JP6743503B2 - Negative electrode active material for electric device and electric device using the same - Google Patents

Description

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

In recent years, in order to deal with air pollution and global warming, reduction of carbon dioxide has been eagerly desired. In the automobile industry, expectations are growing for the reduction of carbon dioxide emissions by the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and electric devices such as secondary batteries for motor drives that hold the key to their practical application. Is being actively developed.

As a secondary battery for driving a motor, it is required to have extremely high output characteristics and high energy as compared with consumer lithium ion secondary batteries used in mobile phones, notebook computers and the like. Therefore, a lithium ion secondary battery, which has the highest theoretical energy among all batteries, has been attracting attention and is currently under rapid development.

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

Conventionally, carbon/graphite-based materials, which are advantageous in terms of charge/discharge cycle life and cost, have been used for the negative electrode of lithium-ion secondary batteries. However, since the carbon/graphite negative electrode material is charged and discharged by occluding/releasing lithium ions into the graphite crystal, the theoretical capacity of 372 mAh/g or more obtained from LiC ₆ which is the maximum lithium-introducing compound is used. There is a drawback that you can not get. For this reason, it is difficult to obtain a capacity and energy density satisfying the practical use level for vehicle applications with the carbon/graphite negative electrode material.

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

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

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

International Publication 2006/129415 pamphlet

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

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

The present inventors have conducted earnest research to solve the above problems. As a result, it has a ternary alloy composition represented by Si-Sn-Ti, and contains amorphous or low crystalline silicon having tin as a solid solution in the crystal structure of silicon as a main component. While using a silicon-containing alloy having a structure in which a phase (hereinafter also referred to as an a-Si phase) is dispersed in a mother phase of a silicide phase containing a silicide of titanium as a negative electrode active material for an electric device, The inventors have found that the above problems can be solved by controlling the relationship between peak intensities of various peaks confirmed in a spectrum obtained by a differential scanning calorimetry (DSC) method for the silicon-containing alloy, and completed the present invention. Came to let.

That is, the present invention relates to a negative electrode active material for electric devices, which is made of a silicon-containing alloy. Specifically, the negative electrode active material is a phase whose main component is amorphous or low crystalline silicon in which tin is solid-dissolved in the crystal structure of silicon in a mother phase of a silicide phase containing TiSi _2. Has a structure in which the following chemical formula (1)

(In the above chemical formula (1), A is an unavoidable impurity, and x, y, z, and a represent the value of mass %, where 0<x<100, 0<y<100, 0<z. <100, 0≦a<0.5, and x+y+z+a=100.)
It consists of a silicon-containing alloy having a composition represented by: And the said negative electrode active material makes Ti(1) the peak intensity of the Si peak observed at 1200-1350 degreeC in the spectrum obtained by a differential scanning calorimetry (DSC) method, and is TiSi observed at 1400-1500 degreeC. An a-Si peak defined as a difference between the peak intensity corresponding to the amount of Si and the peak intensity of the Si peak when assuming that the peak intensity of the _two peaks is I(2) and the a-Si phase is not included. When the peak intensity of is I(3),
I(2)/I(1)>0.59, and
I(3)/I(1)>0.56
Is characterized in that the relationship of is satisfied.

According to the present invention, it is possible to sufficiently promote the amorphization of Si and suppress the volume change during expansion and contraction of the active material by surrounding the phase containing silicon as the main component with the hard silicide phase. It is possible to improve cycle durability of an electric device such as a lithium ion secondary battery.

FIG. 1 is a schematic cross-sectional view schematically showing a stacking type flat non-polar lithium ion secondary battery which is a typical embodiment of the electric device according to the present invention. FIG. 2 is a perspective view schematically showing the appearance of a laminated flat lithium-ion secondary battery that is a typical embodiment of the electric device according to the present invention. FIG. 3 is a spectrum showing the results of differential scanning calorimetry (DSC) of the negative electrode active material (silicon-containing alloy) produced in Example 2 described later. FIG. 4 is a spectrum showing the results of differential scanning calorimetry (DSC) of the negative electrode active material (silicon-containing alloy) produced in Comparative Example 1 described later. FIG. 5A is an observation photograph (low magnification) showing the result of analyzing the structure structure of the silicon-containing alloy (negative electrode active material) produced in Example 1. FIG. 5B is an observation photograph (high magnification) showing the result of analyzing the structure structure of the silicon-containing alloy (negative electrode active material) produced in Example 1. FIG. 6A is an observation photograph (low magnification) showing the result of analysis of the structure of the silicon-containing alloy (negative electrode active material) produced in Example 2. FIG. 6B is an observation photograph (high magnification) showing the result of analyzing the structure structure of the silicon-containing alloy (negative electrode active material) produced in Example 2. FIG. 7A is an observation photograph (low magnification) showing the result of analysis of the structure of the silicon-containing alloy (negative electrode active material) produced in Example 3. FIG. 7B is an observation photograph (high magnification) showing the result of analyzing the structure structure of the silicon-containing alloy (negative electrode active material) produced in Example 3. FIG. 8A is an observation photograph (low magnification) showing the result of analysis of the structure of the silicon-containing alloy (negative electrode active material) produced in Example 4. FIG. 8B is an observation photograph (high magnification) showing the result of analysis of the structure of the silicon-containing alloy (negative electrode active material) produced in Example 4. FIG. 9A is an observation photograph (low magnification) showing the result of analysis of the structure of the silicon-containing alloy (negative electrode active material) produced in Comparative Example 1. FIG. 9B is an observation photograph (high magnification) showing the result of analysis of the structure of the silicon-containing alloy (negative electrode active material) produced in Comparative Example 1.

Embodiments of a negative electrode active material for an electric device of the present invention and an electric device using the same will be described below with reference to the drawings. However, the technical scope of the present invention should be determined based on the description of the claims, and is not limited to the following modes. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Further, the dimensional ratios in the drawings are exaggerated for convenience of description, and may differ from the actual ratios.

Hereinafter, a basic configuration of an electric device to which the negative electrode active material for an electric device of the present invention can be applied will be described with reference to the drawings. In the present embodiment, a lithium ion secondary battery will be described as an example of the electric device.

