JP6705302B2 - 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 deal 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 motor drives 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-use lithium-ion secondary battery used in a mobile phone, a notebook computer 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, since the carbon/graphite negative electrode material is charged and discharged by occluding/releasing lithium ions into the graphite crystal, the theoretical capacity of 372 mAh/g or more obtained from LiC ₆ which is the maximum lithium-introducing compound. There is a drawback that is not obtained. For this reason, it is difficult to obtain a capacity and energy density that satisfy the practical use 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 has an improved energy density as compared with the conventional carbon/graphite-based negative electrode material, and is therefore expected as a negative electrode material for vehicle applications. For example, a Si material absorbs and desorbs _3.75 mol of lithium ions per mol as shown in the following reaction formula (A) during charge and discharge, and has a 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 for the negative electrode has a large expansion and contraction at 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. (About 4 times), there is a problem that the cycle life of the electrode is reduced. Further, in the case of the Si negative electrode active material, there is a trade-off relationship 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 which aims 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 Si-containing alloy obtained by mixing silicon powder and titanium powder by a mechanical alloying method, and wet-milling the mixture. The first phase mainly contains 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.

Patent Document 2 discloses a Si alloy for a negative electrode active material, which contains Si, Al, Ti and other additive elements and has excellent amorphousness. Specifically, using Ti as an amorphization promoting element, a ribbon having a predetermined composition is produced by a single roll type liquid quenching device, or a powder having a predetermined composition is produced by a gas atomizing method.

International Publication No. 2006/129415 Pamphlet Japanese Patent No. 5362502

According to the study by the present inventors, the electric devices such as the lithium ion secondary battery using the Si alloy for the negative electrode material described in Patent Document 1 and Patent Document 2 described above can exhibit good cycle durability. However, it has been found that the cycle durability may not be sufficient in some cases.

Therefore, an object of the present invention is to provide means for improving the cycle durability of electric devices such as lithium ion secondary batteries.

The present inventors have conducted earnest research to solve the above problems. As a result, it has a ternary alloy composition represented by Si-Al-M (M is one or more transition metal elements), and the composition ratio of Si-Al-M falls within a specific composition range. The inventors have found that the above problems can be solved by using the contained Si-containing alloy as a negative electrode active material for electric devices, and have completed the present invention.

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

(In the above chemical formula (I),
M is one or more transition metal elements,
A is an unavoidable impurity,
x, y, z and a represent mass% values, where y is 0.3≦y≦5.0, z is 27≦z≦35, and x and a are , The rest. )
It has a composition represented by.

In the Si-containing alloy constituting the negative electrode active material according to the present invention, the Si-Al-M (hereinafter, Ti will be described as an example) alloy has a predetermined composition, so that the microstructure can be refined. That is, by adding a predetermined amount of Al to the alloy, the phase containing TiSi ₂ (silicide) as a main component can be miniaturized (the mode radius of the phase can be reduced). Also, the eutectic (TiSi ₂ and Si) ratio in the microstructure can be increased. Further, the composition of the Si-containing alloy of the present invention can increase the ability to form amorphous (amorphous or low crystalline Si). Therefore, cycle durability can be improved by suppressing Si expansion during charge and discharge.

FIG. 1 is a schematic cross-sectional view schematically showing 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 drawing showing a cross-sectional SEM (scanning electron microscope) image of the quenched ribbon alloy of Example 1 (Si _67.6 Al _1.2 Ti _31.2 ). FIG. 4A shows that a sample was prepared from negative electrode active material (Si-containing alloy) particles of Example 1 (Si _67.6 Al _1.2 Ti _31.2 ) by the FIB method, and BF-STEM of the sample ( It is an observation image (low magnification) by a bright field-scanning transmission electron microscope image. FIG. 4B is an observation image (low magnification) by HAADF-STEM (high angle scattering dark field-scanning transmission electron microscope image) of the active material particles in the same field of view as FIG. FIG. 5 is a drawing (low magnification) showing quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy). FIG. 5A is the same HAADF-STEM image as that of FIG. 4B. FIG. 5B is a drawing showing Al mapping data measured in the same field of view as HAADF-STEM (FIG. 5A). FIG. 5C is a drawing showing mapping data of Si measured in the same field of view as HAADF-STEM (FIG. 5A). FIG. 5D is a drawing showing mapping data of Ti measured in the same field of view as HAADF-STEM (FIG. 5A). FIG. 5E is a drawing in which the mapping data of FIGS. 5B to 5D are superimposed. FIG. 6A is a BF-STEM image (medium magnification) obtained by enlarging the portion of the eutectic portion (enlarged in FIG. 4) of FIG. 3 from FIG. 4. FIG. 6B is a HAADF-STEM image (medium magnification) in the same field of view as FIG. 6A. FIG. 7A is a BF-STEM image (high magnification) in which the portion of the eutectic portion (enlarged in FIG. 4) of FIG. 3 is enlarged compared to FIG. 6. FIG. 7B is a HAADF-STEM image (high magnification) in the same field of view as FIG. 7A. FIG. 8 is a drawing (high magnification) showing quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy). FIG. 8A is the same HAADF-STEM image as that of FIG. 7B. FIG. 8B is a drawing showing mapping data of Al measured in the same field of view as HAADF-STEM (FIG. 8A). FIG. 8C is a drawing showing mapping data of Si measured in the same field of view as HAADF-STEM (FIG. 8A). FIG. 8D is a drawing showing mapping data of Ti measured in the same field of view as HAADF-STEM (FIG. 8A). FIG. 8E is a drawing in which the mapping data of FIGS. 8B to 8D are superimposed. FIG. 9A is a HAADF-STEM image in which the eutectic structure portion of the Si-containing alloy of Example 1 is enlarged. FIG. 9B is a graph obtained by elemental analysis of the portion surrounded by the thick line (7 in the image) in FIG. 9A. FIG. 10A is a HAADF-STEM image in which the eutectic structure portion of the Si-containing alloy of Example 1 is enlarged, which is the same as FIG. 9A. FIG. 10B is a drawing in which elemental analysis is performed on a portion (8 in the image) surrounded by a thick line in FIG. FIG. 11A is a drawing showing a BF-STEM Image (high-angle scattering dark field-scanning transmission electron microscope image) in which the eutectic structure of the Si-containing alloy of Example 1 is enlarged. FIG. 11B is a diffraction pattern obtained by subjecting the FFT 3 region of FIG. 11A to a fast Fourier transform process by electron diffraction measurement. FIG. 11C is a diffraction pattern obtained by subjecting the FFT 4 region of FIG. 11A to a fast Fourier transform process by electron diffraction measurement. FIG. 12( a) is a logarithmic representation of the frequency distribution of the radii of the independent first phase and the first and second phases in the eutectic structure obtained by the precipitation simulation for the alloy composition of Example 1. Is a graph showing the most frequent radius. FIG. 12B is a graph in which the vertical axis (frequency distribution) of the graph in FIG. 12A is linearly displayed and enlarged, and the radius of the independent first phase and the radius of the second phase in the eutectic structure. It is a graph which shows distribution. FIG. 13A is a diagram showing changes over time in volume fractions of TiSi ₂ and Si obtained by performing a precipitation simulation on the alloy composition of Example 1. FIG. 13B is a TTT diagram for precipitation of Si having a liquid phase composition (Si _77.4 Al _2.0 Ti _20.6 ) at the start of eutectic in the alloy composition of Example 1. 14: is a figure which shows the result of the sill coagulation calculation of Example 1. FIG. FIG. 14A is a drawing showing the relationship between the temperature and the mole fraction of the solid phase. FIG. 14( b) is a diagram showing the transition of the liquid phase composition in the Shill solidification calculation on the Si—Al—Ti ternary composition diagram, and shows the liquid phase at the start of the eutectic in the alloy composition of Example 1. it is a drawing showing a composition of _{(Si 77.4 Al 2.0 Ti 20.6)} . FIG. 15 is a drawing showing a cross-sectional SEM (scanning electron microscope) image of a quenched ribbon alloy of Example 2 (Si _65.0 Al _2.5 Ti _32.5 ). FIG. 16(a) is a logarithmic representation of the frequency distributions of the radii of the independent first phase and the first and second phases in the eutectic structure obtained by the precipitation simulation for the alloy composition of Example 2. Is a graph showing the most frequent radius. FIG. 16B is a graph in which the vertical axis (frequency distribution) of the graph of FIG. 16A is linearly displayed and enlarged, and the radius of the independent first phase and the radius of the second phase in the eutectic structure. It is a graph which shows distribution. FIG. 17A is a diagram showing changes over time in volume fractions of TiSi ₂ and Si obtained by performing a precipitation simulation on the alloy composition of Example 2. FIG. 17B is a TTT diagram for precipitation of Si in the liquid phase composition (Si _76.3 Al _5.0 Ti _18.7 ) at the start of eutectic in the alloy composition of Example 2. FIG. 18(a) is a logarithmic representation of the frequency distribution of the radii of the independent first phase and the first and second phases in the eutectic structure obtained by precipitation simulation for the alloy composition of Example 3. Is a graph showing the most frequent radius. FIG. 18B is a graph in which the vertical axis (frequency distribution) of the graph in FIG. 18A is linearly displayed and enlarged, and the radius of the independent first phase and the radius of the second phase in the eutectic structure. It is a graph which shows distribution. FIG. 19A is a diagram showing changes over time in volume fractions of TiSi ₂ and Si obtained by performing a precipitation simulation on the alloy composition of Example 3. FIG. 19B is a TTT diagram for precipitation of Si having a liquid phase composition (Si _77.8 Al _2.1 Ti _20.1 ) at the start of eutectic in the alloy composition of Example 3. FIG. 20( a) is a logarithmic frequency distribution of the radii of the independent first phase and the first and second phases in the eutectic structure obtained by performing a precipitation simulation on the alloy composition of Example 4. It is a graph which is displayed and which shows a mode radius. 20(b) is a graph in which the vertical axis (frequency distribution) of the graph of FIG. 20(a) is linearly displayed and enlarged, and the radius of the independent first phase and the radius of the second phase in the eutectic structure are shown. It is a graph which shows distribution. FIG. 21A is a diagram showing changes over time in the volume fractions of TiSi ₂ and Si obtained by performing a precipitation simulation on the alloy composition of Example 4. FIG. 21B is a TTT diagram for precipitation of Si in the liquid phase composition (Si _76.9 Al _3.2 Ti _19.9 ) at the start of eutectic in the alloy composition of Example 4. 22(a) is a logarithmic frequency distribution of the radii of the independent first phase and the first and second phases in the eutectic structure obtained by performing a precipitation simulation on the alloy composition of Example 5. FIG. It is a graph which is displayed and which shows a mode radius. FIG. 22B is a graph in which the vertical axis (frequency distribution) of the graph of FIG. 22A is linearly displayed and enlarged, and the radius of the independent first phase and the radius of the second phase in the eutectic structure. It is a graph which shows distribution. FIG. 23A is a diagram showing changes over time in volume fractions of TiSi ₂ and Si obtained by performing a precipitation simulation on the alloy composition of Example 5. FIG. _23B is a TTT diagram for precipitation of Si having a liquid phase composition (Si _77.3 Al _2.7 Ti _20.0 ) at the start of eutectic in the alloy composition of Example 5. FIG. 24( a) is a logarithmic frequency distribution of the radii of the independent first phase and the first and second phases in the eutectic structure obtained by performing the precipitation simulation for the alloy composition of Comparative Example 1. It is a graph which is displayed and which shows a mode radius. FIG. 24B is a graph in which the vertical axis (frequency distribution) of the graph of FIG. 24A is linearly displayed and enlarged, and the radius of the independent first phase and the radius of the second phase in the eutectic structure. It is a graph which shows distribution. FIG. 25( a) is a diagram showing changes over time in volume fractions of TiSi ₂ and Si obtained by performing a precipitation simulation on the alloy composition of Comparative Example 1. FIG. 25( b) is a TTT diagram for precipitation of Si having a liquid phase composition (Si _71.1 Sn _7.8 Ti _21.1 ) at the start of eutectic in the alloy composition of Comparative Example 1. FIG. 26( a) is a logarithmic frequency distribution of the radii of the first phase and the second phase in the independent first phase and the eutectic structure obtained by performing the precipitation simulation for the alloy composition of Comparative Example 2. It is a graph which is displayed and which shows a mode radius. FIG. 26B is a graph in which the vertical axis (frequency distribution) of the graph of FIG. 26A is linearly displayed and enlarged, and the radius of the independent first phase and the radius of the second phase in the eutectic structure. It is a graph which shows distribution. FIG. 27A is a diagram showing changes over time in volume fractions of TiSi ₂ and Si obtained by performing a precipitation simulation on the alloy composition of Comparative Example 2. FIG. 27B is a TTT diagram for precipitation of Si having a liquid phase composition (Si _63.8 Sn _16.3 Ti _19.9 ) at the start of eutectic in the alloy composition of Comparative Example 2. FIG. 28 is a graph showing a temperature profile (temporal change in temperature) used in the precipitation simulation. FIG. 29 is a drawing showing a state of observing the temperature of a quenched ribbon alloy obtained by an apparatus used for the liquid rapid solidification method using an infrared thermograph. FIG. 30A is a graph in which the temperature of the quenched ribbon alloy is plotted at positions (distances) at 2.25 mm intervals from the nozzle in Example 1. FIG. 30B is a graph showing the relationship between the cooling time (elapsed time) and the measured temperature calculated from the peripheral speed of the roll based on FIG. 30A. FIG. 30C is a graph showing the cooling rate (quenching rate) at the position (distance) of 2.25 mm from the nozzle, which is calculated from the temperature difference between the temperature measuring points/the moving time between the temperature measuring points. Is. FIG. 31 is a Si-Ti binary system phase diagram. FIG. 32 is a Si-Al binary system phase diagram. FIG. 33 is a Ti-Al binary system phase diagram. 34: is a figure which shows the result of the sill coagulation calculation of Example 2. FIG. FIG. 34( a) is a drawing showing the relationship between the temperature and the mole fraction of the solid phase. FIG. 34( b) is a diagram showing the transition of the liquid phase composition in the Shill solidification calculation on the Si—Al—Ti ternary composition diagram, and shows the liquid phase at the start of the eutectic in the alloy composition of Example 2. it is a drawing showing a composition of _{(Si 76.3 Al 5.0 Ti 18.7)} . FIG. 35 is a drawing showing the result of Shill solidification calculation of the alloy composition of Patent Document 2. FIG. 35(a) is a drawing showing the relationship between the temperature and the mole fraction of the solid phase. FIG. 35( b) is a diagram showing the transition of the liquid phase composition in the Sill solidification calculation on the Si—Al—Ti ternary composition diagram, and Al is the most in the alloy composition range disclosed in Patent Document 2. illustrates a liquid phase composition at the eutectic start in less Ti is large alloy composition _{(Si 57.3 Al 12.7 Ti 30.0)} (Si 62.1 Al 31.5 Ti 6.4). FIG. 36 is a schematic diagram of the TTT diagram.

