JP2018190564A - Negative electrode active material for electric device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric device which enables the enhancement in cycle durability while retaining a high capacity.SOLUTION: A negative electrode active material for an electric device comprises a SiSnTiAl alloy. The negative electrode active material has a composition within a composition range as follows: Si is 60-69 mass%; Ti is 28-31 mass%; Sn is 1.5-8 mass%; Al is 0.5-2 mass%; and the balance consists of inevitable impurities. The negative electrode active material has a fine structure, having a-Si phases including Sn in a part thereof and amorphous or low-crystallinity silicon as a primary component, in which the a-Si phases are distributed in silicide (TiSi) phases including titanium silicide as a primary component. The negative electrode active material includes Al in the silicide phases.SELECTED DRAWING: None

Description

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

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

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

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

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

On the other hand, a battery using a material that is alloyed with Li for the negative electrode is expected as a negative electrode material for vehicle use because the energy density is improved as compared with a conventional carbon / graphite negative electrode material. For example, the Si material occludes and releases _3.75 mol of lithium ions per mol as shown in the following reaction formula (A) in charge / discharge, and the theoretical capacity is 3600 mAh / liter in Li ₁₅ Si ₄ (= Li _3.75 Si). g.

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

Here, Patent Document 1 discloses an invention that aims to provide a non-aqueous electrolyte secondary battery having a negative electrode pellet having a high capacity and an excellent cycle life. Specifically, it is a Si-containing alloy obtained by mixing Si powder and titanium powder by a mechanical alloying method and wet-pulverizing the first phase mainly composed of Si and a silicide of titanium (such as TiSi ₂ ). It is disclosed that a SiSnTi alloy containing a second phase containing) 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 No. 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 high capacity and good cycle durability. . However, in the SiSnTi alloy negative electrode described in Patent Document 1, the alloy active material particles sometimes break due to expansion and contraction during charge and discharge. Therefore, Si (active material particle pieces) dropped from the conductive network may become irreversible. In addition, a new alloy surface formed by cracking of the alloy active material particles and the electrolytic solution may react to decompose the electrolytic solution, resulting in deterioration of cycle durability. For this reason, it has been found difficult to improve cycle durability while maintaining a high capacity.

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

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research. As a result, the a-Si phase having a specific composition and containing Sn as a microstructure is dispersed in the titanium silicide phase, and a SiSnTiAl alloy containing Al in the silicide phase is used as the negative electrode active material. The present inventors have found that the problem can be solved and have completed the present invention.

  According to the SiSnTiAl alloy constituting the negative electrode active material according to the present invention, by adding a small amount of Al to the SiSnTiAl alloy, the compressive strength of the SiSnTi alloy active material can be improved, and cracking of the alloy active material particles can be suppressed. However, the electrode structure can be maintained. As a result, it is possible to prevent Si (active material particles) from falling off the conductive network and to prevent irreversible capacity. In addition, since a new alloy surface due to cracking of the alloy active material particles is unlikely to occur, the reaction between the new surface and the electrolytic solution is prevented, and the decomposition of the electrolytic solution is prevented, thereby effectively preventing deterioration in cycle durability. it can. Therefore, cycle durability can be improved, maintaining the high capacity | capacitance of the electric device in which the said SiSnTiAl alloy (negative electrode active material) is used.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view schematically showing an outline of a laminated flat non-bipolar lithium ion secondary battery which is a typical embodiment of an electric device according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view schematically showing the appearance of a stacked flat lithium ion secondary battery that is a representative embodiment of an electric device according to the present invention. FIG. 3 is a diagram showing quantitative mapping data by STEM-EDX (scanning transmission electron microscope-energy dispersive X-ray spectroscopy) for the microstructure of the Si-containing alloy of Example 1. The first photograph from the upper left of FIG. 3A is an observation image (high magnification) of the negative electrode active material (Si-containing alloy) of Example 1 using a high-angle annular dark field scanning transmission electron microscope (HAADF-STEM). ). 3 (b) to (e), the second to fourth and lower photographs from the upper left are mapping images for each element of Si, Sn, and Ti from the upper left, and the lower is a mapping image for the Al element. is there. The photograph on the left side of FIG. 4A is an observation image (ultra-high magnification) of the negative electrode active material (Si-containing alloy) of Example 1, which is the same as the first photograph from the upper left of FIG. ). Also, the graph and table on the right side of FIG. 4 (b) show the portion surrounded by a thick line (reference numeral 4) (the silicide (TiSi ₂ ) phase from FIG. 3) in the observation image of the left photograph of FIG. 4 (a). It is the EDX spectrum obtained about the image of the part considered to be). The photograph on the left side of FIG. 5A is an observation image (ultra-high magnification) of the negative electrode active material (Si-containing alloy) of Example 1 which is the same as the first photograph from the upper left of FIG. ). The graph and table on the right side of FIG. 5 (b) show the part surrounded by a thick line (reference numeral 5) in the observation image of the left photograph of FIG. 5 (a) (part where Ti does not exist and Si exists). Is an EDX spectrum obtained for the image of FIG. It is drawing which shows the result of the crushing measurement (compressive strength test) of the Si containing alloy powder produced in Example 4 and Reference Example 1. FIG. It is drawing which represented the relationship between a capacity | capacitance (initial discharge capacity) and discharge capacity maintenance factor [%] about each lithium ion secondary battery (coin cell) produced in Examples 1-4 and the comparative example 1. FIG.

  According to one aspect of the present invention, a negative electrode active material for an electric device made of a SiSnTiAl alloy, the composition ranges are: Si: 60 to 69 mass%, Ti: 28 to 31 mass%, Sn: 1.5 to 8 Mass%, Al: 0.5 to 2 mass%, and the balance is composed of inevitable impurities, and the microstructure is mainly composed of amorphous or low crystalline silicon containing Sn in part. An a-Si phase is dispersed in a silicide phase containing titanium silicide as a main component, and Al is contained in the silicide phase.

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

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

  First, a negative electrode for a lithium ion secondary battery, which is a typical embodiment of a negative electrode including 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 cell layer) ) Voltage 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 vehicle driving power source or an auxiliary power source. As a result, it can be suitably used as a lithium ion secondary battery for a vehicle driving power source or the like. In addition to this, the present invention can be sufficiently applied to lithium ion secondary batteries for portable devices such as mobile phones.

  That is, the lithium ion secondary battery that is the subject of the present embodiment may be any one that uses the negative electrode active material for the lithium ion secondary battery of the present embodiment described below. It should not be restricted in particular.

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

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

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

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

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

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

  Thereby, the adjacent positive electrode, electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked battery 10 shown in FIG. 1 has a configuration in which a plurality of single battery layers 19 are stacked and electrically connected in parallel. The positive electrode current collector 15 located on both outermost layers of the power generation element 21 has the positive electrode active material layer 15 disposed only on one side, but the active material layers may be provided on both sides. . That is, instead of using a current collector dedicated to the outermost layer provided with an active material layer only on one side, a current collector having an active material layer on both sides may be used as it is as an outermost current collector. Further, the arrangement of the positive electrode and the negative electrode is reversed from that in FIG. 1, so that the outermost negative electrode current collector is positioned in both outermost layers of the power generation element 21, and one side of the outermost negative electrode current collector or A negative electrode active material layer may be disposed on both sides.

  The positive electrode current collector 12 and the negative electrode current collector 11 are attached to 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 end portions of the laminate sheet 29. Thus, it has a structure led out of the laminate sheet 29. The positive electrode current collector plate 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, as necessary. Or resistance welding or the like.

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

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

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

(Positive electrode active material)
As the positive electrode active material, for example, LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni—Mn—Co) O _2, and lithium—such as those in which a part of these transition metals are substituted with other elements Examples include transition metal composite oxides, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds. In some cases, two or more positive electrode active materials may be used in combination. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material from the viewpoint of capacity and output characteristics. More preferably, a composite oxide containing lithium and nickel is used, and more preferably Li (Ni-Mn-Co) O ₂ and a part of these transition metals are substituted with other elements (hereinafter, Simply referred to as “NMC composite oxide”). The NMC composite oxide has a layered crystal structure in which a lithium atomic layer and a transition metal (Mn, Ni, and Co are arranged in order) 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 that of the spinel lithium manganese oxide, that is, the supply capacity is doubled, so that a high capacity can be obtained.