First, in a negative electrode for a lithium ion secondary battery, which is a typical embodiment of a negative electrode containing a negative electrode active material for an electric device according to the present invention, and a lithium ion secondary battery using the same, a cell (single battery layer ) Is large, and high energy density and high power density can be achieved. Therefore, the lithium ion secondary battery using the negative electrode active material for the lithium ion secondary battery of the present embodiment is excellent as a drive power source or an auxiliary power source for a vehicle. As a result, it can be suitably used as a lithium-ion secondary battery for a vehicle drive power source or the like. In addition, it can be sufficiently applied 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 with respect to other constituent requirements. , It should not be particularly limited.

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

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

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

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

<Overall structure of battery>
FIG. 1 schematically shows the entire structure of a flat (laminated) lithium ion secondary battery (hereinafter, also simply referred to as “laminated battery”), which is a typical embodiment of the electric device of the present invention. It is the cross-sectional schematic diagram represented.

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

Thus, the adjacent positive electrode, electrolyte layer, and negative electrode form one unit cell layer 19. Therefore, it can be said that the stacked battery 10 shown in FIG. 1 has a configuration in which a plurality of unit cell layers 19 are stacked and electrically connected in parallel. In addition, in each of the outermost positive electrode current collectors located on both outermost layers of the power generation element 21, the positive electrode active material layer 15 is arranged on only one surface, but the active material layers may be provided on both surfaces. .. That is, the current collector having the active material layers on both sides may be used as it is as the current collector for the outermost layer, instead of the current collector dedicated to the outermost layer in which the active material layer is provided on only one surface. Further, by reversing the arrangement of the positive electrode and the negative electrode from that in FIG. 1, the outermost negative electrode current collectors are located on both outermost layers of the power generation element 21, and one surface of the outermost layer negative electrode current collector or You may make it arrange|position the negative electrode active material layer on both surfaces.

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

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

<Active material layer>
The active material layer 13 or 15 contains an active material, and may further contain other additives as needed.

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

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

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

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

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

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

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

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

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

(Binder)
The binder is added for the purpose of binding the active materials to each other or the active material and the current collector to maintain the electrode structure. The binder used for the positive electrode active material layer is not particularly limited, but examples thereof include the following materials. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile (PEN), polyacrylonitrile, polyimide, polyamide, polyamide imide, cellulose, carboxymethyl cellulose (CMC), ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene Rubber (SBR), isoprene rubber, butadiene rubber, ethylene/propylene rubber, ethylene/propylene/diene copolymer, styrene/butadiene/styrene block copolymer and hydrogenated product thereof, styrene/isoprene/styrene block copolymer, and Thermoplastic polymers such as hydrogenated products thereof, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene/hexafluoropropylene copolymer (FEP), tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer Fluorine resin such as polymer (PFA), ethylene/tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene/chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), Vinylidene fluoride-hexafluoropropylene fluororubber (VDF-HFP fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluororubber (VDF-HFP-TFE fluororubber), vinylidene fluoride-pentafluoro Propylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene Examples thereof include vinylidene fluoride-based fluororubbers such as vinylidene fluoride-based fluororubbers (VDF-PFMVE-TFE-based fluororubbers), vinylidene fluoride-chlorotrifluoroethylene-based fluororubbers (VDF-CTFE-based fluororubbers), and epoxy resins. Among them, 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 mass% with respect to the active material layer. And more preferably 1 to 10 mass %.

The positive electrode (positive electrode active material layer) is formed by any of a kneading method, a sputtering method, a vapor deposition method, a CVD method, a PVD method, an ion plating method, and a thermal spraying method, in addition to a method of applying (coating) a usual slurry. 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 this embodiment, the negative electrode active material is made of a silicon-containing alloy. Hereinafter, the composition, structure, and physical properties of the silicon-containing alloy according to this embodiment will be described.

[Composition of silicon-containing alloy]
The silicon-containing alloy forming the negative electrode active material in the present embodiment has a ternary alloy composition represented by Si-Sn-Ti. More specifically, the silicon-containing alloy forming the negative electrode active material in the present embodiment has a composition represented by the following chemical formula (1).

In the above chemical formula (1), A is an unavoidable impurity, and x, y, z, and a represent mass% values, where 0<x<100, 0<y<100, 0<z<. 100, 0≦a<0.5, and x+y+z+a=100.

As is clear from the above chemical formula (1), the silicon-containing alloy (having the composition of Si _x Sn _y Ti _z A _a ) according to this embodiment is a ternary system of Si, Sn, and Ti. With such a composition, high cycle durability can be realized. In addition, in the present specification, the “unavoidable impurities” mean those present in the raw material of the Si-containing alloy or inevitably mixed in the manufacturing process. Although the unavoidable impurities are essentially unnecessary, they are permissible impurities because they are trace amounts and do not affect the characteristics of the Si alloy.

In the present embodiment, by selecting Ti as an additive element to the negative electrode active material (silicon-containing alloy), it is possible to suppress the amorphous-crystal phase transition during Li alloying and improve the cycle life. .. Further, this makes the capacity higher than that of the conventional negative electrode active material (for example, carbon-based negative electrode active material).

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

As described above, the silicon-containing alloy (having the composition of Si _x Sn _y Ti _z A _a ) according to this embodiment is a ternary system of Si, Sn and Ti. Here, the sum of the constituent ratios (mass ratios x, y, z) of the constituent elements is 100% by mass, but there are no particular restrictions on the respective values of x, y, z. x is preferably 58≦x≦73, more preferably 59≦x≦70, from the viewpoint of maintaining durability against charge/discharge (insertion/desorption of Li ions) and balancing the initial capacity. It is preferably 59≦x≦65, and particularly preferably 59≦x≦63. With respect to y, from the viewpoint of enabling solid solution in the Si phase and increasing the distance between Si tetrahedra in the Si phase, reversible insertion and desorption of Li ions at the time of charging and discharging, It is preferably 2≦y≦15, more preferably 5≦y≦13, and further preferably 7≦y≦11. As for z, 25≦z≦35 is preferable, and 27≦z is more preferable, from the viewpoint of maintaining durability against charge/discharge (insertion/desorption of Li ions) and balance of initial capacity, similar to x. ≦33, and more preferably 28≦z≦30. As described above, by including Si in a relatively large amount and Ti in a relatively large amount and also including Sn to some extent, it becomes easy to achieve the microstructure structure of the silicon-containing alloy according to the present embodiment. However, the numerical range of the constituent ratio of each constituent element described above is merely for explaining the preferred embodiment, and is within the technical scope of the present invention as long as it is included in the claims.

