thereto. A laminate film is desirable from the viewpoint that it is excellent in high output and cooling performance, and can be suitably used for a battery for large equipment for EV and HEV.

In addition, said lithium ion secondary battery can be manufactured with a conventionally well-known manufacturing method.

<Appearance structure of lithium ion secondary battery>
FIG. 2 is a perspective view showing the appearance of a stacked flat lithium ion secondary battery.

As shown in FIG. 2, the stacked flat lithium ion secondary battery 50 has a rectangular flat shape, and a positive current collector 58 for taking out power from both sides thereof, a negative current collector, and the like. The electric plate 59 is pulled out. The power generation element 57 is wrapped by the battery outer packaging material 52 of the lithium ion secondary battery 50, and the periphery thereof is heat-sealed. The power generation element 57 pulls out the positive electrode current collector plate 58 and the negative electrode current collector plate 59 to the outside. Sealed. Here, the power generation element 57 corresponds to the power generation element 21 of the lithium ion secondary battery (stacked battery) 10 shown in FIG. The power generation element 57 is formed by laminating a plurality of single battery layers (single cells) 19 including a positive electrode (positive electrode active material layer) 13, an electrolyte layer 17, and a negative electrode (negative electrode active material layer) 15.

The lithium ion secondary battery is not limited to a laminated flat shape (laminate cell). In a wound type lithium ion battery, a cylindrical shape (coin cell), a prismatic shape (square cell), or such a cylindrical shape deformed into a rectangular flat shape Further, it may be a cylindrical cell, and is not particularly limited. The cylindrical or prismatic shape is not particularly limited, for example, a laminate film or a conventional cylindrical can (metal can) may be used as the exterior material. Preferably, the power generation element is covered with an aluminum laminate film. With this configuration, weight reduction can be achieved.

Further, the removal of the positive electrode current collector plate 58 and the negative electrode current collector plate 59 shown in FIG. 2 is not particularly limited. The positive electrode current collector plate 58 and the negative electrode current collector plate 59 may be drawn out from the same side, or the positive electrode current collector plate 58 and the negative electrode current collector plate 59 may be divided into a plurality of parts and taken out from each side. It is not limited to the one shown in FIG. Further, in a wound type lithium ion battery, instead of the current collector plate, for example, a terminal may be formed using a cylindrical can (metal can).

As described above, the negative electrode and the lithium ion secondary battery using the negative electrode active material for the lithium ion secondary battery of the present embodiment are large vehicles such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles. It can be suitably used as a capacity power source. That is, it can be suitably used for a vehicle driving power source and an auxiliary power source that require high volume energy density and high volume output density.

In the above embodiment, the lithium ion battery is exemplified as the electric device. However, the present invention is not limited to this, and can be applied to other types of secondary batteries and further to primary batteries. It can also be applied to capacitors as well as batteries.

The present invention will be described in further detail using the following examples. However, the technical scope of the present invention is not limited only to the following examples.

First, as a reference example, performance evaluation was performed on the Si alloy represented by the chemical formula (1) constituting the negative electrode for an electric device according to the present invention.

(Reference Example _{_{_{A): Si x Al y C}}} z A as the performance evaluation [1] Preparation sputtering apparatus of a negative electrode for _a, 3-way DC magnetron sputtering device independent control system (Yamato Equipment Industries Co., combinatorial sputter coating apparatus A thin film of negative electrode active material alloy having each composition under the following conditions on a substrate (current collector) made of nickel foil having a thickness of 20 μm using a gun-sample distance of about 100 mm): By forming each film, 23 types of negative electrode samples were obtained (Samples 1 to 33 of Reference Example A).

(1) Target (manufactured by Kojundo Chemical Laboratory Co., Ltd.)
Si (4N): 2 inches in diameter and 3 mm in thickness (with an oxygen-free copper backing plate having a thickness of 2 mm)
Al (4N): diameter 2 inches, thickness 5mm
C (5N): 2 inches in diameter and 5 mm in thickness.

