JP6736999B2 - Negative electrode active material for electric device and electric device using the same - Google Patents

Description

The present invention relates to a negative electrode active material for electric devices and an electric device using the same. The negative electrode active material for an electric device of the present invention and the electric device using the same are, for example, a driving power source and 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. Used for.

In recent years, in order to cope with air pollution and global warming, reduction of carbon dioxide has been eagerly desired. In the automobile industry, expectations are growing for the reduction of carbon dioxide emissions by the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and electric devices such as secondary batteries for driving motors 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 consumer-use lithium-ion secondary batteries used in mobile phones, notebook computers and the like. Therefore, a lithium ion secondary battery, which has the highest theoretical energy among all batteries, has been attracting attention and is currently under rapid development.

Lithium ion secondary batteries are generally composed of a positive electrode in which a positive electrode active material or the like is applied to both sides 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 sides of a negative electrode current collector using a binder. However, it is connected via the electrolyte layer and housed in the battery case.

Conventionally, carbon/graphite-based materials, which are advantageous in terms of charge/discharge cycle life and cost, have been used for the negative electrode of lithium-ion secondary batteries. However, in a carbon/graphite-based negative electrode material, charge/discharge is performed by occluding/releasing lithium ions in the graphite crystal. Therefore, a theoretical capacity of 372 mAh/g or more obtained from LiC ₆ which is the maximum lithium-introducing compound is used. There is a drawback in that For this reason, it is difficult to obtain a capacity and energy density that satisfy the practical application level for vehicle applications with the carbon/graphite negative electrode material.

On the other hand, a battery using a material that forms an alloy with Li for the negative electrode is expected to be used as a negative electrode material for vehicle applications because it has an improved energy density as compared with conventional carbon/graphite based negative electrode materials. For example, the Si material absorbs and releases _3.75 mol of lithium ions per mol as shown in the following reaction formula (A) during charge and discharge, and theoretical capacity of 3600 mAh/in Li ₁₅ Si ₄ (=Li _3.75 Si). It is g.

However, a lithium-ion secondary battery using a material that forms an alloy with Li in the negative electrode has a large expansion and contraction in the negative electrode during charging and discharging. For example, the volume expansion in the case of occluding Li ions is about 1.2 times in the graphite material, whereas in the Si material, when Si and Li are alloyed, a transition from an amorphous state to a crystalline state occurs and a large volume change occurs. Therefore, there is a problem that the cycle life of the electrode is shortened. Further, in the case of the Si-based negative electrode active material, there is a trade-off between capacity and cycle durability, and there is a problem that it is difficult to improve cycle durability while exhibiting high capacity.

Here, Patent Document 1 discloses an invention whose object is to provide a non-aqueous electrolyte secondary battery having a negative electrode pellet having a high capacity and an excellent cycle life. Specifically, it is a silicon-containing alloy obtained by mixing silicon powder and titanium powder by a mechanical alloying method and wet pulverizing the mixture, and the first phase mainly composed of silicon and a silicide of titanium (such as TiSi ₂ ). Is used as a negative electrode active material. At this time, it is also disclosed that at least one of these two phases is amorphous or low crystalline.

International Publication 2006/129415 Pamphlet

According to the study by the present inventors, it is said that an electric device such as a lithium ion secondary battery using the negative electrode pellet described in Patent Document 1 can exhibit good cycle durability. Therefore, it was found that the cycle durability may not be sufficient.

Therefore, an object of the present invention is to provide a means capable of improving the cycle durability of an electric device such as a lithium ion secondary battery.

The present inventors have conducted earnest research to solve the above problems. As a result, a silicon-containing alloy having a ternary alloy composition of Si—Sn—Ti and having three predetermined diffraction peak intensities observed by X-ray diffraction measurement has a predetermined relationship. It has been found that the above problems can be solved by using it as a negative electrode active material, and the present invention has been completed.

That is, the present invention relates to a negative electrode active material for electric devices, which is made of a silicon-containing alloy. The silicon-containing alloy has the following chemical formula (I):

(In the above chemical formula (I),
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. )
It has a composition represented by. Then, in the X-ray diffraction (XRD) measurement using CuKα1 ray of the silicon-containing alloy, 2θ=40 with respect to the diffraction peak intensity X of the (311) plane of TiSi ₂ having the C54 structure in the range of 2θ=38 to 40°. It is characterized in that the ratio value (Y/X) of the diffraction peak intensities Y of the (131) plane of TiSi ₂ having a C49 structure in the range of up to 41° is 0.5 or more. Further, the characteristic (Y/Z) of the ratio of the diffraction peak intensity Y to the diffraction peak intensity Z of the (111) plane of Si in the range of 2θ=28 to 30° is 0.6 or more. Have.

According to the negative electrode active material for an electric device of the present invention, the cycle durability of an electric device such as a lithium ion secondary battery can be improved.

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. FIG. 2 is a perspective view schematically showing the appearance of a laminated flat lithium-ion secondary battery that is a typical embodiment of the electric device according to the present invention. FIG. 3 is a diagram for explaining how to obtain the diffraction peak intensity in the X-ray diffraction spectrum. FIG. 4 is an X-ray diffraction spectrum of the silicon-containing alloy (negative electrode active material) obtained in Example 1. FIG. 5 is an X-ray diffraction spectrum of the silicon-containing alloy (negative electrode active material) obtained in Example 2. FIG. 6 is an X-ray diffraction spectrum of the silicon-containing alloy (negative electrode active material) obtained in Example 3. FIG. 7 is an X-ray diffraction spectrum of the silicon-containing alloy (negative electrode active material) obtained in Example 4. FIG. 8 is an X-ray diffraction spectrum of the silicon-containing alloy (negative electrode active material) obtained in Example 5. FIG. 9 is an X-ray diffraction spectrum of the silicon-containing alloy (negative electrode active material) obtained in Comparative Example 1. FIG. 10 is an X-ray diffraction spectrum of the silicon-containing alloy (negative electrode active material) obtained in Comparative Example 2.

Hereinafter, embodiments of the negative electrode active material for an electric device and the electric device using the same according to the present invention 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 claims, and is not limited to the following modes. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Further, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from the actual ratios.

Hereinafter, a basic configuration of an electric device to which the negative electrode active material 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 the electric device.

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

That is, the lithium-ion secondary battery that is the target of the present embodiment may be any one that uses the negative electrode active material for the lithium-ion secondary battery of the present embodiment described below, with respect to other constituent requirements. , Is not particularly limited.

For example, when the above lithium ion secondary batteries are distinguished by form/structure, they can be applied to any conventionally known form/structure such as a stacked type (flat type) battery and a wound type (cylindrical type) battery. It is a thing. By adopting a laminated (flat) battery structure, long-term reliability can be ensured by a sealing technique such as simple thermocompression bonding, which is advantageous in terms of cost and workability.

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

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

Therefore, in the following description, a non-bipolar (internal parallel connection type) lithium ion secondary battery using the negative electrode active material for the lithium ion secondary battery of the present embodiment will be briefly described 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 structure of battery>
FIG. 1 schematically shows the overall structure of a flat type (laminated type) lithium ion secondary battery (hereinafter, also simply referred to as “laminated type battery”), which is a typical embodiment of the electric device of the present invention. It is the cross-sectional schematic diagram represented.