As described above, A is an impurity (unavoidable impurity) other than the above-mentioned three components, which is derived from the raw materials and the manufacturing method. The a is 0≦a<0.5, and preferably 0≦a<0.1. Whether or not the negative electrode active material (silicon-containing alloy) has the composition of the above chemical formula (1) is confirmed by qualitative analysis by fluorescent X-ray analysis (XRF) and quantitative analysis by inductively coupled plasma (ICP) emission spectroscopy. It is possible to

[Structure of Silicon-Containing Alloy]
Subsequently, the silicon-containing alloy constituting the negative electrode active material in the present embodiment also has a structure in which the a-Si phase containing amorphous or low crystalline silicon as a main component is dispersed in the silicide phase. There are features. That is, the feature of the silicon-containing alloy according to the present embodiment is that the silicon-containing alloy according to the present embodiment has a so-called sea-island structure in which islands made of the a-Si phase as the dispersed phase are dispersed in the sea made of the silicide phase as the continuous phase. There is one. Whether or not the silicon-containing alloy has such a microstructure structure is observed, for example, after observing the silicon-containing alloy using a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM). It can be confirmed by performing element intensity mapping by EDX (energy dispersive X-ray spectroscopy) for the same visual field as the image.

<a-Si phase>
Here, in the silicon-containing alloy according to the present embodiment, the a-Si phase is a phase containing amorphous or low crystalline silicon formed by solid solution of tin in the crystal structure of silicon. This a-Si phase is a phase involved in occlusion/release of lithium ions during the operation of the electric device (lithium ion secondary battery) of the present embodiment, and is capable of reacting electrochemically with lithium (that is, per unit weight and It is a phase capable of absorbing and releasing a large amount of lithium per volume). Further, tin is in solid solution inside the crystal structure of silicon constituting the a-Si phase, but since silicon has poor electron conductivity, a trace amount of additional elements such as phosphorus and boron and A transition metal or the like may be included. The size of the a-Si phase is not particularly limited, but from the viewpoint of suppressing expansion during charging, the smaller the size of the a-Si phase, the more preferable it is, specifically, 10 nm or less is preferable, and 8 nm or less is preferable. More preferably. On the other hand, although the lower limit of the size of the a-Si phase is not particularly limited, it is preferably 1 nm or more, more preferably 2 nm or more, further preferably 5 nm or more, and particularly preferably 8 nm or more. Regarding the value of the diameter of the a-Si phase, the EDX element mapping of Si and the EDX element mapping of Ti at high magnification (25 nm scale bar) in HAADF-STEM were compared, and a region where Si was present and Ti was not present was compared. Is regarded as the Si phase, the intensity is 1/10 of the maximum value in the EDX element mapping of Ti as a threshold value, and the binarized image processing is performed on the region where the intensity is equal to or less than this threshold value. It can be obtained as an arithmetic mean value of the measured values obtained by measuring five or more phases by the method of reading the phase dimensions. Similarly, for the value of the diameter of the silicide phase described later, the EDX element mapping of Si at high magnification (25 nm scale bar) in Cs-STEM is compared with the EDX element mapping of Ti, and the region where Si is present and Ti is also present. Is regarded as a silicide phase, 1/10 of the maximum value in the EDX element mapping of Ti is used as a threshold value, and binarized image processing is performed on a region where the intensity is equal to or higher than this threshold value. It can be obtained as an arithmetic mean value of the measured values obtained by measuring five or more phases by the method of reading the phase dimensions.

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

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

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

A plurality of phases may exist in the silicide phase, for example, _two or more phases having different composition ratios of Ti and Si (for example, TiSi ₂ and TiSi) may exist. Ti has a higher electron conductivity than silicides of other elements when forming a silicide and has high strength. In particular, TiSi ₂ , which is one kind of silicide, is preferable because it exhibits extremely excellent electronic conductivity. In view of such properties of silicide and the excellent identification of amorphous Si described above, it is preferable that the silicide is TiSi ₂ and the a-Si phase is amorphous.

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

The size of the silicide phase is not particularly limited, but in a preferred embodiment, the size of the silicide phase is 50 nm or less, more preferably 30 nm or less, and further preferably 25 nm or less. With such a structure, the negative electrode active material (silicon-containing alloy) can have a higher capacity. On the other hand, although the lower limit of the size of the silicide phase is not particularly limited, the diameter of the silicide phase is the diameter of the a-Si phase described above from the viewpoint of suppressing expansion/contraction of the a-Si phase due to Li insertion/desorption. The absolute value is preferably 10 nm or more, more preferably 15 nm or more.

Note that titanium disilicide (TiSi ₂ ) has two types of crystal structures, a C49 structure and a C54 structure. The C49 structure is a phase (metastable phase) exhibiting a high resistivity of about 60 μΩ·cm, and has a base-centered orthorhombic structure. On the other hand, the C54 structure is a phase (stable phase) having a resistivity as low as 15 to 20 μΩ·cm and is a face center-orthorhombic structure. Here, the crystal structure of the disilicide (TiSi ₂ ) contained in the silicide phase of the silicon-containing alloy (negative electrode active material) according to the present embodiment is preferably the C54 structure. The disilicide (TiSi ₂ ) having a C54 structure has a lower resistivity and a higher hardness than those having a C49 structure. Therefore, it is considered that the negative electrode active material according to the present embodiment exhibits high electron conductivity and is also excellent in the effect of alleviating the stress generated by the expansion and contraction of the a-Si phase in the active material during charge and discharge, which is also high. It seems that this contributes to the realization of cycle durability. From the above, in a preferred embodiment of the present invention, when the titanium silicide contained in the silicide phase is titanium disilicide (TiSi ₂ ), the TiSi ₂ having a C54 structure is the main component (mass). 50 mass% or more). Here, the “main component” means that the mass ratio of TiSi ₂ having a C54 structure in 100% by mass of the silicide phase is more than 50% by mass, preferably 80% by mass or more, and more preferably It is 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass.