(2) Film formation conditions Base pressure: up to 7 × 10 ⁻⁶ Pa
Sputtering gas type: Ar (99.9999% or more)
Sputtering gas introduction amount: 10 sccm
Sputtering pressure: 30 mTorr
DC power supply: Si (185 W), C (50 to 200 W), Al (30 to 90 W)
Pre-sputtering time: 1 min.
Sputtering time: 10 min.
Substrate temperature: room temperature (25 ° C.).

That is, using the Si target, the Al target, and the C target as described above, fixing the sputtering time to 10 minutes, and changing the power of the DC power source within the above ranges, respectively, the amorphous alloy on the Ni substrate A thin film was formed, and negative electrode samples provided with alloy thin films having various compositions were obtained. In samples 19 to 33, an alloy thin film was formed so that sample 19 was a Si metal, samples 20 to 27 were Si—C binary alloys, and samples 28 to 33 were Si—Al binary alloys. Specifically, only the necessary target among Si, Al, and C targets is used, the sputtering time is fixed, and the power of the DC power source of the target to be used is changed within the above range, so that it can be formed on the Ni substrate. An amorphous Si thin film or a binary alloy thin film was formed.

Here, if an example of sample preparation is shown, in sample 8, DC power source 2 (Si target): 185 W, DC power source 1 (C target): 100 W, DC power source 3 (Al target): 120 W.

The component compositions of these alloy thin films are shown in Table 1 and FIGS. The obtained alloy thin film was analyzed by the following analysis method and analyzer.

(3) Analysis method Composition analysis: SEM / EDX analysis (JEOL), EPMA analysis (JEOL)
Film thickness measurement (for sputter rate calculation): Film thickness meter (Tokyo Instruments)
Film state analysis: Raman spectroscopy (Bruker).

[2] Production of Battery Each negative electrode sample obtained above and a counter electrode made of lithium foil (Honjo Metal Co., Ltd., diameter: 15 mm, thickness: 200 μm) are opposed to each other through a separator (Celgard Cellguard 2400). Then, CR2032-type coin cells were produced by injecting an electrolyte solution.

As the above electrolyte solution, ethylene carbonate (EC) and diethyl carbonate (DEC) 1: in a mixed nonaqueous solvent were mixed at a volume ratio, the concentration of LiPF ₆ a (lithium hexafluorophosphate) 1M What was dissolved so that it might become was used.

[3] Battery Charging / Discharging Test The following charging / discharging test was performed on each battery obtained as described above.

That is, using a charge / discharge tester (HJ0501SM8A manufactured by Hokuto Denko Co., Ltd.), in a thermostatic chamber (PFU-3K manufactured by Espec Co., Ltd.) set at a temperature of 300K (27 ° C.) In a process of inserting Li into a certain negative electrode), the battery was charged from 2 V to 10 mV at 0.1 mA as a constant current / constant voltage mode. Thereafter, in the discharge process (Li desorption process from the negative electrode), the constant current mode was set, and discharge was performed from 0.1 mA, 10 mV to 2 V. The above charging / discharging cycle was made into 1 cycle, and this was repeated 50 times.

Then, the discharge capacity at the 50th cycle was obtained, and the maintenance ratio relative to the discharge capacity at the first cycle was calculated. In the case of a long-term cycle, the degradation mode of the electrolyte is also included in the cycle characteristics (conversely, the use of a high-performance electrolyte improves the cycle characteristics). It was. The results are also shown in Table 1. At this time, the discharge capacity indicates a value calculated per alloy weight. "Discharge capacity (mAh / g)" is per pure Si or alloy weight, and when Li reacts with Si-Al-M alloy (Si-M alloy, pure Si or Si-Al alloy). Indicates capacity. In addition, what is described as “initial capacity” in this specification corresponds to “discharge capacity (mAh / g)” of the initial cycle (first cycle).

In addition, the “discharge capacity maintenance rate (%)” at the 50th cycle represents an index of “how much capacity is maintained from the initial capacity”. The calculation formula of the discharge capacity retention rate (%) is as follows.

The discharge capacity maintenance rate at the 50th cycle was calculated by the following formula. The results are also shown in Table 1.