As shown in FIG. 1, the stack type battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charging/discharging reaction actually progresses is sealed inside a laminate sheet 29 which is an exterior body. .. Here, in the power generation element 21, the positive electrode in which the positive electrode active material layers 15 are arranged on both surfaces of the positive electrode current collector 12, the electrolyte layer 17, and the negative electrode active material layers 13 are arranged on both surfaces of the negative electrode current collector 11. It has a structure in which a negative electrode is laminated. Specifically, one negative electrode active material layer 15 and the adjacent negative electrode active material layer 13 are opposed to each other with the electrolyte layer 17 in between, and the negative electrode, the electrolyte layer, and the positive electrode are laminated in this order. ..

Thus, the adjacent positive electrode, electrolyte layer, and negative electrode form 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 unit cell layers 19 are stacked and electrically connected in parallel. In addition, in each of the outermost positive electrode collectors located on both outermost layers of the power generation element 21, the positive electrode active material layer 15 is arranged on only one surface, but the active material layers may be provided on both surfaces. .. That is, the current collector having the active material layers on both sides may be used as it is as the current collector for the outermost layer, instead of the current collector dedicated to the outermost layer in which the active material layer is provided on only one surface. Further, by reversing the arrangement of the positive electrode and the negative electrode from that of FIG. 1, the outermost negative electrode current collectors are located on both outermost layers of the power generation element 21, and one surface of the outermost layer negative electrode current collector or You may make it arrange|position the negative electrode active material layer on both surfaces.

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

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

<Active material layer>
The active material layer 13 or 15 contains an active material and, if necessary, further contains other additives.

[Cathode active material layer]
The positive electrode active material layer 15 contains a positive electrode active material.

(Cathode active material)
As the positive electrode active material, for example, lithium such as those _{LiMn 2 O 4, LiCoO 2,} LiNiO 2, Li (Ni-Mn-Co) O 2 , and some of these transition metals are replaced by other elements - Examples thereof include transition metal composite oxides, lithium-transition metal phosphate compounds, lithium-transition metal sulfate compounds, and the like. Depending on the case, two or more positive electrode active materials may be used in combination. From the viewpoint of capacity and output characteristics, a lithium-transition metal composite oxide is preferably used as the positive electrode active material. More preferably, a composite oxide containing lithium and nickel is used, and further preferably, Li(Ni—Mn—Co)O ₂ and those in which some of these transition metals are replaced with other elements (hereinafter, (Also simply referred to as “NMC complex oxide”) is used. The NMC composite oxide has a layered crystal structure in which lithium atomic layers and transition metal (Mn, Ni, and Co are arranged in an ordered manner) atomic layers are alternately stacked via oxygen atomic layers. One Li atom is contained, and the amount of Li that can be taken out is twice as large as that of the spinel-type lithium manganese oxide, that is, the supply capacity is twice as large, and a high capacity can be obtained.

As described above, the NMC composite oxide also includes a composite oxide in which a part of the transition metal element is replaced with another metal element. In this case, other elements include Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu. , Ag, Zn, etc., preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, more preferably Ti, Zr, P, Al, Mg, Cr, and more preferably Ti, Zr, Al, Mg, and Cr from the viewpoint of improving cycle characteristics.

Since the NMC complex oxide has a high theoretical discharge capacity, it is preferable that the NMC composite oxide has the general formula (1): Li _a Ni _b Mn _c Co _d M _x O ₂ (where a, b, c, d, and x are in the formula). Satisfies 0.9≦a≦1.2, 0<b<1, 0<c≦0.5, 0<d≦0.5, 0≦x≦0.3, b+c+d=1, and M is Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr, which is at least one element). Here, a represents the atomic ratio of Li, b represents the atomic ratio of Ni, c represents the atomic ratio of Mn, d represents the atomic ratio of Co, and x represents the atomic ratio of M. Represents. From the viewpoint of cycle characteristics, it is preferable that 0.4≦b≦0.6 in the general formula (1). The composition of each element can be measured by, for example, an inductively coupled plasma (ICP) emission analysis method.

In general, nickel (Ni), cobalt (Co) and manganese (Mn) are known to contribute to the capacity and output characteristics from the viewpoint of improving the material purity and improving the electron conductivity. Ti or the like partially replaces the transition metal in the crystal lattice. From the viewpoint of cycle characteristics, it is preferable that a part of the transition element is replaced with another metal element, and 0<x≦0.3 is particularly preferable in the general formula (1). Since at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr is solid-solved, the crystal structure is stabilized, resulting in charge/discharge. It is considered that the battery capacity can be prevented from being lowered even by repeating the above, and excellent cycle characteristics can be realized.

As a more preferred embodiment, in the general formula (1), b, c and d are 0.44≦b≦0.51, 0.27≦c≦0.31, 0.19≦d≦0.26. Is preferable from the viewpoint of improving the balance between capacity and life characteristics. For example, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ is LiCoO ₂ , LiMn ₂ O ₄ , LiNi _1/3 Mn _1/3 Co _1/3 O _2, etc., which have a proven record in general consumer batteries. Compared with the above, since it has a large capacity per unit weight and can improve the energy density, it has an advantage that a compact and high capacity battery can be manufactured, which is also preferable from the viewpoint of cruising range. Although LiNi _0.8 Co _0.1 Al _0.1 O ₂ is more advantageous in that it has a larger capacity, it has a problem in life characteristics. On the other hand, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ has a life characteristic as excellent as LiNi _1/3 Mn _1/3 Co _1/3 O ₂ .

Depending on the case, two or more positive electrode active materials may be used in combination. From the viewpoint of capacity and output characteristics, a lithium-transition metal composite oxide is preferably used as the positive electrode active material. Needless to say, a positive electrode active material other than the above may be used.

The average particle diameter of the positive electrode active material contained in the positive electrode active material layer 15 is not particularly limited, but from the viewpoint of high output, it is preferably 1 to 30 μm, more preferably 5 to 20 μm. In addition, in the present specification, the “particle diameter” is on the contour line 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). Of the distances between any two points, it means the maximum distance. In addition, in the present specification, the value of “average particle diameter” is observed in several to several tens of visual fields by using an observing means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM) unless otherwise specified. The value calculated as the average value of the particle diameter of the particles to be used shall be adopted. The particle diameters and average particle diameters of the other constituent components can be similarly defined.

The positive electrode active material layer 15 may include a binder.

(Binder)
The binder is added for the purpose of binding the active materials together or the active material and the current collector to maintain the electrode structure. The binder used for the positive electrode active material layer is not particularly limited, but examples thereof include the following materials. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile (PEN), polyacrylonitrile, polyimide, polyamide, polyamide imide, cellulose, carboxymethyl cellulose (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 thereof, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene/hexafluoropropylene copolymer (FEP), tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer Fluorine resin such as polymer (PFA), ethylene/tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene/chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), Vinylidene fluoride-hexafluoropropylene fluororubber (VDF-HFP fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluororubber (VDF-HFP-TFE fluororubber), vinylidene fluoride-pentafluoro Propylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene Examples thereof include vinylidene fluoride-based fluororubbers such as vinylidene fluoride-based fluororubbers (VDF-PFMVE-TFE-based fluororubbers) and vinylidene fluoride-chlorotrifluoroethylene-based fluororubbers (VDF-CTFE-based fluororubbers). Among them, polyvinylidene fluoride, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, polyamide, and polyamide-imide are more preferable. These suitable binders have excellent 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 in the active material layer. These binders may be used alone or in combination of two.

The amount of the binder contained in the positive electrode active material layer is not particularly limited as long as it can bind the active material, but is preferably 0.5 to 15 mass% with respect to the active material layer. And more preferably 1 to 10 mass %.