[Relationship between peak strengths of silicon-containing alloys]
In addition, in the present embodiment, the silicon-containing alloy has a peak intensity of Si peak observed at 1200 to 1350° C. in a spectrum obtained by a differential scanning calorimetry (DSC) method as I(1), and is 1400 to 1500° C. The peak intensity of the observed TiSi ₂ peak is defined as I(2) and is defined as the difference between the peak intensity corresponding to the amount of Si and the peak intensity of the Si peak when it is assumed that the a-Si phase is not included. When the peak intensity of the a-Si peak is I(3),
I(2)/I(1)>0.59, and
I(3)/I(1)>0.56
There is also a feature in satisfying the relationship. Here, the differential scanning calorimetry (DSC) method is a method of measuring the difference in energy input to the substance and the reference substance as a function of temperature while changing the temperature of the substance and the reference substance by a program. The differential scanning calorimetry (DSC) of the silicon-containing alloy in the present invention shall be performed using the method described in the section of Examples described later.

When the differential scanning calorimetry (DSC) is performed on the silicon-containing alloy according to the present invention in this manner, as shown in, for example, FIG. 3 (spectrum measured for the silicon-containing alloy produced in Example 2 described later). In addition, a baseline shift is observed at a temperature around 600 to 700° C. (temperature corresponding to point f shown in FIG. 3). The temperature at this time is the glass transition temperature (Tg) of this alloy. Then, when the temperature rise is continued thereafter, a relatively large and sharp endothermic peak is observed at a temperature around 1200 to 1350° C. (point c shown in FIG. 3 is this peak top, and the endothermic peak is crystalline Si. A relatively small and broad endothermic peak is observed at a temperature around 1400 to 1500° C. (point e shown in FIG. 3 is the top of this peak, and the endothermic peak indicates the heat of fusion of TiSi ₂ ). Represent). In the present invention, the "peak intensity of Si peak" means the distance between the intersection of the perpendicular line drawn from the point c toward the baseline and the baseline (point a shown in FIG. 3) and the point c (of the line segment ac). It means the relative value of (length). Further, the “peak intensity of the TiSi ₂ peak” in the present invention means the distance (line segment) between the intersection point (point d in FIG. 3) of the perpendicular line drawn from the point e toward the baseline and the baseline. (length of de). On the other hand, in the silicon-containing alloy according to the present invention, the glass transition temperature (Tg) exists due to the inclusion of the a-Si phase, and as a result, the baseline shift is observed. Therefore, the intersection point (point b in FIG. 3) and the point c of the perpendicular line drawn from the point c toward the extrapolated virtual baseline on the lower temperature side than the glass transition temperature (Tg) and the virtual baseline. And the relative value of the distance (length of line segment bc) is the Si amount when it is assumed that the a-Si phase is not included (the total Si amount when all Si is assumed to be crystalline Si). Represents the peak intensity corresponding to. In other words, the length obtained by subtracting the length of the line segment ac (the actual amount of crystalline Si) from the length of the line segment bc (the peak intensity corresponding to the amount of Si assuming that the a-Si phase is not included). The relative value of the distance (that is, the distance between the point b and the point a (the length of the line segment ab)) corresponds to the amount of a-Si contained in the silicon-containing alloy. Therefore, in the present specification, the peak intensity corresponding to the length of the line segment ab is the peak intensity corresponding to the amount of Si when the a-Si phase is not included and the peak intensity of the Si peak. The peak intensity of the a-Si peak defined as the difference between

As described above, the negative electrode active material made of the silicon-containing alloy according to the present embodiment has I(2)/I(1)>0.59 and I(3)/I(1)>0.56. It is characterized in that it satisfies the requirements. In a silicon-containing alloy satisfying such requirements, Si is sufficiently amorphized, and a phase containing silicon as a main component is surrounded by a hard silicide phase to suppress volume change during expansion and contraction of the active material. It becomes possible to do. As a result, it is considered possible to improve the cycle durability of electric devices such as lithium ion secondary batteries.

In a preferred embodiment of the present invention, the value of I(2)/I(1) preferably satisfies I(2)/I(1)≧0.70 from the viewpoint of further excellent cycle durability. More preferably, I(2)/I(1)≧0.76 is satisfied, further preferably I(2)/I(1)≧1.27 is satisfied, and particularly preferably I(2)/ I(1)≧1.69 is satisfied. Further, similarly, from the viewpoint of further excellent cycle durability, the value of I(3)/I(1) preferably satisfies I(3)/I(1)≧0.60, and more preferably I (3)/I(1)≧0.76, more preferably I(3)/I(1)≧1.00, and most preferably I(3)/I(1)≧1. .31 is satisfied. Above all, preferably, I(2)/I(1)≧0.76 and I(3)/I(1)≧0.76 are satisfied, and more preferably I(2)/I(1)≧1. .27 and I(3)/I(1)≧1.00, more preferably I(2)/I(1)≧1.69 and I(3)/I(1)≧1.31. To be satisfied.

On the other hand, in the silicon-containing alloy (negative electrode active material) according to this embodiment having excellent cycle durability, the value of the discharge capacity shows a trade-off relationship with the cycle durability. Therefore, from the viewpoint of ensuring a certain discharge capacity while achieving sufficient cycle durability, the relationship of I(2)×I(3)/{I(1)} ² <0.50 is further satisfied. It is preferable that the relationship of I(2)×I(3)/{I(1)} ² <0.48 is further satisfied, and I(2)×I(3)/{I(1) It is particularly preferable that the relationship of ² <0.45 is further satisfied, and it is most preferable that the relationship of I(2)×I(3)/{I(1)} ² <0.42 is further satisfied.