Embodiments of a negative electrode active material for an electric device of the present invention, a negative electrode for an electric device using the same, and an electric device will be described below 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. Also, 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 vehicle drive power source or the like. In addition to this, it is sufficiently applicable to a lithium-ion secondary battery for mobile devices such as mobile phones.

That is, the lithium-ion secondary battery to be the subject of the present embodiment may be one that uses the negative electrode active material for the lithium-ion secondary battery of the present embodiment described below, and 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 type (flat type) 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.

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 that uses a solution electrolyte such as a non-aqueous electrolyte solution for the electrolyte layer, a polymer battery that uses a polymer electrolyte for the electrolyte layer, etc. It can be applied to any type of conventionally known electrolyte layer. The polymer battery is further divided 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). Be done.

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 (laminated) lithium-ion secondary battery (hereinafter, also simply referred to as “laminated 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 laminated battery 10 according to 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 film 29 as an exterior material. .. 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 positive electrode active material layer 15 and the negative electrode active material layer 13 adjacent to the positive electrode active material layer 15 face each other with the electrolyte layer 17 interposed therebetween, and the negative electrode, the electrolyte layer, and the positive electrode are laminated in this order. ..

As a result, 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 in FIG. 1, the outermost negative electrode current collectors are positioned on both outermost layers of the power generation element 21, and one surface of the outermost 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 film 29. It has a structure led out to the outside of the laminate film 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 may further contain other additives as needed.

[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 a lithium atomic layer and a transition metal (Mn, Ni and Co are arranged in order) atomic layers are alternately stacked via an oxygen atomic layer. One Li atom is contained, and the amount of Li that can be taken out is twice as large as that of 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 and the like, preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr, more preferably Ti, Zr, P, Al and Mg, Cr, and more preferably Ti, Zr, Al, Mg, and Cr from the viewpoint of improving cycle characteristics.

Since the NMC composite 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 purity of materials and improving electron conductivity. Ti and the like partially replace the transition metal in the crystal lattice. From the viewpoint of cycle characteristics, it is preferable that a part of the transition element be replaced by 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 and 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 capacity per unit weight is large, and the energy density can be improved, so that a compact and high-capacity battery can be manufactured, which is also preferable from the viewpoint of cruising distance. Note that LiNi _0.8 Co _0.1 Al _0.1 O ₂ is more advantageous in that it has a larger capacity, but it has poor 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 the “average particle diameter” refers to the number of particles observed in several to several tens of visual fields by using an 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 size and average particle size of the other constituents can be defined in the same manner.

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

(Binder)
The binder is added for the purpose of binding the active materials to each other 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 resins 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 are excellent in heat resistance, have a very wide potential window, are stable in both positive electrode potential and 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 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% by 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 represented by Si-Al-M (M is one or two or more transition metal elements). Specifically, the Si-containing alloy that constitutes 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),
M is one or more transition metal elements,
A is an unavoidable impurity,
x, y, z and a represent mass% values, where y is 0.3≦y≦5.0, z is 27≦z≦35, and x and a are , The rest.

In the Si-based negative electrode active material, when Si and Li alloy with each other 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, when the negative electrode active material has the composition represented by the chemical formula (I), 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 an active material is maintained, and the cycle life can be improved.

These effects are that Al atoms attract Si atoms in the liquid phase state, but try to separate in the solid phase state, and Al atoms and Ti atoms tend to bond to each other, though not so much as Si and Ti. It derives from that. The present inventors have found that the inclusion of a small amount of Al as compared with Ti causes the above characteristics to be exhibited.

In the composition represented by the above chemical formula (I), when y is less than 0.3, the refinement of the independent silicide phase (primary crystal silicide phase; first phase) is insufficient, and in addition, amorphous The effect of increasing the forming ability (reducing the critical cooling rate of Si crystal crystallization) is insufficient and the durability cannot be sufficiently improved. If y is more than 5.0, the proportion of eutectic in the microstructure becomes too small (proportion of primary crystal silicide becomes too large), and the refinement of the structure of the alloy as a whole becomes insufficient, resulting in poor durability. It cannot be improved enough. Further, when y is less than 27, the proportion of silicide in the structure becomes too small, the expansion and contraction of Si due to charge and discharge cannot be sufficiently suppressed, and the durability can be sufficiently improved. Can not. When z is more than 35, the amount of silicide becomes too large, and as a result, the amount of Si capable of reacting with Li becomes too small, and the characteristic of high capacity, which is the most attractive feature of the Si-based alloy, cannot be sufficiently exhibited.

In the composition represented by the above chemical formula (I), y is preferably 3.0 or less, more preferably 2.0 or less, still more preferably 1.8 or less, still more preferably 1. It is 5 or less. Further, y is preferably 0.7 or more, more preferably 1.0 or more. Within such a range, the durability can be sufficiently improved.

In the composition represented by the above chemical formula (I), z is preferably 34 or less, more preferably 33 or less, and further preferably 32 or less. Further, z is preferably 28 or more, more preferably 29 or more, and further preferably 30 or more. Within such a range, durability can be sufficiently improved and high capacity can be obtained.

In the composition represented by the chemical formula (I), the range of x is not particularly limited as long as y and z are in the above ranges. x is preferably 60≦x≦72, more preferably 64≦x≦70, and even more preferably from the viewpoint of maintaining durability against charge/discharge (insertion/desorption of Li ions) and balancing the initial capacity. Is 65≦x≦68.

In the composition represented by the chemical formula (I), x+y+z is 100 at the maximum.

In the present specification, the “unavoidable impurities” mean those present in the raw material of the Si-containing alloy and inevitably mixed in the manufacturing process. The unavoidable impurities are originally unnecessary, but are trace amounts and do not affect the characteristics of the Si alloy, and are therefore allowed impurities. In the composition represented by the above chemical formula (I), a is preferably less than 0.5, more preferably less than 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

In a preferred embodiment of the present invention, the ratio of y to z (y/z) is 0.10 (1/10) or less from the viewpoint that expansion and contraction of Si due to charge and discharge can be suppressed. It is more preferably 0.08 or less, still more preferably 0.07 or less, even more preferably 0.06 or less, and particularly preferably 0.05 or less. The lower limit of the ratio of y to z (y/z) is not particularly limited, but is, for example, 0.01 or more, preferably 0.02 or more, and more preferably 0.03 or more.

In the composition represented by the above chemical formula (I), the type of M (transition metal) is an element that forms a silicide (silicide) with Si (also simply referred to as “silicide forming element” in the present specification). ), there is no particular limitation. The silicide forming element is preferably at least one selected from the group consisting of Ti, Zr, Ni, Cu, Mo, V, Nb, Sc, Y, Co, Cr and Fe, and more preferably selected from Ti and Zr. At least one of them is used, and Ti is particularly preferable. These elements have higher electron conductivity than silicides of other elements when forming silicides and have high strength. Among them, by selecting Ti as the transition metal, it is possible to suppress the phase transition of amorphous-crystal during Li alloying and improve the cycle life. Further, this makes the capacity higher than that of the conventional negative electrode active material (for example, carbon-based negative electrode active material). In particular, by selecting Ti as an additive element to the negative electrode active material (Si-containing alloy) and further adding Al as a second additive element, it is possible to further suppress the amorphous-crystal phase transition during Li alloying. The cycle life can be improved. Therefore, in a preferred embodiment of the present invention, M is titanium (Ti) in the composition represented by the chemical formula (I).

Next, the particle diameter of the Si-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. Is. The average particle diameter D90 is preferably 5 to 30 μm, more preferably 10 to 25 μm.

(Microstructure of Si-containing alloy)
The microstructure of the Si-containing alloy that constitutes the negative electrode active material in the present embodiment has (1) a first phase (silicide phase) containing a transition metal silicide (silicide) as a main component, and (2) a single phase. Part has Al and has a second phase (Si phase, preferably amorphous Si phase (a-Si phase)) containing amorphous or low crystalline Si as a main component, and further (3) It is preferable that a part has a plurality of independent first phases, and (4) a part has a eutectic structure of the first phase and the second phase.