The positive electrode (positive electrode active material layer) is formed 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 a usual slurry (coating). Can be formed.

[Negative electrode active material layer]
The negative electrode active material layer 13 contains a negative electrode active material.

(Negative electrode active material)
In the present embodiment, the negative electrode active material has a ternary alloy composition of Si—Sn—Ti, and silicon in which the intensities of three specific diffraction peaks observed by X-ray diffraction measurement have a predetermined relationship. It is made of a contained alloy.

<Composition of silicon-containing alloy>
As described above, the silicon-containing alloy forming the negative electrode active material in the present embodiment first has a ternary alloy composition of Si—Sn—Ti. More specifically, the silicon-containing alloy forming the negative electrode active material in the present embodiment has a composition represented by the following chemical formula (I).

In the above chemical formula (I), A is an unavoidable impurity, and x, y, z, and a represent mass% values, where 0<x<100, 0<y<100, 0<z. <100, 0≦a<0.5, and x+y+z+a=100.

As is clear from the above chemical formula (I), the silicon-containing alloy (having the composition of Si _x Sn _y Ti _z A _a ) according to this embodiment is a ternary system of Si, Sn and Ti. By including Ti as an additive element to the silicon-containing alloy, it is possible to suppress the amorphous-crystal phase transition during Li alloying and achieve high cycle durability. In addition, this makes the capacity higher than that of the conventional negative electrode active material (for example, carbon-based negative electrode active material).

Here, in the Si-based negative electrode active material, when Si and Li are alloyed during charging, the Si phase transitions from an amorphous state to a crystalline state, causing a large volume change (about 4 times). As a result, there is a problem that the active material particles themselves are broken and the function as an active material is lost. Therefore, it is possible to suppress the collapse of the particles themselves by suppressing the phase transition of the amorphous-crystal of the Si phase during charging, the function (high capacity) as the active material is maintained, and the cycle life is also improved. You can

In addition, in this specification, "unavoidable impurities" mean those present in a raw material of a silicon-containing alloy or those unavoidably mixed in the manufacturing process. Although the unavoidable impurities are essentially unnecessary, they are permissible impurities because they are trace amounts and do not affect the characteristics of the silicon-containing alloy.

As described above, the silicon-containing alloy according to the present embodiment (having the composition of Si _x Sn _y Ti _z A _a ) is a ternary system of Si, Sn and Ti. Here, the sum of the constituent ratios (mass ratios x, y, z) of the constituent elements is 100% by mass, but there is no particular limitation on the respective values of x, y, z. However, x is preferably 60≦x≦73, more preferably 60≦x≦70, from the viewpoint of maintaining durability against charge/discharge (insertion/desorption of Li ions) and balancing the initial capacity. , More preferably 60≦x≦66, and particularly preferably 63≦x≦66. In addition, as for y, from the viewpoint of forming a solid solution in the Si phase and increasing the distance between the Si tetrahedra in the Si phase, reversible insertion and desorption of Li ions during charge and discharge can be performed. , Preferably 2≦y≦15, more preferably 2≦y≦10, further preferably 4≦y≦10, particularly preferably 4≦y≦7. Regarding z, from the viewpoint of maintaining durability against charge/discharge (insertion/desorption of Li ions) and balance of initial capacity, it is preferably 25≦z≦35, more preferably 27≦z, as in the case of x. ≦33, and more preferably 28≦z≦30. As described above, by including Ti in a relatively large amount while including Si as a main component, and also including Sn to some extent, a specific amount observed in the X-ray diffraction measurement of the silicon-containing alloy according to the present embodiment is obtained. The intensities of the three diffraction peaks tend to have a predetermined relationship. However, the above numerical range of the constituent ratio of each constituent element is merely for explaining the preferred embodiment, and is within the technical scope of the present invention as long as it is included in the scope of the claims.

As described above, A is an impurity (unavoidable impurity) other than the above-mentioned three components, which is derived from the raw materials and the manufacturing method. The above a is 0≦a<0.5, and preferably 0≦a<0.1. Whether or not the negative electrode active material (silicon-containing alloy) has the composition of the above chemical formula (I) is confirmed by qualitative analysis by fluorescent X-ray analysis (XRF) and quantitative analysis by inductively coupled plasma (ICP) emission spectroscopy. It is possible to

<Microstructure of silicon-containing alloy>
The silicon-containing alloy constituting the negative electrode active material in the present embodiment contains amorphous or low crystalline silicon formed by solid solution of tin in the crystal structure of silicon in the matrix phase of the silicide phase containing TiSi _2. It is preferable to have a structure in which a phase containing a main component (hereinafter, “a phase containing amorphous or low crystalline silicon as a main component” is also referred to as an a-Si phase) is dispersed. That is, it is preferable that the silicon-containing alloy according to the present embodiment has a so-called sea-island structure in which islands of a-Si phase as a dispersed phase are dispersed in the sea of a silicide phase as a continuous phase. Is one of. By having such a structure, the electron conductivity of the negative electrode active material (silicon-containing alloy) can be further improved, and moreover, the stress at the time of expansion of the a-Si phase is relaxed to prevent cracking of the active material. can do. Whether or not the silicon-containing alloy has such a microstructure structure is determined, for example, by using a silicon-containing alloy in a high-angle annular dark-field scanning transmission electron microscope (as described in the section of Examples below). After observing using HAADF-STEM), it can be confirmed by performing element intensity mapping by EDX (energy dispersive X-ray spectroscopy) for the same visual field as the observed image.

<a-Si phase>
Here, in the silicon-containing alloy according to the present embodiment, the a-Si phase is a phase containing amorphous or low crystalline silicon. The a-Si phase is a phase that is involved in occlusion/release of lithium ions during the operation of the electric device (lithium ion secondary battery) of the present embodiment, and is capable of reacting electrochemically with lithium (that is, per unit weight and It is a phase capable of absorbing and releasing a large amount of lithium per volume). Further, it is preferable that tin is in solid solution inside the crystal structure of silicon forming the a-Si phase. Furthermore, since silicon has poor electron conductivity, the a-Si phase may contain a trace amount of additional elements such as phosphorus and boron, or a transition metal.

This a-Si phase is preferably more amorphous than the silicide phase described later. With such a structure, the negative electrode active material (silicon-containing alloy) can have a higher capacity. Whether or not the a-Si phase is more amorphous than the silicide phase can be determined by observing images of the a-Si phase and the silicide phase using a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM). It can be determined from the diffraction pattern obtained by fast Fourier transform (FFT). That is, the diffraction pattern shown in this diffraction pattern shows a two-dimensional dot array net pattern (lattice-like spots) for the single crystal phase, Debye-Scherrer ring (diffraction ring) for the polycrystalline phase, and the amorphous phase. A halo pattern is shown for the phase. By utilizing this, the above confirmation can be performed. In the present embodiment, the a-Si phase may be amorphous or low crystalline, but from the viewpoint of achieving higher cycle durability, the a-Si phase should be amorphous. Is preferred.

The silicon-containing alloy according to the present embodiment essentially contains tin, but since tin is an element that does not form silicide with silicon, it exists in the a-Si phase instead of the silicide phase. When the tin content is low, all tin elements are present in the a-Si phase as a solid solution in the crystal structure of silicon. On the other hand, when the content of tin increases, the tin element that cannot be completely dissolved in silicon of the a-Si phase aggregates and exists as a crystalline phase of tin alone. In the present embodiment, it is preferable that such a crystal phase of elemental tin does not exist.

