JP6798411B2 - Negative electrode active material for electrical devices, and electrical devices using this - Google Patents

Description

The present invention relates to a negative electrode active material for an electric device and an electric device using the negative electrode active material. The negative electrode active material for an electric device of the present invention and an electric device using the negative electrode active material can be used as a secondary battery, a capacitor, or the like as a driving power source or an auxiliary power source for a vehicle motor such as an electric vehicle, a fuel cell vehicle, or a hybrid electric vehicle. Used for.

In recent years, there is an urgent need to reduce the amount of carbon dioxide in order to deal with air pollution and global warming. In the automobile industry, expectations are high for the reduction of carbon dioxide emissions by introducing electric vehicles (EVs) and hybrid electric vehicles (HEVs), and electric devices such as secondary batteries for driving motors that hold the key to their practical application. Is being actively developed.

The secondary battery for driving a motor is required to have extremely high output characteristics and high energy as compared with a consumer lithium ion secondary battery used in mobile phones, notebook computers, and the like. Therefore, the lithium-ion secondary battery, which has the highest theoretical energy among all batteries, is attracting attention and is currently being rapidly developed.

Lithium-ion secondary batteries generally include 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 an electrolyte layer and has a configuration of being housed in a battery case.

Conventionally, a carbon / graphite-based material, which is advantageous in terms of charge / discharge cycle life and cost, has been used for the negative electrode of a lithium ion secondary battery. However, since carbon / graphite-based negative electrode materials are charged / discharged by occluding / discharging lithium ions into graphite crystals, the charging / discharging capacity obtained from LiC ₆ , which is the maximum lithium-introduced compound, has a theoretical capacity of 372 mAh / g or more. Has the drawback of not being obtained. Therefore, it is difficult to obtain a capacity and energy density that satisfy the practical level for vehicle applications with carbon / graphite negative electrode materials.

On the other hand, a battery using a material alloying with Li for the negative electrode is expected as a negative electrode material for vehicle applications because the energy density is improved as compared with the conventional carbon / graphite-based negative electrode material. For example, the Si material occludes and releases _3.75 mol of lithium ions per 1 mol as shown in the reaction formula (A) below during charging and discharging, and the theoretical capacity of 3600 mAh / for Li ₁₅ Si ₄ (= Li _3.75 Si). g.

However, a lithium ion secondary battery using a material that alloys 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 when Li ions are occluded is about 1.2 times that of the graphite material, whereas in the Si material, when Si and Li are alloyed, the volume changes from the amorphous state to the crystalline state and a large volume change occurs. There is a problem that the cycle life of the electrode is shortened because it causes (about 4 times). Further, in the case of the Si negative electrode active material, there is a trade-off relationship between the capacity and the cycle durability, and there is a problem that it is difficult to improve the cycle durability while exhibiting a high capacity.

Here, Patent Document 1 discloses an invention having an object of providing 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 Si powder and titanium powder by a mechanical alloying method and wet pulverizing, and is a Si-based first phase and a silicide of titanium (TiSi _2, etc.). It is disclosed that a material containing the second phase containing) is used as the negative electrode active material. At this time, it is also disclosed that at least one of these two phases is amorphous or low crystallinity.

International Publication No. 2006/129415 Pamphlet

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

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

The present inventors have conducted diligent research in order to solve the above problems. As a result, a first phase containing a transition metal silicide as a main component, a second phase containing Al and having an amorphous or low crystallinity Si as a main component, and a Sn containing Sn as a main component. It has three phases, part of which is a plurality of independent first phases, and part of which is a eutectic structure of a first phase and a second phase, and a third among the eutectic structures. We have found that the above problems can be solved by using a Si-containing alloy having a fine structure in which the phases are finer than those of the first phase and the second phase as the negative electrode active material for an electric device, and the present invention has been developed. It came to be completed.

The Si-containing alloy constituting the negative electrode active material according to the present invention has a fine structure in which the second phase (Si phase) in the eutectic structure is hard and conductive due to the addition of Sn and Al to the Si—Ti alloy. It is included in the first phase (0045 phase) in the larger eutectic structure. As a result, when charged and discharged, the second phase (Si phase) in the eutectic structure is wrapped with the silicide phase (the first phase in the eutectic structure, and a plurality of independent first phases outside the eutectic structure). As a result, expansion and contraction are suppressed, and Si in the first phase reacts uniformly due to the addition of conductivity, so that durability is unlikely to deteriorate. Further, since the third phase (Sn phase) is finely dispersed in the eutectic structure, particularly around the second phase (Si phase), the second phase (Si phase) is likely to be amorphized. As a result, the cycle durability can be improved while showing a high capacity of the electric device in which the negative electrode active material is used.

It is sectional drawing which represented the outline of the laminated type flat non-bipolar lithium ion secondary battery which is a typical embodiment of the electric device which concerns on this invention. It is a perspective view which represented the appearance of the laminated flat lithium ion secondary battery which is a typical embodiment of the electric device which concerns on this invention. FIG. 3A is a drawing schematically showing the microstructure structure of the SiSnTiAl quaternary alloy which is the Si-containing alloy of the present embodiment based on HAADF-STEM and EDX, and FIG. 3B is a drawing. 3 (a) is a drawing schematically showing an enlarged part of a eutectic structure portion. FIG. 4 (a) is an enlarged and schematically representation of a part of the microstructure of the SiSnTi ternary alloy containing no Al based on HAADF-STEM and EDX, and FIG. 4 (b) is a diagram. , HAADF-STEM and EDX, is a drawing schematically showing a part of the eutectic structure portion of the microstructure of the SiSnTiAl quaternary alloy which is a Si-containing alloy. 5 (a) is a state diagram of Si—Al, FIG. 5 (b) is a state diagram of Si—Sn, and FIG. 5 (c) is a state diagram of Al—Sn. FIG. 6A shows BF (Bright-) of Cs-STEM (spherical aberration-corrected scanning transmission electron microscope image) (low magnification) of a sample prepared by the FIB method from the Si-containing alloy (particles) of the present embodiment. It is a drawing which represents a field) -STEM Image (bright field-scanning transmission electron microscope image). FIG. 6B is a drawing showing a HAADF-STEM Image (high-angle scattered darkfield-scanning transmission electron microscope image) of active material particles in the same field of view as in FIG. 6A. FIG. 7 (a) shows the Cs-STEM (spherical aberration-corrected scanning transmission electron microscope image) (medium magnification) in which the portion surrounded by the square frame (the portion of the eutectic structure) of FIG. 6 (b) is enlarged. It is a drawing which shows BF (Bright-field) -STEM Image (bright field-scanning transmission electron microscope image). FIG. 7 (b) is a drawing showing a HAADF-STEM Image (high-angle scattered dark field-scanning transmission electron microscope image) of active material particles in the same visual field as in FIG. 7 (a). FIG. 8 is a drawing showing quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy) for the fine structure of the alloy of Example 1. FIG. 8 (a) shows a Cs-STEM (spherical aberration-corrected scanning transmission electron microscope image) (high magnification) in which the portion surrounded by the square frame (the portion of the eutectic structure) of FIG. 7 (b) is enlarged. It is a drawing which shows HAADF-STEM Image (high angle scattering dark field-scanning transmission electron microscope image). FIG. 8B is a drawing showing the mapping data of Sn (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 8A). FIG. 8 (c) is a drawing showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 8 (a)). FIG. 8D is a drawing showing mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 8A). FIG. 8E is a drawing (upper right) in which the mapping data of Sn, Si, and Ti measured in the same field of view as HAADF-STEM (upper left FIG. 8A) is superimposed. FIG. 9 is a drawing showing quantitative mapping data of the fine structure of the alloy of Example 1 by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy). FIG. 9A shows a Cs-STEM (spherical aberration-corrected scanning transmission electron microscope image) (high magnification) in which the portion surrounded by the square frame (the portion of the eutectic structure) of FIG. 7B is enlarged. It is a drawing which shows HAADF-STEM Image (high angle scattering dark field-scanning transmission electron microscope image). FIG. 9B is a drawing showing mapping data of Al (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 9A). FIG. 9 (c) is a drawing showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 9 (a)). FIG. 9D is a drawing showing mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 9A). FIG. 9E is a drawing (upper right) in which mapping data of Al, Si, and Ti measured in the same field of view as HAADF-STEM (upper left FIG. 9A) is superimposed. FIG. 10A is an enlarged photograph of the lattice image obtained by HAADF-STEM of the Si-containing alloy (specifically, SiSnTiAl alloy) of the present embodiment. FIG. 10B is a photograph showing a diffraction pattern obtained by performing a fast Fourier transform (FFT) treatment on a lattice image (HAADF-STEM image) of the silicon-containing alloy of Example 1 shown in FIG. 10A. Is. FIG. 10C shows an inverse Fourier transform image obtained by performing an inverse fast Fourier transform process on an extracted figure from which the data of the diffraction ring portion corresponding to the Si (220) plane of FIG. 10B is extracted. It is a photograph showing. FIG. 10 (C') is a diagram obtained in the same manner as in FIGS. 10 (A) to 10 (C) below for the second phase (a-Si phase) in the eutectic structure of the alloy of Example 1. It is a drawing corresponding to 10 (C). It is a drawing which represented "the major axis diameter of a periodic array region (MRO)" schematically. 6 is a TTT diagram for the precipitation of Si in the liquid phase composition (Si _70.9 Sn _7.4 Ti _19.9- Al _1.8 ) at the start of eutectic in the alloy composition (alloy type) of Example 1. FIG. 13 is a drawing showing quantitative mapping data of the fine structure (eutectic structure portion) of the alloy of Example 2 by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy). FIG. 13 (a) shows HAADF-STEM of Cs-STEM (spherical aberration-corrected scanning transmission electron microscope image) (high magnification) in which the eutectic structure is enlarged in the fine structure of the alloy of Example 2. It is a drawing which represents Image (high angle scattering dark field-scanning transmission electron microscope image). FIG. 13B is a drawing showing the mapping data of Sn (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 13A). FIG. 13 (c) is a drawing showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 13 (a)). FIG. 13 (d) is a drawing showing mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 13 (a)). FIG. 13 (e) is a drawing (upper right) in which the mapping data of Sn, Si, and Ti measured in the same field of view as HAADF-STEM (upper left FIG. 13 (a)) is superimposed. FIG. 14 is a drawing showing quantitative mapping data of the fine structure (eutectic structure portion) of the alloy of Example 2 by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy). FIG. 14 (a) shows HAADF-STEM of Cs-STEM (spherical aberration-corrected scanning transmission electron microscope image) (high magnification) in which the eutectic structure is enlarged in the fine structure of the alloy of Example 2. FIG. 3 is a drawing showing an image (high-angle scattered dark field-scanning transmission electron microscope image). FIG. 14B is a drawing showing mapping data of Al (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 14A). FIG. 14 (c) is a drawing showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 14 (a)). FIG. 14 (d) is a drawing showing mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 14 (a)). FIG. 14 (e) is a drawing (upper right) in which mapping data of Al, Si, and Ti measured in the same field of view as HAADF-STEM (upper left FIG. 14 (a)) is superimposed. The second phase (a-Si phase) in the eutectic structure of the alloy of Example 2 is a drawing corresponding to FIG. 10 (C) obtained in the same manner as in FIGS. 10 (A) to 10 (C) below. Is. 6 is a TTT diagram for the precipitation of Si in the liquid phase composition (Si _64.6 Sn _14.2 Ti _18.0 Al _3.2 ) at the start of eutectic in the alloy composition (alloy type) of Example 2. FIG. 17 is a drawing showing quantitative mapping data of the fine structure (eutectic structure portion) of the alloy of Comparative Example 1 by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy). FIG. 17A shows the HAADF-STEM Image (high-angle scattering dark field-) of the Cs-STEM (spherical aberration-corrected scanning transmission electron microscope image) (high magnification) in which the fine structure of the alloy of Example 2 is enlarged. It is a drawing which shows the scanning transmission electron microscope image). FIG. 17 (b) is a drawing showing the mapping data of Sn (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 17 (a)). FIG. 17 (c) is a drawing showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 17 (a)). FIG. 17 (d) is a drawing showing mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 17 (a)). FIG. 17 (e) is a drawing (upper right) in which the mapping data of Sn, Si, and Ti measured in the same field of view as HAADF-STEM (upper left FIG. 17 (a)) is superimposed. FIG. 18 shows FIG. 10 (C) obtained in the same manner as in FIGS. 10 (A) to 10 (C) below for the second phase (a-Si phase) in the eutectic structure of the alloy of Comparative Example 1. It is a drawing corresponding to. 6 is a graph (drawing) showing the relationship between the number of charge / discharge cycles and the discharge capacity retention rate for each lithium ion secondary battery (coin cell) produced in Examples 1 and 2 and Comparative Example 1. It is a schematic diagram of the TTT diagram.

Hereinafter, with reference to the drawings, a negative electrode active material for an electric device of the present invention, and an embodiment of a negative electrode for an electric device and an electric device using the same will be described. However, the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following forms. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate description will be omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios.

Hereinafter, the 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 illustrated as an 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 negative electrode, a cell (single battery layer) is used. ) Is large, and high energy density and high output 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 for a vehicle or an auxiliary power source. As a result, it can be suitably used as a lithium ion secondary battery for driving a vehicle. In addition to this, it is fully applicable to lithium ion secondary batteries for mobile devices such as mobile phones.

That is, the lithium ion secondary battery that is the target 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 other constituent requirements are , Should not be particularly restricted.

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

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

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

Therefore, in the following description, a non-bipolar type (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 described very briefly 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 illustrates 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 sectional drawing which showed.

As shown in FIG. 1, the laminated battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminated sheet 29 which is an exterior body. .. Here, in the power generation element 21, the positive electrode active material layers 15 are arranged on both sides of the positive electrode current collector 12, the electrolyte layer 17, and the negative electrode active material layers 13 are arranged on both sides 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 a negative electrode active material layer 13 adjacent thereto are opposed to each other via an electrolyte layer 17, and a negative electrode, an electrolyte layer, and a positive electrode are laminated in this order. ..

As a result, the adjacent positive electrode, electrolyte layer, and negative electrode form one cell cell layer 19. Therefore, it can be said that the laminated battery 10 shown in FIG. 1 has a configuration in which a plurality of single battery layers 19 are laminated and electrically connected in parallel. The positive electrode current collectors in the outermost layers located in both outermost layers of the power generation element 21 have the positive electrode active material layer 15 arranged on only one side, but active material layers may be provided on both sides. .. That is, instead of using a current collector dedicated to the outermost layer in which the active material layer is provided on only one side, a current collector having active material layers on both sides may be used as it is as the current collector in the outermost layer. Further, by reversing the arrangement of the positive electrode and the negative electrode as in FIG. 1, the negative electrode current collector of the outermost layer is located on both outermost layers of the power generation element 21, and one side of the negative electrode current collector of the outermost layer or The negative electrode active material layer may be arranged on both sides.

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 each electrode (positive electrode and negative electrode), and are sandwiched between the ends of the laminate sheet 29. It has a structure that is led out to the outside of the laminated sheet 29. The positive electrode current collector plate 27 and the negative electrode current collector plate 25 are ultrasonically welded to the positive electrode current collector 12 and the negative electrode current collector 11 of each electrode via positive electrode leads and negative electrode leads (not shown), respectively, as necessary. It may be attached by resistance welding or the like.

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

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

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

(Positive electrode active material)
Examples of the positive electrode active material include lithium-, such as LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni-Mn-Co) O _2, and a part of these transition metals substituted with other elements. Examples thereof include transition metal composite oxides, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds. In some cases, two or more kinds of positive electrode active materials may be used in combination. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material from the viewpoint of capacity and output characteristics. More preferably, a composite oxide containing lithium and nickel is used, and more preferably Li (Ni-Mn-Co) O ₂ and a part of these transition metals are substituted with other elements (hereinafter, hereafter. Simply referred to as "NMC composite 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 an orderly manner) atomic layer are alternately stacked via an oxygen atomic layer, and each atom of the transition metal M has a layered crystal structure. It contains one Li atom, and the amount of Li that can be taken out is twice that of spinel-based lithium manganese oxide, that is, the supply capacity is doubled, and it can have a high capacity.

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. Other elements in that case 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, Cr, and more preferably Ti, Zr, P, Al, Mg, It is Cr, and more preferably Ti, Zr, Al, Mg, and Cr from the viewpoint of improving cycle characteristics.

NMC composite oxide, since the theoretical discharge capacity is high, preferably the general formula _{(1): Li a Ni b} Mn c Co d M x O 2 ( In the formula, a, b, c, d, x 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. It has a composition represented by (at least one kind of element selected from Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr). 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, inductively coupled plasma (ICP) emission spectrometry.