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

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

  Generally, nickel (Ni), cobalt (Co), and manganese (Mn) are known to contribute to capacity and output characteristics from the viewpoint of improving the purity of the material and improving the electronic 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 substituted with another metal element, and it is particularly preferable that 0 <x ≦ 0.3 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 dissolved, the crystal structure is stabilized. It is considered that the battery capacity can be prevented from decreasing even if the above is repeated, and that excellent cycle characteristics can be realized.

As a more preferred embodiment, in the general formula (1), b, c and d are 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31, 0.19 ≦ d ≦ 0.26. It 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. that have been proven in general consumer batteries. Compared to the above, the capacity per unit weight is large, and the energy density can be improved, so that a battery having a compact and high capacity can be produced, which is preferable from the viewpoint of cruising distance. In addition, LiNi _0.8 Co _0.1 Al _0.1 O ₂ is more advantageous in terms of a larger capacity, but there are difficulties in life characteristics. On the other hand, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ has life characteristics as excellent as LiNi _1/3 Mn _1/3 Co _1/3 O ₂ .

  In some cases, two or more positive electrode active materials may be used in combination. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material from the viewpoint of capacity and output characteristics. Of course, positive electrode active materials other than those described 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, more preferably 5 to 20 μm from the viewpoint of increasing the output. In the present specification, the “particle diameter” refers to the outline of the active material particles (observation surface) observed using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). It means the maximum distance among any two points. In this specification, the value of “average particle diameter” is the value of particles observed in several to several tens of fields using 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 diameters and average particle diameters of other components can be defined in the same manner.

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

(Binder)
The binder is added for the purpose of maintaining the electrode structure by binding the active materials or the active material and the current collector. Although it does not specifically limit as a binder used for a positive electrode active material layer, For example, the following materials are mentioned. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile (PEN), polyacrylonitrile, polyimide, polyamide, polyamideimide, cellulose, carboxymethylcellulose (CMC), ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene / butadiene Rubber (SBR), isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and hydrogenated product thereof, styrene / isoprene / styrene block copolymer and Thermoplastic polymers such as hydrogenated products, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene hexafluoropropylene Polymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer Fluorine resin such as coalescence (ECTFE), polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber ( VDF-HFP-TFE fluoro rubber), vinylidene fluoride-pentafluoropropylene fluoro rubber (VDF-PFP fluoro rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoro Oroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene-based fluororubber (VDF-PFMVE-TFE-based fluororubber), vinylidene fluoride-chlorotrifluoroethylene-based Examples thereof include vinylidene fluoride-based fluororubbers such as fluororubber (VDF-CTFE-based fluororubber), epoxy resins, and the like. Among these, polyvinylidene fluoride, polyimide, styrene / butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, polyamide, and polyamideimide are more preferable. These suitable binders are excellent in heat resistance, have a very wide potential window, are stable at both the positive electrode potential and the negative electrode potential, and can be used for the active material layer. These binders may be used alone or in combination of two.

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

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

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

(Negative electrode active material)
In the present embodiment, the negative electrode active material has a composition of SiSnTiAl alloy (quaternary alloy represented by Si—Sn—Ti—Al), and the microstructure includes Sn in part and is amorphous. Alternatively, a SiSnTiAl alloy characterized in that an a-Si phase mainly composed of low crystalline silicon is dispersed in a silicide phase mainly composed of titanium silicide, and Al is contained in the silicide phase. Simply referred to as an Si-containing alloy). Preferably, Al is also dispersed in the a-Si phase.

<Composition of Si-containing alloy>
As described above, the Si-containing alloy constituting the negative electrode active material in this embodiment first has a quaternary alloy composition represented by Si—Sn—Ti—Al. More specifically, the Si-containing alloy constituting the negative electrode active material in the present embodiment has a composition range of Si: 60 to 69 mass%, Ti: 28 to 31 mass%, Sn: 1.5 to 8 mass%. , Al: 0.5 to 2% by mass, and the balance is composed of inevitable impurities. Since the SiSnTiAl alloy (Si-containing alloy) according to the present embodiment has the above composition range, high cycle durability can be realized.

  Further, in the present specification, the “inevitable impurities” means an Si-containing alloy that exists in a raw material or is inevitably mixed in a manufacturing process. The inevitable impurities are originally unnecessary impurities, but are a very small amount and do not affect the characteristics of the Si alloy.

  In this embodiment, by selecting Ti, which is a silicide forming element, as an additive element of the negative electrode active material (Si-containing alloy), the cycle life of the amorphous-crystal phase transition is suppressed during Li alloying. Can be improved. This also increases the capacity of conventional negative electrode active materials (for example, carbon-based negative electrode active materials). By selecting Ti as a silicide-forming element as an additive element to the negative electrode active material (Si-containing alloy), and adding Sn as a second additive element and Al as a third additive element, a Li alloy is formed. Further, the cycle life can be improved by further suppressing the amorphous-crystal phase transition. This also increases the capacity of conventional negative electrode active materials (for example, carbon-based negative electrode active materials).

  Here, in the Si-based negative electrode active material, when Si and Li are alloyed during charging, the a-Si phase transitions from an amorphous state to a crystalline state and causes a large volume change (about 4 times). As a result, there is a problem that the active material particles themselves are broken (broken) and the function as the active material is lost. Therefore, in the present embodiment, the negative electrode active material has the above composition range and the above microstructure, and particularly by adding a small amount of Al, the compressive strength of the SiSnTi alloy active material can be improved, and the alloy active material particles The electrode structure can be maintained while suppressing cracking. As a result, it is possible to prevent Si (active material particles) from falling off the conductive network and to prevent irreversible capacity. In addition, since a new alloy surface due to cracking of the alloy active material particles is unlikely to occur, the reaction between the new surface and the electrolytic solution is prevented, and the decomposition of the electrolytic solution is prevented, thereby effectively preventing deterioration in cycle durability. it can. Therefore, cycle durability can be improved, maintaining the high capacity | capacitance of the electric device in which the said SiSnTiAl alloy (negative electrode active material) is used. Furthermore, by suppressing the phase transition of the amorphous-crystal of the a-Si phase during charging, the collapse of the particles themselves can be suppressed, the function (high capacity) as an active material is maintained, and the cycle life is also improved. Can do.

  As described above, the Si-containing alloy according to this embodiment is a quaternary alloy of Si, Sn, Ti, and Al, and the total composition range (mass ratio of each constituent element) is 100% by mass. The composition range (mass ratio of each constituent element) is as follows.

  The composition range (content) of Si is 60 to 69% by mass. The composition range (content) of Si is preferably 65 to 69% by mass, more preferably 66 to 69% by mass, still more preferably 67 to 69% by mass, and particularly preferably 67.5 to 69%. It is mass%, Especially preferably, it is 68.5-69 mass%. Within such a range, it is excellent in terms of maintaining durability against charge / discharge (Li ion insertion / desorption) and (initial) capacity balance, and can sufficiently improve durability and obtain a high capacity. The effect of the present invention can be expressed more efficiently.

  The composition range (content) of Sn is 1.5 to 8% by mass. The composition range (content) of Sn is preferably 1.5 to 5% by mass, more preferably 1.5 to 4% by mass, still more preferably 1.5 to 3% by mass, and particularly preferably 1 0.5 to 2.5% by mass, preferably 2.0 to 2.5% by mass. Within such a range, reversible Li ion insertion / desorption at the time of charging / discharging is possible by increasing the distance between Si tetrahedrons in the a-Si phase by solid solution in the a-Si phase. It is excellent in that it does. Thereby, durability can fully be improved and the effect of the present invention can be expressed more efficiently.

  The composition range (content) of Ti is 28 to 31% by mass. The composition range (content) of Ti is preferably 28 to 30.5% by mass, more preferably 28 to 30% by mass, still more preferably 28 to 29.5% by mass, and particularly preferably 28 to It is 28.5 mass%. Within such a range, it is excellent in terms of maintaining durability against charge / discharge (insertion / desorption of Li ions) and capacity balance, and can sufficiently improve durability and obtain a high capacity. The effect can be expressed more efficiently.