<Silicide phase>
On the other hand, the silicide phase forming the sea (continuous phase) of the sea-island structure described above is a crystal phase containing TiSi ₂ as a main component. Since this silicide phase contains TiSi ₂ , it has excellent affinity with the a-Si phase, and in particular, cracking at the crystal interface due to volume expansion during charging can be suppressed. Furthermore, the silicide phase is superior to the a-Si phase in terms of electronic conductivity and hardness. As described above, the silicide phase plays a role of improving the low electron conductivity of the a-Si phase and maintaining the shape of the active material against the stress during expansion. In the present embodiment, since the silicide phase having such characteristics constitutes the sea (continuous phase) having a sea-island structure, it is possible to further improve the electron conductivity of the negative electrode active material (silicon-containing alloy), Moreover, it is considered that the stress at the time of expansion of the a-Si phase can be relaxed to prevent cracking of the active material, which contributes to the improvement of cycle durability.

<Diffraction peak observed by X-ray diffraction measurement of silicon-containing alloy>
As described above, the silicon-containing alloy that constitutes the negative electrode active material in the present embodiment is also characterized in that the intensities of the three specific diffraction peaks observed by X-ray diffraction measurement have a predetermined relationship. That is, in X-ray diffraction (XRD) measurement using CuKα1 ray of a silicon-containing alloy, 2θ=40 with respect to the diffraction peak intensity X of the (311) plane of TiSi ₂ having a C54 structure in the range of 2θ=38 to 40°. The value (Y/X) of the diffraction peak intensity Y of the (131) plane of TiSi ₂ having a C49 structure in the range of up to 41° is 0.5 or more, and Si in the range of 2θ=28 to 30° The characteristic value (Y/Z) of the ratio of the diffraction peak intensity Y to the diffraction peak intensity Z of the (111) plane is 0.6 or more.

Here, titanium disilicide (TiSi ₂ ) will be described. TiSi ₂ has two types of crystal structures, a C49 structure and a C54 structure. The C49 structure is a metastable phase exhibiting a high resistivity of about 60 μΩ·cm, and has a base-centered orthorhombic structure. On the other hand, the C54 structure is a stable phase having a low resistivity of about 15 to 20 μΩ·cm and a face center-orthorhombic structure. Further, TiSi ₂ having a C49 structure is formed at a low temperature of about 400° C., and TiSi ₂ having a C54 structure is formed at a high temperature of about 800° C. As will be described later, the silicon-containing alloy according to the present embodiment can be manufactured by a liquid rapid solidification method using a mother alloy having the same composition as the silicon-containing alloy. As shown in the examples, in the manufacturing method, when the cooling rate of the alloy is increased, the ratio of TiSi ₂ having a C49 structure to TiSi ₂ having a C54 structure is increased. It is considered that this is due to the difference in formation temperature between the C49 structure and the C54 structure.

In this specification, the X-ray diffraction measurement for calculating the intensity ratio of the diffraction peaks is performed by using the method described in the section of Examples described later.

Next, how to obtain the diffraction peak intensity in the present specification will be described. For example, the diffraction peak intensity X of the (311) plane of TiSi ₂ having a C54 structure in the range of 2θ=38 to 40° can be obtained as follows (see FIG. 3).

First, in the diffraction spectrum obtained by the X-ray diffraction measurement, the point where the perpendicular line at 2θ=38° (2θ=P in FIG. 3) and the diffraction spectrum intersect is A. Similarly, the point where the perpendicular and the X-ray diffraction spectrum intersect at 2θ=40° (2θ=Q in FIG. 3) is designated as B. Here, the line segment AB is used as a baseline, and the point where the perpendicular line in the diffraction peak of the (311) plane of TiSi ₂ having a C54 structure and the baseline intersect is C. Then, as the length of the line segment CD connecting the vertex D and the point of the diffraction peak of (311) plane of the TiSi ₂ C having a C54 structure, the diffraction peak intensity X of (311) plane of the TiSi ₂ having a C54 structure You can ask.

The diffraction peak intensity Y of the (131) plane of TiSi ₂ having a C49 structure in the range of 2θ=40 to 41° and the diffraction peak intensity Z of the (111) plane of Si in the range of 2θ=28 to 30° are also as described above. The peak intensity X can be obtained by the same method.

In X-ray diffraction measurement of the silicon-containing alloy constituting the negative electrode active material according to the present embodiment, 2θ=2θ= with respect to the diffraction peak intensity X of the (311) plane of TiSi ₂ having a C54 structure in the range of 2θ=38 to 40°. It is essential that the ratio value (Y/X) of the diffraction peak intensities Y of the (131) plane of TiSi ₂ having a C49 structure in the range of 40 to 41° is 0.5 or more. The value of the ratio (Y/X) is preferably 1.2 or more, more preferably 1.4 or more, still more preferably 1.7 or more, and particularly preferably 2.8 or more, Most preferably, it is 2.9 or more. When the value (Y/X) of the ratio is 0.5 or more, the cycle durability of an electric device such as a lithium ion secondary battery can be improved. The upper limit of the ratio value (Y/X) is not particularly limited, but is preferably 15 or less from the viewpoint of electronic conductivity.

The method for controlling the value (Y/X) of the above ratio to 0.5 or more is not particularly limited, but the alloy composition of the silicon-containing alloy and the alloy in the method for producing a silicon-containing alloy using the liquid rapid solidification method described below are used. It can be adjusted by appropriately setting the cooling rate (cooling condition). For example, for the alloy composition, when increasing the amount of Ti relative to Si, compared to the amount of TiSi ₂ which crystallized as the primary crystal, the amount of TiSi ₂ which crystallized as the eutectic of Si is increased, the ratio Value (Y/X) tends to increase. In the liquid rapid solidification method, when the alloy cooling rate is increased, TiSi ₂ having a C54 structure formed at a high temperature (about 800° C.) and TiSi having a C49 structure formed at a low temperature (about 400° C.). _Since the ratio of ₂ increases, the value of the above ratio (Y/X) tends to increase.

In addition, in the X-ray diffraction measurement of the silicon-containing alloy according to the present embodiment, the value of the ratio of the diffraction peak intensity Y to the diffraction peak intensity Z of the Si (111) plane in the range of 2θ=28 to 30° (Y /Z) must be 0.6 or more. The value (Y/Z) of the ratio is preferably 0.9 or more, more preferably 1.3 or more, still more preferably 1.4 or more, and particularly preferably 1.6 or more. When the value of the ratio (Y/Z) is 0.6 or more, the cycle durability of an electric device such as a lithium ion secondary battery can be improved. The upper limit of the ratio value (Y/Z) is not particularly limited, but is preferably 10 or less from the viewpoint of charge/discharge capacity.

The method of controlling the value of the above ratio (Y/Z) to 0.6 or more is not particularly limited, but in the alloy composition of the silicon-containing alloy and the method for producing the silicon-containing alloy using the liquid rapid solidification method described below, the alloy is used. It can be adjusted by appropriately setting the cooling rate (cooling condition). For example, regarding the alloy composition, when the blending amount of Ti with respect to Si is increased, the amount of silicide generated is increased, and thus the value of the above ratio (Y/Z) tends to increase. Further, in the liquid rapid solidification method, when the cooling rate of the alloy is increased, the TiSi ₂ having a C54 structure formed at a high temperature (about 800° C.) has a C49 structure formed at a lower temperature (about 400° C.). The proportion of TiSi ₂ increases. Moreover, since the crystal of Si does not grow sufficiently, the ratio of crystalline Si can be reduced. As a result, the ratio value (Y/Z) tends to increase.