In general, nickel (Ni), cobalt (Co) and manganese (Mn) are known to contribute to capacitance and output characteristics from the viewpoint of improving material purity and 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 is substituted with another metal element, and it is particularly preferable that 0 <x ≦ 0.3 in the general formula (1). The crystal structure is stabilized by solid solution of at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr, resulting in charging and discharging. It is considered that the battery capacity can be prevented from decreasing even if the above steps are repeated, and excellent cycle characteristics can be realized.

As a more preferable 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 includes LiCo O ₂ , LiMn ₂ O ₄ , LiNi _1/3 Mn _1/3 Co _1/3 O _2, etc., which have been proven in general consumer batteries. Compared with the above, the capacity per unit weight is large, and the energy density can be improved, which has the advantage that a compact and high-capacity battery can be manufactured, which is preferable from the viewpoint of cruising range. LiNi _0.8 Co _0.1 Al _0.1 O ₂ is more advantageous in that it has a larger capacity, but it has a difficulty in life characteristics. On the other hand, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ has excellent life characteristics comparable to LiNi _1/3 Mn _1/3 Co _1/3 O ₂ .

In some cases, two or more kinds of positive electrode active materials may be used in combination. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material from the viewpoint of capacity and output characteristics. Needless to say, a positive electrode active material other than the above may be used.

The average particle size of the positive electrode active material contained in the positive electrode active material layer 15 is not particularly limited, but is preferably 1 to 30 μm, more preferably 5 to 20 μm from the viewpoint of increasing the output. In the present specification, the "particle size" is on the contour line of the active material particle (observation surface) observed by using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). It means the maximum distance among the distances between any two points. Further, in the present specification, the value of "average particle size" is a value of particles observed in several to several tens of fields 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 size shall be adopted. The particle size and average particle size of other constituents can be defined in the same way.

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, and examples thereof include the following materials. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile (PEN), polyacrylonitrile, polyimide, polyamide, polyamideimide, 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 its hydrogen additive, styrene / isoprene / styrene block copolymer and Thermoplastic polymers such as the hydrogenated products, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether co-weight. Fluororesin such as coalescence (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), etc. Vinylidene Fluoride-Hexafluoropropylene Fluororesin (VDF-HFP Fluororesin), Vinylidene Fluoride-Hexafluoropropylene-Tetrafluoroethylene Fluororesin (VDF-HFP-TFE Fluororesin), Vinylidene Fluoride-Pentafluoro Propylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene Examples thereof include vinylidene fluoride-based fluororubbers such as vinylidene fluoride-chlorotrifluoroethylene-based fluororubbers (VDF-CTFE-based fluororubbers) and epoxy resins. Of these, polyvinylidene fluoride, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, polyamide, and polyamideimide are more preferable. These suitable binders are excellent in heat resistance, have a very wide potential window, are stable 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 the binder contained in the positive electrode active material layer is not particularly limited as long as it can bind the active material, but is preferably 0.5 to 15% by mass with respect to the active material layer. It is more preferably 1 to 10% by mass.

The positive electrode (positive electrode active material layer) can be coated by any 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 normal slurry coating method. 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 quaternary alloy composition represented by Si—Sn—M (M is one or more transition metal elements) -Al, and the microstructure thereof is A first phase (also referred to as a silicide phase) containing a transition metal silicide as a main component and a second phase (Si phase) containing Al and containing amorphous or low crystalline Si as a main component. Alternatively, it has an a-Si phase (also referred to as an amorphous Si phase) and a third phase containing Sn as a main component (also referred to as a Sn phase), and a part thereof is a plurality of independent first phases. In addition, a part is a eutectic structure of the first phase and the second phase, and in the eutectic structure, the third phase is finer than the first phase and the second phase. It is made of a dispersed Si-containing alloy.

In the present embodiment, since the first phase (SiO phase) is mainly composed of a transition metal silicide (SiO), M is a transition metal (referred to as a silicide-forming element) that forms VDD with Si. It has one or more kinds of. That is, when M is one transition metal element, it is a silicide-forming element constituting the first phase (0045 phase). When M is two or more transition metal elements, at least one is a silicide-forming element constituting the first phase (filaicide phase). The remaining transition metal element may be a transition metal element contained in the second phase (a-Si phase) to the third phase (Sn phase), or the silicide constituting the first phase (0045 phase). It may be a forming element. Alternatively, it may be a transition metal element constituting a phase in which transition metals other than the first phase, the second phase and the third phase are crystallized (transition metal phase).

As described above, the Si-containing alloy constituting the negative electrode active material in the present embodiment is first a quaternary system represented by Si—Sn—M (M is one or more transition metal elements) −Al. Has an alloy composition of. More specifically, the Si-containing alloy constituting the negative electrode active material in the present embodiment is a Si—Sn—M (M is one or more transition metal elements) -Al alloy, and has the following chemical formula ( It has the composition represented by 2).

In the above chemical formula (1), A is an unavoidable impurity, M is one or more transition metal elements, and x, y, z, w and a represent values of% by mass. 0 <x <100, 0 <y <100, 0 <z <100, 0 <w <100, a is the rest, and x + y + z + w + a = 100.

Preferably, the Si-containing alloy is a Si—Sn—Ti—Al alloy and has a composition represented by the following chemical formula (1).

In the above chemical formula (1), A is an unavoidable impurity, x, y, z, w and a represent values of mass%, and in this case, x, y, z and w are 58 ≦ x ≦, respectively. 68, 2 ≦ y ≦ 10, 25 ≦ z ≦ 35, 0.3 ≦ w ≦ 3, a is the balance, and x + y + z + w + a = 100.

As is clear from the above chemical formula (2), the Si-containing alloy according to the present embodiment (having _a composition of Si _x Sn _y M _z Al _w A _a ) is made of Si, Sn, M (transition metal) and Al. It is a quaternary system. Having such a composition makes it possible to realize high cycle durability.

Further, in the present specification, the “unavoidable impurity” means an alloy containing Si that is present in the raw material or unavoidably mixed in the manufacturing process. Although the unavoidable impurities are originally unnecessary, they are permissible impurities because they are in trace amounts and do not affect the characteristics of the Si alloy.

In the present embodiment, it is particularly preferable to select Ti, which is one of the silicide-forming elements, as an additive element (M; transition metal) to the negative electrode active material (Si-containing alloy) so that it is amorphous at the time of Li alloying. -The phase transition of the crystal can be suppressed and the cycle life can be improved. Further, this makes the capacity higher than that of the conventional negative electrode active material (for example, carbon-based negative electrode active material). Therefore, according to a preferred embodiment of the present invention, it is preferable that M is titanium (Ti) in the composition represented by the above chemical formula (2). In particular, by selecting Ti as the additive element to the negative electrode active material (Si-containing alloy), Sn as the second additive element, and Al as the third additive element, it is even more amorphous during Li alloying. -The phase transition of the crystal can be suppressed and the cycle life can be improved. Further, this makes the capacity higher than that of the conventional negative electrode active material (for example, carbon-based negative electrode active material). Therefore, according to a preferred embodiment of the present invention, it is preferable that M is titanium (Ti) in the composition represented by the above chemical formula (2).

Here, in the Si-based negative electrode active material, when Si and Li are alloyed during charging, the Si phase shifts from the amorphous state to the 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 the active material is lost. Therefore, by having the negative electrode active material having the composition represented by the chemical formula (2), preferably the chemical formula (1) and the fine structure, the phase transition of the Si phase amorphous-crystal during charging is suppressed. The collapse of the particles themselves can be suppressed, the function as an active material (high capacity) can be maintained, and the cycle life can be improved.

As described above, the Si-containing alloy according to the present embodiment (having _a composition of Si _x Sn _y M _z Al _w Aa) is a quaternary of Si, Sn, M (transition metal, preferably Ti) and Al. It is a system. Here, the total of the composition ratios (mass ratio x, y, z, w, a) of each constituent element is 100% by mass, but there is no particular limitation on the respective values of x, y, z, w. It is preferably as follows.

In the composition represented by the chemical formula (2), preferably the chemical formula (1), x (composition ratio of Si; mass%) is preferably 68 or less, more preferably 67 or less, still more preferably 66. It is as follows. Further, x is preferably 58 or more, more preferably 58.5 or more, and more preferably 59 or more. Within such a range, it is excellent in terms of maintaining durability against charging / discharging (insertion / desorption of Li ions) and balancing the initial capacitance, and the durability can be sufficiently improved to obtain a high capacitance. The effect of can be expressed more efficiently.

In the composition represented by the chemical formula (2), preferably the chemical formula (1), y (composition ratio of Sn; mass%) is preferably 10 or less, more preferably 9 or less, still more preferably 8. It is less than 5.5. Further, y is preferably 2 or more, and more preferably 3 or more. Within such a range, it dissolves in the second phase (Si phase) and increases the distance between Si regular tetrahedrons in the Si phase to prevent reversible Li ion insertion and desorption during charging and discharging. It is excellent in that it enables. Thereby, the durability can be sufficiently improved, and the effect of the present invention can be exhibited more efficiently.

In the composition represented by the chemical formula (2), preferably the chemical formula (1), z (composition ratio of transition metal element M, preferably Ti; mass%) is preferably 35 or less, more preferably 34 or less. Yes, more preferably 33 or less, still more preferably 32 or less, and particularly preferably 31 or less. Further, z is preferably 25 or more, more preferably 28 or more, and further preferably 29 or more. Within such a range, it is excellent in terms of maintaining durability against charging / discharging (insertion / desorption of Li ions) and balancing the initial capacitance, and the durability can be sufficiently improved to obtain a high capacitance. The effect of can be expressed more efficiently.

In the composition represented by the chemical formula (2), preferably the chemical formula (1), w (composition ratio of Al; mass%) is preferably 3 or less, more preferably 2.5 or less. More preferably, it is 2.0 or less. Further, w is preferably 0.3 or more, more preferably 0.35 or more, and more preferably 0.4 or more. Within such a range, the primary crystal silicide precipitate (first phase) can be made finer, the eutectic ratio of VDD can be kept large, and the critical cooling rate for amorphization can be maintained. It is excellent in that it can be made smaller, the durability can be sufficiently improved, and the effect of the present invention can be exhibited more efficiently.

In the composition represented by the chemical formula (2), preferably the chemical formula (1), x + y + z + w is a maximum of 100 (does not exceed 100).

As described above, the transition metal element M, particularly Ti, is contained in a relatively large amount while Si is the main component, Sn is also contained to some extent, and Al is contained in a small amount, thereby containing Si according to the present embodiment. This is preferable because it makes it easier to obtain the fine structure of the alloy. Further, the transition metal element M (particularly Ti) is selected as an additive element to the main component Si of the Si-containing alloy, Sn is added as the second additive element within the above range, and Al is added as the third additive element within the above range. By adding a small amount, Al (further Sn) can be sufficiently dispersed (solid-dissolved) in a part of the Si phase. When Al is further added, the Sn phase (third phase) becomes the eutectic VDD phase (first phase) in the eutectic structure of the silicide phase (first phase) and Si phase (second phase). ) And the eutectic Si phase (second phase) can be dispersed (solidified) more finely. That is, in addition to being dispersed (solid-dissolved) in the Si phase, the Sn phase does not segregate as crystalline Sn in the Si phase, and in the fine structure, the boundary portion between the VDD phase and the Si phase of the eutectic structure, and further Is finely dispersed in the boundary between the independent VDD phase and the eutectic structure. Further, since the Sn phase functions as a Sn active material, sufficient cycle durability can be obtained while maintaining a high capacity. Further, Al can be dispersed fairly uniformly over the entire area of the eutectic Si phase. Therefore, by adding Al to the Si—Sn—Ti alloy, the amorphous forming ability of the Si alloy can be increased, and the degree of amorphous can be increased. Therefore, the chemical structure of the a-Si phase (second phase) is less likely to change even when Li is inserted and removed during charging and discharging, and even higher cycle durability can be obtained. Al that was not dispersed or solid-solved in the Si phase did not segregate as crystalline Al in the Si phase, and in the microstructure, the boundary between the VDD phase and the Si phase of the eutectic structure, and further, an independent silicide. It also disperses (crystallizes) at the boundary between the phase and the eutectic structure. However, the preferable numerical range of the composition ratio of each of the above-mentioned constituent elements is merely for explaining each preferable embodiment, and as long as it is included in the claims, it is within the technical range of the present invention. Is.

In the composition represented by the chemical formula (2), preferably the chemical formula (1), A is an impurity (unavoidable impurity) other than the above four components derived from the raw material or the manufacturing method as described above. In the composition represented by the chemical formula (2), preferably the chemical formula (1), a (mass%) is preferably less than 0.5, more preferably less than 0.1.

Whether or not the negative electrode active material (Si-containing alloy) has a composition represented by the above chemical formula (2), preferably chemical formula (1) is determined by qualitative analysis by fluorescent X-ray analysis (XRF) and inductively coupled plasma (ICP). ) It can be confirmed by quantitative analysis by emission spectroscopic analysis.

(Microstructure structure of Si-containing alloy)
FIG. 3A is a drawing schematically showing the microstructure structure of the SiSnTiAl quaternary alloy which is the Si-containing alloy of the present embodiment based on HAADF-STEM and EDX, and FIG. 3B is a drawing. 3 (a) is a drawing schematically showing an enlarged part of a eutectic structure portion. FIG. 4 (a) is an enlarged and schematically representation of a part of the microstructure of the SiSnTi ternary alloy containing no Al based on HAADF-STEM and EDX, and FIG. 4 (b) is a diagram. , HAADF-STEM and EDX, is a drawing schematically showing a part of the eutectic structure portion of the microstructure of the SiSnTiAl quaternary alloy which is a Si-containing alloy. 5 (a) is a state diagram of Si—Al, FIG. 5 (b) is a state diagram of Si—Sn, and FIG. 5 (c) is a state diagram of Al—Sn.

As shown in FIGS. 3 (a) and 3 (b) and 4 (b), the Si-containing alloy constituting the negative electrode active material in the present embodiment has a fine structure 31 of (1) a transition metal silicide. ) Is the main component, and has a first phase (0045 phase). (2) Al (further Sn) is partially contained (specifically, Al (further Sn) is dispersed (solid solution) inside the crystal structure of Si), and is amorphous or low crystallinity. It has a second phase (a-Si phase) containing Si as a main component. Further, (3) it has a third phase (Sn phase) containing Sn as a main component. Further, (4) a part of the plurality of independent first phases 32, and (5) a part of the first phase 34 and the second phase 35 form a eutectic structure 33. Further, (6) the eutectic structure 33 is characterized in that the third phase 36 is more finely dispersed than the first phase 34 and the second phase 35. The Si-containing alloy of the present embodiment has a configuration in which the second phase 35 is eutectic with the first phase 34 and further enters the gaps of a plurality of independent first phases 32 (FIG. 3A). reference). Further, the first phase (0045 phase) 32 and 34 are superior to the second phase (a-Si phase) 35 in terms of hardness and electron conductivity. Therefore, it can be said that the effect of the present invention can be obtained by the following mechanism of action (see the drawing of the microstructure of Example 1). That is, since the fine structure 31 of the alloy has the above structure, the second phase 35 in the eutectic structure 33 during the charge / discharge process, particularly the expansion of the Si active material as the main component, is eutecticized. It can be suppressed by wrapping the 34, and further suppressing by wrapping the second phase 35 in the eutectic structure by a plurality of independent first phases 32, so to speak, by suppressing the two steps. As a result, the phase transition of the amorphous-crystal (crystallization to Li ₁₅ Si ₄ ) when Si and Li are alloyed during charging is suppressed. As a result, the expansion and contraction of the Si-containing alloy in the charge / discharge process is reduced, and the first phase (SiO phase) 34 composed of a conductive silicide is used to form the second phase (a-Si phase) 35. By eutecticization, the second phase (a-Si phase) 35, particularly the Si active material as the main component, can be uniformly reacted. As a result, the cycle durability can be improved while showing a high capacity of the electric device in which the negative electrode active material is used. In particular, when Al is added to the SiSnTi alloy and the third phase 36 is finely dispersed around the second phase (a-Si phase) 35, the second phase (a-Si phase) 35 is likely to be amorphous. Has excellent durability. More specifically, the reason why the second phase (a-Si phase) 35 is easily amorphized is not only because the third phase 36 is dispersed, but also that Al is added to the second phase (a-Si phase) 35. This is because the dispersion is almost uniformly (see FIG. 5 and the calculation result of the amorphous forming ability (critical cooling rate)). That is, Al is more stable than Al-Si in the liquid phase state, Al-Si is more stable than Al-Si in the solid phase state, and supercooled when it is rapidly cooled with Al in Si. Even if the size is increased, Si crystals are less likely to be formed, and the amorphous forming ability is improved. As a result of Al being almost uniformly dispersed in the second phase (a—Si phase) 35, the third phase (Sn phase) 36 is finely dispersed (Si because Sn is binding to Ti, Si (third phase) Formed at the boundary (periphery) between the _two phases) 35 and the TiSi _two phases (first phase) 34). Fine dispersion of the third phase (Sn phase) 36 is necessary for improving durability, because Sn, which is the main component of the third phase (Sn phase) 36, has a large volume expansion during charging and discharging. Is. Therefore, when Al is contained in the alloy and Sn (third phase) is dispersed more finely than the first phase and the second phase in the eutectic structure 33, the durability is further improved. On the other hand, in the SiSnTi ternary alloy used in Comparative Example 1, as shown in FIG. 4 (a), in the fine structure 31', the silicide phase 32'encloses the Si phase 35' and the Sn phase 36'(fine). Since it does not have a structure), it can be said that the effect of suppressing the expansion of the Si active material by wrapping it (with a two-stage structure) cannot be sufficiently exerted.