In the Si-containing alloy having the above microstructure, in the microstructure, the second phase (Si phase) is eutectic with the first phase (silicide phase), and a plurality of independent first phases (silicide phase) ) Is configured to enter the gap. In addition, the first phase (silicide phase), for example, TiSi ₂ phase, is superior in hardness and electron conductivity to the second phase (Si phase), for example, a-Si phase. Therefore, the expansion of the a-Si phase in the eutectic structure during the charging/discharging process is suppressed by the eutecticized TiSi ₂ phase and further suppressed by a plurality of independent TiSi ₂ phases. You can

Since the first phase (silicide phase) is mainly composed of a transition metal silicide (silicide), M is one or more kinds of transition metal elements selected from the above silicide forming elements. That is, when M is one transition metal element, it is a silicide forming element that constitutes the first phase (silicide phase). When M is a transition metal element of 2 or more, at least one kind is a silicide-forming element forming the first phase (silicide phase). The remaining transition metal element may be a transition metal element contained in the second phase (a-Si phase) or may be a silicide forming element forming the first phase (silicide phase). Alternatively, it may be a transition metal element that constitutes a phase (transition metal phase) in which a transition metal other than the first phase and the second phase (a-Si phase) is crystallized.

Hereinafter, in the present embodiment, the Si-containing alloy (negative electrode active material) having the above preferable microstructure structure will be described.

(1) First phase (silicide phase) containing a transition metal silicide as a main component
In a Si-containing alloy having a microstructure structure, the first phase (silicide phase) is mainly composed of a transition metal silicide (silicide). This first phase (silicide phase) is superior in hardness and electron conductivity to the second phase (a-Si phase). Therefore, the silicide phase (first phase) plays a role of maintaining the shape of the Si active material in the a-Si phase (second phase) with respect to the stress during expansion, and at the same time, the a-Si phase. The low electronic conductivity of (particularly Si active material) can be improved. Furthermore, since this silicide phase (first phase) contains a silicide of a transition metal (for example, TiSi ₂ ), it has an excellent affinity with the a-Si phase (second phase), and especially the volume during charging. It is possible to suppress cracking at the (crystal) interface during expansion.

Further, as described above, in the composition represented by the chemical formula (I), M is preferably titanium (Ti). In particular, by selecting Ti as the additive element to the negative electrode active material (Si-containing alloy) and further adding Al as the second additive element, in the eutectic structure of the Si-containing alloy, the first phase and the second phase The phase can be made finer. As a result, it is possible to further suppress the amorphous-crystal phase transition during Li alloying and improve the cycle life (durability). Further, as a result, the negative electrode active material (Si-containing alloy) of the present invention has a higher capacity than conventional negative electrode active materials (for example, carbon-based negative electrode active materials). Therefore, it is preferable that the silicide phase (first phase) whose main component is a silicide of a transition metal in the microstructure (first phase) is titanium silicide (TiSi ₂ ).

In the silicide phase (first phase), the term "mainly composed of silicide" means 50 mass% or more, preferably 80 mass% or more, more preferably 90 mass% or more, particularly preferably 95 mass% of the silicide phase. % Or more, and most preferably 98% by mass or more is silicide. Ideally, silicide is 100% by mass. However, the alloy may contain unavoidable impurities that are present in the raw material or are unavoidably mixed in the manufacturing process. Therefore, it is practically difficult to obtain 100 mass% of the first phase.

(2) A second phase (amorphous Si phase (a-Si phase)) containing Al as a part and having amorphous or low crystalline Si as a main component
In the Si-containing alloy having a fine structure structure, the second phase (amorphous Si phase (a-Si phase)) partially contains Al (specifically, Al is a solid solution in Si, Alternatively, the main component may be Si which is encapsulated and dispersed in Si) or amorphous or low crystalline Si. The a-Si phase (second phase) is a phase containing amorphous or low crystalline Si as a main component.

The a-Si phase (second phase; phase containing a-Si as a main component) is a phase involved in occlusion/release of lithium ions during operation of the electric device (lithium ion secondary battery) of the present embodiment. It is a phase that can electrochemically react with Li. Since the a-Si phase (second phase) contains Si as a main component, it is possible to store and release a large amount of Li per weight and per volume. However, since Si has poor electron conductivity, the a-Si phase (second phase) may contain a trace amount of additional elements such as phosphorus and boron, a transition metal, or the like. The a-Si phase (second phase; phase containing Si as a main component) is preferably more amorphous than the silicide phase (first phase). With such a configuration, the negative electrode active material (Si-containing alloy) can have a higher capacity. Whether the a-Si phase (second phase) is more amorphous than the silicide phase (first phase) can be confirmed by electron diffraction analysis. Specifically, according to electron diffraction analysis, a net pattern (lattice-like spots) of a two-dimensional point array is obtained for the single crystal phase, and a Debye-Scherrer ring (diffraction ring) is obtained for the polycrystalline phase. A halo pattern is obtained for the amorphous phase. By utilizing this, the above confirmation becomes possible.

As described above, in the composition represented by the chemical formula (I), M is preferably titanium (Ti). In particular, by selecting Ti as an additive element to the negative electrode active material (Si-containing alloy) and further adding Al as a second additive element, it is possible to further suppress the amorphous-crystal phase transition during Li alloying. The cycle life can be improved. Further, as a result, the negative electrode active material (Si-containing alloy) of the present invention has a higher capacity than conventional negative electrode active materials (for example, carbon-based negative electrode active materials). Therefore, it is preferable that the Si phase (second phase) having amorphous or low crystallinity as a main component in the microstructure has amorphous Si as a main component.

From the above, the transition metal silicide of the first phase in the microstructure is titanium silicide (TiSi ₂ ), and the Si phase (second phase) is amorphous. It is preferable that the main component is Si. With such a configuration, the cycle durability can be further improved while showing the high capacity of the electric device.

In the a-Si phase (second phase), the phrase "mainly containing amorphous or low crystalline Si" containing Al means 50% by mass or more, preferably 80% by mass or more of the Si phase. More preferably, 90 mass% or more, particularly preferably 95 mass% or more, most preferably 98 mass% or more is the above Si. However, the alloy may contain unavoidable impurities that are present in the raw material or are unavoidably mixed in the manufacturing process. Therefore, it is practically difficult to obtain the 100% by mass second phase.

In the above Si phase (second phase), the reason why “partly contains Al” is that, for example, comparing FIGS. 8B, 8C, and 8E, most of the Si phase contains Al. It can be seen that Al is a solid solution in Si, or is encapsulated and dispersed in Si, although it is a part that hardly contains it (Si part functions as an active material). Further, it can be confirmed that the remaining part of Al in the eutectic structure is dispersed in the silicide phase in the eutectic structure.

(3) Part of a plurality of independent first phases The Si-containing alloy having the above preferred structure has a structure in which a part thereof is a plurality of independent first phases in the microstructure. Since the Si-containing alloy has the above structure, the expansion of the second phase (a-Si phase) in the eutectic structure in the charge/discharge process can be suppressed and suppressed by the plurality of independent first phases. .. In addition, the low electronic conductivity of the a-Si phase (particularly Si active material) can be improved.

In the microstructure, the upper limit of the mode radius of a part of the plurality of independent first phases is not particularly limited, but is, for example, 280 nm or less, preferably 260 nm or less, more preferably 255 nm or less, More preferably, it is 250 nm or less. The lower limit of the mode radius of the independent first phase in the eutectic structure is not particularly limited, but is preferably 160 nm or more, more preferably 170 nm or more, further preferably 180 nm or more, particularly preferably 190 nm or more. Within such a range, a plurality of independent first phases, some of which are independent, can be finely dispersed in the microstructure. Therefore, the expansion and contraction of Si due to charge and discharge can be effectively suppressed, and the durability can be improved.

In the microstructure, a part of the plurality of independent first phases has a radius distribution of preferably 80 to 1000 nm, more preferably 100 to 800 nm, still more preferably 110 to 500 nm, and particularly preferably 120 to 400 nm. It is preferably 150 to 360 nm. Within such a range, a plurality of independent first phases, some of which are independent, can be finely dispersed in the microstructure. Therefore, the expansion and contraction of Si due to charge and discharge can be effectively suppressed, and the durability can be improved.

(4) Structure in which a part has a eutectic structure of a first phase and a second phase The Si-containing alloy having the above-described preferable structure has a part in the microstructure of the first phase and the second phase. It has a eutectic structure with the phase. Since the first phase and the second phase are partly a eutectic structure in the fine structure, the expansion of the second phase (a-Si phase) in the eutectic structure during the charge/discharge process is suppressed. The eutecticized first phase can be suppressed and suppressed. That is, the expansion of the a-Si phase can be suppressed by the eutecticized first phase (TiSi ₂ phase) and the partially independent first phase (TiSi ₂ phase), that is, the suppression of the two-step stance. Thus, the expansion of the second phase can be suppressed. In addition, the low electronic conductivity of the a-Si phase (particularly Si active material) can be improved.

In the eutectic structure, the upper limit of the mode radius of the first phase is not particularly limited, but is preferably 60 nm or less, more preferably 54 nm or less. The lower limit of the mode radius of the second phase in the eutectic structure is not particularly limited, but is preferably 20 nm or more, more preferably 25 nm or more, and further preferably 30 nm or more. Within such a range, the above effects can be more effectively exhibited.

In the eutectic structure, the upper limit of the mode radius of the second phase is not particularly limited, but is preferably 90 nm or less, more preferably 85 nm or less, and further preferably 80 nm or less. The lower limit of the mode radius of the second phase in the eutectic structure is not particularly limited, but is preferably 40 nm or more, more preferably 50 nm or more, and further preferably 60 nm or more. Within such a range, the above effects can be more effectively exhibited.

In the eutectic structure, the radius distribution of the second phase is preferably 10 to 200 nm, more preferably 20 to 150 nm, and further preferably 25 to 120 nm. Within such a range, the above effects can be more effectively exhibited.

In the present embodiment, the ratio of the mode radius of the first phase to the mode radius of the second phase in the eutectic structure is preferably 1.00 or less, more preferably 0.95 or less. , And more preferably 0.90 or less. The lower limit of the ratio of the modal radius of the first phase to the modal radius of the second phase in the eutectic structure is not particularly limited, but is, for example, 0.40 or more, preferably 0.50 or more. And more preferably 0.60 or more, further preferably 0.70 or more, and particularly preferably 0.80 or more. That is, even if the ratio of the first phase (silicide phase) in the eutectic structure to the second phase (a-Si phase) in the eutectic structure that directly contributes to charging/discharging is not increased, charging is effectively performed. It is possible to suppress the expansion of the second phase (a-Si phase) in the eutectic structure during the discharge process.

The Si-containing alloy having the structures of (1) to (4) above is melted in a liquid quenching roll solidification method to melt a predetermined alloy raw material, and is rapidly cooled at a predetermined cooling rate to be alloyed to form a liquid phase. A plurality of independent first phases are crystallized as primary crystals, and the eutectic structure of the first phase and the second phase is crystallized in the liquid phase in the gap between the independent first phases.

A plurality of phases may exist in the silicide phase (first phase) in which a part of the above is independent and the silicide phase (first phase) in the eutectic structure. Two or more phases having different composition ratios of M and Si (for example, MSi ₂ and MSi) may be present. Moreover, two or more phases may be present by containing silicides with different transition metal elements. Here, the kind of transition metal contained in the silicide phase (first phase) is not particularly limited, but Ti, Zr, Ni, Cu, Mo, V, Nb, Sc, Y, Co, Cr and Fe are preferable. It is at least one selected from the group consisting of, more preferably Ti or Zr, and particularly preferably Ti. These elements have higher electron conductivity than silicides of other elements when forming silicides and have high strength. In particular, TiSi ₂ which is a silicide in the case where the transition metal element is Ti is preferable because it shows extremely excellent electron conductivity.