“Charge / discharge efficiency (%)” in the table represents an index of “how much Li moves in the charge / discharge process” in the first cycle. The calculation formula of charge / discharge efficiency (%) is as follows.

Charge / discharge efficiency (%) = discharge capacity (when Li is desorbed) / charge capacity (when Li reaction = when Li is inserted) x 100

From the results shown in Table 1, the batteries of Samples 1 to 18, particularly the samples in the composition range surrounded by the thick solid line in FIGS. 7 to 9, have a discharge capacity at the first cycle of the existing carbon-based negative electrode active material (carbon / graphite). It has been found that an extremely high capacity that cannot be realized with a negative electrode material) can be realized. Similarly, it was confirmed that a higher capacity (initial capacity of 1113 mAh / g or more) can be realized as compared with the existing high capacity Sn-based alloy negative electrode active material. In addition, in the batteries of samples 1 to 18, the charge / discharge efficiency in the first cycle is as high as 94% or more, preferably 97% or more, as compared with the batteries of samples 19 to 33. It was. It was found that many of the batteries of Samples 19 to 33 have a reduced effective capacity as a battery due to low initial charge / discharge efficiency. Furthermore, the cycle durability, which is in a trade-off relationship with the increase in capacity, is also compared with the existing Sn-based negative electrode active material having a high capacity but inferior in cycle durability and the multi-component alloy negative electrode active material described in Patent Document 1. However, it has been confirmed that the cycle durability can be remarkably improved. Specifically, it was confirmed that a remarkably excellent cycle durability with a high discharge capacity maintenance rate at the 50th cycle of 64% or more, preferably 74% or more, particularly preferably 81% or more can be realized. Therefore, the batteries of Samples 1 to 18, especially the samples in the composition range surrounded by the thick solid line in FIGS. 7 to 9 have a large discharge capacity maintenance rate compared to the other samples of batteries. It was found that high capacity can be maintained more efficiently by suppressing the decrease in capacity and effective capacity.

From the result of Reference Example A, when Li alloying, the second additive element C that suppresses the amorphous-crystal phase transition and improves the cycle life, and the capacity as an electrode increases even when the concentration of the second additive element increases. It has been found that the selection of the first additive element species Al that does not decrease is extremely useful and effective. By selecting the first and second additive elements, it is possible to provide a Si alloy-based negative electrode active material having high capacity, high cycle durability, and high initial charge / discharge efficiency. As a result, it was found that a lithium ion secondary battery with high capacity, good initial charge / discharge efficiency and good cycle durability can be provided. Further, with the Si metals or binary alloys of Samples 19 to 33, a battery having a high capacity, high initial charge / discharge efficiency and high cycle durability in a well-balanced manner could not be obtained.

FIG. 10 shows all charge / discharge curves from 1 to 50 cycles in the charge / discharge test using the battery of sample 7.

From FIG. 10, in the battery of sample 7, a charge / discharge curve having a stable flat voltage is obtained from the 1st to the 50th cycle, a high capacity is maintained until the 50th cycle, and rapid cycle characteristics and capacity characteristics are maintained. It was confirmed that there was no deterioration (abrupt charge / discharge curve = capacity drop, etc.).

From the above experimental results, the ternary alloy of the present embodiment maintains a high cycle characteristic (particularly, a high discharge capacity maintenance rate at the 50th cycle) and has a high balance between the initial capacity and the initial charge / discharge efficiency. The mechanism shown can be inferred as follows.

1. In the battery of Samples 1 to 18 using the ternary alloy having the composition formula Si _x Al _y C _z of the present embodiment, in particular, the sample in the composition range surrounded by the thick solid line in FIGS. -Suppresses the decomposition of the electrolyte solution compared to Si, ternary and quaternary alloys of Patent Document 1, and binary alloys of Samples 20 to 33, and further phase transition of Li-Si alloy to the crystalline phase Can be suppressed.