Whether or not the Si-containing alloy has such a microstructure is determined, for example, after observing the Si-containing alloy using a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM). The same field of view as the image can be confirmed by performing element intensity mapping by EDX (energy dispersive X-ray spectroscopy).

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

(1) First phase (SiO phase) containing silicide (ceiling) of a transition metal as a main component
In a Si-containing alloy having a microstructure, the first phase (SiO phase) is mainly composed of a transition metal silicide (SiO). This first phase (0045 phase) is superior to the second phase (a-Si phase) in terms of hardness and electron conductivity. 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) against the stress during expansion, and the a-Si phase. It is possible to improve the low electron conductivity of (particularly Si active material). Furthermore, since this silicide phase (first phase) contains a transition metal silicide (for example, TiSi ₂ ), it has excellent affinity with the a-Si phase (second phase), and in particular, the volume during charging. Cracking at the (crystal) interface during expansion can be suppressed.

Further, as described above, in the composition represented by the above chemical formula (2), preferably the chemical formula (1), M is preferably titanium (Ti). In particular, by selecting Ti as an additive element to the Si-containing alloy, adding Sn as the second additive element, and adding a small amount of Al as the third additive element, the first element in the eutectic structure of the Si-containing alloy can be obtained. The phase and the second phase can be made finer (compared to the independent silicide phase). As a result, during Li alloying (further charging / discharging), the phase transition of amorphous-crystal can be further suppressed and the cycle life (durability) can be improved. Further, as a result, the negative electrode active material (Si-containing alloy) of the present invention has a higher capacity than the conventional negative electrode active material (for example, a carbon-based negative electrode active material). Therefore, the silicide phase (first phase) containing silicide (ceiling) of the transition metal in the microstructure as a main component is preferably titanium silicide (TiSi ₂ ).

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

(2) A second phase (Si phase or a-Si phase) containing Al in part and containing amorphous or low crystalline Si as a main component.
In the Si-containing alloy having a microstructure structure, the second phase (Si phase) contains Al (preferably Sn) in a part and contains amorphous or low crystallinity Si as a main component. This second phase (Si phase) is a phase containing amorphous or low crystalline Si as a main component. Further, when Al (preferably further Sn) is contained in a part of the second phase, specifically, Al (preferably further Sn) is dispersed in Si and solid-dissolved (dispersed in a solid-dissolved state). It suffices as long as it is (finely) dispersed in the form of being contained in Si.

This second phase (Si phase) is a phase involved in the storage and release of lithium ions during operation of the lithium ion secondary battery which is the electric device of the present embodiment, and is a phase which is electrochemically capable of reacting with Li. Is. Since the second phase contains Si as a main component, it is possible to occlude and release a large amount of Li per weight and per volume. However, since Si has poor electron conductivity, the second phase may contain trace amounts of additive elements such as phosphorus and boron, transition metals, and the like. The second phase is preferably amorphous rather than the first phase (silicide phase). With such a configuration, the negative electrode active material (Si-containing alloy) can have a higher capacity. Whether or not the second phase is more amorphous than the first phase is determined by electron diffraction analysis (high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM)) in the first phase and the second phase. It can be confirmed by a diffraction pattern obtained by performing a fast Fourier transform (FFT) on each observed image of the phase. Specifically, according to electron diffraction analysis, a net pattern (lattice-like spot) of a two-dimensional point arrangement is obtained for a single crystal phase, and a device sheller ring (diffraction ring) is obtained for a polycrystalline phase. A halo pattern is obtained for the amorphous phase. By using this, the above confirmation becomes possible.

As described above, in the composition represented by the chemical formula (2), preferably the chemical formula (1), M is preferably titanium (Ti). In particular, Ti is selected as an additive element to the negative electrode active material (Si-containing alloy), Sn is added as a second additive element, and a small amount of Al is added as a third additive element to form a Li alloy. , It is possible to further suppress the phase transition of amorphous-crystal and improve the cycle life. Further, as a result, the negative electrode active material (Si-containing alloy) of the present invention has a higher capacity than the conventional negative electrode active material (for example, a carbon-based negative electrode active material). Therefore, the Si phase (second phase) whose main component is amorphous or low crystallinity in the microstructure is mainly amorphous (amorphous) Si from the viewpoint of achieving higher cycle durability. It is preferable to use it as an ingredient.

From the above, the silicide of the transition metal of the first phase in the microstructure is titanium silicide (TiSi2), and the second phase is a Si phase containing Al and Sn. Is preferable. With such a configuration, it is possible to improve the cycle durability while showing the high capacity of the electric device. Further, the silicide of the transition metal of the first phase in the microstructure is titanium silicide, and the second phase is amorphous Si containing Al and Sn. It is preferably the main component. 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), "having amorphous or low crystalline Si as a main component" means 50% by mass or more, preferably 80% by mass or more, more preferably 80% by mass or more of the Si phase. 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 98% by mass or more is the above Si. However, the alloy may contain unavoidable impurities that are present in the raw material or are inevitably mixed in the manufacturing process. Therefore, it is practically difficult to obtain a second phase of 100% by mass.

In the second phase (Si phase), "partially contains Al" means that, for example, when comparing FIGS. 9 (b) and 9 (e), most of the Si phases contain Al. This is because there is a portion that does not contain Al (the Si portion functions as an active material), but a portion that contains Al in the Si phase can be seen. In particular, Al is relatively uniformly dispersed over the entire eutectic region. In the eutectic portion, a portion where Al overlaps with Si and is concentrated is observed. It is considered that Al is eutectic with Si in this portion (see FIG. 9B). In the portion containing Al in the Si phase, Al is dispersed and solid-solved in Si, or is dispersed in Si. Further, the remaining portion of Al in the eutectic structure is not the Si phase, but is crystallized in a finely dispersed form as a whole, such as the inside of the silicide phase in the eutectic structure and the boundary portion between the silicide phase and the Si phase. forming an Al phase or _{TiAl x Si y (x + y} = 2) compound phase as a main component. This is the same when viewed as a whole microstructure, and in addition to the inside of the silicide phase in the eutectic structure and the boundary portion between the silicide phase and the Si phase, the inside of the independent silicide phase and the boundary portion with the independent silicide phase, etc. forming an Al phase or _{TiAl x Si y (x + y} = 2) compound phase be totally crystallized in finely finely dispersed form to. Incidentally, in addition to the Al phase composed mainly of Al, the part of the TiSi ₂ Al was added the compound of _{TiAl x Si y (x + y} = 2) compound phase, such as substitutions, EDX of Si-Al-Ti In the mapping composite image (Fig. 9 (e)), there is a part where three elements overlap, and the homepage of NIMS (Material Research Organization) (Inorganic material database, TiAl _0.3 Si _1.7 compound (C49-TiSi) _This is because it is shown that the same crystal structure as in ₂ ) exists. “Al is the main component” means 50% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass of the Al phase. % Or more, particularly preferably 95% by mass or more, most preferably 98% by mass or more of Sn. However, in the alloy, there are unavoidable impurities that are present in the raw material or inevitably mixed in the manufacturing process. It can be included, so it is practically difficult to obtain one with 100% by mass of Al.

This is because it is essential that the second phase (Si phase) contains Al, but it does not necessarily have to contain Sn. By dispersing Al almost uniformly in the second phase, Sn is extruded to the periphery of the second phase, and as a result, the third phase containing Sn as a main component is around the second phase (the second phase). It is considered that the particles are dispersed more finely than the second phase at the boundary between the first phase and the second phase).

In the second phase (Si phase), the reason why "Sn can be partially contained" is that, for example, when FIG. 8 (b) and FIG. 8 (e) are compared, Sn is often added to the Si phase. This is because there is a portion containing Sn in the Si phase, which is a portion that is hardly contained (the Si portion functions as an active material). Further, in the portion where Sn is contained in the Si phase, Sn is dispersed and solid-dissolved in Si, or is dispersed in the form of being encapsulated in Si (Sn-Si solid solution or contained Sn functions as an active material. To do). By distributing Sn in the Si phase, the amorphousness of the second phase (Si phase) can be increased and the durability is excellent. Further, when Sn (Sn dispersed and solid-solved inside the crystal structure of Si) is contained in the second phase (Si phase), the Sn is also heavier than the carbon negative electrode material (carbon negative electrode material). It is possible to occlude and release a large amount of Li per unit and volume.

(3) Third phase containing Sn as a main component In a Si-containing alloy having a microstructure, the third phase contains tin (Sn) as a main component. This third phase (Sn phase) is excellent in that it is a negative electrode active material having a higher capacity than the negative electrode active material of a carbon-based material and contains Sn as a main component, which has a smaller expansion and contraction during charging and discharging than Si. There is. "Containing Sn as a main component" means 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, particularly preferably 95% by mass or more, most preferably 95% by mass or more of the third phase (Sn phase). Is Sn in 98% by mass or more. However, the alloy may contain unavoidable impurities that are present in the raw material or are inevitably mixed in the manufacturing process. Therefore, it is practically difficult to obtain a product having Sn of 100% by mass.

(4) Regarding the configuration in which a part is a plurality of independent first phases The Si-containing alloy is characterized in that a part is a plurality of independent first phases in the microstructure. It is one. Since a part of the microstructure is a plurality of independent silicide phases (first phase), the expansion of the second phase (a-Si phase) in the eutectic structure during the charge / discharge process is multiple. The independent first phase of can be suppressed and suppressed. In addition, the low electron conductivity of the a-Si phase (particularly Si active material) can be improved.

(5) Structure in which a part of the first phase and the second phase have a eutectic structure The above Si-containing alloy has a part of the first phase and the second phase in the microstructure. Is one of the features of the eutectic structure. Since a part of the first phase and the second phase are eutectic structures in the microstructure, the expansion of the second phase (a-Si phase) in the eutectic structure during the charge / discharge process is caused. , The eutectic first phase can be suppressed and suppressed. In addition, the low electron conductivity of the a-Si phase (particularly Si active material) can be improved. Further, the addition of Al rounds the first phase (SiO phase, for example, TiSi ₂ phase) in the eutectic structure (see FIGS. 3 (b), 8 (b), (e), etc.). It is considered that the rounding of the first phase (0045 phase) in the eutectic structure eliminates the stress concentration generated at the corners, so that the durability is further improved.

(6) Structure in which the third phase is finely dispersed in the eutectic structure than in the first phase and the second phase The Si-containing alloy has a fine structure in the eutectic structure. One of the features is that the third phase (Sn phase) is more finely dispersed than the first phase (SiO phase) and the second phase (Si phase). This is because the third phase (Sn phase) is finely dispersed in the eutectic portion by adding a small amount of Al to the Si-containing alloy (FIGS. 7 (b) and 8 (b) to 8). See (e)). Sn in the eutectic structure may be partially contained in the second phase (Si phase), but most of them are not in the second phase (Si phase) but in the first phase in the eutectic structure. It crystallizes at the boundary between the phase and the second phase to form a Sn phase (third phase; functions as an active material) containing Sn as a main component (see FIG. 8 (e)). This is the same when viewed as a whole microstructure, and crystallizes not only at the boundary between the first and second phases in the eutectic structure but also at the boundary with the independent first phase. The Sn phase (third phase; functions as an active material) is formed. The third phase (Sn phase) can also occlude and release a large amount of Li per weight and volume as compared with the carbon negative electrode material (carbon negative electrode material).

The Si-containing alloy is formed into an alloy by melting a predetermined alloy raw material by a liquid quenching roll solidification method and quenching at a predetermined cooling rate to form an alloy, whereby a plurality of independent first phases are formed as primary crystals in the liquid phase. Crystallization, the eutectic structure of the first phase and the second phase crystallizes in the liquid phase in the gap of this independent first phase, and in this eutectic structure, the third phase is the first. It is obtained with finer dispersion than the phase and the second phase.

A plurality of independent phases may be present in each of the first phase (0045 phase) in which a part of the above is independent and the first phase (0045 phase) in the eutectic structure, for example, a transition metal element. Two or more phases (for example, MSi ₂ and MSi) having different composition ratios of M and Si may be present. In addition, two or more phases may be present by containing silicides with different transition metal elements. Here, the type of the transition metal contained in the first phase (0045 phase) is not particularly limited, but is preferably at least one selected from the group consisting of Ti, Zr, Ni, Cu, and Fe, and more. It is preferably Ti or Zr, and particularly preferably Ti. These elements exhibit higher electron conductivity and higher strength than silicides of other elements when forming silicides. In particular, TiSi ₂ , which is a silicide when the transition metal element is Ti, is preferable because it exhibits extremely excellent electron conductivity.

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

The fine structure of the Si-containing alloy has the configurations (structures) of (1) to (6), for example, high-resolution STEM (scanning transmission electron microscope) observation, EDX (energy dispersive X-ray spectroscopy). The fine structure of the Si-containing alloy (particles), which is the negative electrode active material particles, can be clarified by elemental analysis, electron diffraction measurement, and EELS (electron energy loss spectroscopy) measurement. Examples of the analyzer (analysis method) include 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), Cs-STEM (Spherical Abrasion Corrected Scanning Transmission Electron Microscope Image), HAADF-STEM (High Angle Scattered Dark Field-Scanning Transmission Electron Microscope Image), BF- STEM (bright field-scanning transmission electron microscope image) and the like can be used. However, in the present embodiment, the present invention is not limited to these, and various observation devices (device conditions, measurement conditions) used for the fine structure of the existing alloy may be used.

(Analysis of microstructure structure of Si-containing alloy)
In the following, the microstructure of the negative electrode active material having the above microstructure will be described with reference to examples using Si-containing alloys (particles), which are the negative electrode active material particles produced in Example 1, as a sample. However, the structure of the fine structure of the alloy (particles) can be clarified in the same manner for the Si-containing alloy (particles) which is the negative electrode active material obtained in the other present embodiment. Further, Example 2 and Comparative Example 1 can also be analyzed by using the same method.

1: Analytical method 1-1: Sample preparation FIB (focused ion beam) method; Microsampling system (Hitachi, Ltd., FB-2000A)
Use Al grid.

1-2: STEMimage, EDX, EELS (Electron Energy Loss Spectroscopy) measuring device and conditions are as follows.

1) Equipment; Atomic resolution analysis electron microscope JEM-ARM200F manufactured by JEOL
EDX (Energy dispersive X-ray Spectroscopy)
JEOL JED-2300
(100mm ² Silicon Drift (SDD) Type)
System; Analysis Station
EELS (Electron Energy Loss Spectroscopy)
; GATAN GIF Quantum
Image acquisition; Digital Micrograph
2) Measurement conditions; Acceleration voltage: 200 kV
Beam diameter: Approximately 0.2 nmφ (diameter)
Energy resolution: Approximately 0.5 eV FWHM
1-3: The electron diffraction measuring device and conditions are as follows.

1) Equipment; Field emission electron microscope JEM2100F manufactured by JEOL
Image acquisition; Digital Micrograph
2) Measurement conditions; Acceleration voltage: 200 kV
Beam diameter: Approximately 1.0 nmφ (diameter) 2: (Quantitative mapping) analysis by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy) FIG. 6 (a) shows the Si-containing alloy of the present embodiment. Of the Cs-STEM (spherical aberration-corrected scanning transmission electron microscope image) (low magnification) of the sample prepared by the FIB method (particles), BF (Bright-field) -STEM Image (bright field-scanning transmission electron microscope image). ) Is a drawing. FIG. 6B is a drawing showing a HAADF-STEM Image (high-angle scattered darkfield-scanning transmission electron microscope image) of active material particles in the same field of view as in FIG. 6A. The measurement target is 2% by mass on the surface of the Si-containing alloy (particles) having the average particle size D50 = 7 μm (D90 = 18 μm) of the negative electrode active material particles obtained by crushing the quenching thin band alloy having the alloy composition of the present embodiment. The cross section of the negative electrode active material particles prepared by coating the alumina of No. 1 was used as an observation target. As the quenching thin band alloy, the alloy composition of Example 1 represented by Si ₆₅ Sn _4.8 Ti ₂₉ Al _1.2 was used.