The composition range (content) of Al is 0.5 to 2% by mass. The composition range (content) of Al is preferably 0.5 to 1.5% by mass, and more preferably 0.5 to 1.0% by mass. Within such a range, the a-Si phase mainly containing amorphous or low crystalline silicon is partially dispersed in the silicide (TiSi ₂ ) phase, and Al is contained in the silicide phase. Can be contained. Further, the a-Si phase can be made amorphous, and Al can be contained (dispersed) in the a-Si phase. In particular, Al is dispersed and dissolved in the a-Si phase to increase the distance between the Si tetrahedrons and to be uniformly dispersed in the a-Si phase, so that Sn present in the a-Si phase is present. Is superior in that it is dispersed more finely. By these, durability can fully be improved and a high capacity | capacitance can be obtained and the effect of this invention can be expressed more efficiently.

  Here, Si—Ti is very strong bonding, Si—Sn is repulsive, and Ti—Sn is bonding, so that the effects as described above can be obtained. In this embodiment, Si—Ti—Sn is obtained. In a quaternary alloy in which a small amount of Al is added, Si-Al is repulsive, Ti-Al is bonding and Al functions similarly to Sn, and Si-Al is stable in the liquid phase state. It has the property of being. As a result, Al is easier to dissolve and disperse in the a-Si phase than Sn, and the distance between the tetrahedrons of the a-Si phase can be increased, resulting in charging / discharging (insertion and desorption of Li ions). It is considered that the durability against expansion and contraction of the a-Si phase can be improved more effectively. Further, since Al has a different valence electron number from Si, Al is uniformly dispersed in the a-Si phase, thereby improving the conductivity of the a-Si phase, and charging / discharging in the a-Si phase (Li (Ion insertion / desorption) easily proceeds uniformly. Therefore, also from this point, it is considered that the charge / discharge cycle durability can be effectively improved by the addition of Al. Furthermore, by containing Al in the silicide phase, the compressive strength of the alloy active material can be improved, and the electrode structure can be maintained while cracking of the alloy active material particles is suppressed. As a result, it is possible to prevent Si (active material particles) from falling off the conductive network and to prevent irreversible capacity. In addition, since a new alloy surface due to cracking of the alloy active material particles is unlikely to occur, the reaction between the new surface and the electrolytic solution is prevented, and the decomposition of the electrolytic solution is prevented, thereby effectively preventing deterioration in cycle durability. it can. Therefore, cycle durability can be improved, maintaining the high capacity | capacitance of the electric device in which the said SiSnTiAl alloy (negative electrode active material) is used.

  That is, in the present embodiment, the composition range of the Si-containing alloy is Si: 60 to 69% by mass, Ti: 28 to 31% by mass, Sn: 1.5 to 8% by mass, Al: 0.5 to 2% by mass. It is. As described above, the microstructure (structure) of the Si-containing alloy according to the present embodiment is obtained by containing a relatively large amount of Ti while containing Si as a main component, a certain amount of Sn, and a small amount of Al. Can be obtained. However, the preferred numerical range of the composition range (composition ratio) of each constituent element described above is merely for explaining a preferred embodiment, and is within the technical scope of the present invention as long as it is included in the scope of the claims. belongs to. In the composition range of Si, Sn, Ti, and Al, the total of each composition range is 100% by mass at maximum (not exceeding 100% by mass).

  Further, Ti is selected as a silicide-forming element for the main component Si of the Si-containing alloy, Sn is added as the second additive element within the above composition range, and a small amount of Al is added as the third additive element within the above composition range. Thus, Sn (further Al) can be dispersed (solid solution) in a part of the a-Si phase. Further, Al can be dispersed relatively uniformly throughout the a-Si phase and the silicide phase. Therefore, by adding Al to the Si—Sn—Ti alloy, the amorphous forming ability of the Si alloy can be increased, and the degree of amorphousness can be increased. Therefore, the chemical structure of the a-Si phase hardly changes even when Li is inserted and desorbed due to charge and discharge, and higher cycle durability is obtained.

  In the Si-containing alloy, the balance other than the composition range (composition ratio) of each constituent element of Si, Sn, Ti, and Al is an impurity other than the four components of Si, Sn, Ti, and Al derived from the raw materials and the manufacturing method ( Inevitable impurities). The balance of inevitable impurities should not be contained as much as possible, preferably less than 0.5% by mass, more preferably less than 0.1% by mass.

  Whether or not the negative electrode active material (Si-containing alloy) has the above composition range can be confirmed by qualitative analysis by fluorescent X-ray analysis (XRF) and quantitative analysis by inductively coupled plasma (ICP) emission spectroscopy. It is.

(Microstructure of Si-containing alloy)
As described above, the Si-containing alloy constituting the negative electrode active material in the present embodiment has a structure in which the a-Si phase is dispersed in the silicide phase as a microstructure, and Al is contained in the silicide phase. There is also a feature in having. Further, the a-Si phase has a structure containing (dispersed) Sn, preferably Sn and Al. That is, the Si-containing alloy according to the present embodiment has a so-called sea-island structure in which islands composed of a-Si phases as dispersed phases are dispersed in a sea composed of silicide phases as continuous phases. One. The continuous phase silicide phase (sea structure) contains Al, and the dispersed phase a-Si phase (island structure) contains Sn, preferably Sn, Al (dispersion). Is. Note that whether or not the Si-containing alloy has such a microstructure is determined by, for example, using a high-angle annular dark-field scanning transmission electron microscope (see FIG. After observing using HAADF-STEM), the same visual field as the observed image can be confirmed by performing element intensity mapping by EDX (energy dispersive X-ray spectroscopy).

<A-Si phase>
Here, in the Si-containing alloy (SiSnTiAl alloy) according to the present embodiment, the a-Si phase partially includes Sn, and preferably includes (disperses) Al also in the a-Si phase. It is. More preferably, it is a phase mainly composed of amorphous or low crystalline Si in which Sn (preferably Sn, Al) is dispersed (solid solution) inside the crystal structure of Si. This a-Si phase is a phase involved in occlusion / release of lithium ions during operation of the electrical device (lithium ion secondary battery) of the present embodiment, and can electrochemically react with lithium (that is, per weight and This is a phase in which a large amount of lithium can be occluded and released per volume. In addition, Sn (preferably Sn, Al) is dispersed and dissolved in the crystal structure of Si constituting the a-Si phase, but since Si has poor electron conductivity, Trace amounts of additive elements such as phosphorus and boron, transition metals, and the like may be included. Although there is no restriction | limiting in particular about the size of an a-Si phase, The dimensional change of the a-Si phase at the time of charge (at the time of Li ion insertion in a fine structure) and discharge (at the time of Li ion detachment | desorption from a fine structure) From the viewpoint of reducing the size, the size of the a-Si phase is preferably as small as possible, specifically 10 nm or less, and more preferably 8 nm or less. On the other hand, the lower limit of the size of the a-Si phase is not particularly limited, but is preferably 5 nm or more. As for the size (diameter) value of the a-Si phase, high magnification (25 nm scale bar) Si EDX element mapping and Ti EDX element mapping in HAADF-STEM were compared. The region that does not exist is regarded as the Si phase, and the intensity of 1/10 of the maximum value in the EDX element mapping of M is set as a threshold, and the binarized image processing is performed for the region that is equal to or less than this threshold. Further, it can be obtained as an arithmetic average value of measured values obtained by measuring five or more phases by a method of reading the dimensions of each Si phase. Similarly, with respect to the size (diameter) of the silicide phase described later, high magnification (25 nm scale bar) Si EDX element mapping and Ti EDX element mapping in Cs-STEM are compared. The region that is also present as a silicide phase, the intensity of 1/10 of the maximum value in the EDX element mapping of Ti is set as a threshold value, and binarized image processing is performed for a region that is equal to or greater than this threshold value. Thus, it can be obtained as an arithmetic average value of measured values obtained by measuring five or more phases by a method of reading the dimensions of each silicide phase.

  The a-Si phase is preferably made amorphousr than a silicide phase described later. By setting it as such a structure, a negative electrode active material (Si containing alloy) can be made into a higher capacity | capacitance. Whether or not the a-Si phase is more amorphous than the silicide phase is determined based on observation images of the a-Si phase and the silicide phase using a high-angle annular dark field scanning transmission electron microscope (HAADF-STEM). It can be determined from a 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 spot) for a single crystal phase, a Debye-Scherrer ring (diffraction ring) for a polycrystalline phase, and an amorphous The temperate phase shows a halo pattern. By using this, the above confirmation can be performed. In the present embodiment, the a-Si phase may be amorphous or low crystalline, but the a-Si phase is amorphous from the viewpoint of realizing higher cycle durability. Is preferred.