As described above, in the present embodiment, by using the negative electrode active material made of the silicon-containing alloy having the specific three diffraction peak intensities observed in the X-ray diffraction measurement have the predetermined relationship, Although the mechanism by which the cycle durability is improved is unknown, the present inventors presume as follows. That is, a silicon-containing alloy according to the present embodiment is can be manufactured by the manufacturing method using the liquid quenching solidification method described below, as to increase the cooling rate of the alloy, with respect to TiSi ₂ having a C54 structure, C49 structure The proportion of TiSi ₂ having is increased. When the alloy is cooled at a cooling rate such that TiSi ₂ having a C49 structure is sufficiently crystallized, crystals containing TiSi ₂ and/or Si cannot be sufficiently grown, and It is considered that the size of the crystal becomes smaller. As described above, as the crystal size becomes smaller, the absolute amount of change in expansion/contraction of the a-Si phase accompanying the reversible insertion/desorption reaction of lithium ions during charge/discharge becomes smaller. As a result, it is considered that the negative electrode active material (silicon-containing alloy) according to the present embodiment brings about improvement in cycle durability of electric devices such as a lithium ion secondary battery. However, the above mechanism is only speculation, and the present invention should not be limitedly interpreted by the above mechanism.

The particle diameter of the silicon-containing alloy constituting the negative electrode active material in the present embodiment is not particularly limited, but the average particle diameter D50 is preferably 0.1 to 20 μm, more preferably 0.2 to 10 μm.

(Method for producing negative electrode active material)
The method for producing the negative electrode active material for an electric device according to the present embodiment is not particularly limited, and conventionally known knowledge can be appropriately referred to. However, in the present invention, three specific diffractions observed by X-ray diffraction measurement are performed. As an example of a method for producing a negative electrode active material composed of a silicon-containing alloy having a peak strength having a predetermined relationship, a ribbon-shaped alloy (quenched ribbon alloy) may be produced using a liquid rapid solidification method as follows. A manufacturing method is provided. That is, according to another aspect of the present invention, there is provided a method for producing a negative electrode active material for an electric device, which is made of a silicon-containing alloy having a composition represented by the chemical formula (I), and has the same composition as the silicon-containing alloy. A negative electrode for an electric device, wherein a ribbon-shaped alloy is produced by a liquid rapid solidification method using a mother alloy having an alloy, and the ribbon-shaped alloy is pulverized to obtain a negative electrode active material for an electric device made of the silicon-containing alloy. A method of making the active material is also provided. As described above, by performing the liquid rapid solidification method to produce the negative electrode active material (silicon-containing alloy), the intensities of the three specific diffraction peaks observed in the above X-ray diffraction measurement have a predetermined relationship. It becomes possible to manufacture alloys. This provides a method for producing a negative electrode active material that can effectively contribute to improving cycle durability. Hereinafter, the manufacturing method according to the present embodiment will be described step by step.

<Liquid rapid solidification method (process for producing ribbon alloy)>
First, a liquid rapid solidification method is carried out using a mother alloy having the same composition as the desired silicon-containing alloy. Thereby, a ribbon-shaped alloy (quenched ribbon alloy) is produced.

Here, in order to obtain a mother alloy, high-purity raw materials (single ingot, wire, plate, etc.) are prepared as raw materials for silicon (Si), tin (Sn), and titanium (Ti). Then, in consideration of the composition of the silicon-containing alloy (negative electrode active material) to be finally manufactured, a master alloy in the form of an ingot or the like is manufactured by a known method such as an arc melting method.

Then, a liquid rapid solidification method is implemented using the master alloy obtained above. This step is a step of rapidly cooling and solidifying a melt obtained by melting the mother alloy obtained above, and for example, it is performed by a high frequency induction melting-liquid rapid solidification method (twin roll or single roll rapid cooling method). You can Thereby, a ribbon-shaped alloy (quenched ribbon alloy) is obtained. The liquid rapid solidification method is often used as a method for producing an amorphous alloy, and there is much knowledge about the method itself. The liquid rapid solidification method can be carried out using a commercially available liquid rapid solidification apparatus (for example, liquid rapid solidification apparatus NEV-A05 manufactured by Nisshin Giken Co., Ltd.).

For details, in a liquid quenching coagulation device NEV-A05 type manufactured by Nisshin Giken Co., Ltd., in a melting device with a spray nozzle (for example, a quartz nozzle) installed in a chamber whose gauge pressure is reduced after Ar replacement. Then, the above master alloy is put into a container and melted in a predetermined temperature range by an appropriate melting means (for example, high-frequency induction heating), and then, at a predetermined injection pressure, made of metal or ceramics (especially thermal conductivity) at a predetermined rotation speed. It is possible to produce a ribbon-shaped alloy (quenched ribbon alloy) that is continuously formed horizontally from the roll by spraying onto a roll.

At this time, it is desirable to replace the atmosphere in the chamber with an inert gas (He gas, Ne gas, Ar gas, N ₂ gas, etc.). After the replacement with the inert gas, the gauge pressure in the chamber is preferably adjusted within the range of -0.03 to -0.07 MPa (absolute pressure 0.03 to 0.07 MPa).

Further, the melting temperature of the mother alloy in the melting device with the injection nozzle may be equal to or higher than the melting point of the alloy. Further, as the melting means, conventionally known melting means such as high frequency induction heating can be used.

Further, the injection pressure of the mother alloy from the nozzle of the melting device with the injection nozzle is preferably adjusted to a range of 0.03 to 0.09 MPa in gauge pressure. The injection pressure can be adjusted by a conventionally known method. Further, it is desirable to adjust the differential pressure between the chamber internal pressure and the injection pressure within the range of 0.06 to 0.16 MPa.

In addition, it is desirable that the rotation speed and the peripheral speed of the roll when the mother alloy is injected are adjusted within the range of 4000 to 6000 rpm (the peripheral speed is 40 to 65 m/sec).

Further, the cooling rate of the alloy when the molten mother alloy is jetted onto the roll from the nozzle of the melting device to cool the alloy is preferably 1,000,000°C/sec or more, more preferably 1.6 million°C/sec or more. And more preferably 2,000,000° C./sec or more, particularly preferably 3 million° C./sec or more, and most preferably 5 million° C./sec or more. The cooling rate of the alloy can be measured using a high speed infrared camera. As described above, in order to increase the cooling rate, (1) the rotation speed of the roll is increased; (2) the melt temperature of the master alloy is increased, and the injection pressure is adjusted, whereby the roll and the melt are melted. The thickness of the ribbon alloy (quenched ribbon alloy) may be adjusted by a method such as improving wettability.

<Crushing process>
After that, the strip-shaped alloy (quenched strip alloy) obtained above is pulverized. For example, using a ball mill device (for example, a planetary ball mill device) as used in Examples described later, the crushing balls and the ribbon-shaped alloy (quenched ribbon alloy) are put into a crushing pot, and the crushing treatment is performed. The ribbon-shaped alloy (quenched ribbon alloy) may be coarsely pulverized in advance with an appropriate pulverizer to a size that can be easily loaded into the apparatus.

When a ball mill device is used, the rotation speed of the device during the pulverization treatment is preferably less than 500 rpm, more preferably 100 to 480 rpm, and further preferably 300 to 450 rpm. The crushing time is preferably less than 12 hours, more preferably 0.5 to 10 hours, and further preferably 0.5 to 3 hours.