FIG. 7 (a) shows the Cs-STEM (spherical aberration-corrected scanning transmission electron microscope image) (medium magnification) in which the portion surrounded by the square frame (the portion of the eutectic structure) of FIG. 6 (b) is enlarged. It is a drawing which shows BF (Bright-field) -STEM Image (bright field-scanning transmission electron microscope image). FIG. 7 (b) is a drawing showing a HAADF-STEM Image (high-angle scattered dark field-scanning transmission electron microscope image) of active material particles in the same visual field as in FIG. 7 (a).

FIG. 8 is a drawing showing quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy). FIG. 8 (a) shows a Cs-STEM (spherical aberration-corrected scanning transmission electron microscope image) (high magnification) in which the portion surrounded by the square frame (the portion of the eutectic structure) of FIG. 7 (b) is enlarged. It is a drawing which shows HAADF-STEM Image (high angle scattering dark field-scanning transmission electron microscope image). FIG. 8B is a drawing showing the mapping data of Sn (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 8A). FIG. 8 (c) is a drawing showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 8 (a)). FIG. 8D is a drawing showing mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 8A). FIG. 8E is a drawing (upper right) in which the mapping data of Sn, Si, and Ti measured in the same field of view as HAADF-STEM (upper left FIG. 8A) is superimposed. Since the mapping in FIGS. 8 (b) to 8 (e) can actually be colored, for example, if Sn is green, Si is blue, and Ti is red, VDD (TiSi ₂ ) is , Si blue and Ti red are mixed and become pink, so it can be distinguished at a glance, but since it is necessary to submit a black and white image in the application drawing, the analysis information clarified by such coloring is used. It is included in FIGS. 6 (b) and 7 (b). If you are a person in the art, you can easily obtain the same analysis information by the same image analysis as the present application 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. 8 (b) to 8 (d), the portion where Sn, Si, and Ti are not present is represented by black, and the portion where these elements are present is represented by shades of gray or white. As a result, the presence and distribution of Si, Sn, and Ti among the elements constituting the active material alloy Si ₆₅ Sn _4.8 Ti ₂₉ Al _1.2 (negative electrode active material of Example 1) to be measured can also be confirmed. ..

FIG. 9 is a drawing showing quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy). FIG. 9A shows a Cs-STEM (spherical aberration-corrected scanning transmission electron microscope image) (high magnification) in which the portion surrounded by the square frame (the portion of the eutectic structure) of FIG. 7B is enlarged. It is a drawing which shows HAADF-STEM Image (high angle scattering dark field-scanning transmission electron microscope image). FIG. 9B is a drawing showing mapping data of Al (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 9A). FIG. 9 (c) is a drawing showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 9 (a)). FIG. 9D is a drawing showing mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 9A). FIG. 9E is a drawing (upper right) in which mapping data of Al, Si, and Ti measured in the same field of view as HAADF-STEM (upper left FIG. 9A) is superimposed. Since the mapping in FIGS. 9 (b) to 8 (e) can actually be colored, if, for example, Al is green, Si is blue, and Ti is red, VDD (TiSi ₂ ) is , Si blue and Ti red are mixed and become pink, so it can be distinguished at a glance, but since it is necessary to submit a black and white image in the application drawing, the analysis information clarified by such coloring is used. It is included in FIGS. 6 (b) and 7 (b). If you are a person in the art, you 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. 9 by the same image analysis as in the present application. This is because it can be obtained. Incidentally, in FIGS. 9 (b) to 9 (d), the portion where Al, Si, and Ti are not present is represented by black, and the portion where these elements are present is represented by shades of gray or white. As a result, the presence and distribution of Al, Sn, and Ti among the elements constituting the active material alloy Si ₆₅ Sn _4.8 Ti ₂₉ Al _1.2 (negative electrode active material of Example 1) to be measured can also be confirmed. ..

In the above analysis, the STEM image observation includes a bright-field (BF) STEM image formed by using an electron beam transmitted through the sample and a dark field image formed by using an electron beam scattered from the sample. There are two types of observation methods for (Dark-field: DF) STEM images. In the BF-STEM images shown in FIGS. 6 (a) and 7 (a), transmission images showing the internal structure of the sample, FIGS. 6 (b), 7 (b), and 8 are similar to the normal TEM image. In the (HAA) DF-STEM image shown in (a) and FIG. 9 (a), a composition image in which a contrast reflecting the composition of the sample can be obtained can be observed. In particular, in HAADF (high-angle scattering annular dark field), the elastic scattered electron contrast caused by the atomic number (Z) is predominant, so that it is an imaging method also called a Z-contrast image. A substance having a large atomic number looks bright (see FIGS. 6 (b), 7 (b), 8 (a), and 9 (a)). In HAADF-STEM (high-angle scattering annular dark-field scanning transmission microscopy), an image is applied by applying a finely focused electron beam to a sample while operating it, and among the transmitted electrons, those scattered at a high angle are detected by an annular detector. can get. Heavy elements are darker in the STEM image and brighter in the HAADF-STEM image because materials with larger Z ² ρ are scattered at higher angles. 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 the EDS (Energy-Dispersive-Spectroscopic) detector while scanning the sample with a thin electron beam to obtain information on the composition distribution of the sample. Can be obtained. In transmission electron microscope (TEM) measurement, there is almost no diffusion of electron beams as seen in scanning electron microscope (SEM) measurement, so measurement is possible with the spatial resolution of a nanometer.

From FIG. 6B, there are a plurality of (relatively large) light gray parts corresponding to the silicide (TiSi ₂ ) indicated by the three arrows, other than the part surrounded by the square frame (eutectic structure). It can be confirmed that they exist independently (multiple independent first phases). The fact that this is silicide means that the same light gray portion as in FIG. 6 (b) exists in FIG. 7 (b), which is an enlargement of the portion (eutectic structure) surrounded by the square frame in FIG. 6 (b). Further, there are a plurality of portions (eutectic structure) surrounded by a square frame in FIG. 7 (b) in FIGS. 8 (a) and 9 (a). When the same light gray part as in FIG. 6 (b) in FIGS. 8 (a) and 9 (a) is colored in FIGS. 8 (e) and 9 (e), the blue of Si and the red of Ti are displayed. This is because it has been confirmed that the colors are mixed pink (that is, the silicide phase). This is a gray part indicating the presence of Ti in the microstructure of the sample from the Ti mapping data of FIGS. 8 (d) and 9 (d) even when FIGS. 8 and 9 are viewed as black and white images. It can be confirmed that there are multiple. Further, from the Si mapping data of FIGS. 8 (c) and 9 (c), Si overlaps with the gray portion indicating the presence of Ti in FIGS. 8 (d) and 9 (d) in the microstructure of the sample. You can see the gray part that indicates the existence of. This can be determined by comparing FIGS. 8 (a) (c) (d) (e) and FIGS. 9 (a) (c) (d) (e). Further, it can be confirmed that Sn (white portion) is hardly present in the (relatively large) light gray portion corresponding to the silicide (TiSi ₂ ) in FIG. 6 (b). This means that, from the Sn mapping data of FIG. 8 (b), there is almost a gray portion indicating the presence of Sn that overlaps with the gray portion indicating the presence of Ti in FIG. 8 (d) in the microstructure of the sample. It can be confirmed that it is not done. From these facts, the fine structure of the Si-containing alloy (particles) of the present embodiment has a first phase (finished hand phase) containing silicide (ceiling) of the transition metal of the above (1) as a main component. However, it can be confirmed that a part of the above (4) has a plurality of independent first phases (0045 phase).

Next, from the mapping data in which Sn, Si, and Ti are superimposed in FIG. 8 (e) on the upper right and the mapping data in which Ti, Si, and Ti are superimposed in FIG. 9 (e) on the upper right, the fine structure of the sample is obtained. Among them, the first phase (SiO phase) and the second phase (a-Si phase) containing Al and Sn have a eutectic structure ((solid solution) crystals having different component ratios or amorphous or low. It can be confirmed that the structure is crystalline, in which the first phase and the second phase are mixed).

Specifically, in FIGS. 8 (e) and 9 (e), it corresponds to the second phase (a-Si phase) in which Al and Sn are partially contained in the microstructure of the sample (relatively first). It can be confirmed that the dark gray part (Si + Sn part) smaller than the phase of No. 1 and the gray part corresponding to the first phase (SiO phase) (relatively larger than the second phase) are mixed. .. From this, it can be seen that the second phase (a-Si phase) and the first phase (0045 phase), which are fine to each other, are eutectic (eutectic structure). The eutectic structure can be confirmed by the following when coloring FIGS. 8 (e) and 9 (e). That is, the dark gray portion (second phase) (relatively smaller than the first phase) in FIGS. 8 (e) and 9 (e) is mainly Si blue (including a small amount of Al and Sn) and The blue of Si and the green of Sn are mixed to form a blue-green, and one gray portion (first phase) is a pink in which the blue of Si and the red of Ti are mixed. Then, the blue or blue-green portion (relatively smaller than the first phase) corresponding to the Si phase (second phase) containing Al and Sn, and the silicide phase (first phase) correspond to (the first phase). It can be confirmed that these are eutectic structures because the pink parts (relatively larger than the second phase) are mixed.

Further, even when viewed as a black-and-white image, the Ti mapping data in FIGS. 8 (d) and 9 (d) indicate the presence of Ti in the fine structure (eutectic structure) of the sample (relatively small). It can be confirmed that many gray-colored parts are present (spotted). Furthermore, from the Si mapping data of FIGS. 8 (c) and 9 (c), a gray-colored portion indicating the presence of Si in almost the entire microstructure of the samples of FIGS. 8 (d) and 9 (d). Can be confirmed. Further, from the comparison between the Sn mapping data of FIG. 8 (b) and the Ti mapping data of FIG. 8 (d), the portion where Ti is scattered in the microstructure (eutectic structure) of FIG. 8 (d). , It can be confirmed that there is almost no gray portion indicating the presence of Sn in FIG. 8 (b). That is, both Si and Ti are present in the microstructure (eutectic structure) of FIGS. 8 (b) (c) (d) to 8 (d) (relatively larger than the second phase). It can be confirmed that many gray parts are scattered. From the comparison between the Al mapping data of FIG. 9 (b) and the Ti mapping data of FIG. 9 (d), the figure shows that Ti is scattered in the microstructure (eutectic structure) of FIG. 9 (d). It can be confirmed that there is not much gray portion indicating the presence of Al in 9 (b). That is, both Si and Ti are present in the microstructure (eutectic structure) of FIGS. 9 (b) (c) (d) to 9 (d) (relatively larger than the second phase). It can be confirmed that many gray parts are scattered. Further, in the microstructure (eutectic structure) of FIGS. 8 (d) and 9 (d), a portion where gray portions (SiO) are not scattered (a portion where a large number of relatively small black portions are scattered). ) Is mainly interspersed with Si (including a small amount of Al and Sn), Sn + Si, and Al + Si from FIGS. 8 (b) and 9 (b) and 9 (c). It can be confirmed that there is. From these facts, from the microstructure (eutectic structure) of FIGS. 8 (e) and 9 (e), the silicide phase (first phase) and the Si phase (second phase) partially containing Al and Sn. ) And can be confirmed to have a eutectic structure.

From these facts, in the fine structure of the Si-containing alloy (particles) of the present embodiment, Al and Sn are contained in a part of the above (2) (specifically, inside the crystal structure of Si). It has a second phase (a-Si phase) containing amorphous or low crystalline Si as a main component (which is formed by dispersing and solidifying Al and Sn), and a part of the above (5) is the first. It can be confirmed that the first phase and the second phase have a eutectic structure.

In the microstructures of FIGS. 7 (b), 8 (a), and 9 (a), and further in the eutectic structure, the white portion is the third phase (Sn phase, trace amount of Si) containing Sn as a main component. , Ti, Al may be included). Further, from FIGS. 8 (a) to 8 (e), the third phase (Sn phase) in the eutectic structure is more finely dispersed than the first phase and the second phase in the eutectic structure. You can see that. In particular, by adding Al to the SiSnTi alloy, it can be confirmed that the third phase is finely dispersed at the boundary (periphery) of the first phase and the second phase in the eutectic structure (FIG. 8 (a)). )-(E)). As shown in FIG. 6B, the Sn phase in the white portion may crystallize in a portion other than the independent first phase and the eutectic structure. These also function as Sn active materials, but they do not expand and contract as much as Si in the charge and discharge process, and the expansion and contraction of the third phase (Sn phase) in the eutectic structure is the expansion and contraction of the Si phase in the eutectic structure. It can be prevented as well as the suppression mechanism of. Further, since the independent first phase and the Sn in the portion other than the eutectic structure also have an independent first phase in the vicinity thereof, the expansion and contraction suppression mechanism by the independent first phase is the same. It can prevent shrinkage. Therefore, even if the white portion (Sn phase) as seen in FIG. 6B is present, the deterioration of the negative electrode active material alloy can be sufficiently suppressed.

From these facts, it was confirmed that the fine structure of the Si-containing alloy (particles) of the present embodiment further has a third phase (Sn phase) containing (3) Sn as a main component of the above (3). it can. Further, it can be confirmed that the third phase (Sn phase) is finely dispersed in the eutectic structure of the above (6) than the first phase and the second phase in the eutectic structure.

3: Analysis by electron diffraction and (powder) X-ray diffraction (XRD) measurement A relatively large gray part in the HAADF-STEM Image (high-angle scattered dark field-scanning transmission electron microscope image) in FIG. 6 (b). Indicates an independent first phase (SiO phase) as described above. Further, the portion surrounded by the square frame includes a relatively small dark gray portion (Si + Sn portion) corresponding to the second phase (a-Si phase) partially containing Al and Sn, and the first phase (SiO). It shows a eutectic structure in which relatively small gray parts corresponding to (phase) are mixed. A diffraction pattern (not shown) is obtained by performing a fast Fourier transform process on the independent silicid phase region of FIG. 6B, the silicide phase region in the eutectic structure, and the a-Si phase region by electron diffraction measurement. obtain. From these diffraction patterns, a net pattern (lattice-like spots) of a two-dimensional point arrangement can be obtained for the single crystal phase, a device sheller ring (diffraction ring) can be obtained for the polycrystalline phase, and a halo for the amorphous phase. A pattern is obtained. Further, it is possible to specify the crystal structure of the net pattern (0045 phase) of the two-dimensional point arrangement. That is, from these diffraction patterns, a net pattern of a two-dimensional point array can be obtained, and it can be confirmed that the phase is a single crystal phase. Further, from the diffraction pattern, it can be confirmed that the Si phase (second phase) in the eutectic structure is a polycrystalline phase in which a device sheller ring (diffraction ring) is obtained. Further, a halo pattern diffracted ring is obtained, and it can be confirmed that the Si phase (second phase) is an amorphous phase having amorphous or low crystallinity Si (a-Si). That is, it was confirmed by electron diffraction analysis that the Si phase (second phase) in the eutectic structure had amorphous or low crystallinity Si (a-Si) by being amorphized. it can. Furthermore, it can be confirmed from the diffraction pattern that the a-Si phase (second phase) is more amorphous than the silicide phase (first phase). Similar results can be obtained for other examples.

(Size of each phase in the microstructure of Si-containing alloy)
1. 1. Relationship between the size of the independent first phase and the size of the eutectic structure Next, in the Si-containing alloy (particles) of the present embodiment, the size of the independent first phase in the microstructure of the alloy is determined. It is preferably larger than the size of the eutectic structure of the first phase and the second phase (see FIGS. 3 (a) and 6). This is because having such a configuration makes it possible to more effectively exhibit the effects of the present invention. That is, a relatively small-sized eutectic structure (the second phase is eutectic with the first phase) enters the gaps between a plurality of independent relatively large-sized first phases in the microstructure. It can be configured. As a result, the expansion of the second phase (a-Si phase) in the relatively small-sized eutectic structure during the charge / discharge process is suppressed (the eutectic first phase is suppressed), and a plurality of independent relatives are suppressed. This is because the first phase, which has a large size, makes it easier to suppress.

(Independent first phase size)
Here, the domain size of the independent first phase (0045 phase) in the microstructure of the alloy is preferably in the range of 200 to 600 nm. If the domain size of the independent first phase is in the above range, the relatively small size (the second phase is the second phase) in the gaps of the plurality of independent relatively large size first phases in the microstructure. It can be configured to include a eutectic structure (which is eutectic with one phase). As a result, the expansion of the second phase (a-Si phase) in the relatively small size eutectic structure during the charge / discharge process is suppressed (the eutectic first phase is suppressed), and a plurality of independent relatives are suppressed. This is because the first phase, which has a large size, makes it easier to suppress.