  In the a-Si phase, “mainly composed of amorphous or low crystalline Si” means 50 mass% or more, preferably 80 mass% or more, more preferably 90 mass% or more of the a-Si phase. Particularly preferably, 95% by mass or more, and most preferably 98% by mass or more is the Si. However, the alloy may contain inevitable impurities that are present in the raw material or are inevitably mixed in the manufacturing process. Therefore, it is practically difficult to obtain 100% by mass of the second phase.

  In the a-Si phase, “partially contains Sn” means that the a-Si phase has a portion containing almost no Sn (a portion where the Si portion functions as an active material), but the a-Si phase This is because a portion containing Sn is seen as a part of the region (see FIGS. 3B to 3D). Further, in the portion containing Sn in the a-Si phase, Sn is dispersed and dissolved in Si, or is dispersed in the form of being encapsulated in Si (Sn-Si solid solution or encapsulated Sn is an active material). Function as). When Sn is distributed (dispersed) in the a-Si phase, the amorphous degree of the a-Si phase can be increased and the durability is excellent. In addition, when the a-Si phase contains Sn (Sn which is dispersed and dissolved in the crystal structure of Si, or is dispersed in the form of being included in Si), the Sn is also a carbon negative electrode. Compared to the material (carbon negative electrode material), it is possible to occlude and release a large amount of Li per weight and per volume.

<Silicide phase>
On the other hand, the silicide phase constituting the sea (continuous phase) having the above-described sea-island structure is a crystalline phase mainly composed of titanium silicide (silicide). The silicide phase contains titanium silicide (TiSi ₂ ) and thus has excellent affinity with the a-Si phase, and can suppress cracks at the crystal interface particularly during volume expansion during charging. Furthermore, the silicide phase is superior in terms of electron conductivity and hardness compared to the a-Si phase. Thus, the silicide phase also 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 this embodiment, the silicide phase having such characteristics constitutes a sea (continuous phase) having a sea-island structure, so that the electron conductivity of the negative electrode active material (Si-containing alloy) can be further improved. Moreover, the stress during expansion of the a-Si phase can be relaxed to prevent cracking of the active material, which is considered to contribute to the improvement of cycle durability.

A plurality of phases may exist in the silicide phase, for example, _two or more phases (for example, TiSi ₂ and TiSi) having different composition ratios of Ti and Si may exist. Titanium elements exhibit higher electron conductivity and higher strength than silicides of other elements when silicides are formed. In particular, TiSi ₂ which is a kind of titanium silicide (silicide) is preferable because it shows very excellent electron conductivity. In view of such characteristics of silicide and the excellent identification of amorphous Si described above, it is preferable that the silicide of titanium (silicide) is TiSi ₂ and the a-Si phase is amorphous. .

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

  In the above-described silicide phase, “having silicide as a main component” means 50% by mass or more of the silicide phase, preferably 80% by mass or more, more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 98 mass% or more is silicide. Ideally, the silicide is 100% by mass. However, the alloy may contain inevitable impurities that are present in the raw material or are inevitably mixed in the manufacturing process. Therefore, it is practically difficult to obtain 100% by mass of the first 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 even more preferably 25 nm or less. By setting it as such a structure, a negative electrode active material (Si containing alloy) can be made into a higher capacity | capacitance. On the other hand, the lower limit value of the size of the silicide phase is not particularly limited, but the size (diameter) of the silicide phase is the above-described a-Si from the viewpoint of suppressing expansion / contraction of the a-Si phase accompanying Li insertion / desorption. It is preferably larger than the size (diameter) of the phase, and the absolute value thereof is preferably 10 nm or more, more preferably 15 nm or more.

  Furthermore, the Si-containing alloy according to the present embodiment includes Sn as an essential element, but since Sn is an element that does not form silicide with Si, it exists in the a-Si phase instead of the silicide phase. . That is, the a-Si phase partially contains Sn (preferably formed by dispersion and solid solution). When the Sn content is low, all Sn elements are present in solid solution (dispersed) in the Si crystal structure in the a-Si phase. On the other hand, when the Sn content increases, Sn elements that can no longer be completely dissolved (dispersed) in Si in the a-Si phase aggregate and exist as a crystalline phase of Sn alone. In the present embodiment, it is preferable that such a crystal phase of Sn alone does not exist.

Further, the Si-containing alloy according to this embodiment includes Al as essential, but since Si—Al is repulsive, Al is an element that does not form silicide with Si, but Si—Ti is very much. Strong bondability, Ti-Al has bondability. Therefore, Al can be (uniformly) dispersed (solid solution) in the silicide phase. When Al enters the silicide (SiTi ₂ ) phase, the toughness is increased, the elasticity is increased, the compressive strength of the alloy can be improved, and the electrode structure can be maintained while cracking of the alloy active material particles is suppressed. As a result, it is possible to prevent Si (active material particles) from falling off the conductive network and to prevent irreversible capacity. Furthermore, it is preferable to disperse (solidly) Al in the a-Si phase (uniformly). When Al is also contained in the a-Si phase, the toughness is further increased, the compressive strength of the alloy can be improved, and the electrode structure can be maintained while effectively suppressing the cracking of the alloy active material particles. As a result, it is possible to prevent Si (active material particles) from falling off the conductive network and effectively prevent irreversible capacity. In addition, due to the interaction between the atoms described above, Al is more easily dissolved and dispersed in the a-Si phase than Sn, and the durability against expansion and contraction of the a-Si phase can be more effectively improved. it can. Further, since Al has a different valence electron number from Si, Al is uniformly dispersed in the a-Si phase, thereby improving the conductivity of the a-Si phase, and charging / discharging in the a-Si phase (Li (Ion insertion / desorption) easily proceeds uniformly. Therefore, the addition of Al can effectively improve the charge / discharge cycle durability. Furthermore, by containing Al in the silicide phase, the compressive strength of the alloy active material can be improved, and the electrode structure can be maintained while cracking of the alloy active material particles is suppressed. As a result, it is possible to prevent Si (active material particles) from falling off the conductive network and to prevent irreversible capacity. In addition, since a new alloy surface due to cracking of the alloy active material particles is unlikely to occur, the reaction between the new surface and the electrolytic solution is prevented, and the decomposition of the electrolytic solution is prevented, thereby effectively preventing deterioration in cycle durability. it can. Therefore, cycle durability can be improved, maintaining the high capacity | capacitance of the electric device in which the said SiSnTiAl alloy (negative electrode active material) is used. Thus, Al is preferably dispersed (solid solution) in both the silicide phase and the a-Si phase, and when Al is contained in a small amount as shown in the composition range, all Al elements are contained in the silicide phase and the a-Si. It is preferable that the phase is uniformly dispersed (solid solution) and there is no crystal phase of Al alone.

  When Al is dispersed also in the a-Si phase, it is more preferable that the amount of Al in the a-Si phase is larger than the amount of Al in the silicide phase. Thereby, toughness can be made higher, the compressive strength of the alloy can be further improved, and the electrode structure can be maintained while cracking of the alloy active material particles is more effectively suppressed. As a result, it is possible to prevent Si (active material particles) from falling off the conductive network and more effectively prevent irreversible capacity. Here, the amount of Al in the a-Si phase and the amount of Al in the silicide phase depends on the amount of Al (mass%) or peak height (count) obtained from the EDX spectra of the a-Si phase and the silicide phase. The quantity can be confirmed by comparing (for example, see FIGS. 4 and 5 of Example 1. The same applies to the alloys of Examples 2 to 4).