Regarding the composition, structure, and physical properties of the negative electrode active material described above, the control means for satisfying these is not particularly limited, but the composition of the raw material used when producing the silicon-containing alloy is adjusted. Alternatively, by adopting a manufacturing method according to another embodiment of the present invention described later, or by setting a relatively small amount of Sn when the amount of Ti is constant, the above-mentioned stipulations can be obtained. It is possible to control to satisfy.

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

(Method for producing negative electrode active material)
The method for producing the negative electrode active material for an electric device according to this embodiment is not particularly limited, and conventionally known knowledge can be appropriately referred to. However, in the present application, a structure in which an a-Si phase is dispersed in a silicide phase is provided. In addition, a high energy type mechanical alloying treatment can be used as an example of a method for producing a negative electrode active material made of a silicon-containing alloy in which each peak intensity value satisfies a predetermined relationship. Specifically, the powder of the mother alloy having the same composition as the silicon-containing alloy is subjected to mechanical alloying treatment by using a ball milling device such that a centrifugal force of 15 [G] or more is applied. A negative electrode active material for electric devices made of a silicon-containing alloy is obtained. As described above, the alloy having the above-mentioned microstructure structure is manufactured by performing the mechanical alloying treatment using the ball mill device to which a relatively large centrifugal force is applied to manufacture the negative electrode active material (silicon-containing alloy). It becomes possible to do. Further, the manufacturing method, it becomes possible to control the value of each peak intensity in the resulting alloy also to satisfy the above predetermined relationship, such as effective cycle compatibility and charge-discharge efficiency of the negative electrode active material. This is a manufacturing method that can contribute. Hereinafter, the above-described manufacturing method will be described in more detail, but the manufacturing method described below is only an example for manufacturing the present embodiment, and there is no particular limitation as long as it is a method capable of manufacturing the negative electrode active material of the present invention. ..

First, in order to obtain a mother alloy, powders of high-purity raw materials of silicon (Si), tin (Sn), and titanium (Ti) are prepared as raw materials.

Subsequently, a mechanical alloying process is performed using the raw material powder prepared above.

By alloying by mechanical alloying process, the state of the phase can be easily controlled.Therefore, mechanical alloying process uses ball mill equipment to crush the crushed balls and the raw material powder of the alloy into the crushing pot. By throwing in and applying energy, alloying can be aimed at. That is, heat is generated by the application of energy, the raw material powder is alloyed, the a-Si phase is made amorphous, the solid solution of tin into the phase, and the formation of the silicide phase proceed.

The manufacturing method according to this embodiment is characterized in that the centrifugal force applied to the contents by the ball mill device used for the mechanical alloying treatment is 15 [G] or more. A silicon-containing alloy (negative electrode active material) capable of exhibiting cycle durability equal to or higher than that of a shorter time treatment by performing mechanical alloying treatment using a ball mill device to which a relatively large centrifugal force is applied. Can be manufactured. In addition, since it is possible to reduce the amount of Sn, which is a relatively expensive raw material, it is also possible to reduce the manufacturing cost of the silicon-containing alloy (negative electrode active material). The value of the centrifugal force is preferably 50 [G] or more, more preferably 100 [G] or more, still more preferably 120 [G] or more, and particularly preferably 150 [G] or more. Yes, and most preferably 175 [G] or more. On the other hand, although the upper limit of the centrifugal force is not particularly limited, it is usually about 200 [G] in reality.

Here, the value of the centrifugal force applied to the contents in the ball mill device is calculated by the following mathematical formula:

In the above formula, Gnl is the centrifugal force [G], rs is the revolution radius [m], rpl is the revolution radius [m], iw is the revolution revolution ratio [-], and rpm is the rotation speed [revolutions/minute]. Therefore, it can be understood that the value of the centrifugal force Gnl increases as the revolution radius rs increases, the rotation radius rpl decreases, and the rotation speed increases.

The specific configuration of the ball mill device is not particularly limited, and conventionally known ball mill devices such as a planetary ball mill device and a stirring ball mill device can be used as long as they satisfy the above-mentioned centrifugal force regulation. However, in the manufacturing method according to the present embodiment, a stirred ball mill device is preferably used. This stirring ball mill device includes a container having a cylindrical inner surface and a stirring blade provided inside the container. Raw material powder, balls, a solvent, and a treating agent are charged in the container of the stirring ball mill device. Unlike the planetary ball mill device, the stirring blade provided in the container rotates to alloy the raw material powder without rotating the container. When such an agitating ball mill device is used, the content of the container can be vigorously agitated by the agitating blades, and thus a centrifugal force larger than that of other ball mill devices can be applied to the content of the container.

In general, as the time for carrying out the mechanical alloying treatment is increased, a silicon-containing alloy having a suitable microstructure can be obtained. However, in the production method according to the present embodiment, as described above, a relatively large centrifugal force is applied. Since the mechanical alloying treatment is performed so that force is applied to the contents, it is possible to achieve the same or higher cycle durability even if the mechanical alloying treatment time is shortened. From such a viewpoint, in the production method according to the present embodiment, the mechanical alloying treatment time is preferably 45 hours or less, more preferably 40 hours or less, further preferably 36 hours or less, and further preferably Is 30 hours or less, particularly preferably 24 hours or less, and most preferably 20 hours or less. The lower limit of the time for mechanical alloying treatment is not particularly set, but it is usually 12 hours or more.

Further, since the alloying treatment can be performed in a short time by applying high energy, the progress of Si oxidation can be suppressed, and therefore the value of each peak intensity can be controlled so as to satisfy the above predetermined relationship. From this viewpoint as well, it is preferable to obtain the silicon-containing alloy according to the present invention by increasing the value of the centrifugal force of the device used in the mechanical alloying treatment as described above.

In the mechanical alloying process using the ball mill device, it is possible to alloy the raw material powder using conventionally known balls, but it is preferable that the balls have a diameter of 1 mm or less, particularly 0.1 to 1 mm. Those made of titanium or zirconia having a diameter are used. Particularly, in the present embodiment, titanium balls produced by the plasma rotating electrode method are preferably used. Balls made of titanium or zirconia having a diameter of 1 mm or less produced by such a plasma rotary electrode method have a uniform spherical shape, and are particularly preferable as balls for obtaining a silicon-containing alloy.