Regarding the value of the domain size (diameter) of the independent first phase in the microstructure of the alloy, among the low magnification (0.5 μm scale bar) of the microstructure portion at Cs-STEM, other than the eutectic structure. The gray part (TiSi ₂ part indicated by the arrow in FIG. 6B) is regarded as an independent first phase. That is, the EDX element mapping of low-magnification Si and the EDX element mapping of M (for example, Ti) in Cs-STEM are compared, and among the regions in which Si is present and M is also present, the regions other than the eutectic structure are independent. It is regarded as the first phase, and 1/10 of the maximum value of the intensity is set as the threshold in the EDX element mapping of M, and the binarized image processing is performed on the region where the intensity exceeds this threshold, and the obtained binarized image is used. It can be obtained as an arithmetic mean value of the measured values obtained by measuring five or more phases by a method of reading the dimensions of each independent first phase.

2. 2. About the magnitude relationship between the first phase and the third phase in the eutectic structure The domain size of the second phase in the eutectic structure is smaller than the domain size of the first phase, and the domain size of the third phase. Is preferably smaller than the domain size of the second phase. This is because a small amount of Al is contained in the Si-containing alloy, so that the second phase becomes finer than the first phase in the eutectic structure, and the third phase becomes the first phase and the second phase in the eutectic structure. This is because it is finely dispersed by the grain boundaries of the phase. That is, in the eutectic structure, the domain size of the second phase is smaller than the domain size of the first phase, and the second phase is encapsulated in the harder, more conductive first phase. Therefore, when charged and discharged, the second phase (Si phase) in the eutectic structure is surrounded by the first phase (0045 phase), so that expansion and contraction is suppressed, and Si reacts uniformly by imparting conductivity. Therefore, durability does not deteriorate easily. Further, since the third phase (Sn phase) is more finely dispersed around the first phase and the second phase (Si phase) in the eutectic structure, the second phase (Si phase) becomes amorphous. It is easy and has excellent durability. From these facts, the domain size of the independent first phase is larger than the size of the eutectic structure of the first phase and the second phase, and the domain size of the second phase is the first phase. It is preferable that the domain size of the third phase is smaller than the domain size of the second phase. As a result, the expansion of the second phase in the eutectic structure during the charge / discharge process, especially the Si active material as the main component, is suppressed by being wrapped by the eutectic first phase, and a plurality of independent first phases are further suppressed. The phase can be suppressed by wrapping the second phase in the eutectic structure, and can be suppressed by suppressing the two-stage stance. Then, the phase transition of the amorphous-crystal (crystallization to Li ₁₅ Si ₄ ) when Si and Li are alloyed during charging is suppressed. As a result, the expansion and contraction of the Si-containing alloy during the charge / discharge process is reduced, and the first phase (SiO phase) composed of conductive silicide is eutectic with the second phase (a-Si phase). The second phase (a-Si phase), particularly the Si active material as the main component, can be uniformly reacted. As a result, the cycle durability can be improved while showing a high capacity of the electric device in which the negative electrode active material is used. In particular, when Al is added to the SiSnTi alloy and the third phase is finely dispersed around the second phase, the second phase (a-Si phase) is easily amorphized and has excellent durability. More specifically, the reason why the second phase (a-Si phase) is easily amorphized is that Al is almost uniformly dispersed in the second phase (a-Si phase). Then, Al is dispersed almost uniformly (homogeneously) in the second phase (a-Si phase) to extrude Sn to the peripheral portion of the second phase, and as a result, the third containing Sn as the main component. Is dispersed around the second phase (the boundary between the first phase and the second phase) more finely than the first phase and the second phase. Therefore, when the third phase is finely dispersed around the second phase (Al is dispersed almost uniformly in the second phase), the second phase (a-Si phase) is likely to be amorphous. It can be said that That is, Al is more stable than Al-Si in the liquid phase state, Al-Si is more stable than Al-Si in the solid phase state, and supercooled when it is rapidly cooled with Al in Si. Even if the size is increased, Si crystals are less likely to be formed, and the amorphous forming ability is improved. As a result of Al being almost uniformly dispersed in the second phase (a-Si phase), the third phase (Sn phase) is finely dispersed (Si because Sn has a binding property with Ti, Si (second phase) (Phase) and TiSi ₂ phase (formed at the boundary (periphery)). Fine dispersion of the third phase (Sn phase) is necessary for improving durability, because Sn, which is the main component of the third phase (Sn phase), has a large volume expansion during charge and discharge. .. Therefore, when Al is contained in the alloy and Sn (third phase) is dispersed more finely than the first phase and the second phase in the eutectic structure, the durability is further improved.

(Domain size of the first phase in the eutectic structure)
The domain size (diameter) of the first phase (SiO phase) in the eutectic structure should be larger than the domain size (diameter) of the fine third phase (Sn phase) in the eutectic structure as described above. However, it is preferably larger than the domain size (diameter) of the second phase (a-Si phase) in the eutectic structure. As a result, the expansion of the second phase in the eutectic structure, especially the Si active material as the main component, is suppressed by being wrapped by the eutectic first phase having a relatively large size (see FIG. 3 (b)). ), Cycle durability can be improved. From this point of view, the domain size (diameter) of the first phase (0045 phase) in the eutectic structure is preferably in the range of 20 to 70 nm. The domain size of the first phase in the eutectic structure is more preferably 60 nm or less, further preferably 55 nm or less, and particularly preferably 50 nm or less. The domain size of the first phase in the eutectic structure is more preferably 25 nm or more, more preferably 30 nm or more.

Regarding the value of the domain size (diameter) of the first phase (0045 phase) in the eutectic structure, the EDX element mapping of Si at high magnification (25 nm scale bar) at Cs-STEM for the eutectic structure portion and Compare the EDX element mapping of M (eg Ti). Then, the region where Si exists and M also exists is regarded as the VDD phase, 1/10 of the maximum value of the intensity is set as the threshold value in the EDX element mapping of M, and the region where the intensity exceeds this threshold value is subjected to binarized image processing. From the obtained binarized image, it can be obtained as an arithmetic mean value of the measured values obtained by measuring five or more phases by a method of reading the dimensions of each first phase in the eutectic structure. ..

(Size of the second phase in the eutectic structure)
The size of the second phase (a-Si phase) in the eutectic structure may be larger than the domain size (diameter) of the fine third phase (Sn phase) in the eutectic structure as described above. However, it is preferable that the size is smaller than the domain size (diameter) of the first phase (SiOSn phase). As a result, the expansion of the second phase in the eutectic structure, especially the Si active material as the main component, is suppressed by being wrapped by the eutectic first phase having a relatively large size (see FIG. 3 (b)). ), Cycle durability can be improved. From this point of view, the smaller the size of the second phase, the more preferable. Specifically, the size of the second phase in the eutectic structure is preferably 30 nm or less, more preferably 28 nm or less, and even more preferably 25 nm or less. On the other hand, the lower limit of the size of the second phase is not particularly limited, but is preferably 5 nm or more, more preferably 8 nm or more, and further preferably 10 nm or more.

Regarding the value of the domain size (diameter) of the second phase (a-Si phase), the EDX element mapping of Si at high magnification (25 nm scale bar) in HAADF-STEM and the EDX of M (for example, Ti) The element mappings are compared, the region where Si is present and M is not present is regarded as the second phase (a-Si phase), and 1/10 of the maximum value of the EDX element mapping of M is set as the threshold value, which is equal to or less than this threshold value. It is obtained by measuring 5 or more phases by a method of performing binarized image processing on the region to be, and reading the dimensions of each second phase (a-Si phase) from the obtained binarized image. It can be obtained as an additive average value of the measured values.

(Size of third phase in eutectic structure)
As described above, the domain size (diameter) of the third phase (Sn phase) in the eutectic structure should be smaller than that of the first and second phases in the eutectic structure and should be finely dispersed. Just do it. Specifically, Al is substantially uniformly dispersed in the second phase (a-Si phase) in the eutectic structure, so that the third phase is finely dispersed around the second phase. When the third phase is finely dispersed around the second phase (Al is dispersed substantially uniformly in the second phase), the second phase (a-Si phase) is likely to be amorphized. That is, Al is more stable than Al-Si in the liquid phase state, Al-Si is more stable than Al-Si in the solid phase state, and supercooled when it is rapidly cooled with Al in Si. Even if the size is increased, Si crystals are less likely to be formed, and the amorphous forming ability is improved. As a result of Al being almost uniformly dispersed in the second phase (a-Si phase), the third phase (Sn phase) is finely dispersed (Si because Sn has a binding property with Ti, Si (second phase) (Phase) and TiSi ₂ phase (formed at the boundary (periphery)). Fine dispersion of the third phase (Sn phase) is necessary for improving durability, because Sn, which is the main component of the third phase (Sn phase), has a large volume expansion during charge and discharge. .. Therefore, when Al is contained in the alloy and Sn (third phase) is finely dispersed (smaller) than the first phase and the second phase in the eutectic structure, the durability is further improved. From this point of view, the smaller the domain size of the third phase, the more preferable. Specifically, the size of the third phase in the eutectic structure is preferably 10 nm or less, more preferably 9 nm or less, and even more preferably 8 nm or less. The domain size of the third phase is preferably 3 nm or more, more preferably 4 nm or more, and further preferably 5 nm or more.

Regarding the value of the domain size (diameter) of the third phase (Sn phase), high magnification (25 nm scale bar) Sn EDX element mapping, Si EDX element mapping and M (for example, for example) in HAADF-STEM. Compare the EDX element mappings of Ti). Then, the region in which Si is present and M is also present is regarded as the first phase (SiO phase), and the region in which Si is present and M is not present is regarded as the second phase (a-Si phase). Then, the region where the Sn phase is finely dispersed around the periphery (boundary) of the first phase (SiO phase) and the second phase (a-Si phase) is regarded as the third phase (Sn phase), and Sn In EDX element mapping, 1/10 of the maximum intensity is set as the threshold value, and binarized image processing is performed on the region below this threshold value, and from the obtained binarized image, each third phase in the eutectic structure is obtained. It can be obtained as an eutectic average value of the measured values obtained by measuring five or more phases by a method of reading the dimension of (Sn phase).

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

Further, in the present embodiment, a preferable range of the size of the periodic arrangement region (MRO) for the second phase (a-Si phase) in the eutectic structure of the alloy described above is defined. Here, the size of the periodic sequence region (MRO) for the second phase (a-Si phase) shall be measured by the following TEM-MRO analysis. Similar measurements were made for the examples.

(Measurement of the size of the periodic array region (MRO) of the second phase (a-Si phase) by TEM-MRO analysis)
In this measurement, a Fourier transform process is performed on a lattice image obtained by a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) of a Si-containing alloy to obtain a diffraction pattern. In this diffraction pattern, the inverse Fourier transform process was performed on the diffraction ring portion existing in the width of 0.7 to 1.0 when the distance between Si regular tetrahedrons was 1.0. From the Fourier transform image, it is possible to pay attention to the periodic array and measure the size of the periodic array region (MRO).

Lattice image by HAADF-STEM observation Here, observation using a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) can usually be performed using HAADF-STEM and a computer. For the observation by HAADF-STEM, a method of applying an electron beam to the observed sample, magnifying the lattice image (interference image) produced by the electrons transmitted through the observed sample, and observing (monitoring) with a computer can be used. According to a transmission electron microscope (TEM), it is possible to obtain a high-resolution observation image magnified to the atomic level and having a high contrast. For example, FIG. 10 (A) is an enlarged photograph of a lattice image obtained by HAADF-STEM of the Si-containing alloy (specifically, SiSnTiAl alloy) of the present embodiment.

Next, a Fourier transform process is performed on the lattice image obtained by HAADF-STEM to obtain a diffraction pattern. At this time, the Fourier transform process can be performed by, for example, the software "digital micrograph" manufactured by Gatan. For the Fourier transform process from the lattice image obtained by HAADF-STEM, other general-purpose software that can be easily reproduced (implemented) by those skilled in the art may be used. Here, the HAADF-STEM image shown in FIG. 10A has a bright portion and a dark portion. The bright part corresponds to the part where the atomic sequence exists, and the dark part corresponds to the part between the atomic sequences.

-Diffraction figure Next, the 40 nm square portion (the portion surrounded by the broken line) of the lattice image (HAADF-STEM image) shown in FIG. 10 (A) is subjected to Fourier transform (FT) processing. Here, the Fourier transform process is performed on the range surrounded by the broken line of the acquired lattice image to acquire a diffraction pattern (diffraction data) including a plurality of diffraction spots corresponding to a plurality of atomic planes. This Fourier transform process can be performed by, for example, software "digital micrograph" manufactured by Gatan. For this Fourier transform process, other general-purpose software that can be easily reproduced (implemented) by those skilled in the art may be used.

FIG. 10B is a photograph showing a diffraction pattern obtained by performing a fast Fourier transform (FFT) treatment on a lattice image (HAADF-STEM image) of the silicon-containing alloy of Example 1 shown in FIG. 10A. Is. In the diffraction pattern shown in FIG. 10B, a plurality of diffraction ring portions (diffraction spots) are observed in a ring shape (annular shape) centering on the brightest spot visible in the center as the intensity indicating the absolute value. To.

In the diffraction pattern shown in FIG. 10B, the diffraction ring portion existing in the width of 0.7 to 1.0 is determined when the distance between Si regular tetrahedrons is 1.0. Here, the distance between Si regular tetrahedrons corresponds to the distance between the central Si atom of the Si regular tetrahedron structure and the central Si atom of the Si regular tetrahedron structure (simply abbreviated as the distance between Si and Si). To do. By the way, this distance corresponds to the surface spacing of the Si (220) planes in the Si diamond structure. From this, in this step, among the plurality of diffraction ring portions (diffraction spots), the diffraction ring portion corresponding to the Si (220) plane is assigned, and the diffraction ring portion is set to the Si regular tetrahedron distance of 1. When it is set to 0, it is a diffraction ring portion existing in a width of 0.7 to 1.0. For the attribution of the diffraction ring portion (diffraction line), for example, a known document (publication, academic book, etc.) or a document relating to various silicon electron diffraction lines published on the Internet can be used. For example, "Technical Report", Faculty of Engineering, Graduate School of Engineering, Nagoya University, Vol. 9, March 2007, I.D. Technical Department Technical Workshop 8. Mastered techniques related to electron diffraction diagram observation with a transmission electron microscope, Noriyuki Saito, Shigeyuki Arai, Graduate School of Engineering, Faculty of Engineering, Faculty of Engineering, Materials and Analysis Technology (http://etch.engg.nagoya-u.ac.jp/gihou This can be done with reference to literature on electron diffraction lines of silicon such as /v9/047.pdf).

Inverse Fourier transform image Next, when the distance between the Si regular tetrahedrons of the diffraction pattern is 1.0, the diffraction ring portion existing in the width of 0.7 to 1.0, that is, the Si (220) plane. Inverse Fourier transform processing is performed on the corresponding diffraction ring portion. An inverse Fourier transform image is acquired by performing an inverse Fourier transform process on the diffraction ring portion (extracted figure / extracted data from which the data is extracted) corresponding to the Si (220) plane. The inverse Fourier transform process can be performed by, for example, the software "Digital Micrograph" manufactured by Gatan. For this inverse Fourier transform process, other versatile software that can be easily reproduced (implemented) by those skilled in the art may be used.

FIG. 10C shows an inverse Fourier transform image obtained by performing an inverse fast Fourier transform process on an extracted figure from which the data of the diffraction ring portion corresponding to the Si (220) plane of FIG. 10B is extracted. It is a photograph showing. As shown in FIG. 10C, in the obtained inverse Fourier transform image, a light-dark pattern composed of a plurality of bright parts (bright parts) and a plurality of dark parts (dark parts) is observed. Most of the bright and dark areas are amorphous regions (Si amorphous regions) that are irregularly arranged without periodic arrangement. However, as shown in FIG. 10 (C), regions in which bright areas are periodically arranged (periodic array portions existing in an ellipse surrounded by a broken line in FIG. 10 (C)) are scattered (scattered). ing. That is, in the inverse Fourier transform image shown in FIG. 10C, in the amorphous region other than the periodic array portion existing in the ellipse surrounded by the broken line, the bright part and the dark part are straight lines such as being bent in the middle. It is not stretched in a shape and is not lined up regularly. In addition, there is a part where the contrast of brightness is weakened between the bright part and the dark part. The structure of the light-dark pattern consisting of the bright part and the dark part in the amorphous region other than the periodic array portion existing in the ellipse surrounded by the broken line is such that the observed sample is amorphous or fine in the amorphous region. It is shown to have a crystalline (precursor of MRO) structure. Therefore, by acquiring the inverse Fourier transform image as shown in FIG. 10C, a region (crystallization region or crystallization region) having a periodic array existing in an ellipse surrounded by a broken line in the amorphous region (amorphous region). Whether or not it has a crystal structure region) can be easily analyzed. This "region having a periodic sequence" is also referred to as a "periodic sequence region (Middle Range Order; MRO)" in the present specification.