When the transition metal element M is Ti and there are two or more phases having different composition ratios in the silicide phase (for example, TiSi ₂ and TiSi), 50% by mass or more, preferably 80% by mass or more of the silicide phase, and further preferably Is 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass is the TiSi ₂ phase.

Further, when the transition metal element M is Ti, according to the chemical thermodynamics (CALPHAD method=calculation phase diagram method), Si-Ti has a very strong bonding property from the Si-Ti binary system phase diagram of FIG. Show. From the Si-Al binary system phase diagram of FIG. 32, Si-Al attracts in a liquid state, but repels in a solid phase. Further, from the Ti-Al binary system phase diagram of FIG. 33, it can be seen that Ti-Al exhibits binding properties. That is, in the Si-Al-Ti alloy of the present invention, by containing a small amount of Al as compared with Ti, when cooling from a liquid state by, for example, a rapid solidification method, Al remains in the liquid phase and Ti and Si Can be attracted and crystallization of TiSi ₂ can be suppressed. Therefore, the primary crystal TiSi ₂ can be made finer, and the independent primary crystal TiSi ₂ phase is finely dispersed in the structure, so that the expansion and contraction of Si due to charge and discharge can be effectively suppressed, and the durability can be improved. Can be improved.

The above binary system phase diagram uses a solid solution general-purpose database as a thermodynamic database using an integrated thermodynamic calculation system: Thermo-Calc Ver2015a manufactured by Sweden Thermo-Calc software AB (Japanese agency: ITOCHU Technosolutions Co., Ltd.). : SSOL5 (SGTE* Solution Database, ver. 5.0) can be used for the calculation.
*SGTE: Scientific Group Thermodata Europe.

The fact that the microstructure of the Si-containing alloy has the configuration (structure) of (1) to (4) above means that, for example, high-resolution STEM (scanning transmission electron microscope) observation, EDX (energy dispersive X-ray spectroscopy) The structure of the fine structure of the Si-containing alloy (particles) that is the negative electrode active material particles can be clarified by elemental analysis by means of, electron diffraction measurement, and EELS (electron energy loss spectroscopy) measurement. Examples of the analyzer (analysis method) are XPS (X-ray photoelectron spectroscopy), TEM-EDX (transmission electron microscope-energy dispersive X-ray spectroscopy), STEM-EDX/EELS (scanning transmission electron microscope-). Energy dispersive X-ray spectroscopy/electron energy loss spectroscopy analyzer), HAADF-STEM (high angle scattering dark field-scanning transmission electron microscope image), BF-STEM (bright field-scanning transmission electron microscope image), etc. are used. be able to. However, the present embodiment is not limited to these, and various observation devices (device conditions and measurement conditions) used for the microstructure of existing alloys may be used.

(Analysis of microstructure of Si-containing alloy)
Hereinafter, the fine structure of the negative electrode active material having the above-described fine structure will be described with reference to an example in which the Si-containing alloy (particles) produced in Example 1 is used as a sample. However, the microstructure structure of the alloy (particles) can be clarified in the same manner for the other Si-containing alloy (particles) that is the negative electrode active material obtained in this embodiment. In addition, Examples 2 to 5 and Comparative Examples 1 and 2 can also be analyzed by using the same method.

1. Analysis method 1-1. Sample preparation FIB (Focused Ion Beam) method: Micro sampling system (Hitachi, FB-2000A)
Use an Al grid.

1-2. STEMimage, EDX, EELS (electron energy loss spectroscopy) measuring device and conditions 1) Device: atomic resolution analysis electron microscope JEM-ARM200 manufactured by JEOL Ltd.
EDX (Energy dispersive X-ray Spectroscopy): JED-2300 (100 mm ² silicon drift (SDD) type, manufactured by JEOL Ltd.)
System: Analysis Station
EELS (Electron Energy Loss Spectroscopy): GATAN GIF Quantum
Image acquisition; Digital Micrograph
2) Measurement conditions Acceleration voltage: 200kV
Beam diameter: about 0.2 nmφ (diameter)
Energy resolution: about 0.5 eV FWHM.

1-3. Electron Diffraction Measuring Device and Conditions 1) Device; Field Emission Electron Microscope JEM2100F manufactured by JEOL Ltd.;
Image acquisition; Digital Micrograph
2) Measurement conditions Acceleration voltage: 200kV
Beam diameter: about 1.0 nmφ (diameter).

2. (Quantitative Mapping) Analysis by STEM-EDX (Scanning Transmission Electron Microscope-Energy Dispersive X-ray Spectroscopy) FIG. 3 is a graph of a quenched ribbon of Si _67.6 Al _1.2 Ti _31.2 of Example 1. It is drawing showing a cross-sectional SEM (scanning electron microscope) image. From the analysis results of FIG. 3 and FIGS. 4 to 8 described below, the Si-containing alloy of Example 1 has a partially independent first phase (TiSi ₂ phase) and a partially first phase and a second phase. It can be confirmed that the structure has a eutectic structure with the second phase.

4 to 8 analyze the structure of the eutectic portion shown in FIG.

FIG. 4 shows a sample prepared from the negative electrode active material (Si-containing alloy) particles of Example 1 by the FIB method, and BF-STEM (bright field-scanning transmission electron microscope image) and HAADF-STEM (high-angle scattering) of the sample. It is an observation image (low magnification) by a dark field-scanning transmission electron microscope image. The measurement target was the Si-containing alloy (negative electrode active material) particles produced in Example 1. The average particle diameter D50 of the Si-containing alloy (negative electrode active material) particles was 6 μm, and the average particle diameter D90 of the Si-containing alloy (negative electrode active material) particles was 19 μm. Then, the surface of the Si-containing alloy (negative electrode active material) particles was coated with 2% by mass of alumina, and the cross section of the coated particles was observed.

FIG. 5 is a drawing (low magnification) showing quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy). FIG. 5A is the same HAADF-STEM image as that of FIG. 4B. FIGS. 5B to 5D are drawings showing mapping data of Al, Si, and Ti measured in the same field of view as HAADF-STEM (FIG. 5A). FIG. 5E is a drawing in which the mapping data of FIGS. 5B to 5D are superimposed. In addition, since the mappings of FIGS. 5B to 5E can actually be colored (colored), for example, when Al is green, Si is blue, and Ti is red, silicide (TiSi ₂ ) is not generated. , And blue of Si and red of Ti are mixed to form a pink, which can be identified at a glance. However, since it is necessary to submit a black and white image in the application drawing, analysis information clarified by such coloring is included in FIG. 4(b) and FIG. 5(e). Those skilled in the art can easily obtain similar analysis information by image analysis similar to the present application from quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy) as in FIG. This is because it can be obtained. Incidentally, in FIGS. 5B to 5D, the presence of each of Al, Si and Ti is represented by gray shades or white, and the portions where these elements do not exist are represented by black. From this, it is possible to confirm the existence and distribution state of Si, Al and Ti which are the elements constituting the active material alloy Si _67.6 Al _1.2 Ti _31.2 (negative electrode active material of Example 1) to be measured.

In the above analysis, for the STEM image observation, a bright field (Bright-field: BF) STEM image formed by using an electron beam transmitted through the sample and a dark field formed by using an electron beam scattered from the sample There are two types of (Dark-field: DF) STEM image observation methods. In the BF-STEM image shown in FIG. 4A, the transmission image showing the internal structure of the sample is shown in the same manner as the normal TEM image, and in the (HAA)DF-STEM image shown in FIG. 4B, the composition of the sample is shown. The composition image that provides the reflected contrast can be observed. Particularly, in HAADF (high-angle scattering annular dark field), elastic scattering electron contrast due to atomic number (Z) is predominant, so this is an imaging method also called Z-contrast image. A substance with a large atomic number looks bright (FIG. 4(b), FIG. 5(a), FIG. 6(b), FIG. 7(b), FIG. 8(a), FIG. 9(a), FIG. 10(a)). reference). In HAADF-STEM (High Angle Scattering Annular Dark Field Scanning Transmission Microscopy), the image is applied by operating a sample with a narrowed electron beam, and high-angle scattered electrons among the transmitted electrons are detected by a circular detector. can get. The heavier element is darker in the STEM image and brighter in the HAADF-STEM image because the material having a large Z2ρ is scattered at a higher angle. It is also called a Z-contrast image because a contrast proportional to the atomic weight (Z) can be obtained. In the STEM-EDX quantitative mapping, the characteristic X-rays generated from each point are taken into an EDS (Energy-Dispersive-Spectroscopy) detector while scanning the sample with a narrow electron beam and information on the composition distribution of the sample is obtained. Can be obtained. In the transmission electron microscope (TEM) measurement, there is almost no diffusion of the electron beam as seen in the scanning electron microscope (SEM) measurement, and therefore the measurement can be performed with a spatial resolution of nanometer.

From the mapping data in which Al, Si, and Ti are overlapped with each other in FIG. 5E, the silicide phase (first phase) and the Si phase containing Al (second phase) are eutectic in the microstructure of the sample. It can be confirmed that it has a structure (a structure in which the first phase and the second phase are mixed, which are (solid solution) crystals or amorphous or low crystalline with different component ratios).

The eutectic structure can be confirmed by the following when colored. That is, by comparing with FIGS. 5B to 5D, the eutectic of the silicide phase (first phase) and the Si phase containing Al (second phase) is formed on the entire surface of FIG. 5E. It can be confirmed that there is.

FIG. 6 is a STEM image in which the portion of the eutectic portion (FIG. 4) in FIG. 3 is enlarged as compared with FIG. 4 (medium magnification). From the observation result of FIG. 8 below, in FIG. 6B, the relatively light gray portion corresponds to the silicide phase (first phase), and the relatively dark gray portion corresponds to the Si phase containing Al (second It is understood that it corresponds to the phase). Further, it can be confirmed that in the eutectic structure, the silicide phase (first phase) and the Si phase containing Al (second phase) are miniaturized and are adjacent to each other.

FIG. 7 is a STEM image in which the portion of the eutectic portion (FIG. 4) in FIG. 3 is enlarged as compared with FIG. 6 (high magnification).

Similar to FIG. 5, FIG. 8 is a drawing (high magnification) showing quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy). FIG. 8A is the same HAADF-STEM image as that of FIG. 7B. FIGS. 8B to 8D are drawings showing mapping data of Al, Si and Ti measured in the same field of view as HAADF-STEM (FIG. 8A). FIG. 5E is a drawing in which the mapping data of FIGS. 8B to 8D are superimposed. In addition, since the mappings of FIGS. 8B to 8E can actually be colored (colored), for example, if Al is green, Si is blue, and Ti is red, silicide (TiSi ₂ ) is not generated. , The blue color of Si and the red color of Ti are mixed to make a pink color, which can be identified at a glance, but it is necessary to submit a black and white image in the application drawing. It is included in FIGS. 8B and 8D. Those skilled in the art can easily obtain the same analysis information from the quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy) as in FIG. This is because it can be obtained.

Incidentally, in FIGS. 8B to 8D, portions where Al, Si and Ti are not present are shown in black, and portions where these elements are present are shown in gray or white. This confirms the presence and distribution state of Si, Sn, and Ti which are the elements constituting the Si-containing alloy (negative electrode active material) Si _67.6 Al _1.2 Ti _31.2 of Example 1 which is the measurement target. it can.