Furthermore, in this embodiment, preferably, when the mass ratio of the available-Si phase, which is a Si phase that can function as an active material, and the silicide phase is a value within a predetermined range, further excellent cycle durability is realized. Is possible. Specifically, similarly, the ratio of the mass (m ₂ ) of the silicide phase to the mass (m ₁ ) of the available-Si phase in the Si-containing alloy (ratio of silicide phase / active-Si phase = m ₂ / m ₁ ) The value is preferably 1.75 or more, more preferably 1.75 to 2.00, and even more preferably 1.75 to 1.80. Here, in this embodiment, there is no particular limitation on the mass ratio of the available-Si phase in the Si-containing alloy, but from the viewpoint of ensuring a sufficient capacity while exhibiting the characteristics of other constituent elements, The ratio of the mass (m ₁ ) of the available-Si phase in 100% by mass is preferably 33% by mass or more, more preferably 34% by mass or more, still more preferably 35% by mass or more, and particularly preferably. Is 35% by mass to the total amount of Si (% by mass) in the alloy, and preferably 35 to 45% by mass. According to this embodiment, even if the total number of atoms (number of atomic moles) of Sn and Al is constant by replacing a part of Sn (atomic weight = 18.7) with Al (atomic weight = 26.98), These mass ratios can be reduced. As a result, it is possible to increase the capacity of the negative electrode active material made of the Si-containing alloy while keeping the value of m ₂ / m ₁ relatively high. In addition, since Al is extremely inexpensive as compared with Sn, it can greatly contribute to the cost reduction of the negative electrode active material.

From the same viewpoint, when the mass of the available-Si phase and the mass of the silicide phase in the Si-containing alloy are m ₁ and m ₂ , respectively, m ₁ ≧ 61-14.3 × (m ₂ / m ₁ ) Is preferably satisfied. The mass of the available-Si phase (m ₁ ) and the mass of the silicide phase (m ₂ ) in the Si-containing alloy for calculating the value of m ₂ / m ₁ are the mass% of the constituent metal elements in the alloy composition. It is a theoretical value calculated by the following formula on the assumption that all Ti is converted to TiSi ₂ by conversion to atomic%, and the available-Si amount and the TiSi ₂ amount are also calculated by this method in the examples described later. doing.

amount of available-Si (mass%) =
([At% Si] − [at% Ti] × 2) × 28.0855 (Si atomic weight) / {([at% Si] − [at% Ti] × 2) × 28.0855 (Si atomic weight) + [ at% Sn] × 118.71 (Sn atomic weight) + [at% Ti] × 104.038 (TiSi ₂ formula weight)}
Here, the calculation is made by taking a quaternary alloy having a composition of Si ₆₀ Sn ₂ Ti _28.5 Al _0.5 as an example. At% Si of the alloy is 79.6 atomic%, and at% Ti of the alloy is 19. Since it is 3 atomic%, the amount of available-Si (mass%) is calculated as 35.1 mass%.

Similarly, the amount of silicide (TiSi ₂ ) is
TiSi ₂ amount (% by mass) =
([At% Ti] × 104.038 (TiSi ₂ formula amount)) / {([[at% Si] − [at% Ti] × 2) × 28.0855 (Si atomic weight) + [at% Sn] × 118 .71 (Sn atomic weight) + [at% Ti] × 104.038 (TiSi ₂ formula weight)}
Can be calculated. Here again, the quaternary alloy having a composition of Si ₆₀ Sn ₂ Ti _28.5 Al _0.5 is taken as an example. At% Si of the alloy is 79.6 atomic%, and at% Ti of the alloy is 19.3. Since it is atomic%, the amount of silicide (TiSi ₂ ) (mass%) is calculated to be 62.4 mass%.

  Although the particle diameter of the Si-containing alloy constituting the negative electrode active material in the present embodiment is not particularly limited, the average particle diameter is preferably 0.1 to 20 μm, more preferably 0.2 to 10 μm. In the present specification, the “average particle diameter” means a particle diameter (D50) at an integrated value of 50% in a particle size distribution measured by a laser diffraction scattering method.

(Method for producing negative electrode active material)
There is no restriction | limiting in particular about the manufacturing method of the negative electrode active material for electric devices which concerns on this embodiment, A conventionally well-known knowledge can be referred suitably. In the present embodiment, the negative electrode is made of a Si-containing alloy having the specific composition range described above, in which an a-Si phase containing Sn as a microstructure is dispersed in a titanium silicide phase, and Al is contained in the silicide phase. As an example of the production method of the active material, a mechanical alloy method (production of an alloy by mechanical alloying treatment) is preferable. However, you may use the manufacturing method which uses together preparation of the quenching thin strip by a liquid rapid solidification method, and preparation of the alloy by a mechanical alloying process. That is, according to another embodiment of the present invention, there is provided a method for producing a negative electrode active material for an electrical device comprising a Si-containing alloy having the specific composition range and microstructure described above, and, if necessary, the Si-containing material. A quenched ribbon is produced by a liquid rapid solidification method using a mother alloy having the same composition as the alloy. Next, the quenching ribbon (pulverized product) or a mother alloy having the same composition as the Si-containing alloy is subjected to mechanical alloying to obtain a negative electrode active material for an electric device comprising the Si-containing alloy. A method for producing a negative electrode active material for a device is provided. As described above, the negative electrode active material (Si-containing alloy) may be manufactured by performing the liquid rapid solidification method before the mechanical alloying process. Regardless of which method is used, an alloy having the above-described specific composition range and microstructure can be manufactured by finally performing mechanical alloying treatment. Hereinafter, the manufacturing method according to this embodiment will be described for each step.

<Liquid quenching (roll) solidification method>
If necessary, first, a liquid quenching (roll) solidification method is performed using a mother alloy having the same composition as the desired Si-containing alloy. Thereby, a rapidly cooled ribbon is produced.

  Here, in order to obtain a master alloy, high-purity raw materials (single ingots, wires, plates, etc.) for silicon (Si), tin (Sn), aluminum (Al), and titanium (Ti) as raw materials. Prepare. Subsequently, in consideration of the composition of the Si-containing alloy (negative electrode active material) to be finally produced, a master alloy in the form of an ingot or the like is produced by a known technique such as an arc melting method.

Thereafter, a liquid rapid solidification method is performed using the mother alloy obtained above. This step is a step in which the melt obtained by melting the master alloy obtained above is rapidly cooled and solidified, for example, by high-frequency induction melting-liquid rapid solidification method (double roll or single roll rapid cooling method). Can do. Thereby, a rapidly cooled ribbon (ribbon) alloy is obtained. The liquid rapid solidification method is often used as a method for producing an amorphous alloy, and there are many knowledges about the method itself. The liquid rapid roll coagulation method can be performed using a commercially available liquid rapid solidification apparatus (for example, a liquid rapid solidification apparatus NEV-A05 type manufactured by Nisshin Giken Co., Ltd.). At this time, the atmosphere in the chamber is preferably replaced with an inert gas (He gas, Ne gas, Ar gas, N ₂ gas, or the like). After replacement with an inert gas, the injection pressure is preferably about 0.03 to 0.09 MPa in terms of gauge pressure. The internal pressure of the vacuum chamber is -0.03 to -0.07 MPa in gauge pressure (0.03 to 0.07 MPa in absolute pressure), and the differential pressure between the chamber internal pressure and the injection pressure is 0.06 to 0.16 MPa. It is good to do. The rotation speed of the roll is preferably 4000 to 6000 rpm (peripheral speed is 40 to 65 m / sec).

(Mechanical alloying process)
(1) A ribbon-like alloy (quenched ribbon (ribbon) alloy) obtained above, or (2) a master alloy having the same composition as a desired Si-containing alloy prepared without undergoing a liquid quench roll solidification method On the other hand, a mechanical alloying process is performed. Here, if necessary, the quenched ribbon alloy obtained above is roughly pulverized with an appropriate pulverizer to a size that can be easily put into a ball mill apparatus or the like used for mechanical alloying treatment, and the obtained pulverization You may perform a mechanical alloying process with respect to a thing.