2. Regarding the decomposition of the electrolytic solution, the apparent charge / discharge capacity decreases and the charge / discharge efficiency deteriorates due to this decomposition. As a result, the charge-discharge efficiency of the pure-Si sample 19, the ternary and quaternary alloys of Patent Document 1, and the binary alloys of samples 20 to 33 are lowered due to the deterioration of the charge / discharge efficiency. . In contrast, in the batteries of samples 1 to 18 using the ternary alloy having the composition formula Si _x Al _y C _z of the present embodiment, in particular, the samples in the composition range surrounded by the thick solid lines in FIGS. It can be seen that the reduction in the discharge capacity retention rate and the deterioration in the charge / discharge efficiency are suppressed at a high capacity (see Table 1).

3. Regarding the phase transition of the Li—Si alloy to the crystal phase, when this phase transition occurs, the volume change of the active material increases. As a result, the destruction of the active material itself, the destruction of the electrode and the chain start. In the batteries of Samples 1 to 18 using the ternary alloy having the composition formula Si _x Al _y C _z of the present embodiment, in particular, the samples in the composition range surrounded by the thick solid lines in FIGS. It is possible to suppress the reduction of charge / discharge capacity and the deterioration of charge / discharge efficiency due to the destruction of the active material itself and the electrode. Therefore, stable performance can be achieved, such as a high discharge capacity maintenance rate and a small capacity reduction rate even at the 50th cycle. From this, it can be determined that the phase transition can be suppressed.

(Reference Example _{_{_{B): Si x Al y Nb}}} z A performance evaluation of _a [1] Production of Negative Electrode Reference Example A (1) in the target "C (5N): diameter of 2 inches, thickness 5mm" and " Nb (3N): 2 inches in diameter, 5 mm in thickness ”, except that“ C (50-200 W) ”of DC power source in (2) was changed to“ Nb (60-120 W) ” For convenience, 21 types of negative electrode samples were prepared in the same manner as in Reference Example A (Reference Examples B1 to B11 and Comparative Reference Examples B1 to B10).

Regarding (2), if several examples of sample preparation are shown, in Reference Example B5, DC power source 1 (Si target): 185 W, DC power source 2 (Al target): 60 W, DC power source 3 (Nb target): 90W. In Comparative Reference Example B3, the DC power source 1 (Si target): 185 W, the DC power source 2 (Al target): 72 W, and the DC power source 3 (Nb target): 0 W. Furthermore, in Comparative Reference Example B9, the DC power source 1 (Si target): 185 W, the DC power source 2 (Al target): 0 W, and the DC power source 3 (Nb target): 55 W.

The component compositions of these alloy thin films are shown in Table 2 and FIG.

[2] Production of Battery A CR2032-type coin cell was produced in the same manner as in Reference Example A.

[3] Battery charge / discharge test 100 cycles of charge / discharge cycles were performed, the discharge capacities of the 50th cycle and the 100th cycle were obtained, and the maintenance ratio relative to the discharge capacity of the first cycle was calculated. A battery charge / discharge test was conducted in the same manner. The results are shown in Table 2.

Also, the “discharge capacity maintenance rate (%)” at the 50th cycle or the 100th cycle represents an index of “how much capacity is maintained from the initial capacity”. The calculation formula of the discharge capacity retention rate (%) is as follows.

From Table 2, an alloy containing more than 27 mass% and less than 100 mass% Si, more than 0 mass% and less than 73 mass% Al, and more than 0 mass% and less than 58 mass% Nb, with the balance being inevitable impurities. It can be seen that the battery of Reference Example B including the negative electrode active material has excellent cycle characteristics while maintaining a high discharge capacity as compared with the carbon-based negative electrode active material having a charge / discharge capacity of about 300 mAh / g. The range of A in FIG. 11 represents such an alloy.

And the range of the code | symbol B of FIG. 12 is Si content is more than 47 mass% and less than 95 mass%, Al content is more than 2 mass% and less than 48 mass%, and Nb content is 1 mass. An alloy whose content is more than 23% and less than 23% by mass, with the balance being inevitable impurities. The range of the symbol B corresponds to the range of the reference examples B1 to B11. From Table 2, it can be seen that a lithium ion secondary battery using this alloy is particularly excellent in discharge capacity retention after 50 cycles.