By comparing FIG. 8A and the mapping data of FIG. 8E in which Al, Si, and Ti are superimposed, the silicide phase (first phase) and the Si phase containing Al (second phase) are compared. ) And have a eutectic structure (a (solid solution) crystal or amorphous or low crystallinity with different composition ratios, a structure in which the first phase and the second phase are mixed). Can be confirmed.

Specifically, it can be seen from FIG. 8B that the relatively light gray or white portion in FIG. 8E is the Al phase. From FIG. 8C and FIG. 8D, it can be seen that the relatively darkest gray portion (for example, the central portion) of FIG. 8E is the place where Ti does not exist, that is, the Si phase. Further, it is understood from FIGS. 8C and 8D that the portions other than the portions corresponding to the Al phase and the Si phase are the silicide phases.

From the above, it can be seen that in the eutectic structure, the silicide phase (first phase) and the Si phase containing Al (second phase) have a eutectic structure.

The eutectic structure can be confirmed by the following when colored. That is, pink, blue, and green parts are present in FIG. From FIG. 8D, it can be seen that Ti does not exist or hardly exists in the blue portion of FIG. 8E. That is, it can be confirmed that the blue portion in FIG. 8E is the Si phase. On the other hand, the pink portion is a mixture of blue (a portion where Si exists) in FIG. 8C and red (a portion where Ti exists) in FIG. 8D. That is, it can be confirmed that the pink portion in FIG. 8E is the silicide phase (TiSi ₂ ). In addition, it can be confirmed that the green part (the part where Al exists) is included in the blue part of FIG. This indicates that a part of Al is solid-dissolved in Si. It can also be confirmed that Al other than that is dispersed in the Si phase and the TiSi ₂ phase.

3. Analysis by HAADF-STEM Image (High Angle Scattering Dark Field-Scanning Transmission Electron Microscope Image) and Elemental Analysis FIGS. 9 and 10 show the fineness of the silicide phase or amorphous Si phase in the eutectic structure of the Si-containing alloy of Example 1. It is a photograph and a graph which show the result of having analyzed the organization structure.

FIG. 9A is a HAADF-STEM image in which the eutectic structure portion of the Si-containing alloy of Example 1 is enlarged. FIG. 9B is a graph obtained by elemental analysis of a portion surrounded by a thick line in FIG. 9A (7 in the image; a portion thought to have a silicide phase).

FIG. 10A is a HAADF-STEM image in which the eutectic structure portion of the Si-containing alloy of Example 1 is enlarged, which is the same as FIG. 9A. FIG. 10B is a drawing in which an elemental analysis is performed on a portion surrounded by a thick line in FIG. 10A (8 in the image; a portion considered to have an a-Si phase).

From FIG. 9B, the peak of the Si element and the peak of the Ti element are observed and the peak of the Al element is almost observed in the portion 7 of FIG. 9A, which is the portion where the element distribution is to be observed. Not done. Further, from FIG. 9B, it was confirmed that Si and Ti exist in an atomic ratio of approximately 2:1. From this, it can be confirmed that the relatively light gray portion including the portion 7 is silicide (TiSi2 phase).

From FIG. 10B, the Si element peak is observed and the Al element and Ti element peaks are scarcely observed in the portion 8 of FIG. 10A, which is the portion where the element distribution is to be observed. That is, it can be confirmed that the portion 8 in FIG. 10A is the Si phase (second phase).

4. Analysis by Electron Diffraction Diagram FIG. 11A is a drawing showing a BF-STEM Image (high-angle scattering dark field-scanning transmission electron microscope image) in which the eutectic structure of the Si-containing alloy of Example 1 is enlarged. In FIG. 11A, the upper left enclosure (FFT3) shows the silicide phase in the eutectic structure, and the right enclosure (FFT4) shows the Si phase (a-Si phase) in the eutectic structure. FIG. 11B is a diffraction pattern obtained by subjecting the region of the silicide phase in the eutectic structure to fast Fourier transform by electron diffraction measurement. FIG. 11C is a diffraction pattern obtained by subjecting the Si phase (a-Si phase) region in the eutectic structure to fast Fourier transform by electron diffraction measurement.

In the diffraction pattern obtained by the fast Fourier transform processing by electron diffraction measurement, a net pattern (lattice-like spots) of a two-dimensional dot array is obtained for the single crystal phase, and a Debye-Scherrer ring (diffraction ring) is obtained for the polycrystalline phase. ) Is obtained, and a halo pattern is obtained for the amorphous phase. Furthermore, the crystal structure of the two-dimensional dot array net pattern (silicide phase) can be specified.

A net pattern (Laue pattern) of a two-dimensional point array is obtained from the diffraction pattern shown in FIG. Therefore, it can be confirmed that the silicide phase (TiSi ₂ phase) in the eutectic structure is a single crystal phase.

Also, from the diffraction pattern shown in FIG. 11C, a Debye-Scherrer ring (diffraction ring) and a halo pattern diffraction ring are obtained. Therefore, it can be confirmed that the Si phase (second phase) in the eutectic structure is a polycrystalline phase and is an amorphous phase having amorphous or low crystalline Si (a-Si).

From the above, it is confirmed that the microstructure of the Si-containing alloy of Example 1 has the eutectic structure of the silicide phase (first phase) and the Si phase (Alpha) partially containing Al (second phase). it can. From FIG. 6 to FIG. 8 as well, in the microstructure of the Si-containing alloy of Example 1, a silicide phase (first phase) whose main component is a silicide of a transition metal (first phase) and Al in part thereof are included. And an a-Si phase (second phase) containing amorphous or low crystalline Si as a main component, and further, a part of the plurality of independent first phases, and a part of the first phase. It can be confirmed that it has a eutectic structure of the first phase and the second phase.

(Analysis of precipitate size)
Precipitation calculation Precipitation growth prediction software: TC-PRISMA Ver2015a manufactured by Sweden Thermo-Calc software AB (Japanese agency: ITOCHU Techno Solutions Co., Ltd.), SSOL5 as a thermodynamic database, and MOB2 manufactured by the same company as a kinetic database ( Precipitation calculation was performed using TCS Alloy Mobility Database Ver.2.5) under the conditions of Examples 1 to 5 and Comparative Examples 1 and 2. The precipitation growth prediction software TC-PRISMA performs precipitation calculation based on the theory of Langer-Schwartz and Kampmann-Wagner [3][4].

The precipitation calculation is performed under the conditions of Examples 1-5 and Comparative Examples 1-2. The calculation conditions and temperature profile (FIG. 28) shown below are used.

[3]: Q. Chen, H.; J. Jou, G.; Sterner. TC-PRISMA User's Guide, http://www. thermocalc. com/, 2011
[4]: Q. Chen, J.; Jepsson, and J.M. Agren. , Acta Materialia, Vol. 56, pp, 1890-1896, 2008.

Calculation conditions Temperature profile: FIG. 28 (Examples 1-5, Comparative Examples 1-2)
Alloy composition (mass %): Si _67.6 Al _1.2 Ti _31.2 (Example 1)
Si _65.0 Al _2.5 Ti _32.5 (Example 2)
Si _66.6 Al _1.2 Ti _32.2 (Example 3)
Si _67.0 Al _1.8 Ti _31.2 (Example 4)
Si _67.3 Al _1.5 Ti _31.2 (Example 5)
Si _65.0 Sn _5.0 Ti _30.0 (Comparative Example 1)
Si _60.0 Sn _10.0 Ti _30.0 (Comparative Example 2)
Mother phase/precipitation phase: Liquid/TiSi ₂ , Si (crystallized in liquid phase)
Nucleation Model: Homogeneous Nucleation Nucleation Site: Bulk Interface Energy: Estimated value (calculated for each temperature)
Mother phase/precipitated phase volume: 1E-4 (1×10 ⁻⁴ )m ³ .

Here, the temperature profile used for the precipitation simulation of FIG. 28 was obtained by the following.

FIG. 29 is a drawing showing a state (thermal image) of observing the temperature of a quenched ribbon alloy obtained by an apparatus used for a liquid quench roll solidification method using an infrared thermograph. For the temperature measurement, a high-resolution infrared thermography CPA-SC7500 (light-receiving element: InSb) manufactured by FLIR Systems Inc. (handled by Chino Co., Ltd.) and a 50 mm lens for the same machine were used for measurement. Specifically, a master nozzle is injected from a quartz nozzle containing a master alloy melted at 1450° C. onto a Cu roll having a rotation speed of 4000 rpm (peripheral speed: 41.9 m/sec), and is continuously formed horizontally from the roll. This is an observation of the temperature of the ribbon-shaped alloy. The part that shines yellowish white is the heated quartz nozzle containing the mother alloy, and the molten alloy stored in this part is sprayed onto the surface of the quenching roll to bring the temperature of the alloy ribbon on the roll to a frame rate of 350 Hz. Then, the temperature was continuously measured with a thermal image of 320×256 pixels. Average of temperature during melt injection for ribbon-shaped alloy temperatures (observation positions are indicated by numerals 1 to 8) at positions (distances) at 2.25 mm intervals from the roll portion immediately below the nozzle (zero distance from the nozzle) Each value is measured.

FIG. 30( a) is a graph in which the temperature of the quenched ribbon alloy is plotted at positions (distances) every 2.25 mm from the nozzle. FIG. 30B is a graph showing the relationship between the cooling time (elapsed time) and the measured temperature calculated from the peripheral speed of the roll based on FIG. 30A. FIG. 30C is a graph showing the cooling rate (quenching rate) at the position (distance) of 2.25 mm from the nozzle, which is calculated from the temperature difference between the temperature measuring points/the moving time between the temperature measuring points. Is. In Example 1, since the cooling time from 1350° C. to 1100° C. was 5.37×10 ⁻⁵ seconds in FIG. 30B, the cooling temperature was 4.67×10 ⁶ ° C./second. Can be calculated.

The temperature profile used for the precipitation simulation in FIG. 28 can be calculated by linear approximation based on the graph of the relationship between the cooling time and the measured temperature in FIG. 30(b).

From the above precipitation calculation, the mode radius and the radius distribution of the precipitate can be obtained. Hereinafter, an example using the Si-containing alloy (negative electrode active material) produced in Example 1 will be described. In addition, also about Examples 2-5 and Comparative Examples 1-2, it analyzed by the same method (refer FIG. 16, 18, 20, 22, 24 and 26).

FIG. 12A shows the frequency distribution of the radii of the independent first phase and the first phase and the second phase in the eutectic structure obtained by the precipitation simulation in logarithmic form, and shows the mode radius. It is a graph. In FIG. 12A, the silicide phase (first phase) is shown by a bimodal graph. From the analysis of FIGS. 3 to 10 described above, it is found that the peak with the largest mode radius is the independent first phase and the peak with the smallest mode radius is the first phase in the eutectic structure.

The modal radius of the independent first phase is 250 nm. In the eutectic structure, the modal radius of the first phase is 53 nm and the modal radius of the second phase is 63 nm.

FIG. 12B is a graph in which the vertical axis (frequency distribution) of the graph in FIG. 12A is linearly displayed and enlarged, and the radius of the independent first phase and the radius of the second phase in the eutectic structure. It is a graph which shows distribution. The radius distribution shall be read at the location where the height is 5% of the peak height.

The radius distribution of the independent first phase is 190-340 nm. In the eutectic structure, the mode radius of the second phase is 30 to 100 nm.

3 is a drawing showing a cross-sectional SEM (scanning electron microscope) image of the quenched ribbon alloy of Si _67.6 Al _1.2 Ti _31.2 of Example 1. FIG.