  By performing the alloying process by the mechanical alloying process, the microstructure (phase state) can be easily controlled. Therefore, the mechanical alloying process is performed by a ball mill apparatus ( For example, using a planetary ball mill device, alloying can be achieved by putting pulverized balls and alloy raw material powder into a pulverizing pot and increasing the rotational speed to give high energy. The alloying treatment can be alloyed by increasing the rotational speed and imparting high energy to the raw material powder. That is, heat is generated by applying high energy, and the raw material powder is alloyed to amorphize the a-Si phase, and Sn (preferably Sn, Al) (solid solution) into the phase, and formation of the silicide phase and the phase. Al dispersion (solid solution) proceeds. By increasing the number of revolutions (applied energy) of the apparatus used in the alloying treatment (in the case of the apparatus used in the examples, 500 rpm or more, preferably 1000 rpm or more, more preferably 1500 rpm or more), the specific composition range described above is set. The alloy having the above-described microstructure can be obtained. Thereby, the compressive strength of the obtained alloy can be improved, and the electrode structure can be maintained while suppressing cracking of the alloy active material particles. As a result, it is possible to prevent Si (active material particles) from falling off the conductive network and to prevent irreversible capacity. In addition, since a new alloy surface due to cracking of the alloy active material particles is unlikely to occur, the reaction between the new surface and the electrolytic solution is prevented, and the decomposition of the electrolytic solution is prevented, thereby effectively preventing deterioration in cycle durability. it can. Therefore, cycle durability can be improved, maintaining the high capacity | capacitance of the electric device in which the said SiSnTiAl alloy (negative electrode active material) is used. Moreover, the Si-containing alloy which has a suitable fine structure can be obtained and the said effect can be show | played more notably, so that time to implement a mechanical alloying process is lengthened. From such a viewpoint, the mechanical alloying time is preferably 12 hours or more, more preferably 24 hours or more, still more preferably 30 hours or more, and even more preferably 36 hours or more, particularly Preferably it is 42 hours or more, and most preferably 48 hours or more. In addition, although the upper limit of the time for alloying process is not set in particular, it may usually be 72 hours or less.

  In this embodiment, in addition to the time for the alloying treatment, the energy given to the Si-containing alloy is also changed by changing the number of revolutions of the apparatus to be used, the number of pulverized balls, the amount of the sample (raw material powder of the alloy), etc. Since it changes, it is possible to control a suitable fine structure.

  The mechanical alloying process by the above-described method is usually performed in a dry atmosphere, but the particle size distribution after the mechanical alloying process may have a very large or small width. For this reason, it is preferable to perform the grinding | pulverization process and / or classification process for adjusting a particle size.

  In the present embodiment, as a more preferable example of the method for producing a negative electrode active material made of an Si-containing alloy having a predetermined composition range and a microstructure described above, an alloy is obtained by mechanical alloying using a ball mill apparatus having a large applied energy. There is provided a manufacturing method for performing a chemical treatment. That is, according to another embodiment of the present invention, there is provided a method for producing a negative electrode active material for an electrical device comprising a Si-containing alloy having the above-described predetermined composition range and microstructure, which is the same as the Si-containing alloy. A negative alloy active material for an electrical device made of the Si-containing alloy is obtained by subjecting the powder of the mother alloy having a composition to mechanical alloying using a ball mill apparatus in which a centrifugal force of 20 [G] or more is applied. A method for producing a negative electrode active material for an electrical device is also provided.

  In the manufacturing method which concerns on this form, it is preferable that the centrifugal force added to the content by the ball mill apparatus used for a mechanical alloying process is 20 [G] or more. Si-containing alloy (negative electrode active material) that can exhibit equivalent or higher cycle durability even in shorter time processing by performing mechanical alloying using a ball mill device that applies a relatively large centrifugal force. Can be manufactured. In addition, since the amount of Sn, which is a relatively expensive raw material, can be reduced, the manufacturing cost of the Si-containing alloy (negative electrode active material) can also be reduced. 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, most preferably 175 [G] or more. On the other hand, the upper limit value of the centrifugal force is not particularly limited, but normally about 200 [G] is realistic.

  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 rotation radius [m], iw is the rotation / revolution ratio [−], and rpm is the rotation speed [times / minute]. Therefore, it can be seen that 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 apparatus is not particularly limited, and conventionally known ball mill apparatuses such as a planetary ball mill apparatus and a stirring ball mill apparatus can be used as long as the above-described centrifugal force is satisfied. However, in the manufacturing method according to this embodiment, a stirring ball mill device is preferably used. The stirring ball mill device includes a container having a cylindrical inner surface and a stirring blade provided in the container. In the container of the stirring ball mill apparatus, raw material powder, balls, a solvent, and a processing agent are charged. Unlike the planetary ball mill apparatus, the stirring blade provided in the container rotates to alloy the raw material powder without rotating the container. When such a stirring ball mill apparatus is used, the contents of the container can be vigorously stirred by the stirring blades, so that a centrifugal force larger than that of other ball mill apparatuses can be applied to the contents of the container.

  In general, as the time for performing the mechanical alloying process is increased, a Si-containing alloy having a suitable microstructure can be obtained. However, in the manufacturing method according to this embodiment, a relatively large centrifugal force is used as described above. Since the mechanical alloying process is performed so that force is applied to the contents, even if the mechanical alloying process time is shortened, it is possible to achieve the same or higher cycle durability. From such a viewpoint, in the manufacturing method according to this embodiment, the mechanical alloying treatment time is preferably 45 hours or less, more preferably 30 hours or less, even more preferably 20 hours or less, and even more preferably. Is 15 hours or less, particularly preferably 10 hours or less, and most preferably 5 hours or less. In addition, although the lower limit of the time of a mechanical alloying process is not set in particular, Usually, what is necessary is just 0.5 hours or more.

  In the mechanical alloying process using a ball mill apparatus, a raw material powder can be alloyed using a conventionally known ball. Preferably, the ball is 1 mm or less, particularly 0.1 to 1 mm. A titanium or zirconia having a diameter is used. In particular, in this embodiment, a titanium ball manufactured by the plasma rotating electrode method is preferably used. A titanium or zirconia ball having a diameter of 1 mm or less manufactured by such a plasma rotating electrode method has a uniform spherical shape, and is particularly preferable as a ball for obtaining a Si-containing alloy.

  In the present 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 this embodiment, the processing agent charged in the container is not particularly limited. Examples of such a treatment agent include a surfactant and / or a fatty acid in addition to carbon powder for preventing the contents from adhering to the inner wall of the container.

  The mechanical alloying process by the above-described method is usually performed in a dry atmosphere, but the particle size distribution after the mechanical alloying process may have a very large or small width. For this reason, it is preferable to perform the grinding | pulverization process and / or classification process for adjusting a particle size.

Titanium disilicide (TiSi ₂ ) has two types of crystal structures, a C49 structure and a C54 structure. Although data is not shown, it was also confirmed that disilicide (TiSi ₂ ) contained in the negative electrode active material (Si-containing alloy) finally obtained by mechanical alloying treatment has a C54 structure. Yes. Since the C54 structure shows a lower resistivity (high electron conductivity) than the C49 structure, it has a more preferable crystal structure as a negative electrode active material.

As described above, the predetermined alloy included in the negative electrode active material layer has been described, but the negative electrode active material layer may contain other negative electrode active materials. Examples of the negative electrode active material other than the predetermined alloy include natural graphite, artificial graphite, carbon black, activated carbon, carbon fiber, coke, soft carbon, carbon such as hard carbon, pure metal such as Si and Sn, and the predetermined composition. Alloy-based active material out of ratio, or metal oxide such as TiO, Ti ₂ O ₃ , TiO ₂ , SiO ₂ , SiO, SnO ₂ , lithium such as Li _4/3 Ti _5/3 O ₄ or Li ₇ MnN And transition metal composite oxides (composite nitrides), Li—Pb alloys, Li—Al alloys, Li, and the like. However, from the viewpoint of sufficiently exerting the effects exhibited by using the predetermined alloy as the negative electrode active material, the content of the predetermined alloy in the total amount of 100% by mass of the negative electrode active material is preferably It is 50-100 mass%, More preferably, it is 80-100 mass%, More preferably, it is 90-100 mass%, Especially preferably, it is 95-100 mass%, Most preferably, it is 100 mass%.

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

(Binder)
The binder is added for the purpose of maintaining the electrode structure by binding the active materials or the active material and the current collector. There is no restriction | limiting in particular also about the kind of binder used for a negative electrode active material layer, What was mentioned above as a binder used for a positive electrode active material layer can be used similarly. Therefore, detailed description is omitted here.

  Note that the amount of the binder contained in the negative electrode active material layer is not particularly limited as long as it is an amount capable of binding the active material, but is preferably 0.5 to It is 20 mass%, More preferably, it is 1-15 mass%.

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

  The positive electrode active material layer 15 and the negative electrode active material layer 13 contain a conductive additive, an electrolyte salt (lithium salt), an ion conductive polymer, and the like as necessary. In particular, the negative electrode active material layer 13 essentially includes a conductive additive.

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

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

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

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

(Ion conductive polymer)
Examples of 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 nonaqueous electrolyte secondary battery.