The pulverization treatment by the above-mentioned method is usually performed in a dry atmosphere, but the particle size distribution after the pulverization treatment may have a very large width. For this reason, it is preferable to perform a crushing treatment and/or a classification treatment for adjusting the particle size.

Although the predetermined alloy that is essentially contained in the negative electrode active material layer has been described above, the negative electrode active material layer may include other negative electrode active materials. As the negative electrode active material other than the above-mentioned predetermined alloy, natural graphite, artificial graphite, carbon black, activated carbon, carbon fiber, carbon such as coke, soft carbon or hard carbon, pure metal such as Si or Sn, or the above predetermined composition is used. Alloy active materials out of the ratio, metal oxides such as TiO, Ti ₂ O ₃ , TiO ₂ or SiO ₂ , SiO, SnO ₂ , lithium such as Li _4/3 Ti _5/3 O ₄ or Li ₇ MnN And a transition metal, a complex oxide (composite nitride), a Li-Pb-based alloy, a Li-Al-based alloy, Li, and the like. However, from the viewpoint of sufficiently exhibiting the action and effect exhibited by using the predetermined alloy as the negative electrode active material, the content of the predetermined alloy in the total amount of the negative electrode active material of 100% by mass is preferably It is 50 to 100% by mass, more preferably 80 to 100% by mass, still more preferably 90 to 100% by mass, particularly preferably 95 to 100% by mass, and most preferably 100% by mass.

Subsequently, the negative electrode active material layer 13 may include a binder.

(Binder)
The binder is added for the purpose of binding the active materials together or the active material and the current collector to maintain the electrode structure. The type of binder used in the negative electrode active material layer is also not particularly limited, and the binder described above as the binder used in the positive electrode active material layer can be similarly used. Therefore, detailed description is omitted here.

The amount of the binder contained in the negative electrode active material layer is not particularly limited as long as it can bind the active material, but is preferably 0.5 to 0.5 with respect to the negative electrode active material layer. It is 20 mass %, and more preferably 1 to 15 mass %.

(Requirements common to the positive electrode and negative electrode active material layers 15 and 13)
The requirements common to the positive electrode and negative electrode active material layers 15 and 13 will be described below.

The positive electrode active material layer 15 and the negative electrode active material layer 13 include a conductive auxiliary agent, an electrolyte salt (lithium salt), an ion conductive polymer, and the like, if necessary. In particular, the negative electrode active material layer 13 also essentially contains a conductive auxiliary agent.

Conductive Aid The conductive aid refers to an additive that is added to improve the conductivity of the positive electrode active material layer or the negative electrode active material layer. Examples of the conduction aid include carbon black such as acetylene black, carbon materials such as 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.

The content of the conductive additive mixed in the active material layer is 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. 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, based on the total amount of the active material layer. is there. The electronic conductivity of the active material itself is low, and the electrode resistance can be reduced by the amount of the conductive additive. By defining the compounding ratio (content) of the conductive additive in the active material layer within the above range, the following effects are exhibited. It That is, the electron conductivity can be sufficiently ensured without inhibiting the electrode reaction, the decrease in energy density due to the decrease in electrode density can be suppressed, and the energy density due to the increase in electrode density can be improved. ..

Further, a conductive binder having the functions of the above-mentioned conductive additive and a binder may be used instead of the conductive additive and the binder, or may be used in combination with one or both of the conductive additive and the binder. .. Commercially available TAB-2 (manufactured by Hosen Co., Ltd.) can be used as the conductive binder.

Electrolyte salt (lithium salt)
As the electrolyte salt (lithium _{salt), 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 positive electrode active material layer and the negative electrode active material layer is not particularly limited. The compounding 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 surface of the current collector) is not particularly limited, and conventionally known knowledge about batteries 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 in consideration of the purpose of use of the battery (emphasis on output, emphasis on energy, etc.) and ionic conductivity.

<Current collector>
The current collectors 11 and 12 are made of a conductive material. The size of the current collector is determined according to the intended use of the battery. For example, in the case of being used for a large battery requiring high energy density, a current collector having a large area is used.

The thickness of the current collector is also not particularly limited. The thickness of the current collector is usually about 1 to 100 μm.

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

When a thin film alloy of the negative electrode active material is directly formed on the negative electrode current collector 12 by a sputtering method or the like, it is desirable to use a current collector foil.

There is no particular limitation on the material forming 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 adopted.

Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, copper and the like. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plated material of a combination of these metals can be preferably used. Further, a foil having a metal surface coated with aluminum may be used. Of these, aluminum, stainless steel, copper, and nickel are preferable from the viewpoints of electron conductivity, battery operating potential, and adhesion of the negative electrode active material to the current collector by sputtering.

In addition, examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylenevinylene, 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 and reducing the weight of the current collector.

Examples of the non-conductive polymer material include 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), polystyrene (PS), and the like. Such a non-conductive polymer material may have excellent potential resistance or solvent resistance.

A conductive filler may be added to the above-mentioned conductive polymer material or non-conductive polymer material, if necessary. In particular, when the resin serving as the base material of the current collector is composed only of the non-conductive polymer, the conductive filler is indispensable in order to impart conductivity to the resin.

The conductive filler can be used without particular limitation as long as it is a substance having conductivity. For example, as a material having excellent conductivity, potential resistance, or lithium ion barrier property, metal and conductive carbon can be cited. 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 a metal thereof. It is preferable to include an alloy or a metal oxide containing. The conductive carbon is not particularly limited. Preferably, 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 is included.

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

<Electrolyte layer>
A liquid electrolyte or a polymer electrolyte may be used as the electrolyte that constitutes 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), Illustrative are 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 adopted.

On the other hand, the polymer electrolyte is classified into a gel electrolyte containing an electrolytic solution and an intrinsic polymer electrolyte containing no electrolytic solution.

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

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

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

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 forms of the separator (including non-woven fabric) include, for example, a microporous film made of polyolefin such as polyethylene and polypropylene, a porous flat plate, and further 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 which 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 exhibit excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, a suitable polymerization initiator may be used to perform thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization or the like on a polymerizable polymer for forming a polyelectrolyte (for example, PEO or PPO). Polymerization may be performed.

<Current collector and lead>
A current collector plate may be used for the purpose of extracting an electric current to the outside of the battery. The current collector plate is electrically connected to the current collector and the leads and taken out to the outside of the laminate sheet that is the battery exterior material.

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

The positive electrode terminal lead and the negative electrode terminal lead are also used as needed. As a material for the positive electrode terminal lead and the negative electrode terminal lead, a terminal lead used in a known lithium ion secondary battery can be used. In addition, the portion taken out from the battery exterior material 29 has a heat-resistant insulating property so as not to affect a product (for example, an automobile part, especially an electronic device, etc.) by coming into contact with a peripheral device, a wiring or the like and leaking electricity. It is preferable to cover with a heat-shrinkable tube.

<Battery exterior material>
As the battery exterior material 29, a well-known metal can case can be used, and a bag-shaped case that can cover the power generation element and that uses a laminate film containing aluminum can be used. As the laminate film, for example, a laminate film having a three-layer structure formed by laminating PP, aluminum and nylon in this order can be used, but the laminate film is not limited thereto. A laminated film is desirable from the viewpoint of high output and excellent cooling performance, and the fact that it can be suitably used for batteries for large-sized equipment for EVs and HEVs.

The above lithium-ion secondary battery can be manufactured by a conventionally known manufacturing method.

<External structure of lithium-ion secondary battery>
FIG. 2 is a perspective view showing the appearance of a laminated flat lithium ion secondary battery.