Further, in this embodiment, the solvent charged in the container of the stirring ball mill is not particularly limited. Examples of such a solvent include water (particularly ion-exchanged water), methanol, ethanol, propanol, butanol, pentanol, dimethyl ketone, diethyl ketone, diethyl ether, dimethyl ether, diphenyl ether, toluene and xylene. These solvents are used alone or in appropriate combination.

Furthermore, in the present invention, the treating agent charged in the container is not particularly limited. Examples of such a treating agent include a carbon powder for preventing the adhesion of the contents to the inner wall of the container, a surfactant and/or a fatty acid.

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

In addition to the above-described manufacturing method, the mechanical alloying treatment may be performed after a process such as rapid solidification. As compared with the case of alloying from powder by rapid cooling, Si becomes amorphous and TiSi ₂ is alloyed in the initial state, so that alloying can be performed in a short time. Further, the steps can be appropriately combined as long as the negative electrode active material according to the present invention can be produced.

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

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

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

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

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

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

Conductive Aid The conductive aid refers to an additive that is added to improve the conductivity of the positive electrode active material layer or the negative electrode active material layer. Examples of the conductive aid include carbon black such as acetylene black, carbon materials such as graphite and vapor grown carbon fiber. When the active material layer contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of output characteristics of the battery.

The content of the conductive additive mixed in the active material layer is preferably 1% by mass or more, more preferably 3% by mass or more, and further preferably 5% by mass or more with respect to the total amount of the active material layer. is there. The content of the conductive additive mixed in the active material layer is preferably 15% by mass or less, more preferably 10% by mass or less, and further preferably 7% by mass or less with respect to the total amount of the active material layer. It is a range. The electron conductivity of the negative electrode active material itself made of the above-described silicon-containing alloy is low, the electrode resistance can be reduced by the amount of the conductive additive, and the compounding ratio (content) of the conductive additive in the active material layer is the above. By defining within the range, the following effects are exhibited. That is, the electron conductivity can be sufficiently ensured without hindering the electrode reaction, the decrease in energy density due to the decrease in electrode density can be suppressed, and the energy density due to the increase in electrode density can be improved. ..

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

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

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

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

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

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

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

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

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

There is no particular limitation on the material forming the current collector. For example, a metal or a resin in which a conductive filler is added to a conductive polymer material or a non-conductive polymer material can be adopted.

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

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

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

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

The conductive filler can be used without particular limitation as long as it is a substance having conductivity. For example, as a material having excellent conductivity, potential resistance, or lithium ion barrier property, metal and conductive carbon can be cited. The metal is not particularly limited, but at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb, and K or a metal thereof. It is preferable to include an alloy or a metal oxide containing. The conductive carbon is not particularly limited. Preferably, at least one selected from the group consisting of acetylene black, vulcan, black pearl, carbon nanofiber, ketjen black, carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene is included.

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

<Electrolyte layer>
A liquid electrolyte or a polymer electrolyte may be used as the electrolyte that constitutes the electrolyte layer 17.

The liquid electrolyte has a form in which a lithium salt (electrolyte salt) is dissolved in an organic solvent. Examples of the organic solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), Illustrative are carbonates such as methylpropyl carbonate (MPC). The above organic solvents may be used alone or in combination of two or more.

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

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

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

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

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

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

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

The matrix polymer of the gel electrolyte or the intrinsic polymer electrolyte can exhibit excellent mechanical strength by forming a crosslinked structure. In order to form a cross-linked structure, a suitable polymerization initiator may be used to perform thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. on a polymerizable polymer for forming a polyelectrolyte (for example, PEO or PPO). Polymerization may be performed.

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

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

The positive electrode terminal lead and the negative electrode terminal lead are also used as necessary. As a material for the positive electrode terminal lead and the negative electrode terminal lead, a terminal lead used in a known lithium ion secondary battery can be used. The portion taken out from the battery exterior material 29 has a heat-resistant insulating property so as not to contact the peripheral devices or wirings to leak electric current and affect the products (for example, automobile parts, especially electronic devices). It is preferable to coat with a heat-shrinkable tube.

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

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

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

As shown in FIG. 2, the laminated flat lithium ion secondary battery 50 has a rectangular flat shape, and a positive electrode current collector plate 59 and a negative electrode current collector plate 59 for extracting electric power from both sides thereof. The electric plate 58 is pulled out. The power generation element 57 is wrapped by the battery outer casing material 52 of the lithium-ion secondary battery 50 and its periphery is heat-sealed, and the power generation element 57 draws out the positive electrode current collector plate 59 and the negative electrode current collector plate 58 to the outside. It is sealed in the closed state. Here, the power generation element 57 corresponds to the power generation element 21 of the lithium ion secondary battery (multilayer battery) 10 shown in FIG. 1. The power generation element 57 is formed by stacking a plurality of single battery layers (single cells) 19 including a positive electrode (positive electrode active material layer) 13, an electrolyte layer 17, and a negative electrode (negative electrode active material layer) 15.

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

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

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

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

The present invention will be described in more detail using the following examples. However, the technical scope of the present invention is not limited to the following examples. In the present application, the composition ratio of metal is expressed as mass %.

(Comparative Example 1)
[Production of Silicon-Containing Alloy (Negative Electrode Active Material)]
A silicon-containing alloy having a composition of Si ₅₉ Sn ₁₁ Ti ₃₀ (composition ratio is mass ratio) was manufactured by the following liquid rapid solidification method.

Specifically, using a high-purity metal Si ingot (5N), a high-purity Ti wire (3N), and a high-purity Sn shot (3N), an ingot of a silicon-containing alloy Si ₅₉ Sn ₁₁ Ti ₃₀ was obtained by using an arc melting method. It was made.