  There is no particular limitation on the thickness of each active material layer (active material layer on one side of the current collector), and conventionally known knowledge about the battery can be referred to as appropriate. For example, the thickness of each active material layer is usually about 1 to 500 μm, preferably 2 to 100 μm in consideration of the intended use of the battery (emphasis on output, energy, etc.) and ion conductivity.

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

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

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

  In the case where the negative electrode active material is formed directly on the negative electrode current collector 12 by sputtering or the like, it is desirable to use a current collector foil.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  Further, the removal of the positive electrode current collector plate 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. It is not limited to the one shown in FIG. Further, in a wound type lithium ion battery, instead of the current collector plate, for example, a terminal may be formed using a cylindrical can (metal can).

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

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

  The invention is explained in more detail using the following examples. However, the technical scope of the present invention is not limited only to the following examples. In the following examples, the composition ratio of the alloy (metal) is expressed as mass%.

Example 1
[Production of Si-containing alloy (alloy active material)]
A Si-containing alloy having a composition of Si _67.5 Sn ₂ Ti ₂₉ Al _1.5 (composition ratio is mass ratio) was manufactured by mechanical alloying treatment (mechanical alloy method).

  Specifically, using a stirring ball mill device C-01M manufactured by ZOZ, Germany, 1920 g of zirconia pulverized balls (φ5 mm) and 1 g of carbon (SGL) were put into a SUS pulverized pot, and then at 1000 rpm for 10 minutes. A pre-grinding process was performed. Thereafter, 100 g of each raw material powder of each alloy was charged, and processing was performed at 1500 rpm for 45 seconds, processing at 1200 rpm for 15 seconds was set as one set, and alloying was performed for 5 hours by repeating a total of 300 sets (alloying processing). Moreover, the scraping process which removes the powder adhering to the pot every 150 sets (2.5 hour process) was performed. Thereafter, a fine pulverization treatment was performed at 400 rpm for 1 hour to obtain a Si-containing alloy (negative electrode active material) powder having the above composition. High purity metal Si ingot (5N), high purity Ti wire (3N), high purity Sn shot (3N), and high purity Al shot (4N) were used for each raw material powder of each alloy. In the stirring ball mill apparatus used in this example, the revolution radius rs = 0.070 [m], the rotation radius rpl = 0 [m], and the rotation speed rpm = 1500 [times / minute]. The force Gnl was calculated to be 176.0 [G]. Moreover, the average particle diameter (D50) of the obtained Si-containing alloy (negative electrode active material) powder was 6.8 μm.

[Production of negative electrode]
80 parts by mass of the Si-containing alloy (Si _67.5 Sn ₂ Ti ₂₉ Al _1.5 ) prepared above as a negative electrode active material, 5 parts by mass of acetylene black as a conductive auxiliary agent, and 15 parts by mass of polyamideimide as a binder Were mixed and dispersed in N-methylpyrrolidone to obtain a negative electrode slurry. The negative electrode slurry was prepared using a defoaming kneader (Thinky AR-100). Thereafter, the obtained negative electrode slurry was uniformly applied to 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 a vacuum for 24 hours. Obtained.

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

In addition, as said electrolyte solution, six which is lithium salt (supporting salt) in the organic solvent which mixed ethylene carbonate (EC) and diethyl carbonate (DEC) in the ratio of EC: DEC = 1: 2 (volume ratio). A solution obtained by dissolving lithium fluorophosphate (LiPF ₆ ) so as to have a concentration of 1 mol / L was used.

(Example 2)
Example except that the composition of the Si-containing alloy produced by the mechanical alloying process (mechanical alloy method) was changed to Si _68.5 Sn _1.5 Ti _28.5 Al _1.5 (composition ratio is mass ratio). 1 was used to prepare a Si-containing alloy (negative electrode active material), a negative electrode, and a lithium ion secondary battery (coin cell). The average particle diameter (D50) of the obtained Si-containing alloy (negative electrode active material) powder was 7.1 μm.

Example 3
Except for changing the composition of the Si-containing alloy produced by mechanical alloying (mechanical alloy method) to Si ₆₉ Sn ₂ Ti _28.5 Al _0.5 (composition ratio is a mass ratio), the same as in Example 1 A Si-containing alloy (negative electrode active material), a negative electrode, and a lithium ion secondary battery (coin cell) were prepared by the method. The average particle diameter (D50) of the obtained Si-containing alloy (negative electrode active material) powder was 6.4 μm.

(Example 4)
Example except that the composition of the Si-containing alloy produced by the mechanical alloying process (mechanical alloy method) was changed to Si _68.5 Sn _2.5 Ti _28.5 Al _0.5 (composition ratio is mass ratio). 1 was used to prepare a Si-containing alloy (negative electrode active material), a negative electrode, and a lithium ion secondary battery (coin cell). The average particle diameter (D50) of the obtained Si-containing alloy (negative electrode active material) powder was 7.8 μm.

(Comparative Example 1)
The Si-containing alloy (by the same method as in Example 1) except that the composition of the Si-containing alloy produced by mechanical alloying (mechanical alloy method) was changed to Si ₆₈ Sn ₅ Ti ₂₇ (composition ratio is a mass ratio). Negative electrode active material), negative electrode and lithium ion secondary battery (coin cell) were prepared. The average particle diameter (D50) of the obtained Si-containing alloy (negative electrode active material) powder was 7.2 μm.

(Reference Example 1)
The Si-containing alloy (by the same method as in Example 1) except that the composition of the Si-containing alloy produced by mechanical alloying (mechanical alloy method) was changed to Si ₆₅ Sn ₅ Ti ₃₀ (composition ratio is a mass ratio). Negative electrode active material), negative electrode and lithium ion secondary battery (coin cell) were prepared. The average particle diameter (D50) of the obtained Si-containing alloy (negative electrode active material) powder was 5.4 μm.

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

The first photograph from the upper left of FIG. 3A is an observation image (high magnification) of the negative electrode active material (Si-containing alloy) of Example 1 using a high-angle annular dark field scanning transmission electron microscope (HAADF-STEM). ). 3B to 3E, the second to fourth sheets from the upper left and the lower photograph were subjected to element intensity mapping by EDX (energy dispersive X-ray spectroscopy) for the same field of view as the observed image. It is an image. Specifically, the second to fourth sheets from the upper left and the lower photographs in FIGS. 3B to 3E are mapping images for each element of Si, Sn, and Ti from the upper left, and the lower is Al. It is a mapping image with respect to an element. From these results, it is considered from FIGS. 3A, 3B, and 3D that since Si is also present in the portion where Ti is present, a silicide (TiSi ₂ ) phase is present in the portion. It was. Further, from FIGS. 3A, 3B, 3C, and 3D, it can be seen that Si is also present in a portion where Ti is not present, and Sn is a portion where Ti is not present and Si is present (a-Si). It was found that it was partly contained (mostly dispersed). It can also be seen that Sn partially exists at the boundary (periphery) of the silicide (TiSi ₂ ) phase and the a-Si phase. 3 (a), (b), (d), and (e), Al is a portion where Ti is present and Si is present (Si is also present in the silicide (TiSi ₂ ) phase). 3 (a), (b), and (d) show that the a-Si phase is silicide (TiSi _2). Specifically, a so-called sea-island structure in which islands composed of a-Si phases as dispersed phases are dispersed in a sea composed of continuous-phase silicide (TiSi ₂ ) phases. You can see that

Subsequently, the photograph on the left side of FIG. 4A is an observation image by HAADF-STEM of the negative electrode active material (Si-containing alloy) of Example 1 which is the same as the first photograph from the upper left of FIG. Ultra high magnification). The graph and table on the right side of FIG. 4 (b) show the portion surrounded by a thick line (reference numeral 4) in the observation image of the photograph on the left side of FIG. 4 (a) (in which a silicide (TiSi ₂ ) phase exists from FIG. 3). This is an EDX spectrum obtained for an image of a part considered to be. In the graph and table of the EDX spectrum of FIG. 4B, since Si and Ti were present at an atomic ratio of approximately 2: 1, it was confirmed that the part was a silicide (TiSi ₂ ) phase. . In the EDX spectrum of FIG. 4B, it is also confirmed that Al is contained in the silicide (TiSi ₂ ) phase, and since Al does not form silicide with Si, Al is silicide (TiSi ₂ ). It was thought that it was dispersed (solid solution) in the phase.