Above 1. ~3. As described above, in FIG. 3, the relatively light gray portion is the independent first phase (silicide phase), and the relatively dark gray portion is the first phase and the second phase (a). -Si phase).

In FIG. 3, the intermediate circle (diameter 500 nm) of the mode diameter based on the mode radius (250 nm) of the independent first phase obtained by the above precipitation calculation was applied to some of the independent first phases. , Illustrated. As a result, it was confirmed that the intermediate circles of these most frequent diameters (diameter 500 nm) substantially matched the actual equivalent circle diameters (average value) of the intermediate size of the independent first phase.

Similarly, in FIG. 3, the maximum circle (diameter 680 nm) and the minimum circle (diameter 380 nm) based on the independent first phase radius distribution (190 to 340 nm) obtained by the above precipitation calculation are independent. Applied to some of the phases and illustrated. As a result, the maximum circle (diameter 600 nm) and the minimum circle (diameter 320 nm) substantially match the actual independent first phase large and small equivalent circle diameters (diameter distribution). Was confirmed.

In addition, the HAADF-STEM Image is used to calculate the intermediate circle of the mode diameter based on the mode radius of the Si phase (second phase) in the eutectic structure obtained by the precipitation calculation, and the maximum circle and the minimum circle based on the radius distribution. It can be applied to and illustrated in an electron micrograph. As a result, the middle circle of the mode diameter based on the mode radius of the Si phase (second phase) in these eutectic structures and the maximum circle and the minimum circle based on the radius distribution are the actual Si phase (second It can be confirmed that the circle diameters (phases) and the equivalent circular diameters (average value and diameter distribution) almost match.

(Equivalent circle radius)
Regarding the microstructure of the Si-containing alloy of the present embodiment, the equivalent circular radii (average value) of 10 to 100 pieces, preferably 30 to 100 pieces on a number basis, using electron micrographs and the like as shown in FIGS. Can be asked.

The equivalent circular radius (average value) of the independent first phase (silicide phase) is 280 nm or less, preferably 260 nm or less, more preferably 255 nm or less, and further preferably 250 nm or less. The lower limit of the equivalent circle radius (average value) of the independent first phase (silicide phase) is not particularly limited, but is preferably 160 nm or more, more preferably 170 nm or more, further preferably 180 nm or more, particularly preferably 190 nm or more. Is.

The equivalent circular radius (average value) of the second phase (Si phase) in the eutectic structure is 90 nm or less, preferably 85 nm or less, more preferably 80 nm or less, still more preferably 70 nm or less, and particularly preferably 65 nm or less. .. The lower limit of the equivalent circular radius (average value) of the second phase (Si phase) in the eutectic structure is not particularly limited, but is preferably 25 nm or more, more preferably 30 nm or more, and further preferably 35 nm or more.

The equivalent circle radius (average value) of the first phase (silicide phase) in the eutectic structure is 80 nm or less, preferably 70 nm or less, more preferably 60 nm or less, and further preferably 54 nm or less. The lower limit of the equivalent circle radius (average value) of the first phase (silicide phase) in the eutectic structure is not particularly limited, but is preferably 25 nm or more, more preferably 30 nm or more, further preferably 35 nm or more. Is.

From the above, the modal radii of the independent first phase and the second phase in the eutectic structure obtained by the above precipitation calculation are the actual independent first phase and the second mode in the eutectic structure. It can be said that it almost matches the mode radius of the phase. This is almost in agreement with the equivalent circle radii (average value) of 10 to 100 pieces, preferably 30 to 100 pieces on the number basis measured from electron micrographs, etc., and is a new index in place of these equivalent circle radii. As a result, the inventors have found that the above-mentioned mode radius and radius distribution can be applied without problems.

<Method for producing negative electrode active material>
The method for producing the negative electrode active material for an electric device according to this embodiment is not particularly limited, and conventionally known knowledge can be appropriately referred to. As described above, in the present embodiment, the Si-containing alloy has a first phase and a second phase in its microstructure, and further, a part thereof includes a plurality of independent first phases, and a single phase. It is preferable that the part has a structure having a eutectic structure of the first phase and the second phase. As an example of a method for producing a negative electrode active material made of such a Si-containing alloy, a quenched ribbon alloy is prepared by a liquid quench roll solidification method (also simply referred to as “liquid rapid solidification method” in the present specification) as follows. A 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 Si-containing alloy having a composition represented by the chemical formula (I), and has the same composition as the Si-containing alloy. Also provided is a method for producing a negative electrode active material for an electric device, which comprises producing a quenched ribbon alloy by a liquid rapid solidification method using a mother alloy having a To be done. As described above, by carrying out the liquid rapid solidification method to manufacture the negative electrode active material (Si-containing alloy), it becomes possible to manufacture the alloy having the above-described microstructure structure. Further, in the obtained Si-containing alloy, the mode radius of the second phase and the mode radius of the independent first phase in the above-described eutectic structure can be reduced. These provide a manufacturing method that can effectively contribute to improving cycle durability while exhibiting a high capacity of the Si-containing alloy active material.

As described above, when Ti is used as the transition metal element, in the Si—Al—Ti ternary alloy, according to chemical thermodynamics (CALPHAD method=calculated phase diagram method), Si—Ti has a very strong bondability. Is shown (FIG. 31). Si-Al attracts in the liquid state, but repels in the solid phase (Fig. 32). Further, it can be seen that Ti-Al exhibits a bondability (FIG. 33).

The Si-containing alloy (negative electrode active material) according to the present invention contains a small amount of Al as compared with Ti (transition metal element). For example, when a Si-containing alloy (negative electrode active material) is manufactured using a liquid rapid solidification method, Al can attract Ti and Si in the liquid phase and suppress crystallization of TiSi ₂ . That is, the primary crystal TiSi ₂ can be miniaturized, and the independent TiSi ₂ phase (first phase) is finely dispersed in the alloy structure, so that the expansion and contraction of Si due to charge and discharge can be suppressed. Therefore, the cycle durability of an electric device such as a lithium ion secondary battery using the negative electrode active material (Si-containing alloy) of the present invention can be improved.

Further, as the cooling progresses, the crystallization of the primary crystal TiSi ₂ ends, and the process enters into the stage where TiSi ₂ and Si are eutectic. In this step, Al in the liquid phase in order to suppress the crystallization of TiSi _2, the Al content in the liquid phase increases, the TiSi ₂ eutectic structure in smaller (finer). As a result, TiSi ₂ is relatively small with respect to Si in the eutectic structure, and the Si phase and the TiSi ₂ phase in the eutectic structure are adjacent to each other as a structure, Of Si becomes relatively large.

Therefore, the expansion of the Si phase (a-Si phase) in the eutectic structure during the charge/discharge process is suppressed by the eutecticized TiSi ₂ phase, and further suppressed by a plurality of independent TiSi ₂ phases. Can be suppressed with.

Hereinafter, the manufacturing method according to this embodiment will be described.

(Liquid quench roll solidification method (liquid quench solidification method))
First, a liquid quench roll solidification method (liquid quench solidification method) is carried out using a mother alloy having the same composition as the desired Si-containing alloy. This produces a quenched ribbon alloy.

Here, in order to obtain the mother alloy, high-purity raw materials (single ingot, wire, plate, etc.) are used as raw materials for silicon (Si), aluminum (Al), and transition metal (for example, titanium (Ti)). ) Is prepared. Then, in consideration of the composition of the Si-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 quench roll solidification method is carried out using the mother alloy obtained above. This step is a step of rapidly cooling and solidifying a melt obtained by melting the mother alloy obtained above, and is performed by, for example, a high frequency induction melting-liquid quenching roll solidification method (twin roll or single roll quenching method). be able to. This gives a quenched ribbon alloy. The liquid quenching roll solidification method is often used as a method for producing an amorphous alloy, and there is much knowledge about the method itself. The liquid quench roll solidification method can be carried out using a commercially available liquid quench solidification device (for example, liquid quench solidification device NEV-A05 type manufactured by Nisshin Giken Co., Ltd.).

Specifically, using a liquid rapid solidification device NEV-A05 type manufactured by Nisshin Giken Co., Ltd., a melting device with an injection nozzle (for example, a quartz nozzle, which is installed in a chamber whose Ar pressure is reduced and the gauge pressure is reduced and adjusted). ) Inside, 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 heat). By spraying on a roll having excellent conductivity) made of Cu, a ribbon-shaped alloy (quenched ribbon (ribbon) alloy) that is continuously formed horizontally from the roll can be produced.

At this time, the atmosphere in the chamber is preferably replaced 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).

The melting temperature of the master alloy in the melting device with the injection nozzle (for example, a quartz 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.

The injection pressure of the mother alloy from the nozzle of the melting device with the injection nozzle (for example, a quartz 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.

It is desirable to adjust the rotation speed and the peripheral speed of the roll when the mother alloy is injected within a range of 4000 to 6000 rpm (peripheral speed of 40 to 65 m/sec).

The cooling rate of the above ribbon-shaped alloy (quenched ribbon (ribbon) alloy) is preferably 1.6 million °C/second or more, more preferably 2 million °C/second or more, still more preferably 3 million °C/second or more, and particularly preferably. Is 4,000,000° C./sec or more. The method of obtaining the cooling rate is as described with reference to FIGS. By adjusting the cooling rate within the above range, the Si-containing alloy having the microstructure according to the above-described embodiment of the present invention can be produced.

(Process of crushing quenched ribbon (ribbon) alloy)
Subsequently, the ribbon-shaped alloy (quenched ribbon (ribbon) alloy) obtained above is pulverized. For example, using a suitable crushing device (for example, a planetary ball mill device P-6 manufactured by Fritsch GmbH in Germany), a suitable crushing ball (for example, zirconia crushing ball) in a suitable crushing pot (for example, zirconia crushing pot). Then, the quenched ribbon (ribbon) alloy is charged, and the pulverization process is performed at a predetermined rotation speed for a predetermined time. The quenched ribbon (ribbon) alloy may be coarsely crushed by an appropriate crusher to a size that can be easily charged into the crusher.

As the pulverization conditions, the rotation speed of the pulverizer (mill device) may be within a range that does not impair the alloy microstructure formed by the liquid quench roll solidification method, for example, and is less than 500 rpm, preferably 100 to 480 rpm. It is preferably in the range of 300 to 450 rpm. The crushing time may be within a range that does not impair the alloy microstructure formed by the liquid quench roll solidification method, for example, and is less than 12 hours, preferably 0.5 to 10 hours, more preferably 0.5 to 3 It is a range of time.

The pulverization treatment is usually performed in a dry atmosphere, but the particle size distribution after the pulverization treatment may have a wide range of magnitude. Therefore, the pulverization treatment and the classification treatment for adjusting the particle size may be combined and performed once or more.

(Mechanical alloying process)
Following the step of producing a quenched ribbon (ribbon) alloy, a mechanical alloying treatment may be performed on the obtained ribbon-shaped alloy (quenched ribbon (ribbon) alloy), if necessary. At this time, if necessary, the crushing step of the quenched ribbon (ribbon) alloy may be performed, and the resulting crushed material may be mechanically alloyed.

The mechanical alloying treatment can be performed using a conventionally known method. For example, by using a ball mill device (for example, a planetary ball mill device), the grinding balls and the raw material powder of the alloy are put into a grinding pot, and the rotation speed is increased to impart high energy, whereby alloying can be achieved. The rotation speed of the ball mill device is, for example, 500 rpm or more, preferably 600 rpm or more. The mechanical alloying treatment time is, for example, 12 hours or longer, preferably 24 hours or longer, more preferably 30 hours or longer, further preferably 36 hours or longer, and particularly preferably 42 hours or longer. Yes, and most preferably 48 hours or more. Although the upper limit of the time for alloying treatment is not particularly set, it is usually 72 hours or less.