Subsequently, a silicon-containing alloy was produced by a liquid rapid solidification method using the ingot obtained above as a mother alloy. Specifically, using a liquid rapid solidification apparatus NEV-A05 type manufactured by Nisshin Giken Co., Ltd., Si ₅₉ Sn was placed in a quartz nozzle installed in a chamber whose Ar pressure was replaced and the gauge pressure was reduced to −0.03 MPa. ₁₁ Ti ₃₀ ingot (mother alloy) was put in, melted by high frequency induction heating, and then sprayed onto a Cu roll at a rotation speed of 4000 rpm (peripheral speed: 41.9 m/sec) at a spray pressure of 0.03 MPa. , Ribbon-shaped alloy (quenched ribbon) was prepared.

Then, pulverization processing was performed. Specifically, using a planetary ball mill device P-6 manufactured by Germany Fritsch GmbH, the zirconia grinding balls and the respective raw material powders of each alloy were put into a zirconia grinding pot, and the grinding treatment was carried out at 400 rpm for 1 hour. , A silicon-containing alloy (negative electrode active material) was obtained. The average particle size of the obtained silicon-containing alloy (negative electrode active material) was 10 μm.

[Preparation of negative electrode]
80 parts by mass of the silicon-containing alloy (Si ₅₉ Sn ₁₁ Ti ₃₀ ) produced as described above, which is a negative electrode active material, 5 parts by mass of acetylene black, which is a conductive additive, and 15 parts by mass of polyimide, which is a binder, are mixed, A defoaming kneader (Thinky AR-100) was used to disperse it in N-methylpyrrolidone to obtain a negative electrode slurry. Next, the obtained negative electrode slurry was uniformly applied onto both surfaces of a negative electrode current collector made of copper foil so that the thickness of the negative electrode active material layer was 30 μm, and dried in vacuum for 24 hours to give a negative electrode. Obtained.

[Preparation of lithium-ion secondary battery (coin cell)]
The negative electrode prepared above and the counter electrode Li foil (manufactured by Honjo Metal Co., Ltd., diameter 15 mm, thickness 200 μm) were opposed to each other, and a separator (Celguard 2400 manufactured by Celgard Co., Ltd.) was placed therebetween. Next, the laminated body of the negative electrode, the separator, and the counter electrode Li was placed on the bottom side of the coin cell (CR2032, material: stainless steel (SUS316)). Furthermore, a gasket is attached to maintain the insulation between the positive electrode and the negative electrode, the following electrolytic solution is injected with a syringe, a spring and a spacer are laminated, and the upper side of the coin cell is overlapped and caulked to seal it. A lithium ion secondary battery (coin cell) was obtained.

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

(Example 1)
The ribbon-shaped alloy (quenched ribbon) obtained in Comparative Example 1 described above was pulverized to a size of about 15 μm in diameter, and the obtained pulverized product was subjected to mechanical alloying treatment. Specifically, using a planetary ball mill device P-6 manufactured by Germany Fritsch GmbH, the zirconia crushed balls and the crushed product are put into a zirconia crushing pot, and mechanically alloyed at 600 rpm for 24 hours. Alloyed. Then, pulverization treatment was performed at 400 rpm for 1 hour to obtain a silicon-containing alloy (negative electrode active material). In the planetary ball mill device used in this embodiment, the revolution radius rs=0.060 [m], the revolution radius rpl=0.033 [m], the revolution revolution ratio iw=-1.818 [-], and the rotation speed. Since the rpm was 600 [times/minute], the centrifugal force Gnl was calculated to be 19.4 [G]. The average particle size of the obtained silicon-containing alloy (negative electrode active material) was 10 μm.

A negative electrode and a lithium ion secondary battery (coin cell) were produced in the same manner as in Comparative Example 1 except that the silicon-containing alloy (negative electrode active material) obtained above was used.

(Example 2)
A silicon-containing alloy (negative electrode active material), a negative electrode, and a lithium ion secondary battery (coin cell) were produced in the same manner as in Example 1 except that the mechanical alloying treatment time was 48 hours. The average particle size of the obtained silicon-containing alloy (negative electrode active material) was 10 μm.

(Example 3)
A silicon-containing alloy having a composition of Si ₆₃ Sn ₇ Ti ₃₀ (composition ratio is mass ratio) was manufactured by the following mechanical alloying method.

Specifically, using a stirring ball mill C-01M manufactured by Germany ZOZ, 1620 g of zirconia grinding balls (φ5 mm) and 1 g of carbon (SGL) were put into a SUS grinding pot, and then 1000 rpm for 10 minutes. A pre-milling process was performed. Then, 100 g of each raw material powder of each alloy was added in total, and alloying was performed at 1500 rpm for 20 hours (alloying treatment), and then fine pulverization treatment was performed at 400 rpm for 1 hour to obtain a silicon-containing alloy (negative electrode active material). Substance) was obtained. In the stirring ball mill device used in this example, the revolution radius rs=0.070 [m], the rotation radius rpl=0 [m], and the rotation speed rpm=1500 [times/min], the centrifugal The force Gnl=176.0 [G] was calculated. The average particle size of the obtained silicon-containing alloy (negative electrode active material) was 10 μm.

A negative electrode and a lithium ion secondary battery (coin cell) were produced in the same manner as in Comparative Example 1 except that the silicon-containing alloy (negative electrode active material) obtained above was used.
(Example 4)
A silicon-containing alloy (negative electrode active material), a negative electrode, and a lithium ion secondary battery (coin cell) were produced in the same manner as in Example 3 except that the composition of the alloy was changed to Si ₆₁ Sn ₉ Ti ₃₀ . .. The average particle size of the obtained silicon-containing alloy (negative electrode active material) was 10 μm.

[Differential scanning calorimetry (DSC) of silicon-containing alloy (negative electrode active material)]
The silicon-containing alloy (negative electrode active material) produced in each of the above-described comparative example and Examples 1 to 4 was analyzed by a differential scanning calorimetry (DSC) method using the following conditions and apparatus.

(Conditions and equipment for DSC method)
Contractor: Seiko Eye Techno Research Co., Ltd. Experimental equipment: Differential scanning calorimeter (DSC-6300 manufactured by SII Nano Technology Co., Ltd.)
Temperature range: room temperature to 1500°C
Temperature increase/decrease rate: 10°C/min
Atmosphere: Argon atmosphere Reference substance: Alumina powder Sample container: Made of alumina.