FIG. 10 (C') is a diagram obtained in the same manner as in FIGS. 10 (A) to 10 (C) below for the second phase (a-Si phase) in the eutectic structure of the alloy of Example 1. It is a drawing corresponding to 10 (C). Specifically, for the second phase (a-Si phase) in the eutectic structure of Example 1, the data of the diffraction ring portion corresponding to the Si (220) plane of the drawing corresponding to FIG. 10 (B) was extracted. It is a photograph which shows the inverse Fourier transform image obtained by performing the inverse fast Fourier transform process on the extracted figure. FIG. 15 shows FIG. 10 (C) obtained in the same manner as in FIGS. 10 (A) to 10 (C) below for the second phase (a-Si phase) in the eutectic structure of the alloy of Example 2. It is a drawing corresponding to. Specifically, for the second phase (a-Si phase) in the eutectic structure of Example 2, the data of the diffraction ring portion corresponding to the Si (220) plane of the drawing corresponding to FIG. 10 (B) was extracted. It is a photograph which shows the inverse Fourier transform image obtained by performing the inverse fast Fourier transform process on the extracted figure. FIG. 18 shows FIG. 10 (C) obtained in the same manner as in FIGS. 10 (A) to 10 (C) below for the second phase (a-Si phase) in the eutectic structure of the alloy of Comparative Example 1. It is a drawing corresponding to. Specifically, for the second phase (a-Si phase) in the eutectic structure of Comparative Example 1, the data of the diffraction ring portion corresponding to the Si (220) plane of the drawing corresponding to FIG. 10 (B) was extracted. It is a photograph which shows the inverse Fourier transform image obtained by performing the inverse fast Fourier transform process on the extracted figure.

In the present embodiment, the "periodic arrangement region (MRO)" refers to a region in which at least three or more bright areas are continuously arranged in a substantially linear shape and two or more rows are regularly arranged. In this periodic sequence region (MRO), it is shown that the observed sample has a crystal structure. That is, the [periodic array region (MRO)” indicates a crystallization (crystal structure) region scattered in the Si amorphous region that occupies most of the Fourier image.

Further, FIG. 11 is a drawing schematically showing the “major axis diameter of the periodic array region (MRO)”. In FIG. 11, the dark part A (the bright part of FIG. 10C) of the periodic arrangement region (MRO) is indicated by a black circle ● for convenience, and is irregularly arranged region (Si) adjacent to the region having the periodic arrangement. The dark part B (the bright part in FIG. 10C) of the amorphous region) is indicated by a white circle for convenience. Further, in FIG. 11, as a “periodic array region (MRO)”, three dark areas (bright areas in FIG. 10 (C)) are arranged in a straight line at three points in a row, and two rows are adjacent and arranged in parallel. It is explained using the area. In this embodiment, the "major axis diameter of the periodic array region (MRO)" can be obtained as follows. First, as shown in FIG. 11, the midpoint of the shortest route connecting the dark portion A (●) of the “periodic array region (MRO)” and the dark portion B (○) of the irregularly arranged region adjacent to these regions. Take C. Four points D1 to D4 in the semimajor axis direction and the semimajor axis direction are selected from the one-point broken line frame (which does not have to match the elliptical equation) drawn by connecting these intermediate points C, and at least the semimajor axis is selected. An ellipse drawn by an ellipse equation using two points in the direction (preferably all four points) (an ellipse surrounded by a broken line in FIG. 10C; an ellipse drawing software that can be drawn on an image can be used). The semimajor axis (L) can be obtained. For example, as shown in FIG. 11, image analysis software (for example,) capable of measuring the length of dark portions A1 (●) at both ends, which is the longest in the long axis direction of the “periodic array region (MRO)”, and the distance between two points. , Data of semimajor axis by ellipse drawing software). Next, the length of the dark portion B1 (◯) of the irregularly arranged region adjacent to the dark portions A1 (●) at both ends in the major axis direction of the “periodic array region (MRO)” is measured in the same manner. From these, the midpoint between both ends connecting the dark parts A1 (●) at both ends in the long axis direction of the "periodic arrangement area (MRO)" and the dark parts B1 (○) at both ends of the irregularly arranged area adjacent to them. The length of C1 can be obtained, and this length can be used as the major axis diameter (L). In FIG. 10C, the ellipse surrounded by a broken line has a periodic arrangement with two points in the semimajor axis as the semimajor axis and two points in the minor axis direction as the semimajor axis as shown in FIG. An ellipse is drawn by the ellipse equation (using ellipse drawing software that can be drawn on the image) so that the entire area is included.

Further, in the present embodiment, the "size obtained by the average value of the semimajor axis diameters of up to 5 points" is a plurality of obtained by specifying the "periodic array region (MRO)" in the inverse Fourier transform image. The semi-major axis of the "periodic array region (MRO)" is obtained from the ellipse drawn according to the definition of the "semi-major axis of the periodic array region (MRO)". From the obtained plurality of major axis diameters, 5 points are obtained from the one having the larger major axis diameter value, the average value is calculated, and the average value is used as the size of the periodic array region (MRO). The "maximum 5 points" is defined as the "major axis diameter of the periodic array region (MRO)" obtained from the inverse Fourier transform image (in the field of view of 40 × 40 nm; see FIG. 10 (C)). This is because there are cases where the score is less than 5 (4 points or less). In this case, the average value of all the major axis diameters of the "periodic array region (MRO)" obtained from the inverse Fourier transform image is calculated, and the size of the average value is calculated as the periodic array region (MRO). The size of. In this embodiment, there may be a plurality of (two or more) "periodic array regions (MROs)" in the inverse Fourier transform image (field of view of 40 x 40 nm), but preferably three or more, more preferably. It is 4 or more, more preferably 5 or more. Further, the upper limit of the number of "periodic array regions (MRO)" in the inverse Fourier transform image (field of view of 40 x 40 nm) may be 10 as long as the characteristics (action effect) of Si amorphous are not impaired. The following is preferable.

(Size of periodic array area (MRO))
In a preferred embodiment of the present invention, the size of the periodic sequence region (MRO) is preferably 6 nm or less, more preferably 5 nm or less, still more preferably 4 nm or less, particularly preferably 3 nm or less, and particularly preferably 2.5 nm or less. Is. When the size of the periodic array region (MRO) satisfies the above range (requirement), Si becomes a sufficiently amorphous state, the expansion of Si particles during charging and discharging can be alleviated, and the durability is greatly improved. It is possible to provide a Si alloy active material that can be improved. That is, when Si is in a sufficiently amorphous state, the diffraction ring portion of the Si (220) surface required for obtaining a Si alloy having high durability performance can be expressed (confirmed). In addition, a regular MRO (Si crystallization region) is formed in the amorphous from the inverse Fourier transform image of the diffraction ring portion of the Si (220) plane, and the size of this MRO is made smaller to make it amorphous. As the degree increases, it becomes difficult to form an irreversible Li—Si alloy crystal phase when used as an active material. Further, as the degree of amorphization increases, the expansion of the active material particles during charging and discharging can be alleviated, and the durability can be significantly improved. The lower limit of the size of the periodic array region (MRO) is not particularly limited, but may be 1 nm or more from a theoretical point of view.

Further, in another preferable embodiment of the present invention, a preferable range of the distance between Si tetrahedra for the second phase (a-Si phase) in the eutectic structure of the alloy described above is also defined. Here, the value of the Si regular tetrahedron distance for the second phase (a-Si phase) in the eutectic structure is also measured by the above-mentioned TEM-MRO analysis for the measurement of the periodic arrangement region (MRO). (Similar measurements were made for the examples described below). Specifically, first, in the region (amorphous region) that does not include the periodic array region (MRO) existing in the ellipse surrounded by the broken line of the inverse Fourier transform image as shown in FIG. 10 (C) described above. For example, an arbitrary 20 nm square (20 × 20 nm visual field) region is secured (selected), and the number of bright parts (dots = equivalent to Si regular tetrahedron units) in this visual field region is measured. Next, the value obtained by dividing the length of one side of the field of view, 20 nm, by the square root of the number of bright parts is defined as the Si regular tetrahedron distance. For example, if the number of bright areas (dots = equivalent to Si regular tetrahedron units) in an arbitrary 20 nm square visual field region is 100, 20 nm ÷ √ (100) = 20 nm / 10 = 2 nm is a Si regular tetrahedron. It becomes a distance.

(Distance between Si regular tetrahedrons)
In a preferred embodiment of the present invention, the distance between Si regular tetrahedrons in the amorphous region is preferably more than 0.36 nm, more preferably 0.40 nm or more, still more preferably 0.44 nm or more. , Especially preferably 0.48 nm or more. When the distance between Si regular tetrahedrons in the amorphous region satisfies the above range, the amorphous region can be amorphized. As a result, Li ions can be easily inserted and removed between the expanded Si and Si during charging and discharging. The durability of the negative electrode and the electric device using the negative electrode active material of the present embodiment can be significantly improved. The upper limit of the distance between Si regular tetrahedrons in the amorphous region is not particularly limited, but can be said to be 0.55 nm or less from a theoretical point of view.

(Manufacturing method of negative electrode active material)
The method for producing the negative electrode active material for an electric device according to the present embodiment is not particularly limited, and conventionally known findings can be appropriately referred to. However, in the present embodiment, the Si-containing alloy has a second phase in its microstructure. The (Si phase) is eutectic with the first phase (0045 phase) and further enters the gaps between a plurality of independent first phases. Further, the third phase (Sn phase) is more finely dispersed in the eutectic structure than the first phase and the second phase. In particular, due to the addition of Al, the third phase has a structure finely dispersed by the grain boundaries of the second phase and the first phase in the eutectic structure. Further, it is preferable that the second phase in the eutectic structure is finer than the first phase and the third phase (Sn phase) is finer than the second phase. As a method for producing a negative electrode active material made of such a Si-containing alloy, a method for producing a quenching thin band alloy by a liquid quenching roll solidification method (simply also referred to as a liquid quenching solidification method) is provided as follows. That is, according to another embodiment of the present invention, it is a method for producing a negative electrode active material for an electric device, which is made of a Si-containing alloy having the fine composition and preferably the structure of the chemical formula (1). Specifically, a method for producing a negative electrode active material for an electric device, which comprises producing a quenching thin band (ribbon) alloy of a Si-containing alloy by a liquid quenching solidification method using a mother alloy having the same composition as the Si-containing alloy. Is also provided. Preferably, after producing a quenching thin band of a Si-containing alloy, a negative electrode active material for an electric device is obtained by subjecting a pulverization treatment to the above-mentioned average particle size to obtain a negative electrode active material for an electric device made of the Si-containing alloy. It is a manufacturing method. As described above, by carrying out the liquid quenching solidification method to produce the negative electrode active material (Si-containing alloy), it is possible to produce the alloy having the above-mentioned microstructure structure. This provides a manufacturing method that can effectively contribute to the improvement of cycle durability while exhibiting a high capacity of the Si-containing alloy active material. Hereinafter, the manufacturing method according to this embodiment will be described.

<Liquid quenching roll solidification method (quenching thin band (ribbon) alloy manufacturing process)>
First, a liquid quenching roll solidification method is carried out using a mother alloy having the same composition as the desired Si-containing alloy. As a result, a quenching thin band is produced.

Here, in order to obtain a mother alloy, high-purity raw materials (elemental ingots) are used for each of silicon (Si), tin (Sn), aluminum (Al), and transition metal (for example, titanium (Ti)) as raw materials. , Wires, boards, etc.). Subsequently, in consideration of the composition of the Si-containing alloy (negative electrode active material) to be finally produced, a mother alloy in the form of an ingot or the like is produced by a known method such as an arc melting method.

Then, the liquid quenching roll solidification method is carried out using the mother alloy obtained above. This step is a step of quenching and solidifying the melt obtained by melting the mother alloy obtained above, and is carried out by, for example, a high-frequency induction melting-liquid quenching roll solidification method (double roll or single roll quenching method). be able to. As a result, a quenching thin band (ribbon) alloy is obtained. 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 quenching roll coagulation method can be carried out using a commercially available liquid quenching coagulator (for example, a liquid quenching coagulator NEV-A05 type manufactured by Nissin Giken Co., Ltd.).

Specifically, a melting device with an injection nozzle (for example, a quartz nozzle) installed in a chamber adjusted by reducing the gauge pressure after Ar replacement using a liquid quenching and solidifying device NEV-A05 manufactured by Nissin Giken Co., Ltd. ), Then melted in a predetermined temperature range by an applicable melting means (for example, high frequency induction heating), and then made of metal or ceramics (particularly heat) at a predetermined rotation speed at a predetermined injection pressure. By injecting it onto a roll (made of Cu) having excellent conductivity, a thin band-shaped alloy = a quenching thin band (ribbon) alloy formed horizontally and continuously from the roll can be produced.

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

Further, the melting temperature of the mother alloy in the melting device with the injection nozzle (for example, 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.

Further, it is desirable that the injection pressure of the mother alloy from the nozzle of a melting device with an injection nozzle (for example, a quartz nozzle) is adjusted to a gauge pressure in the range of 0.03 to 0.09 MPa. 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 in the range of 0.06 to 0.16 MPa.

Further, it is desirable to adjust the rotation speed and peripheral speed of the roll when injecting the mother alloy in the range of 4000 to 6000 rpm (40 to 65 m / sec as the peripheral speed).

Further, the cooling rate of the thin band-shaped alloy = quenching thin band (ribbon) alloy is preferably 1.6 million ° C./sec or more, more preferably 2 million ° C./sec or more, still more preferably 3 million ° C./sec or more, particularly. It is preferably 5 million ° C./sec or higher. The method of obtaining the cooling rate is as described above. By adjusting the cooling rate within the above range, the Si-containing alloy having the fine structure of the present invention described above can be produced, and it is excellent in that the action and effect of the alloy can be effectively exhibited.

In the present embodiment, by adjusting the cooling rate, injection pressure, etc. in the liquid quenching roll solidification method within the ranges specified above, a Si-containing alloy having the above-mentioned desired microstructure = a quenching thin band (ribbon) alloy can be obtained. It can be manufactured.

(Crushing process of quenching thin band (ribbon) alloy)
Subsequently, the thin band alloy (quenched thin band (ribbon) alloy) obtained above is pulverized. For example, a suitable crushing ball (for example, a zirconia crushing ball) can be used in a suitable crushing pot (for example, a zirconia crushing pot) using a suitable crushing device (for example, a planetary ball mill device P-6 manufactured by Frichchu, Germany). And quenching thin band (ribbon) alloy is put in, and pulverization treatment is carried out at a predetermined rotation speed for a predetermined time. The quenching thin band (ribbon) alloy may be roughly pulverized with an appropriate pulverizer to a size that can be easily put into the pulverizer.

As the crushing treatment condition at this time, the rotation speed of the crusher (mill device) may be within a range that does not damage the alloy microstructure formed by the liquid quenching roll solidification method, and is less than 500 rpm, preferably 100 to 480 rpm. , More preferably, it is desirable to adjust to the range of 300 to 450 rpm. The pulverization time may be, for example, as long as it does not damage the alloy microstructure formed by the liquid quenching roll solidification method, and is less than 12 hours, preferably 0.5 to 10 hours, more preferably 0.5 to 3. It is desirable to adjust to the time range.

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

(Mechanical alloying process)
Following the step of producing the quenching thin band (ribbon) alloy, the thin band alloy (quenched thin band (ribbon) alloy) obtained above may be subjected to a mechanical alloying treatment, if necessary. At this time, if necessary, the quenching thin band (ribbon) alloy may be pulverized, and the obtained pulverized product may be subjected to a mechanical alloying treatment. By performing the mechanical alloying treatment after the liquid quenching solidification method, the distance between Si regular tetrahedrons in the obtained alloy can be further increased, and the size of the periodic array region (MRO) can also be reduced.

The mechanical alloying treatment can be performed by using a conventionally known method. For example, by using a ball mill device (for example, a planetary ball mill device), the crushed balls and the raw material powder of the alloy are put into the crushing pot, the number of rotations is increased, and high energy is applied, so that 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 time of the mechanical alloying treatment is, for example, 12 hours or more, preferably 24 hours or more, more preferably 30 hours or more, further preferably 36 hours or more, and particularly preferably 42 hours or more. Yes, most preferably 48 hours or more. The upper limit of the time for the alloying treatment is not particularly set, but 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 or small range. Therefore, it is preferable to carry out a pulverization treatment and / or a classification treatment for adjusting the particle size.