Further, the range of C in FIG. 13 is that the Si content is more than 61 mass% and less than 84 mass%, the Al content is more than 2 mass% and less than 25 mass%, and the Nb content is 2 mass. An alloy whose content is more than 23% and less than 23% by mass, with the balance being inevitable impurities. The range of C in FIG. 13 corresponds to Reference Examples B2 to B6.

Further, the range of the symbol D in FIG. 13 is that the Si content is more than 47 mass% and less than 56 mass%, the Al content is more than 33 mass% and less than 48 mass%, and the Nb content is 1 mass. An alloy whose content is more than% and less than 16% by mass and the balance is an inevitable impurity. The range of the symbol D in FIG. 13 corresponds to Reference Examples B8 to B11.

From Table 2, it can be seen that lithium ion secondary batteries using alloys in the ranges of C and D are particularly excellent in discharge capacity retention after 100 cycles.

Next, as an example, performance evaluation was performed on a negative electrode for an electric device having a negative electrode active material layer containing a conductive additive and a binder using Si ₅₀ Al ₄₇ C ₃ among the Si alloys.

Incidentally, the _Si 50 _Al 47 _{C 3} other than the other alloys used in the present invention _{_{_{_{(Si x Al y C z A}}}} a, and among the _{_{_{_{Si x Al y Nb z A a}}}} , other than Si _{50 Al} 47 _{C 3} ), The same or similar results as in the following examples using Si ₅₀ Al ₄₇ C ₃ are obtained. This is because, as shown in the reference example, the other alloys used in the present invention have the same characteristics as Si ₅₀ Al ₄₇ C ₃ . That is, when an alloy having the same characteristics is used, the same result can be obtained even if the type of the alloy is changed.

Next, in the following examples and comparative examples, performance evaluation of negative electrodes for electric devices using Si ₅₀ Al ₄₇ C ₃ as the negative electrode active material among the above-mentioned Si alloys and changing the type (elastic elongation) of the current collector Went.

[Manufacture of Si alloy]
The Si alloy was manufactured by a mechanical alloy method (or an arc plasma melting method). Specifically, using a planetary ball mill device P-6 manufactured by Fricht, Germany, zirconia pulverized balls and raw material powders of each alloy were charged into a zirconia pulverized pot and alloyed at 600 rpm for 48 hours.

[Production of negative electrode]
(Example 1)
A negative electrode active material slurry was prepared by mixing 80 parts by mass of a negative electrode active material, 5 parts by mass of a conductive additive, and 15 parts by mass of a binder in N-methyl-2-pyrrolidone (NMP) as a solvent. Here, the Si alloy powder produced above (Si ₅₀ Al ₄₇ C ₃ , average particle diameter of primary particles 0.3 μm) was used as the negative electrode active material. Moreover, the short-chain acetylene black was used as the short-chain carbon black for the conductive assistant, and the polyimide was used for the binder.

A copper alloy foil (copper alloy 1: Cu added with about 0.3% by mass of Cr, Sn, and Zn, respectively) having an elastic elongation of 1.43% and a tensile strength of 580 N / mm ² and a thickness of 10 μm was prepared.

In this example, the elastic elongation (%) and tensile strength (N / mm ² ) of the current collector were measured using a digital material tester 5565 type manufactured by INSTRON at a test speed of 10 mm / min and between chucks of 50 mm. did. The sample used was a current collector foil formed into a wedge shape having a total length of 70 mm and a parallel part width of 5 mm.

The obtained negative electrode active material slurry was uniformly applied on both sides of the copper alloy foil (copper alloy 1) so that the thickness after drying was 50 μm, respectively, and dried in vacuum for 24 hours. Got.

(Example 2)
Other than using a copper alloy foil (copper alloy 2: Cu added with about 0.3% by mass of Zr) having a thickness of 10 μm and an elastic elongation of 1.53% and a tensile strength of 450 N / mm ² as the negative electrode current collector Produced a negative electrode in the same manner as in Example 1.