Here, in the spectrum obtained by the DSC method, the peak intensity of the Si peak observed at 1200 to 1350° C. is I(1), and the peak intensity of the TiSi ₂ peak observed at 1400 to 1500° C. is I(1). 2), and the peak intensity of the a-Si peak defined as the difference between the peak intensity corresponding to the amount of Si and the peak intensity of the Si peak when it is assumed that the a-Si phase is not included is I(3). The value of "I(2)/I(1)", the value of "I(3)/I(1)", and "I(2)×I(3)/{I(1)" } ² "values are shown in Table 1 below. In addition, the spectrum which shows the result of the differential scanning calorimetry (DSC) measured about the negative electrode active material (silicon containing alloy) produced in Example 2 mentioned above is shown in FIG. Further, FIG. 4 shows a spectrum showing the results of differential scanning calorimetry (DSC) measured on the negative electrode active material (silicon-containing alloy) produced in Comparative Example 1 described above.

[Analysis of microstructure of silicon-containing alloy (negative electrode active material)]
The microstructure of the silicon-containing alloy (negative electrode active material) produced in Example 1 was analyzed.

The photograph on the upper left of FIG. 5A is an observation image (low magnification) of the silicon-containing alloy (negative electrode active material) of Example 1 by a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM). The photograph on the upper left of FIG. 5B is an observation image (high magnification) of the silicon-containing alloy (negative electrode active material) of Example 1 by a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM). The photographs in the upper right of FIGS. 5A and 5B are images obtained by performing element intensity mapping by EDX (energy dispersive X-ray spectroscopy) for the same visual field as the observed image in the upper left. The photographs in the lower part of FIGS. 5A and 5B are mapping images for the respective elements of Sn, Si, and Ti from the left. From these results, it was considered that Si (TiSi ₂ ) phase was present at the site where Ti was present since Si was also present at the site. It was also found that Si exists also in the part where Ti does not exist, and Sn exists in the part where Ti does not exist and Si exists. Summarizing the above results, the silicon-containing alloy (negative electrode active material) of Example 1 has an a-Si phase containing amorphous or low crystalline Si formed by solid solution of Sn in the crystal structure of Si. Has a structure in which it is dispersed in a silicide (TiSi ₂ ) phase containing a transition metal silicide as a main component. Further, the silicon-containing alloys (negative electrode active materials) of Examples 2 to 4 also have the same structure, and the observations shown in FIGS. 6A and 6B, 7A and 7B, and FIGS. 8A and 8B, respectively. Confirmed by the results.

On the other hand, as can be seen from the observation results shown in FIGS. 9A and 9B, in the silicon-containing alloy of Comparative Example 1 (negative electrode active material), unlike the structure of the example, coarsening of crystals of silicide (TiSi ₂ ) and Sn were observed. Segregation of the aggregates was observed.

[Evaluation of charge/discharge efficiency and cycle durability]
With respect to the lithium ion secondary battery (coin cell) produced in each of the above-described comparative example and Examples 1 to 4, the charge/discharge efficiency and the cycle durability were evaluated according to the following charge/discharge test conditions.

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

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

From the results shown in Table 1 above, the negative electrode active material according to the present invention satisfied the relationship of I(2)/I(1)>0.59 and I(3)/I(1)>0.56. .. This shows that the electric device (lithium ion secondary battery) of the example maintains a high discharge capacity retention rate after 50 cycles. Further, in Examples 2 to 4 satisfying the relations of I(2)/I(1)≧0.76 and I(3)/I(1)≧0.76, particularly excellent discharge capacity retention rates were achieved. I understand that No significant decrease in the initial charge/discharge efficiency was confirmed, and the initial charge/discharge efficiency almost equal to or higher than that in Comparative Example 1 could be secured. On the other hand, when the value of I(2)×I(3)/{I(1)} ² is less than 0.50, the discharge capacity is maintained at a high value, and the balance between capacity and cycle durability is excellent. A silicon-containing alloy (negative electrode active material) may be provided.

In the analysis of the structure of the silicon-containing alloy (negative electrode active material) produced in Comparative Example 1, as described above, coarsening of silicide (TiSi ₂ ) crystals and segregation of Sn agglomerates were observed. .. From this, in the silicon-containing alloy (negative electrode active material) of Comparative Example 1, Sn was not sufficiently solid-soluted in the Si phase, so that the Si was not sufficiently amorphized, and It is considered that sufficient cycle durability is not exhibited as a result of the fact that the phase mainly composed of is not sufficiently surrounded by the hard silicide phase.

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

Claims (5)

In a mother phase of a silicide phase containing TiSi ₂ , a structure having an amorphous or low crystalline silicon-based phase in which tin is formed as a solid solution in the crystal structure of silicon is dispersed, The following chemical formula (1)
Chemical formula (1)
Si _x Sn _y Ti _z A _a
(In the above chemical formula (1), A is an unavoidable impurity, and x, y, z, and a represent the value of mass %, where 58≦x≦73, 2≦y≦15, 25≦z ≦35, 0≦a<0.5, and x+y+z+a=100.)
Consisting of a silicon-containing alloy having a composition represented by
In the spectrum obtained by the differential scanning calorimetry (DSC) method, the peak intensity of the Si peak observed at 1200 to 1350° C. is I(1), and the peak intensity of the TiSi ₂ peak observed at 1400 to 1500° C. is I( 2), and the peak intensity of the a-Si peak defined as the difference between the peak intensity corresponding to the amount of Si and the peak intensity of the Si peak when it is assumed that the a-Si phase is not included is I(3). And when
I(2)/I(1)>0.59, and
I(3)/I(1)>0.56
A negative electrode active material for an electric device, characterized in that I(2)/I(1)≧0.76, and
I(3)/I(1)≧0.76
The negative electrode active material for an electric device according to claim 1, further satisfying the relationship of. The negative electrode active material for an electric device according to claim 1, further satisfying the relationship of I(2)×I(3)/{I(1)} ² <0.50. A negative electrode for an electric device, comprising the negative electrode active material for an electric device according to claim 1. An electric device comprising the negative electrode for an electric device according to claim 4.