Although the predetermined alloy essentially contained in the negative electrode active material layer has been described above, the negative electrode active material layer may contain 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, coke, soft carbon, carbon such as hard carbon, pure metal such as Si and Sn, and the above-mentioned predetermined composition. Alloy active materials that are out of proportion, 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. Examples thereof include composite oxides (composite nitrides) of and transition metals, Li-Pb-based alloys, Li-Al-based alloys, and Li. However, from the viewpoint of sufficiently exerting the effects exhibited by using the above-mentioned predetermined alloy as the negative electrode active material, the content of the above-mentioned predetermined alloy in 100% by mass of the total amount of the negative electrode active material is preferable. 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 a first phase mainly composed of a transition metal silicide and Al (further Sn) as a main component, and is amorphous. It has a second phase containing high-quality or low-crystalline Si as a main component, and a third phase containing Sn as a main component. 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, and in the eutectic structure, the third phase is the first phase. It has a structure that is more finely dispersed than the phase and the second phase. 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 an index of a specific amorphous forming ability, the critical cooling rate, the liquidus temperature, T ₀ curve, the glass transition temperature, such as the crystallization temperature it is used. Above all, the critical cooling rate makes it possible to compare the amorphous forming ability even when the alloy system is different.

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

In a preferred embodiment of the production method of the present invention, the critical cooling rate F of the liquid phase composition at the start of eutectic in the mother alloy composition from the viewpoint of sufficiently advancing the amorphization of the second phase in the eutectic structure. Is 4 × 10 ⁷ K / sec or less, preferably 3 × 10 ⁷ K / sec or less. It is more preferably 2.8 × 10 ⁷ K / sec or less, further preferably 2.5 × 10 ⁷ K / sec or less, and particularly preferably 2.2 × 10 ⁷ K / sec or less. The lower limit of the critical cooling rate F is not particularly limited, and is, for example, 1 × 10 ⁶ K / sec or more.

In the following, the calculation of the critical cooling rate of the liquid phase composition at the start of eutectic in the alloy composition will be described using the alloy composition used in Example 1 as an example. For the alloy compositions of Example 2 and Comparative Example 1, the critical cooling rate of the liquid phase composition at the start of eutectic can be determined by the same method.

[Calculation of liquid phase composition at the start of eutectic by the Scheil solidification simulator of Thermo-Calc]
Integrated thermodynamic calculation system: Thermo-Calc Ver2015a manufactured by Sweden Thermo-Calc software AB (Japan agency: ITOCHU Techno Solutions Co., Ltd.) is used as a thermodynamic database, solid solution general-purpose database: SSOL5 (SGTE * Solution Tabase). Using ver. 5.0), a shile solid solution calculation is performed on the Si—Sn—Ti—Al quaternary alloy of Example 1 using a shile model. For the shile model and shile solidification calculation, see Metal vol. 77, No. 8 (p.898-p.904) shall be followed. Under the shile model conditions, atomic diffusion in the solid phase is negligible, complete mixing in the liquid phase, the solid-liquid interface is smooth, local equilibrium is established at the solid-liquid interface, and the solidification direction is unidirectional. It is assumed that solidification begins at the liquidus temperature and that the latent heat of solidification moves rapidly.
* SGTE: Scientific Group Thermodata Europe
The liquid phase composition at the start of eutectic in the alloy composition can be obtained by the shile solidification calculation.

In the alloy composition of Example 1, the structure is composed of primary crystal silicide (TiSi ₂ ) and eutectic (TiSi ₂ + Si), and there are few Si phase and Al single phase. That is, the precipitated phase becomes the silicide (TiSi ₂ ) phase and the Si phase. Here, since the composition of the solid phase is considered to be constant regardless of the temperature, it is considered that the actual state can be reproduced well even if such a shile model is used. Further, in the alloy composition of Example 1, the liquid phase composition at the start of eutectic is Si _70.9 Sn _7.4 Ti _19.9 Al _1.8 . Similar results were obtained with the alloy composition of Example 2 (the liquid phase composition at the start of eutectic is shown in FIG. 12 (Example 1) and FIG. 16 (Example 2)).

[Amorphous forming ability calculation]
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 crystals to grow until the volume fraction reaches X when rapidly cooled from the liquid phase single phase region to a temperature T below the liquidus temperature and maintained at an isothermal temperature. Obtain and calculate the critical cooling rate from this. Using the thermodynamic calculation software Thermo-Calc Ver2015a and the thermodynamic database: SSOL5, the required thermodynamic quantity is obtained and the TTT curve is calculated.

Hereinafter, a method of calculating the TTT curve will be described. 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 kinetic treatment of Johnson-Mehl-Avrami based on the uniform nucleation growth theory (retention time: volume fraction of crystals produced at t: X, nucleation frequency: I, nucleation rate) : U) is derived by Davies and Uhlmann as shown in the following equation (2).

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

G ^* can be expressed by the following formula (3) as σ _m (solid-liquid interface energy). Further, G _m can be approximated by the following equation (4). σ _m is empirically expressed by the following equation (5), and is shown to be about 0.41 by Sanders and Miodownik.

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

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

For the composition of the alloy of Example 1 (the mother alloy having the same composition as the Si-containing alloy), the eutectic start composition was obtained by the above-mentioned shile solidification simulation, and then the glass transition temperature, the liquidus temperature and the melting enthalpy were obtained. The TTT curve (FIG. 20) was calculated from the above equation (2), and the critical cooling rate R _c was calculated from the following equation (9). FIG. 12 (Example 1) shows a TTT diagram relating to the composition of the alloy of Example 1 (a mother alloy having the same composition as the Si-containing alloy). FIG. 16 shows a TTT diagram relating to the alloy composition of Example 2 obtained in the same manner as in Example 1. Further, the TTT diagram relating to the alloy composition of Comparative Example 1 is omitted.

From the above, in the composition (master alloy having the same composition as the Si-containing alloy) Alloy of Example 1, the critical cooling rate is calculated as 2.0 × ¹⁰ 7 K / sec. Further, in (mother alloy having the same composition as the Si-containing alloy) alloy of Example 2, the critical cooling rate is calculated as 1.9 × ¹⁰ 7 K / sec, and an alloy (Si containing alloys Comparative Example 1 in mother alloy) having the same composition, the critical cooling rate is calculated as 4.3 × ¹⁰ 7 K / sec.

Subsequently, the negative electrode active material layer 13 includes 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 for the negative electrode active material layer is also not particularly limited, and the above-mentioned binder can be similarly used as the binder used for the positive electrode active material layer. Therefore, detailed description thereof will be 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 to the negative electrode active material layer. It is 20% by mass, more preferably 1 to 15% by mass.

(Requirements common to 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 contain a conductive auxiliary agent, an electrolyte salt (lithium salt), an ionic conductive polymer, and the like, if necessary. In particular, the negative electrode active material layer 13 also essentially contains a conductive auxiliary agent.

(Conductive aid)
The conductive auxiliary agent 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 conductive auxiliary agent include carbon black such as acetylene black, and carbon materials such as graphite and vapor-grown carbon fiber. When the active material layer contains a conductive auxiliary agent, an electronic network inside the active material layer is effectively formed, which can contribute to the improvement of the output characteristics of the battery.

The content of the conductive auxiliary agent mixed in the active material layer is in the range of 1% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more, based on the total amount of the active material layer. The content of the conductive additive mixed in the active material layer is in the range of 15% by mass or less, more preferably 10% by mass or less, still more preferably 7% by mass or less, based on the total amount of the active material layer. is there. The electron conductivity of the active material itself is low, and the electrode resistance can be reduced by the amount of the conductive auxiliary agent. The following effects are exhibited by defining the compounding ratio (content) of the conductive auxiliary agent in the active material layer within the above range. To. 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 can be improved by improving the electrode density. ..

Further, a conductive binder having both the functions of the conductive auxiliary agent and the binder may be used in place of the conductive auxiliary agent and the binder, or may be used in combination with one or both of the conductive auxiliary agent and the binder. .. As the conductive binder, TAB-2 (manufactured by Hosen Co., Ltd.) already on the market 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 the ionic conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

The compounding ratio of the components contained in the positive electrode active material layer and the negative electrode active material layer is not particularly limited. The compounding ratio can be adjusted by appropriately referring to known knowledge about the non-aqueous electrolyte secondary battery.

The thickness of each active material layer (active material layer on one side of the current collector) is also 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 about 2 to 100 μm, in consideration of the purpose of use of the battery (emphasis on output, 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, if it is used for a large battery that requires high energy density, a current collector having a large area is used.

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

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

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

There are no particular restrictions on the materials that make up the current collector. For example, a metal or a resin obtained by adding a conductive filler to a conductive polymer material or a non-conductive polymer material can be adopted.

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

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

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), and polyimide. (PI), Polyethyleneimide (PAI), Polyethylene (PA), Polytetrafluoroethylene (PTFE), Styrene-butadiene rubber (SBR), Polyacrylonitrile (PAN), Polymethylacrylate (PMA), Polymethylmethacrylate (PMMA) , Polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), polystyrene (PS) and the like. Such non-conductive polymer materials can have excellent potential resistance or solvent resistance.

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

The conductive filler can be used without particular limitation as long as it is a conductive substance. For example, materials having excellent conductivity, potential resistance, or lithium ion blocking property include metals and conductive carbon. The metal is not particularly limited, but is 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 contain an alloy or a metal oxide containing. Further, the conductive carbon is not particularly limited. Preferably, it contains at least one selected from the group consisting of acetylene black, vulcan, black pearl, carbon nanofiber, ketjen black, carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene.

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

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

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), and the like. Examples thereof include carbonates such as methylpropyl carbonate (MPC).

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

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

The gel electrolyte has a structure in which the above liquid electrolyte (electrolyte solution) is injected into a matrix polymer made of an ionic conductive polymer. By using a gel polymer electrolyte as the electrolyte, the fluidity of the electrolyte is lost, and it is easy to block the ionic conduction between the layers, which is excellent.

Examples of the ionic conductive polymer used as the matrix polymer include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. Electrolyte salts such as lithium salts can be well dissolved in such polyalkylene oxide-based polymers.

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. In this embodiment, it is particularly effective for a gel electrolyte having a large amount of electrolyte and having a proportion of the electrolyte of 70% by mass or more.

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

The true 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 as a plasticizer. Therefore, when the electrolyte layer is composed of the intrinsic polymer electrolyte, there is no concern about liquid leakage from the battery, and the reliability of the battery can be improved.

Matrix polymers of gel electrolytes and true polymer electrolytes can exhibit excellent mechanical strength by forming crosslinked structures. In order to form a crosslinked structure, a suitable polymerization initiator is used, and a polymerizable polymer for forming a polymer electrolyte (for example, PEO or PPO) is subjected to thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. It may be polymerized.

<Current collector plate and lead>
A current collector may be used for the purpose of extracting current to the outside of the battery. The current collector plate is electrically connected to the current collector and the lead, and is taken out of the laminated sheet which is the battery exterior material.

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

The positive electrode terminal lead and the negative electrode terminal lead are also used as necessary. As the material of the positive electrode terminal lead and the negative electrode terminal lead, the terminal lead used in a known lithium ion secondary battery can be used. The portion taken out from the battery exterior material 29 has heat-resistant insulation so as not to come into contact with peripheral devices or wiring and cause an electric leakage to affect the product (for example, automobile parts, especially electronic devices). It is preferable to cover with a heat-shrinkable tube or the like.

<Battery exterior material>
As the battery exterior material 29, a known metal can case can be used, or a bag-shaped case using a laminated film containing aluminum that can cover the power generation element can be used. As the laminate film, for example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated 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 can be suitably used for batteries for large devices for EVs and HEVs.

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

<Appearance 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 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 the periphery thereof is heat-sealed. The power generation element 57 pulls 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 (stacked battery) 10 shown in FIG. The power generation element 57 is formed by stacking a plurality of single battery layers (single cells) 19 composed of a positive electrode (positive electrode active material layer) 13, an electrolyte layer 17, and a negative electrode (negative electrode active material layer) 15.

The lithium ion secondary battery is not limited to a laminated flat battery (laminated cell). Winding lithium-ion batteries include those with a cylindrical shape (coin cell) and those with a prismatic shape (square cell), and those that are shaped like a rectangular flat shape by deforming such a cylindrical shape. Further, the cell may be a cylindrical cell, and the like is not particularly limited. The cylindrical or prismatic shape is not particularly limited, for example, a laminated film may be used for the exterior material, or a conventional cylindrical can (metal can) may be used. Preferably, the power generation element is exteriorized with an aluminum laminate film. By this form, weight reduction can be achieved.

Further, the removal 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 pulled 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 each and taken out from each side. It is not limited to what is shown in FIG. 2, such as good. Further, in the winding 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 made of the negative electrode active material for the lithium ion secondary battery of the present embodiment include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, fuel cell vehicles, and hybrids. It can be suitably used as a large-capacity power source for fuel cell vehicles and the like. That is, it can be suitably used for a vehicle driving power source or an auxiliary power source that requires a high volume energy density and a high volume output density.

In the above embodiment, the lithium ion battery is exemplified as the electric device, but the present invention is not limited to this, and the present invention can be applied to other types of secondary batteries and further to primary batteries. Moreover, it can be applied not only to a battery but also to a capacitor.

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

(Example 1)
[Preparation of Si-containing alloy (alloy active material)]
The alloy type was Si ₆₅ Sn _4.8 Ti ₂₉ Al _1.2 (Si ₆₅ % by mass-Sn _4.8 % by mass-Ti ₂₉ % by mass-Al _1.2 % by mass), and the alloy was prepared by a liquid quenching solidification method. This will be described in detail below. Specifically, a high-purity metal Si ingot (5N), a high-purity Sn plate (3N), a high-purity Ti wire (3N), and a high-purity Al shot (3N) are used, and a Si alloy (3N) is used by an arc melting method. An ingot alloy of (Si65% by mass, Sn4.8% by mass, Ti29% by mass, Al1.2% by mass) was produced. The ingot alloy was pulverized and roughly pulverized to a diameter of about 2 mm so that it could be easily put into a quartz nozzle. This was used as the mother alloy of the liquid quenching solidification method (quenching roll solidification method).

Subsequently, the coarsely pulverized powder of the ingot alloy was used as a mother alloy, and a thin band alloy = a quenching thin band (ribbon) alloy was produced as a Si-containing alloy by a liquid quenching solidification method. Specifically, using a liquid quenching and solidifying device NEV-A05 manufactured by Nissin Giken Co., Ltd., Si ₆₅ Sn was placed in a quartz nozzle installed in a chamber in which Ar was replaced and the gauge pressure was reduced to -0.03 MPa. A mother alloy of _4.8 Ti ₂₉ Al _1.2 was added and melted by high frequency induction heating. Then, it was injected onto a Cu roll having a rotation speed of 4000 rpm (peripheral speed: 41.9 m / sec) at an injection pressure of 0.03 MPa to prepare a thin band alloy. The cooling rate of the alloy in the liquid quenching solidification method was 4.6 × 10 ⁶ ℃ / sec. The critical cooling rate of the mother alloy composition was 2.0 × ¹⁰ 7 K / sec. The thickness of the obtained thin band alloy (quenched thin band alloy) was 18 μm.

Then, the obtained thin band alloy (quenched thin band alloy) was pulverized. Specifically, the thin band alloy (quenched thin band alloy) was pulverized and roughly pulverized 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 Fritsch of Germany, zirconia crushed balls and coarsely crushed thin band alloy (quenched thin band alloy) powder were put into a zirconia crushing pot and crushed at 400 rpm for 1 hour. The treatment was carried out to obtain a Si-containing alloy (negative electrode active material) having the same alloy composition as the alloy type. The average particle size D50 of the obtained Si-containing alloy (negative electrode active material) powder was 7.2 μm, and D90 was 18 μm.

[Preparation of negative electrode]
80 parts by mass of the Si-containing alloy (Si ₆₅ Sn _4.8 Ti ₂₉ Al _1.2 ) produced above, which is the negative electrode active material, 5 parts by mass of acetylene black, which is a conductive auxiliary agent, and 15 parts by mass of polyamide-imide, which is a binder. The parts were mixed and dispersed in N-methylpyrrolidone to obtain a negative electrode slurry. Next, the obtained negative electrode slurry was uniformly applied to both sides of the 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 obtain the negative electrode. Obtained.

[Manufacturing 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 placed between them. Next, a laminate of the negative electrode, the separator, and the counter electrode Li was arranged 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 electrolyte is injected with a syringe, springs and spacers are laminated, and the upper side of the coin cell is overlapped and sealed by crimping. Then, a lithium ion secondary battery (coin cell) was obtained.

The electrolytic solution is a lithium salt (supporting salt) in an organic solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a ratio of EC: DEC = 1: 2 (volume ratio). A solution prepared by dissolving lithium fluorophosphate (LiPF ₆ ) so as to have a concentration of 1 mol / L was used.