  Similarly, the photograph on the left side of FIG. 5A is an observation image by HAADF-STEM of the negative electrode active material (Si-containing alloy) of Example 1 which is the same as the first photograph from the upper left of FIG. Ultra high magnification). The graph and table on the right side of FIG. 5 (b) show the part surrounded by a thick line (reference numeral 5) in the observation image of the left photograph of FIG. 5 (a) (part where Ti does not exist and Si exists). Is an EDX spectrum obtained for the image of FIG. In the graph and table of the EDX spectrum in FIG. 5B, since Si was present as a main component, it was confirmed that the part was an a-Si phase. In the EDX spectrum of FIG. 5B, it is also confirmed that Sn and Al are contained in the a-Si phase. Since Sn does not form silicide with Si, Sn and Al are a-Si. It was thought that it was dispersed (solid solution) in the phase. From FIG. 4B and FIG. 5B, it was also confirmed that Al was dispersed in the a-Si phase, and the amount of Al in the a-Si phase was larger than the amount of Al in the silicide phase. .

  To summarize the above results, the negative electrode active material (Si-containing alloy) of Example 1 partially contains Sn, and the a-Si phase mainly containing amorphous or low crystalline Si is Ti. The microstructure is dispersed in a silicide phase containing silicide as a main component and contains Al in the silicide phase. Furthermore, it was found that the microstructure was a structure in which Al was dispersed in the a-Si phase. Further, it was confirmed that the amount of Al in the a-Si phase was larger than the amount of Al in the silicide phase. Furthermore, although the results are not shown in the figure, the negative electrode active materials (Si-containing alloys) of Examples 2 to 4 also have the same microstructure, etc., and the observation results and mapping images of HAADF-STEM Furthermore, it is confirmed by the graph and table of the EDX spectrum.

  On the other hand, although the results are not shown, since the negative electrode active materials (Si-containing alloys) of Comparative Example 1 and Reference Example 1 do not contain Al, the same structure as in the examples was not confirmed.

[Results of crush measurement (compressive strength test) of powder (Si-containing alloy)]
The following compressive strength tests were performed on each negative electrode active material (Si-containing alloy) produced in Example 4 and Reference Example 1. Specifically, after each negative electrode active material (Si-containing alloy) powder sample prepared in Example 4 and Reference Example 1 was dispersed on a glass substrate, single indentation measurement of isolated particles was performed 50 times for each sample. went. The obtained data (relationship between load and displacement) was analyzed, and the crush load was calculated. The equipment names and measurement conditions used are shown below.

(Device name and measurement conditions)
Device name: TriboIndenter made by Hystron
Working indenter: Spherical indenter (tip radius: 100 μm)
Measurement temperature: 23 ± 1 ° C
Measurement humidity: 50 ± 10% RH.

  6 is a drawing showing the results of crush measurement (compressive strength test) of the Si-containing alloy powders produced in Example 4 and Reference Example 1. FIG. From the results of FIG. 6, it was found that the compressive strength was improved by adding Al to the SiSnTiAl alloy of Example 4 with respect to the SiSnTi alloy of Reference Example 1. Note that Reference Example 1 having a Si composition ratio (content) smaller than that of Comparative Example 1 was used as the SiSnTi alloy because the a-Si (part that is more brittle than Ti silicide) region as Si in the alloy increased. Increases the compression strength. From this, as SiSnTi alloy, Reference Example 1 having a higher compressive strength than Comparative Example 1 was used. On the other hand, among SiSnTiAl alloys, the Si content was relatively large (in Examples, the compressive strength was relatively high). This is a comparison of the compressive strength with Example 4.

[Evaluation of cycle durability]
Each lithium ion secondary battery (coin cell) produced in each of Examples 1 to 4 and Comparative Example 1 was subjected to cycle durability evaluation according to the following charge / discharge test conditions.

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

  The evaluation cell is in a constant current / constant voltage mode in the charging process (referring to the Li insertion process to the evaluation electrode) in a thermostat set to the above evaluation temperature using a charge / discharge tester. The battery was charged from 2 V to 10 mV at 0.3 C. Thereafter, in the discharge process (referring to the Li desorption process from the electrode for evaluation), a constant current mode was set and discharge was performed from 0.3 C, 10 mV to 2 V. The charge / discharge test was conducted from the initial cycle (1 cycle) to 50 cycles under the same charge / discharge conditions with the above charge / discharge cycle as one cycle. Table 1 below shows the results of determining the ratio of the discharge capacity at the 50th cycle (discharge capacity retention rate [%]) to the discharge capacity at the first cycle (initial discharge capacity). FIG. 7 shows the relationship between the capacity (initial discharge capacity) and the discharge capacity retention rate [%] for each lithium ion secondary battery (coin cell) manufactured in Examples 1 to 4 and Comparative Example 1. It is.

  From the results of Table 1, the lithium ion battery using the SiSnTiAl quaternary alloy (negative electrode active material) of Examples 1 to 4 has a higher capacity than the SiSnTi ternary alloy of Comparative Example 1. However, it can be seen that the discharge capacity retention ratio after 50 cycles is high and the cycle durability is excellent. Further, in Examples 1 to 4 using the Si alloy negative electrode, the capacity is very high as compared with the negative electrode active material using the carbon material (this point is not limited to showing a comparative example using the carbon material). In other words, since it is known (see background art), the comparative example is omitted). Thus, high cycle durability was able to be achieved while maintaining a high capacity because the quaternary alloy in which the Si-containing alloy constituting the negative electrode active material is represented by Si—Sn—Ti—Al has a specific composition. It can be said that this is due to having the above-mentioned fine structure.

  Since the negative electrode active material (SiSnTi ternary alloy) of Comparative Example 1 does not contain Al, the same microstructure as in the example was not confirmed. Therefore, unlike the SiSnTiAl quaternary alloy of the example, Al cannot enter the Si-Si bond and extend the bond, and the toughness of the a-Si phase and the silicide phase cannot be increased, and the compressive stress It can be said that it was not possible to improve sufficiently. Thereby, it can be said that the cracking of the alloy active material particles could not be sufficiently suppressed and the electrode structure could not be sufficiently maintained. As a result, at the 50th cycle, the detachment of Si particles from the conductive network has not occurred yet, and the irreversible capacity has not been surfaced. It can be said that it decomposed and caused a significant decrease in cycle durability.

  Moreover, when it compares in Examples 1-4, it turns out that the direction of Examples 3-4 is higher than Examples 1-2, and is excellent in cycle durability. In Examples 3 to 4, the composition range in the alloy, particularly the Al composition ratio (content), can be optimized, and as a result, the above-described effects of the invention can be expressed more remarkably. It is thought that it was made.

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 layer,
21, 57 power generation element,
25, 58 negative electrode current collector plate,
27, 59 positive current collector,
29, 52 Battery exterior material (laminate film).

Claims (8)

A negative electrode active material for an electrical device made of a SiSnTiAl alloy,
As composition range, Si: 60-69 mass%, Ti: 28-31 mass%, Sn: 1.5-8 mass%, Al: 0.5-2 mass%, and the composition which the remainder consists of inevitable impurities Have
As the microstructure, an a-Si phase mainly containing amorphous or low crystalline silicon is partially dispersed in a silicide phase mainly containing titanium silicide, and the silicide phase A negative electrode active material for an electric device, characterized by containing Al therein.   2. The negative electrode active material for an electric device according to claim 1, wherein the alloy has a composition range of Al: 0.5 to 1.5 mass%.   The negative electrode active material for an electric device according to claim 1, wherein Al is contained in the a-Si phase.   The negative electrode active material for an electric device according to claim 3, wherein the amount of Al in the a-Si phase is larger than the amount of Al in the silicide phase.   The negative electrode active material for an electric device according to any one of claims 1 to 4, wherein a mass ratio of an available-Si phase in 100% by mass of the SiSnTiAl alloy is 33% by mass or more.   6. The negative electrode active material for an electric device according to claim 1, wherein a ratio of silicide phase / available-Si phase in the microstructure of the alloy is 1.75 or more.   A negative electrode for an electric device comprising the negative electrode active material for an electric device according to any one of claims 1 to 6.   An electric device comprising the negative electrode for an electric device according to claim 7.