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

The above has described the predetermined alloy that is essentially included in the negative electrode active material layer, but the negative electrode active material layer may include other negative electrode active materials. Examples of the negative electrode active material other than the above-mentioned predetermined alloy include natural graphite, artificial graphite, carbon black, activated carbon, carbon fiber, carbon such as coke, soft carbon or hard carbon, pure metal such as Si and Sn, and the above-mentioned predetermined composition. Alloy active materials out of the ratio, or 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 compound oxide (composite nitride), a Li-Pb-based alloy, a Li-Al-based alloy, and Li. However, from the viewpoint of sufficiently exerting the operational effects exhibited by using the above-mentioned predetermined alloy as the negative electrode active material, the content of the above-mentioned 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, further preferably 90 to 100% by mass, particularly preferably 95 to 100% by mass, and most preferably 100% by mass.

(Amorphous forming ability)
As described above, in the present embodiment, the microstructure of the Si-containing alloy preferably contains the first phase containing a transition metal silicide as a main component, and Al in part, and is amorphous or low crystalline. And a second phase containing Si as a main component, and further, a part is a plurality of independent first phases, and a part is a eutectic structure of the first phase and the second phase. Have a structure. In order to efficiently exhibit the effects of the present invention, it is preferable that the Si phase (second phase) in the eutectic structure is sufficiently amorphized.

As a concrete index of the amorphous forming ability, a critical cooling rate, a liquidus temperature, a T ₀ curve, a glass transition temperature, a crystallization temperature and the like are used. Among them, regarding the critical cooling rate, it is possible to compare the amorphous forming ability even when the alloy systems are different.

The critical cooling rate is the minimum cooling rate at which an atom or molecule becomes an amorphous phase. By setting the cooling rate in the production of the alloy to be equal to or higher than the critical cooling rate, the alloy having the amorphous phase can be produced. That is, an alloy composition having a slow critical cooling rate is considered to have a high amorphous forming ability because it can be made amorphous even if slowly cooled.

In a preferred embodiment of the production method of the present invention, from the viewpoint of sufficiently promoting the amorphization of the second phase in the eutectic structure, the critical cooling rate F of the liquid phase composition at the start of the eutectic in the master alloy composition is F. Is 3.0×10 ⁸ K/sec or less, more preferably 2.0×10 ⁸ K/sec or less, and further preferably 1.5×10 ⁸ K/sec or less. The lower limit of the critical cooling rate F is not particularly limited and is, for example, 4.0×10 ⁷ K/sec or more.

Hereinafter, the calculation of the critical cooling rate of the liquid phase composition at the start of the eutectic in the alloy composition will be described using the alloy composition used in Example 1 as an example. Also for the alloy compositions of Examples 2 to 5 and Comparative Examples 1 and 2, the critical cooling rate of the liquid phase composition at the start of the eutectic can be determined by the same method.

[Calculation of liquid phase composition at start of eutectic by Thermo-Calc's Scheil solidification simulator]
Sweden Thermo-Calc software AB (Japan agency: ITOCHU Techno Solutions Co., Ltd.) integrated thermodynamic calculation system: Thermo-Calc Ver2015a is used as a thermodynamic database, solid solution general-purpose database: SSOL5 (SGTE* Solution Database). Ver.5.0), for the Si-Al-Ti ternary alloy of Example 1, a sille solidification calculation is performed using a sille model. For the Shill model and Schill solidification calculation, see Metal Vol. 77, No. 8 (p.898 to p.904). It should be noted that in the Shyle model condition, atomic diffusion in the solid phase can be ignored, complete mixing in the liquid phase, smooth solid-liquid interface, local equilibrium is established at the solid-liquid interface, solidification direction is unidirectional, It is assumed that solidification begins and the latent heat of solidification moves rapidly at the liquidus temperature.
*SGTE: Scientific Group Thermodata Europe.

The liquid phase composition at the start of the eutectic in the alloy composition can be obtained by the Shill solidification calculation.

As shown in FIG. 14A, the alloy composition of Example 1 has a structure composed of primary crystal silicide (TiSi ₂ ) and eutectic (TiSi ₂ +Si), and has a small Al single phase. In other words, the precipitation phases are the silicide (TiSi ₂ ) phase and the Si phase, and the composition of the solid phase here is considered to be constant regardless of temperature. Therefore, even when using such a sille model, the actual state is well reproduced. It is thought to do. Further, as shown in FIG. 14B, in the alloy composition of Example 1, the liquid phase composition at the start of the eutectic is Si _77.4 Al _2.0 Ti _20.6 .

Note that, also in the alloy composition of Example 2, as shown in FIG. 34( a ), the structure was composed of primary crystal silicide (TiSi ₂ ) and eutectic (TiSi ₂ +Si), and the Al single phase was small. Further, as shown in FIG. 34B, in the alloy composition of Example 2, the liquid phase composition at the start of the eutectic is Si _76.3 Al _5.0 Ti _18.7 .

On the other hand, in the alloy composition of Patent Document 2, as shown in FIG. 35(a), the amount of primary crystal silicide (TiSi ₂ ) is too large to cause coarsening, and the eutectic (TiSi ₂ +Si) is small, and the Al single layer is Many. Further, in the range of the alloy composition disclosed in Patent Document 2, the eutectic in the alloy composition (Si _57.3 Al _12.7 Ti _30.0 ) which is considered to have the best durability and which has the smallest amount of Al and the large amount of Ti. Since the amount of liquid Al at the start is too large (point of arrow in FIG. 35(b); liquid phase composition Si _62.1 Al _31.5 Ti _6.4 ), the liquidus temperature at the start of eutectic is Since it is considerably low at 1150° C., it is expected that the quenching roll method will not sufficiently solidify.

[Amorphous forming ability calculation]
The amorphous forming ability is evaluated by the critical cooling rate at which crystals crystallize from the liquid phase. A TTT diagram (constant temperature transformation curve) showing the time required for a crystal to grow to a volume fraction X when rapidly cooled from a liquid phase single phase region to a temperature T below the liquidus temperature and kept isothermally Then, the critical cooling rate is calculated from this. Using a thermodynamic calculation software Thermo-Calc Ver2015a and a thermodynamic database: SSOL5, a required thermodynamic amount is calculated and a TTT curve is calculated.

The method of calculating the TTT curve will be described below. For the calculation method of the critical cooling rate, for example, Metal Vol. 77 (2007) No. 10 (p. 1148 to p. 1153) can be referred to.

The following equation (1) of the Johnson-Mehl-Avrami kinetic treatment based on the homogeneous nucleation and growth theory (retention time: volume fraction of crystals produced at t: X, nucleation frequency: I, growth rate of nuclei) : U) is derived by Davies and Uhlmann as in the following equation (2).

Here, G _m is a driving force for crystallizing a crystal from a liquid phase, G ^* is a free energy for generating a spherical crystal nucleus from the liquid phase, η is a viscosity coefficient, and Nv is the number of atoms per unit volume. Represents.

G ^* can be represented by the following formula (3) as σ _m (solid-liquid interface energy). Further, G _m can be approximated by the following equation (4). Empirically, σ _m is represented by the following formula (5), and it is shown by Saunders and Miowdown that it is about 0.41.

f is the ratio of the sites where atoms can move at the solid-liquid interface, and is represented by the following formula (6) according to Uhlmann.

The viscosity coefficient η of the liquid alloy can be approximated by the Doolittle equation (Equation (7) below). Here, A, B and C are constants. f _T is the relative free volume in the liquid, and E _H is the hole formation energy. According to Ramachandrarao, E _H can be estimated from T _g (glass transition temperature) as in the following formula (8). Here, assuming that T _g =0.6T _m , f _T =0.03, η=10 ¹² Pa·S, and B=1, constants A and C in the following formula (7) were calculated.

Regarding the alloy composition of Example 1, after the eutectic initiation composition was determined by the above-mentioned Shill solidification simulation, the glass transition temperature, the liquidus temperature, and the enthalpy of fusion were determined, and from the above equation (2), the TTT curve (FIG. 36). Was calculated, and the critical cooling rate R _c was calculated from the following formula (9). A TTT diagram relating to the alloy composition of Example 1 is shown in FIG.

From the above, in the alloy composition of Example 1, the critical cooling rate is calculated to be 1.4×10 ⁸ K/sec.

Further, in the production method of the present invention, the critical cooling rate F of the liquid phase composition at the start of eutectic in the master alloy composition of the Si-containing alloy and the above-mentioned co- The ratio E of the transition metal silicide in the crystal structure is preferably E/F>3.0×10 ⁻⁹ sec/K, and E/F>3.5×10 ⁻⁹ sec/K. It is more preferable that E/F>4.0×10 ⁻⁹ sec/K. The upper limit of E/F is not particularly limited as long as it satisfies the range of the critical cooling rate F and the range of the following ratio F.

As described above, the critical cooling rate F of the liquid phase composition at the start of the eutectic in the master alloy composition of the Si-containing alloy is preferably low from the viewpoint of the amorphous forming ability. On the other hand, the transition metal silicide (first phase) is more present in the eutectic structure from the viewpoint of suppressing the expansion of the a-Si phase (second phase) in the eutectic structure during the charge/discharge process. Preferably.

Therefore, since the E/F is in the above range, the effect of the present invention can be more efficiently exhibited.

The ratio E of the transition metal silicide in the eutectic structure to the total transition metal silicide in the quenched ribbon of the Si-containing alloy can be calculated by the above-described precipitation calculation.

FIG. 13A is a graph showing the result of TiSi ₂ and Si precipitation simulation in Example 1. In FIG. 13A, the vertical axis represents the volume fraction and the horizontal axis represents time. FIG. 13A shows that silicide (TiSi ₂ ) is crystallized as a primary crystal and then Si is crystallized. That is, it can be seen that TiSi ₂ is crystallized as a primary crystal until Si crystallization, and is a eutectic of TiSi ₂ and Si after Si crystallization. From the above, the ratio E of the transition metal silicide in the eutectic structure to the total transition metal silicide in the quenched ribbon of the Si-containing alloy can be calculated.

From the viewpoint that the ratio E of the transition metal silicide in the eutectic structure to the silicide of all transition metals suppresses the expansion of the a-Si phase (second phase) in the eutectic structure in the charge/discharge process. , Preferably 0.30 or more, more preferably 0.40 or more, still more preferably 0.50 or more, still more preferably 0.55 or more. The upper limit of the ratio E is not particularly limited, but is, for example, 0.80 or less, preferably 0.70 or less.

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

(Binder)
The binder is added for the purpose of binding the active materials to each other 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% by mass, more preferably 1 to 15% by 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 agent)
The conduction aid refers to an additive 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 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. 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. 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 hindering 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 in place of the conductive additive and the binder, or may be used in combination with one or both of the conductive additive and the binder. .. As the conductive binder, commercially available TAB-2 (manufactured by Hosen Co., Ltd.) can be used.

(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 ion conductive polymers include polyethylene oxide (PEO)-based and polypropylene oxide (PPO)-based polymers.

The mixing ratio of the components contained in the positive electrode active material layer and the negative electrode active material layer is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about the non-aqueous electrolyte 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 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 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 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 facilitating the manufacturing process or 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 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 provide the current collector with sufficient conductivity, and is generally about 5 to 35 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 made 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 the 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 a nonwoven fabric) include, for example, a microporous film made of a polyolefin such as polyethylene or polypropylene, a porous flat plate, and a nonwoven 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 conduct a thermal polymerization, an ultraviolet polymerization, a radiation polymerization, an 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 film that is the battery exterior material.