(Example 2)
The alloy type was changed to Si ₆₁ Sn _7.2 Ti ₃₀ Al _1.8 (Si ₆₁ mass% -Sn _7.2 mass% -Ti ₃₀ mass% -Al _1.8 mass%), and the injection pressure in the liquid quenching solidification method was set to 0. A negative electrode active material, a negative electrode, and a lithium ion secondary battery (coin cell) were produced by the same method as in Example 1 described above except that the pressure was set to 05 MPa. The cooling rate of the alloy by the liquid quenching solidification method was 4.0 × ¹⁰⁶ ° C./sec. The critical cooling rate of the mother alloy composition was 1.9 × ¹⁰ 7 K / sec. The thickness of the obtained thin band alloy (quenched thin band alloy) was 20 μm. The average particle size D50 of the obtained Si-containing alloy (negative electrode active material) powder was 6.8 μm, and D90 was 20 μm.

(Comparative Example 1)
A negative electrode active material, a negative electrode, and a lithium ion secondary battery (coin cell) were produced by the same method as in Example 1 described above except that the alloy type was changed to Si ₆₀ Sn ₁₀ Ti ₃₀ . The cooling rate of the alloy in the liquid quenching solidification method was 4.6 × 10 ⁶ ℃ / sec. The critical cooling rate of the mother alloy composition was 4.3 × ¹⁰ 7 K / sec. The thickness of the obtained thin band alloy (quenched thin band alloy) was 18 μm. The average particle size of the obtained Si-containing alloy (negative electrode active material) powder was D50 = 6.5 μm (D90 = 17 μm).

[Analysis of the tissue structure of the negative electrode active material]
The structural structure (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. 6 to 9, and from the fine structure of the alloy of Example 1, the first phase containing silicide (ceiling) of Ti element, which is a transition metal, as a main component. (SiO phase), a second phase (a-Si phase) containing Al in part and containing amorphous or low crystallinity Si as a main component, and a third phase (Sn as a main component). Sn phase) and was confirmed to have. Further, from the microstructure of the alloy of Example 1, a plurality of independent first phases and a part of the first phase and the second phase have a eutectic structure. It was confirmed that the third phase was finer dispersed in the crystal structure than the first phase and the second phase. The third phase (Sn phase) in this eutectic structure is finely dispersed in the grain boundary portion (co-external portion) between the first phase and the second phase, especially around the second phase. It was confirmed that it was crystallized. From the microstructure of the alloy of Example 1, the domain size of the second phase in the eutectic structure is smaller than the domain size of the first phase, and the domain size of the third phase is larger than the domain size of the second phase. It was confirmed that it was small. Further, it was confirmed that the Si phase (second phase) in the eutectic structure is an amorphous phase having amorphous or low crystallinity Si (a-Si). That is, it was confirmed that the Si phase (second phase) in the eutectic structure had amorphous or low crystallinity Si (a-Si) by being amorphized.

Also in Example 2, the same results as in FIGS. 6 to 9 were obtained. Further, in Comparative Example 1, as shown in FIG. 4 (a), results different from those in FIGS. 4 (b) and 6 to 9 are obtained. FIG. 13 is a drawing showing quantitative mapping data of the fine structure (eutectic structure portion) of the alloy of Example 2 by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy). FIG. 13 (a) shows HAADF-STEM of Cs-STEM (spherical aberration-corrected scanning transmission electron microscope image) (high magnification) in which the eutectic structure is enlarged in the fine structure of the alloy of Example 2. It is a drawing which represents Image (high angle scattering dark field-scanning transmission electron microscope image). FIG. 13B is a drawing showing the mapping data of Sn (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 13A). FIG. 13 (c) is a drawing showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 13 (a)). FIG. 13 (d) is a drawing showing mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 13 (a)). FIG. 13 (e) is a drawing (upper right) in which the mapping data of Sn, Si, and Ti measured in the same field of view as HAADF-STEM (upper left FIG. 13 (a)) is superimposed. FIG. 14 is a drawing showing quantitative mapping data of the fine structure (eutectic structure portion) of the alloy of Example 2 by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy). FIG. 14 (a) shows HAADF-STEM of Cs-STEM (spherical aberration-corrected scanning transmission electron microscope image) (high magnification) in which the eutectic structure is enlarged in the fine structure of the alloy of Example 2. FIG. 3 is a drawing showing an image (high-angle scattered dark field-scanning transmission electron microscope image). FIG. 14B is a drawing showing mapping data of Al (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 14A). FIG. 14 (c) is a drawing showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 14 (a)). FIG. 14 (d) is a drawing showing mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 14 (a)). FIG. 14 (e) is a drawing (upper right) in which mapping data of Al, Si, and Ti measured in the same field of view as HAADF-STEM (upper left FIG. 14 (a)) is superimposed. FIG. 17 is a drawing showing quantitative mapping data of the fine structure (eutectic structure portion) of the alloy of Comparative Example 1 by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy). FIG. 17A shows the HAADF-STEM Image (high-angle scattering dark field-) of the Cs-STEM (spherical aberration-corrected scanning transmission electron microscope image) (high magnification) in which the fine structure of the alloy of Example 2 is enlarged. It is a drawing which shows the scanning transmission electron microscope image). FIG. 17 (b) is a drawing showing the mapping data of Sn (lower left) measured in the same field of view as HAADF-STEM (upper left FIG. 17 (a)). FIG. 17 (c) is a drawing showing mapping data of Si (lower center) measured in the same field of view as HAADF-STEM (upper left FIG. 17 (a)). FIG. 17 (d) is a drawing showing mapping data of Ti (lower right) measured in the same field of view as HAADF-STEM (upper left FIG. 17 (a)). FIG. 17 (e) is a drawing (upper right) in which the mapping data of Sn, Si, and Ti measured in the same field of view as HAADF-STEM (upper left FIG. 17 (a)) is superimposed.

That is, also from the fine structure of the alloy of Example 2, a first phase (SiO phase) containing silicide (ceiling) of Ti element which is a transition metal as a main component and Al (further Sn) in a part thereof. It has a second phase (a-Si phase) containing amorphous or low crystalline Si as a main component and a third phase (Sn phase) containing Sn as a main component. (See FIGS. 13 and 14, Cs-STEM (spherical aberration-corrected scanning transmission electron microscope image) (low magnification) and (medium magnification) have the same fine structure as in FIGS. 6 and 7 of Example 1. Therefore, the drawing is omitted). Further, from the microstructure of the alloy of Example 2, a plurality of independent first phases and a part of the first phase and the second phase have a eutectic structure. It was confirmed that the third phase was finer dispersed in the crystal structure than the first phase and the second phase (see FIGS. 13 and 14). The third phase (Sn phase) in this eutectic structure is finely dispersed in the grain boundary portion (co-external portion) between the first phase and the second phase, especially around the second phase. It was confirmed that the crystals were crystallized (see FIGS. 13 and 14). From the microstructure of the alloy of Example 2, the domain size of the second phase in the eutectic structure is smaller than the domain size of the first phase, and the domain size of the third phase is larger than the domain size of the second phase. It was confirmed that it was small. Further, it was confirmed that the Si phase (second phase) in the eutectic structure was an amorphous phase having amorphous or low crystallinity Si (a-Si). That is, it was confirmed that the Si phase (second phase) in the eutectic structure had amorphous or low crystallinity Si (a-Si) by being amorphized (FIG. 13,). See FIG. 14). On the other hand, in the SiSnTi ternary alloy used in Comparative Example 1, as shown in FIG. 4A and FIG. Since it does not have a wrapping (microstructure) structure, it can be said that the effect of suppressing the expansion of the Si active material by wrapping (two-stage stance) cannot be sufficiently exerted.

Further, the domain size of the independent first phase (TiSi ₂ phase) and the first phase in the eutectic structure in the microstructure of the Si-containing alloy of the negative electrode active material prepared in Examples 1 and 2 and Comparative Example 1. , The domain sizes of the second phase and the third phase are as described above. Specifically, for the alloy compositions of Examples 1 and 2 and Comparative Example 1, the domain size of the independent first phase and the first phase in the eutectic structure (TiSi ₂ phase) obtained by the measurement method described above. The results of each domain size of the second phase (Si phase) and the third phase (Sn phase) are shown in Table 1 below.

[Evaluation of amorphous forming ability (critical cooling rate)]
In the negative electrode active material (Si-containing alloy) produced in Example 1, the critical cooling rate in the liquid phase composition at the start of eutectic of the mother alloy composition is as described above with reference to FIG. 12, and Example 1 Described in the text of. In the negative electrode active material (Si-containing alloy) produced in Example 2, the critical cooling rate in the liquid phase composition at the start of eutectic of the mother alloy composition was calculated. This result is shown in FIG. 16 and described in the text of Example 2. In the negative electrode active material (Si-containing alloy) produced in Comparative Example 1, the critical cooling rate in the liquid phase composition at the start of eutectic of the mother alloy composition was calculated. This result is described in the sentence of Comparative Example 1.

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

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

The evaluation cell is set to a constant current / constant voltage mode in the charging process (referring to the process of inserting Li into the evaluation electrode) in a constant temperature bath set to the above evaluation temperature using a charge / discharge tester. , 0.3C was charged from 2V to 10mV. After that, in the discharge process (referring to the Li desorption process from the evaluation electrode), the constant current mode was set, and the discharge was performed from 0.3 C, 10 mV to 2 V. The charge / discharge test was performed from the initial cycle (1 cycle) to 50 cycles under the same charge / discharge conditions, with the above charge / discharge cycle as one cycle. The results of determining the ratio of the discharge capacity in the 50th cycle (discharge capacity retention rate [%]) to the discharge capacity in the first cycle (initial discharge capacity) are shown in Table 2 and FIG. 19 below. Here, FIG. 19 is a drawing showing the relationship between the number of charge / discharge cycles and the discharge capacity retention rate [%] for each lithium ion secondary battery (coin cell) produced in Examples 1 and 2 and Comparative Example 1. is there.

From the results shown in Table 1 above, the lithium ion batteries using the negative electrode active materials of Examples 1 and 2 are maintained at a high discharge capacity retention rate after 50 cycles, and are excellent in cycle durability. You can see that. Further, in Examples 1 and 2 using the Si alloy negative electrode, the capacity is higher than that of the negative electrode active material using the carbon material (this point does not need to show a comparative example using the carbon material, so to speak. Since it is known (see background technology), the comparative example is omitted). The reason why high cycle durability was realized while exhibiting such high capacity is that the Si-containing alloy constituting the negative electrode active material is a quaternary system represented by Si-Sn-M (transition metal element) -Al. By having an alloy composition. Further, the microstructure contains a first phase containing VDD as a main component, a second phase containing Al in part and containing amorphous or low crystalline Si as a main component, and Sn as a main component. It has a third phase. Then, in such a microstructure, a part is a plurality of independent first phases and a part is a eutectic structure of the first phase and the second phase, and the eutectic structure is formed. This is because the third phase is more finely dispersed than the first and second phases.

On the other hand, it can be seen that the lithium ion battery using the negative electrode active material of Comparative Example 1 does not sufficiently obtain cycle durability. This is because the negative electrode active material of Comparative Example 1 does not have Al added as in the example, so that an independent first phase is formed as shown in Table 1, but the second phase in the eutectic structure is formed. And the first phase are about the same size. Therefore, the expansion of the second phase (Si phase) in the eutectic structure during the charge / discharge process cannot be sufficiently suppressed by the eutectic first phase, so to speak, it is suppressed by suppressing the two-stage stance. It seems that it cannot be done. Further, since Al is not added, the second phase in the eutectic structure is not finer than the first phase, and the third phase is also finely dispersed at the grain boundaries of the first phase and the second phase. However, relatively large phases are not dispersed and are localized and formed. Therefore, since the second phase cannot be sufficiently included in the first phase, when charged and discharged, the second phase cannot sufficiently suppress expansion and contraction by the first phase, and the conductivity is not sufficiently imparted. The second phase (Si) could not react uniformly, and it is considered that the durability deteriorated. Further, since the relatively large phase of the third phase is not dispersed and is localized and formed around the second phase (Si), the second phase is difficult to be amorphized. It is considered that the cycle durability was not sufficiently obtained due to the difference from the microstructure.

Further, when comparing Examples 1 and 2, it is considered that the reason why Example 2 is superior in cycle durability is as follows. This is because the domain size of the independent first phase is larger in Example 2. As a result, the expansion of the second phase in the eutectic structure during the charge / discharge process, especially the Si active material as the main component, is suppressed by being wrapped by the eutectic first phase, and a larger number of independent phases are suppressed. This is probably because the effect of suppressing the eutectic structure (particularly the second phase) by wrapping it in one phase and suppressing it by suppressing the two-stage stance is more remarkable. As a result, the phase transition of the amorphous-crystal (crystallization to Li ₁₅ Si ₄ ) when Si and Li are alloyed during charging is suppressed. As a result, the expansion and contraction of the Si-containing alloy during the charge / discharge process is reduced (and the first phase (0045 phase) composed of conductive silicide is eutectic with the second phase (a-Si phase). By silicide, the second phase (a-Si phase), particularly the Si active material as the main component, can be uniformly reacted. As a result, it is considered that the cycle durability is improved while showing the high capacity of the electric device in which the negative electrode active material is used.

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 Single battery layer,
21,57 Power generation elements,
25, 58 Negative current collector plate,
27, 59 Positive current collector plate,
29, 52 Battery exterior material (laminated film),
31 Microstructure of SiSnTiAl quaternary alloy (Si-containing alloy) of the present embodiment,
Fine structure of 31'SiSnTi ternary alloy (Si-containing alloy),
32 Multiple independent first phases (0045 phase),
32'silicide phase,
33 Eutectic structure,
34 First phase (silicide phase) in the eutectic structure,
35 Second phase (a-Si phase) in the eutectic structure,
35'Si phase,
36 The third phase (Sn phase), which is finer than the first phase and the second phase in the eutectic structure,
36'Sn phase.

Claims (12)

A negative electrode active material for electrical devices made of a Si-containing alloy.
The microstructure of the Si-containing alloy contains a first phase containing a transition metal silicide as a main component and a first phase containing Al as a main component and having amorphous or low crystallinity Si as a main component. It has two phases and a third phase whose main component is Sn.
Furthermore, a part is a plurality of independent first phases, and a part is a eutectic structure of a first phase and a second phase.
A negative electrode active material for an electric device, wherein the third phase is finer dispersed in the eutectic structure than the first phase and the second phase. The first aspect of the present invention is characterized in that the domain size of the second phase in the eutectic structure is smaller than the domain size of the first phase, and the domain size of the third phase is smaller than the domain size of the second phase. The negative electrode active material for electrical devices described. The invention according to claim 1 or 2, wherein the silicide which is the main component of the first phase in the microstructure is TiSi ₂ , and the second phase is a Si phase containing Sn. Negative electrode active material for electrical devices. The domain size of the first phase in the eutectic structure in the microstructure is 20 to 70 nm, the domain size of the second phase in the eutectic structure is 5 to 30 nm, and the domain size of the third phase is. The negative electrode active material for an electric device according to any one of claims 1 to 3, wherein the negative electrode active material is in the range of 3 to 10 nm. The Si-containing alloy is a Si—Sn—Ti—Al alloy.
The following chemical formula (1):
(In the above chemical formula (1),
A is an unavoidable impurity,
x, y, z, w and a represent values of mass%, where x, y, z and w are 58 ≦ x ≦ 68, 2 ≦ y ≦ 10, 25 ≦ z ≦ 35 and 0, respectively. .3 ≦ w ≦ 3, a is the balance, and x + y + z + w + a = 100. )
The negative electrode active material for an electric device according to any one of claims 1 to 4, which has a composition represented by. The claim is characterized in that x, y, z, and w are 59 ≦ x ≦ 66, 3 ≦ y ≦ 8.5, 28 ≦ z ≦ 31, and 0.4 ≦ w ≦ 2.5, respectively. 5. The negative electrode active material for an electric device according to 5. The negative electrode active material for an electric device according to any one of claims 1 to 6, wherein the domain size of the independent first phase in the microstructure is in the range of 200 to 600 nm. The method for producing a negative electrode active material for an electric device according to any one of claims 1 to 7.
A method for producing a negative electrode active material for an electric device, which comprises producing a quenching thin band of a Si-containing alloy by a liquid quenching solidification method using a mother alloy having the same composition as the Si-containing alloy. The method for producing a negative electrode active material for an electric device according to claim 8, wherein the quenching thin band is subjected to a mechanical alloying treatment. The method for producing a negative electrode active material for an electric device according to claim 8 or 9, wherein the critical cooling rate in the liquid quenching solidification method is 2.2 × 10 ⁷ K / sec or less. A negative electrode for an electric device, which comprises using the negative electrode active material for an electric device according to any one of claims 1 to 7. An electric device according to claim 11, wherein the negative electrode for an electric device is used.