(Example 3)
Other than using a copper alloy foil (copper alloy 3: Cu added with about 0.1% by mass of Zr) having a thickness of 10 μm and an elastic elongation of 1.39% and a tensile strength of 420 N / mm ² as the negative electrode current collector Produced a negative electrode in the same manner as in Example 1.

(Comparative Example 1)
Example except that a 10 μm thick copper foil (tough pitch copper: Cu purity of 99.9% by mass or more) having an elastic elongation of 1.28% and a tensile strength of 139 N / mm ² was used as the negative electrode current collector A negative electrode was produced in the same manner as in Example 1.

(Comparative Example 2)
A negative electrode was produced in the same manner as in Comparative Example 1 except that 80 parts by mass of silicon (pure Si) powder (purity: 99.999 mass%, average particle diameter of primary particles: 45 μm) was used as the negative electrode active material.

(Comparative Example 3)
A negative electrode was produced in the same manner as in Comparative Example 2 except that polyvinylidene fluoride (PVdF) was used as the binder material.

[Production of positive electrode]
Li _1.85 Ni _0.18 Co _0.10 Mn _0.87 O ₃ which is a positive electrode active material was produced by the method described in Example 1 (paragraph 0046) of JP2012-185913. Then, 90 parts by mass of this positive electrode active material, 5 parts by mass of acetylene black as a conductive auxiliary agent, and 5 parts by mass of polyvinylidene fluoride as a binder are mixed and dispersed in N-methylpyrrolidone to obtain a positive electrode slurry. It was. Next, the obtained positive electrode slurry was uniformly applied to both surfaces of a positive electrode current collector made of aluminum foil so that the thickness of the positive electrode active material layer was 30 μm, and dried to obtain a positive electrode.

[Production of battery]
The positive electrode produced above and the negative electrode were made to face each other, and a separator (polyolefin, film thickness: 20 μm) was disposed therebetween. Next, the laminate of the negative electrode, the separator, and the positive electrode was disposed on the bottom side of a coin cell (CR2032, material: stainless steel (SUS316)). Furthermore, in order to maintain insulation between the positive electrode and the negative electrode, a gasket is attached, the following electrolyte is injected with a syringe, a spring and a spacer are stacked, the upper side of the coin cell is overlapped, and sealed by caulking. Thus, a lithium ion secondary battery was obtained.

In addition, as said electrolyte solution, hexafluorophosphoric acid which is a supporting salt in the organic solvent which mixed ethylene carbonate (EC) and diethyl carbonate (DEC) in the ratio of EC: DC = 1: 2 (volume ratio). lithium (LiPF _6), was used as the concentration was such that 1 mol / L.

[Battery charge / discharge test]
A charge / discharge test of the battery was performed in the same manner as in Reference Example A.

Then, the discharge capacity at the 50th cycle was obtained, and the discharge capacity retention rate (%) relative to the discharge capacity at the first cycle was calculated. The “discharge capacity maintenance ratio (%)” at the 50th cycle represents an index of “how much capacity is maintained from the initial capacity”. The calculation formula of the discharge capacity retention rate (%) is as follows.

Further, the results of the obtained discharge capacity retention ratio (%) are shown as the ratio (improvement ratio (%) of discharge capacity retention ratio) when the discharge capacity retention ratio of Comparative Example 1 is 100 as shown in Table 3 As shown in FIG.

From the results shown in Table 3 and FIG. 14, the batteries of Examples 1 to 3 using the current collector having an elastic elongation of 1.30% or more showed a higher discharge capacity maintenance rate than the batteries of Comparative Examples 1 to 3. It was confirmed that it could be realized. This is because the current collector used in Examples 1 to 3 elastically followed the volume change of the negative electrode active material layer containing the Si alloy accompanying charging / discharging of the battery, thereby suppressing the deformation of the electrode layer. It is thought that. In particular, in Examples 1 and 2 in which the elastic elongation of the current collector was 1.40% or more, or 1.50% or more, a higher discharge capacity retention rate was obtained.

On the other hand, in the battery of Comparative Example 1 using a current collector having an elastic elongation of a predetermined value or less, the current collector is likely to be plastically deformed along with the volume change of the negative electrode active material layer accompanying charge / discharge of the battery, As a result, the negative electrode active material layer is distorted, and it becomes difficult to maintain a uniform interelectrode distance from the positive electrode in the planar direction of the negative electrode, and it is considered that a high discharge capacity retention rate was not obtained.