The material forming the current collector is not particularly limited, and a well-known highly conductive material that has been conventionally used as a current collector 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 light weight, 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. The portion taken out from the battery exterior material 29 has a heat insulating property so as not to affect the products (for example, automobile parts, particularly electronic devices) by contacting peripheral devices or wirings 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 obtained 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 configuration 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 current collector plate 59 and a negative electrode current 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 exterior 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. 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 may be a laminate film or a conventional cylindrical can (metal can) as the exterior material. 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 current 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 driving power supply or an auxiliary power supply that requires high volume energy density and high volume output density.

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

The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited to the following examples.

(Example 1)
[Production of Si-containing alloy]
The alloy species was Si _67.6 Al _1.2 Ti _31.2, and it was produced by the liquid rapid solidification method. This will be described in detail below. Specifically, using a high-purity metal Si ingot (5N), a high-purity Ti wire (3N), and a high-purity Al shot (3N), and using an arc melting method, a Si alloy (Si67.6 mass%, Al1. 2% by mass, Ti 31.2% by mass) was prepared. The ingot alloy was crushed and roughly crushed to a diameter of about 2 mm so as to be easily put into a quartz nozzle.

Successively, a ribbon-shaped alloy=quenched ribbon (ribbon) alloy was produced as a Si-containing alloy by a liquid rapid solidification method using the powder of the roughly crushed ingot alloy as a mother alloy. Specifically, using a liquid rapid solidification apparatus NEV-A05 type manufactured by Nisshin Giken Co., Ltd., Si _67. 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 master} alloy of ₆ Al _1.2 Ti _31.2 was put and melted by high frequency induction heating. Then, it was jetted onto a Cu roll at a rotation speed of 4000 rpm (peripheral speed: 41.9 m/sec) at a jet pressure of 0.05 MPa to produce a ribbon alloy. The cooling rate of the alloy in the liquid rapid solidification method was 4.67×10 ⁶ ° C./sec. The thickness of the obtained ribbon-shaped alloy (quenched ribbon alloy) was 20 μm.

Then, the obtained ribbon-shaped alloy (quenched ribbon alloy) was pulverized. Specifically, the ribbon alloy (quenched ribbon alloy) was crushed and roughly crushed to a diameter of about 2 mm so that it could be easily put into a ball mill device. Next, using a planetary ball mill device P-6 manufactured by German Fritsch GmbH, a zirconia crushing ball and coarsely crushed ribbon-shaped alloy (quenched ribbon alloy) powder were put into a zirconia crushing pot, and crushed at 400 rpm for 1 hour. The treatment was performed to obtain a Si-containing alloy (negative electrode active material). The Si-containing alloy (negative electrode active material) powder thus obtained had an average particle diameter D50 of 6 μm and D90 of 19 μm.

[Fabrication of negative electrode]
80 parts by mass of the Si-containing alloy (Si _67.6 Al _1.2 Ti _31.2 ) manufactured as the negative electrode active material, 5 parts by mass of acetylene black as a conductive additive, and 15 parts by mass of polyamide imide as a binder. Parts and were mixed and dispersed in N-methylpyrrolidone to obtain a negative electrode slurry. Next, the obtained negative electrode slurry was uniformly applied onto both surfaces 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.

[Fabrication 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, and the upper sides of the coin cells are overlapped and caulked to seal. Thus, a lithium ion secondary battery (coin cell) was obtained.

As the above-mentioned electrolytic solution, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in an organic solvent in which EC:DEC=1:2 (volume ratio), and hexafluorophosphoric acid which is a lithium salt. Lithium (LiPF ₆ ) was used by dissolving it so that the concentration was 1 mol/L.

(Example 2)
A 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 alloy type was changed to Si _65.0 Al _2.5 Ti _32.5 . The thickness of the obtained ribbon-shaped alloy (quenched ribbon alloy) was 21 μm. The average particle diameter D50 of the obtained Si-containing alloy (negative electrode active material) powder was 4 μm, and D90 was 16 μm.

(Example 3)
A 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 alloy type was changed to Si _66.6 Al _1.2 Ti _32.2 .

(Example 4)
A 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 alloy type was changed to Si _67.0 Al _1.8 Ti _31.2 .

(Example 5)
A 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 alloy type was changed to Si _67.3 Al _1.5 Ti _31.2 .

(Comparative Example 1)
A 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 alloy species was changed to Si _65.0 Sn _5.0 Ti _30.0 . The thickness of the obtained ribbon-shaped alloy (quenched ribbon alloy) was 20 μm. The average particle diameter D50 of the obtained Si-containing alloy (negative electrode active material) powder was 7 μm, and D90 was 20 μm.
(Comparative example 2)
A 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 alloy type was changed to Si _60.0 Sn _10.0 Ti _30.0 . The thickness of the obtained ribbon-shaped alloy (quenched ribbon alloy) was 21 μm. The average particle diameter D50 of the obtained Si-containing alloy (negative electrode active material) powder was 7 μm, and D90 was 20 μm.

[Analysis of organization structure of negative electrode active material]
The microstructure of the negative electrode active material (Si-containing alloy) produced in Example 1 was analyzed. The details are as described above with reference to FIGS. From the microstructure of the Si-containing alloy of Example 1, a first phase containing a transition metal Ti element silicide (TiSi ₂ ) as a main component and a part of aluminum (Al) were included, and the amorphous Or a second phase (a-Si phase) having low crystallinity Si as a main component, and further, a part is a plurality of independent first phases, and a part is a first phase and a second phase. It was confirmed that the structure had a eutectic structure with the second phase.

In addition, about Example 2-5, although the result is not illustrated except the cross-sectional SEM image (FIG. 15) of Example 2, the same result as Example 1 was obtained.

Regarding the negative electrode active material (Si-containing alloy) produced in Example 1, the modal radii of the independent first phase and the first phase and the second phase in the eutectic structure are as described above using FIG. As explained. Further, regarding the negative electrode active materials (Si-containing alloys) produced in Examples 2 to 5 and Comparative Examples 1 and 2, the independent first phase and the most frequent first phase and second phase in the eutectic structure The radius was calculated by the above precipitation calculation. The results obtained are shown in Figures 16, 18, 20, 22, 24 and 26. The results of the modal radius of each precipitation phase are shown in Table 1 below.

In addition, from the results of TiSi ₂ and Si precipitation simulation (FIG. 13) in the alloy composition of Example 1, the transition metal in the eutectic structure with respect to the silicide of all the transition metals in the quenched ribbon of the Si-containing alloy was determined. The silicide ratio E was calculated. Similarly, in the alloy compositions of Examples 2 to 5 and Comparative Examples 1 and 2, from the results of TiSi ₂ and Si precipitation simulations, the eutectic structure for the silicide of all transition metals in the quenched ribbon of the Si-containing alloy was obtained. The ratio E of the transition metal silicide therein was calculated (FIGS. 17(a), 19(a), 21(a), 23(a), 25(a) and 27(a)). The results are shown in Table 1.

[Evaluation of amorphous forming ability (critical cooling rate)]
In the negative electrode active material (Si-containing alloy) manufactured in Example 1, the critical cooling rate in the liquid phase composition at the start of the eutectic of the mother alloy composition is as described above with reference to FIG. Further, in the negative electrode active materials (Si-containing alloys) produced in each of Examples 2 to 5 and Comparative Examples 1 and 2, the critical cooling rate in the liquid phase composition at the start of eutectic of the mother alloy composition was calculated (Fig. 17(b), 19(b), 21(b), 23(b), 25(b) and 27(b)). The results are shown in Table 1.

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

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

The evaluation cell was set in a constant current/constant voltage mode during 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 mA was charged from 2 V to 10 mV. After that, in the discharging process (referring to the process of desorbing Li from the evaluation electrode), a constant current mode was set, and discharging was performed from 0.3 C, 10 mV to 2 V. 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, Table 2 below shows the results of obtaining the ratio of the discharge capacity at the 50th cycle to the discharge capacity at the first cycle (discharge capacity retention rate [%]).

From the results shown in Table 2 above, it is found that the lithium ion 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. Recognize. In addition, the example using the Si-containing alloy negative electrode has a higher capacity than the negative electrode active material using the carbon material (this point is, so to speak, well-known (not to mention a comparative example using the negative electrode material). (See background art), so the comparative example is omitted). As described above, it was possible to realize high cycle durability while exhibiting high capacity because the Si-containing alloy constituting the negative electrode active material is Si-Al-M (M is 1 or 2 or more transition metal elements). It is considered that this is due to having a ternary alloy composition represented by On the other hand, it is found that the lithium ion battery using the negative electrode active material of the comparative example has lower cycle durability than the lithium ion battery using the negative electrode active material of the example. This is because Si-Al attracts each other in the liquid phase, but repels in the solid phase. Therefore, the Si-Al-Ti alloy of the example containing a small amount of Al is compared with the Si-Sn-Ti alloy of the comparative example. Therefore, it is considered that the stability of the Si-containing alloy in the liquid state becomes relatively high. As a result, the amorphous forming ability of the Si-containing alloy can be increased, and the degree of amorphousness of the Si phase in the eutectic structure can be increased. Therefore, the chemical structure of the Si phase changes due to the insertion and desorption of Li accompanying charge and discharge. It is considered that it becomes difficult to exhibit higher cycle durability.

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 element,
25, 58 negative electrode current collector,
27, 59 Positive electrode current collector,
29, 52 Battery exterior material (laminate film).

Claims (10)

The following chemical formula (I):

(In the above chemical formula (I),
M is Ti ,
A is an unavoidable impurity,
x, y, z and a represent mass% values, where x is 60≦x≦72, y is 0.3≦y≦5.0 and z is 27≦ z≦35, a is 0≦a<0.5, the ratio of y to z is 0.10 or less, and x+y+z+a=100 . )
A negative electrode active material for an electric device, comprising a Si-containing alloy having a composition represented by: The microstructure of the Si-containing alloy contains a first phase containing a transition metal silicide as a main component and Al in part, and at least a part of the Al is in solid solution in Si or in Si. are encapsulated dispersed, and a second phase composed mainly of Si in the amorphous, first phase independent of multiple, and the first phase and the second phase The negative electrode active material for an electric device according to claim 1, having a structure having a eutectic structure of. The negative electrode active material for an electric device according to claim 2 , wherein the mode radius of the first phase in the eutectic structure is 20 nm or more and 60 nm or less. The independent modal radius of the first phase is 160nm or more 250nm or less, the negative electrode active material for an electric device according to claim 2 or 3. The eutectic structure in, the modal radius ratio of the first phase with respect to the modal radius of the second phase is 1 or less, the negative electrode for an electric device according to any one of claims 2-4 Active material. The liquid quenching solidification method using a master alloy having the same composition as the Si-containing alloy, having to produce a quenched ribbon of the Si-containing alloy, electric device according to any one of claims 1 to 5 For manufacturing negative electrode active material for automobile. The production method according to claim 6 , wherein the critical cooling rate F of the liquid phase composition at the start of eutectic in the mother alloy composition is 2×10 ⁸ K/sec or less. The critical cooling rate F and the volume ratio E of the transition metal silicide in the eutectic structure to the total transition metal silicide in the quenched ribbon of the Si-containing alloy are E/F>3×10 ^−. The manufacturing method according to claim 7 , which is ⁹ sec/K. Obtained by using the negative electrode active material for an electric device according to any one of claims 1 to 5 negative electrode for an electric device. An electric device comprising the negative electrode for an electric device according to claim 9 .