As shown in FIG. 2, the laminated flat lithium ion secondary battery 50 has a rectangular flat shape, and a positive electrode collector plate 59 and a negative electrode collector plate 59 for extracting electric power from both sides thereof. The electric plate 58 is pulled out. The power generation element 57 is wrapped by the battery outer casing material 52 of the lithium-ion secondary battery 50 and its periphery is heat-sealed, and the power generation element 57 draws out the positive electrode current collector plate 59 and the negative electrode current collector plate 58 to the outside. It is sealed in a closed state. Here, the power generation element 57 corresponds to the power generation element 21 of the lithium ion secondary battery (laminated battery) 10 shown in FIG. 1. The power generation element 57 is formed by stacking a plurality of single cell 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 the laminated flat type (laminate cell). The winding type lithium-ion battery has a cylindrical shape (coin cell), a prismatic shape (square cell), or a shape obtained by deforming such a cylindrical shape 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, and a laminate film or a conventional cylindrical can (metal can) may be used as the exterior material thereof. Preferably, the power generating element is covered with an aluminum laminate film. With this configuration, weight reduction can be achieved.

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

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 can be used for electric vehicles, hybrid electric vehicles, fuel cell vehicles, hybrid fuel cell vehicles, and the like. It can be suitably used as a capacity power source. That is, it can be suitably used as a vehicle drive power source or an auxiliary power source that requires high volume energy density and high volume output density.

In addition, in the said embodiment, although the lithium ion battery was illustrated as an electric device, it is not limited to this, It can apply to another type of secondary battery, and also to a primary battery. Further, it can be applied not only to batteries but also to capacitors.

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

(Example 1)
[Manufacture of silicon-containing alloy]
Using Si (purity 11N), Sn (purity 4N), and Ti (purity 3N), an ingot of a Si alloy (Si 61 mass %, Sn 9 mass %, Ti 30 mass %) was produced by an arc melting method.

Subsequently, using the ingot obtained above as a mother alloy, a silicon-containing alloy was produced by a liquid rapid solidification method. Specifically, using a liquid rapid solidification system NEV-A05 type manufactured by Nisshin Giken Co., Ltd., Si ₆₁ Sn was placed in a quartz nozzle installed in a chamber whose Ar pressure was replaced and the gauge pressure was reduced to −0.03 MPa. _{A 9} Ti ₃₀ ingot (mother alloy) was placed. Then, after melting by high frequency induction heating with a current value of 7.5 A (melt temperature: about 1420° C.), a Cu roll with a rotation speed of 4000 rpm (peripheral speed: 42 m/sec) was applied at an injection pressure of 0.05 MPa. Then, a ribbon-shaped alloy (quenched ribbon alloy) was produced. At this time, the gap between the Cu roll and the nozzle was 0.5 mm. The thickness of the obtained ribbon alloy (quenched ribbon alloy) was 24.4 μm.

Then, the ribbon-shaped alloy (quenched ribbon alloy) obtained above was pulverized. Specifically, first, a ribbon-shaped alloy (quenched ribbon) was roughly crushed to a size of 2 mm in diameter. Next, using a planetary ball mill device P-6 manufactured by Fritsch Germany, the zirconia crushed balls and the coarsely crushed product were placed in a zirconia crushing pot, and crushed at 400 rpm for 1 hour to obtain a silicon-containing alloy. (Negative electrode active material) was obtained. The average particle diameter D50 of the obtained silicon-containing alloy (negative electrode active material) powder was 7.4.

[Preparation of negative electrode]
80 parts by mass of the above-produced silicon-containing alloy (Si ₆₁ Sn ₉ Ti ₃₀ ) which is a negative electrode active material, 5 parts by mass of acetylene black which is a conductive additive, and 15 parts by mass of polyamide imide which is a binder are mixed. , N-methylpyrrolidone to obtain a negative electrode slurry. Next, the obtained negative electrode slurry was uniformly applied to both sides of a negative electrode current collector made of copper foil so that the thickness of the negative electrode active material layer was 30 μm, and dried in vacuum for 24 hours to give a negative electrode. Obtained.

[Preparation of lithium-ion secondary battery (coin cell)]
The negative electrode prepared above and the counter electrode Li were opposed to each other, and a separator (polyolefin, film thickness 20 μm) was arranged therebetween. Next, the laminated body of the negative electrode, the separator, and the counter electrode Li was placed on the bottom side of the coin cell (CR2032, material: stainless steel (SUS316)). Furthermore, a gasket is attached to maintain the insulation between the positive electrode and the negative electrode, the following electrolytic solution is injected with a syringe, a spring and a spacer are stacked, the upper side of the coin cell is overlapped, and the coin cell is sealed by caulking. A lithium ion secondary battery (coin cell) was obtained.

In addition, as the above-mentioned electrolytic solution, hexafluorophosphoric acid, which is a lithium salt, is added to an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a ratio of EC:DEC=1:2 (volume ratio). Lithium (LiPF ₆ ) dissolved at a concentration of 1 mol/L was used.

(Example 2)
A silicon-containing alloy (negative electrode active material), a negative electrode, and lithium were prepared in the same manner as in Example 1 except that the high-frequency induction heating current value in the liquid rapid solidification method was 9 A (melt temperature: about 1500° C.). An ion secondary battery (coin cell) was produced. The thickness of the obtained ribbon alloy (quenched ribbon alloy) was 23.0 μm. The average particle diameter D50 of the obtained silicon-containing alloy (negative electrode active material) powder was 8.8 μm.

(Example 3)
A silicon-containing alloy (negative electrode) was prepared in the same manner as in Example 1 except that the high-frequency induction heating current value in the liquid rapid solidification method was 9 A (melt temperature: about 1500° C.) and the injection pressure was 0.03 MPa. An active material), a negative electrode, and a lithium ion secondary battery (coin cell) were produced. The thickness of the obtained ribbon alloy (quenched ribbon alloy) was 21.5 μm. The average particle size D50 of the obtained silicon-containing alloy (negative electrode active material) powder was 7.9 μm.

(Example 4)
A silicon-containing alloy (negative electrode active material), a negative electrode, and a lithium ion secondary battery (coin cell) were produced in the same manner as in Example 1 except that the composition of the mother alloy was Si ₆₆ Sn ₄ Ti ₃₀ . .. The thickness of the obtained ribbon alloy (quenched ribbon alloy) was 21.8 μm. The average particle diameter D50 of the obtained silicon-containing alloy (negative electrode active material) powder was 9.2 μm.

(Example 5)
A silicon-containing alloy (negative electrode) was prepared in the same manner as in Example 4 except that the current value of high-frequency induction heating in the liquid rapid solidification method was 9 A (melt temperature: about 1500° C.) and the injection pressure was 0.03 MPa. An active material), a negative electrode, and a lithium ion secondary battery (coin cell) were produced. The thickness of the obtained ribbon alloy (quenched ribbon alloy) was 19.4 μm. The average particle diameter D50 of the obtained silicon-containing alloy (negative electrode active material) powder was 8.3 μm.

(Comparative Example 1)
In the liquid rapid solidification method, the gauge pressure inside the chamber was -0.01 MPa, the current value of the high frequency induction heating was 6.5 A (melt temperature: about 1400°C), and the injection pressure was 0.01 MPa. By the same method as in Example 1, a silicon-containing alloy (negative electrode active material), a negative electrode, and a lithium ion secondary battery (coin cell) were produced. The thickness of the obtained ribbon alloy (quenched ribbon alloy) was 28.0 μm. The average particle diameter D50 of the obtained silicon-containing alloy (negative electrode active material) powder was 10.3 μm.