Further, in the battery of Comparative Example 2 using pure Si as the negative electrode active material, the volume change due to the expansion / contraction of the negative electrode active material accompanying charging / discharging of the battery is larger than that in the case of the Si alloy. Therefore, since the volume change of the negative electrode active material layer is larger, it is considered that the decrease in capacity due to the fact that the current collector cannot follow the volume change of the negative electrode active material layer is larger.

Furthermore, in the battery of Comparative Example 3 using PVdF as the binder for the negative electrode active material layer, the discharge capacity retention rate is lower. This is because the elastic modulus (1.0 GPa) of PVdF which is the binder used in Comparative Example 3 is smaller than the elastic modulus (3.73 GPa) of the polyimide used in Examples 1 to 3 and Comparative Examples 1 and 2. This is because the binder cannot follow the expansion / contraction of the active material due to charge / discharge, and the volume change of the negative electrode active material layer is increased. As a result, it is considered that the capacity decrease due to the current collector being unable to follow the volume change of the negative electrode active material layer is further increased.

This application is based on Japanese Patent Application No. 2012-256940 filed on November 22, 2012, the disclosure of which is incorporated by reference in its entirety.

10, 50 Lithium ion secondary battery (stacked battery),
11 positive electrode current collector,
12 negative electrode current collector,
13 positive electrode active material layer,
15 negative electrode active material layer,
17 electrolyte layer,
19 cell layer,
21, 57 power generation element,
25, 58 positive current collector,
27, 59 negative electrode current collector plate,
29, 52 Battery exterior material (laminate film).

Claims

A negative electrode for an electrical device comprising: a current collector; and a negative electrode active material disposed on a surface of the current collector, a conductive auxiliary agent, and an electrode layer comprising a binder,
The negative electrode active material has the following formula (1):

(In the above formula (1),
M is at least one metal selected from the group consisting of C, Nb and combinations thereof;
A is an unavoidable impurity;
x, y, z, and a represent mass% values, where 0 <x <100, 0 <y <100, 0 <z <100, and 0 ≦ a <0.5, and x + y + z + a = 100. And an alloy represented by
The negative electrode for an electrical device, wherein the current collector has an elastic elongation of 1.30% or more.
The negative electrode for an electrical device according to claim 1, wherein the current collector has an elastic elongation of 1.40% or more.
The negative electrode for an electric device according to claim 2, wherein the elastic elongation of the current collector is 1.50% or more.
Said M is C;
The negative electrode for an electric device according to any one of claims 1 to 3, wherein x, y, and z satisfy 36≤x <100, 0 <y <64, and 0 <z <64. .
The negative electrode for an electric device according to claim 4, wherein the x, y, and z are 36 ≦ x ≦ 80, 10 ≦ y ≦ 56, and 3 ≦ z ≦ 37.
6. The negative electrode for an electric device according to claim 4, wherein x, y, and z are 41 ≦ x ≦ 71, 10 ≦ y ≦ 56, and 3 ≦ z ≦ 29.
The negative electrode for an electric device according to claim 6, wherein the y is 15 or more.
The negative electrode for an electric device according to claim 6, wherein x is 43 to 61, and y is 20 to 54.
Said M is Nb;
The negative electrode for an electrical device according to any one of claims 1 to 3, wherein x, y, and z are 27 <x <100, 0 <y <73, and 0 <z <58.
The negative electrode for an electric device according to claim 9, wherein the x, y, and z are 47 <x <95, 2 <y <48, and 1 <z <23.
11. The negative electrode for an electrical device according to claim 9, wherein x, y, and z are 61 <x <84, 2 <y <25, and 2 <z <23.
The negative electrode for an electrical device according to claim 9 or 10, wherein x, y, and z are 47 <x <56, 33 <y <48, and 1 <z <16.
An electric device comprising the negative electrode for an electric device according to any one of claims 1 to 12.