(Comparative example 2)
A silicon-containing alloy (negative electrode active material), a negative electrode, and a lithium ion secondary battery (coin cell) were produced by the same method as in Example 1 except that the composition of the mother alloy was Si ₆₀ Sn ₂₀ Ti ₂₀ . .. The thickness of the obtained ribbon-shaped alloy (quenched ribbon alloy) was 23.2 μm. The average particle diameter D50 of the obtained silicon-containing alloy (negative electrode active material) powder was 6.4 μm.

[Analysis of organization structure of negative electrode active material]
After observing the structure of the negative electrode active material (silicon-containing alloy) produced in each of Examples 1 to 5 and Comparative Examples 1 to 2 using a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM). It was confirmed by performing element intensity mapping by EDX (energy dispersive X-ray spectroscopy) for the same field of view as the observed image. As a result, for Examples 1 to 5 and Comparative Example 1, amorphous or low crystalline silicon formed by solid solution of tin in the crystal structure of silicon was formed in the matrix phase of the silicide phase containing TiSi _2. It was confirmed to have a structure in which the phase as the main component was dispersed. On the other hand, in Comparative Example 2, a silicide phase containing TiSi ₂ was dispersed in a mother phase mainly composed of amorphous or low crystalline silicon in which tin was solid-solved in the crystal structure of silicon. It was confirmed to have the following structure.

Moreover, the crystal structure of the negative electrode active material (silicon-containing alloy) produced in each of Examples 1 to 5 and Comparative Examples 1 and 2 was analyzed by an X-ray diffraction measurement method. The apparatus and conditions used for the X-ray diffraction measurement method are as follows.

Device name: X-ray diffractometer (SmartLab9kW) manufactured by Rigaku Corporation
Voltage/current: 45kV/200mA
X-ray wavelength: CuKα1.

The X-ray diffraction spectra obtained for the negative electrode active materials (silicon-containing alloys) of Examples 1 to 5 and Comparative Examples 1 and 2 are shown in FIGS. According to the X-ray diffraction spectra shown in FIGS. 4 to 10, the diffraction peaks of the (311) plane of TiSi ₂ having the C54 structure (in FIGS. 4 to 10) were obtained in each of Examples 1 to 5 and Comparative Examples 1 and ₂ . (Peak indicated by “a”), diffraction peak of (131) plane of TiSi ₂ having a C49 structure (peak indicated by “b” in FIGS. 4 to 10), and diffraction peak of (111) plane of Si (FIG. 4). 4-10, the peak shown by "c" was observed.

From the X-ray diffraction spectra obtained for the negative electrode active materials (silicon-containing alloys) of Examples 1 to 5 and Comparative Examples 1 and ₂ , TiSi ₂ (311) having a C54 structure in the range of 2θ=38 to 40° was obtained. ) Plane diffraction peak intensity X, diffraction peak intensity Y of the (131) plane of TiSi ₂ having a C49 structure in the range of 2θ=40 to 41°, and Si (111) plane in the range of 2θ=28 to 30°. The respective values of the diffraction peak intensities Z of were calculated, and the values of these ratios (Y/X, Y/Z) were calculated. The results are shown in Table 1 below. It was also confirmed by this X-ray diffraction measurement that all the transition metal elements (Ti) contained in the silicon-containing alloy were present as a silicide (TiSi ₂ ) phase.

[Evaluation of cycle durability]
The cycle durability of each lithium ion secondary battery (coin cell) produced in each of Examples 1 to 5 and Comparative Examples 1 to 2 was evaluated according to the following charge and discharge test conditions.

(Charge/discharge test conditions)
1) Charge/discharge tester: HJ0501SM8A (manufactured by Hokuto Denko Co., Ltd.)
2) Charge/discharge conditions [charging process] 0.1 mA, 10 mV → 2 V (constant current/constant voltage mode)
[Discharging process] 0.3 C, 2 V→10 mV (constant current mode)
3) Constant temperature bath: PFU-3K (manufactured by ESPEC CORPORATION)
4) Evaluation temperature: 300K (27°C).

The evaluation cell was set to a constant current/constant voltage mode in the charging process (referring to the process of inserting Li into the evaluation electrode) in a constant temperature bath set to the above evaluation temperature using a charge/discharge tester. , 0.1 mV, and charged from 10 mV to 2V. After that, in the discharging process (the process of desorbing Li from the evaluation electrode), a constant current mode was set and discharging was performed from 2 V to 10 mV at 0.3C. With the above charge/discharge cycle as one cycle, a charge/discharge test was performed from the initial cycle (1 cycle) to 50 cycles under the same charge/discharge conditions. Then, the ratio of the discharge capacity at the 50th cycle to the discharge capacity at the first cycle (discharge capacity maintenance rate [%]) was obtained. The results are shown in Table 1 below.

From the results shown in Table 1 above, the lithium ion secondary battery using the negative electrode active material according to the present invention has a high discharge capacity retention rate after 50 cycles and is excellent in cycle durability. I understand.

Comparing Examples 1 to 3 in which the alloy composition of the silicon-containing alloy is Si ₆₁ Sn ₉ Ti ₃₀ , as the thickness of the alloy on the ribbon decreases (that is, as the cooling rate of the alloy increases), Y/ It was shown that the values of X and Y/Z were increased, and the discharge point maintenance rate was further improved. Further, a comparison between Example 4 and Example 5 in which the alloy composition is Si ₆₆ Sn ₄ Ti ₃₀ showed the same tendency as this.

From the comparison between Example 1 and Example 4 in which the cooling conditions of the alloy in the rapid solidification method are the same, and the comparison between Example 3 and Example 5, the alloy composition of the silicon-containing alloy has the chemical formula (I): It was shown that in Si _x Sn _y Ti _z A _a , the ranges of 63≦x≦66, 4≦y≦7, and 28≦z≦30 are particularly preferable.

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

Claims (5)

The following chemical formula (I):

(In the above chemical formula (I),
A is an unavoidable impurity,
x, y, z, and a represent mass% values, where 60≦x≦73 , 2≦y≦15 , 25≦z≦35 , and 0≦a<0.5, and x+y+z+a =100. ) Consisting of a silicon-containing alloy having a composition represented by
In the X-ray diffraction measurement using CuKα1 ray of the silicon-containing alloy, 2θ=40 to 41° with respect to the diffraction peak intensity X of the (311) plane of TiSi ₂ having a C54 structure in the range of 2θ=38 to 40°. The ratio value (Y/X) of the diffraction peak intensities Y of the (131) plane of TiSi ₂ having the C49 structure in the range is 0.5 or more,
A negative electrode activity for an electric device in which a value (Y/Z) of a ratio of the diffraction peak intensity Y to a diffraction peak intensity Z of Si (111) plane in a range of 2θ=28 to 30° is 0.6 or more. material. The negative electrode active material for an electric device according to claim 1, wherein the Y/X is 1.7 or more. In the silicon-containing alloy, a phase having amorphous or low crystalline silicon as a main component in which tin is solid-dissolved in a crystal structure of silicon is dispersed in a matrix of a silicide phase containing TiSi _2. The negative electrode active material for an electric device according to claim 1 or 2, which has the following structure. A negative electrode for an electric device, comprising the negative electrode active material for an electric device according to claim 1. An electric device comprising the negative electrode for an electric device according to claim 4.