WO2016098208A1

WO2016098208A1 - Negative-electrode active material for electrical device, and electrical device using same

Info

Publication number: WO2016098208A1
Application number: PCT/JP2014/083474
Authority: WO
Inventors: 智裕蕪木; 千葉　啓貴; 渡邉　学; 文博三木
Original assignee: 日産自動車株式会社
Priority date: 2014-12-17
Filing date: 2014-12-17
Publication date: 2016-06-23

Abstract

[Problem] To provide a means for improving cycle durability in an electrical device such as a lithium-ion secondary cell. [Solution] A negative-electrode active material comprising a silicon-containing alloy and having an oxygen content of 0.5-20 mass% is used as a negative-electrode active material for an electrical device.

Description

Negative electrode active material for electric device and electric device using the same

The present invention relates to a negative electrode active material for an electric device and an electric device using the same. The negative electrode active material for an electric device 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.

Motor drive secondary batteries are required to have extremely high output characteristics and high energy compared to consumer lithium ion secondary batteries used in mobile phones and notebook computers. 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 introduction 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, in the pamphlet of International Publication No. 2006/129415, an invention that aims to provide a non-aqueous electrolyte secondary battery having a negative electrode pellet having a high capacity and excellent cycle life is disclosed. Specifically, a silicon-containing alloy obtained by mixing silicon powder and titanium powder by a mechanical alloying method and wet-pulverizing the first phase mainly composed of silicon and a silicide of titanium (such as TiSi ₂ ) ) Containing a second phase containing) is disclosed 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.

According to the study by the present inventors, an electrical device such as a lithium ion secondary battery using the negative electrode pellet described in International Publication No. 2006/129415 can exhibit good cycle durability. However, it has been found that the cycle durability may not be sufficient.

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

The present inventors have conducted intensive research to solve the above problems. As a result, it has been found that the above problem can be solved by using a negative electrode active material made of a silicon-containing alloy and having an oxygen content of 0.5 to 20% by mass as a negative electrode active material for electric devices. It came to complete.

That is, the present invention relates to a negative electrode active material for electric devices. The negative electrode active material for an electric device is characterized by being made of a silicon-containing alloy and having an oxygen content of 0.5 to 20% by mass.

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. It is a figure which shows the result of the curve fitting (peak fitting) of the Raman spectrum measured about the silicon containing alloy (negative electrode active material) produced in Example 4. FIG. It is the photograph obtained by EDX analysis (energy dispersive X-ray analysis) about the silicon containing alloy (negative electrode active material) produced in Example 4. FIG. In FIG. 4, red indicates the presence site of Ti, green indicates the presence site of O, and blue indicates the presence site of Si.

One embodiment of the present invention is a negative electrode active material for an electric device which is made of a silicon-containing alloy and has an oxygen content of 0.5 to 20% by mass. According to the present invention having such a configuration, the amorphous-crystal phase transition (crystallization to Li ₁₅ Si ₄ ) when Si and Li are alloyed is suppressed. Thereby, the expansion | contraction and shrinkage | contraction of the silicon containing alloy which comprises the negative electrode active material in the charging / discharging process of an electrical device are suppressed. As a result, cycle durability of an electric device using the negative electrode active material can be improved.

Hereinafter, embodiments of a negative electrode active material for an electric device of the present invention and an electric device using the same will be described 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, in 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, by reversing the arrangement of the positive electrode and the negative electrode as compared with FIG. 1, the outermost negative electrode current collector is positioned on 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 the positive electrode current collector plate 27 and the negative electrode current collector plate 25 that are electrically connected to the respective electrodes (positive electrode and negative electrode), and are sandwiched between the end portions of the laminate sheet 29. Thus, it has a structure led out of the laminate sheet 29. The positive electrode current collector 27 and the negative electrode current collector 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 a negative electrode. Hereinafter, main components of the battery including the negative electrode will be described.

<Active material layer>
The

active material layer

13 or 15 contains an active material, and further contains 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)
Examples of the positive electrode active material include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni—Mn—Co) O _2, and lithium-- such as those in which some 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, from the viewpoint of capacity and output characteristics, a lithium-transition metal composite oxide is used as the positive electrode active material. 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 substituted with other elements (hereinafter, referred to as “following”) 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 stacked alternately 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, the general formula: Li _a Ni _b Mn _c Co _d M _x O ₂ (where a, b, c, d, x is 0) .9 ≦ a ≦ 1.2, 0 <b <1, 0 <c ≦ 0.5, 0 <d ≦ 0.5, 0 ≦ x ≦ 0.3, b + c + d = 1, where M is Ti, Zr Nb, W, P, Al, Mg, V, Ca, Sr, Cr, and at least one kind of element. Here, a represents the atomic ratio of Li, b represents the atomic ratio of Ni, c represents the atomic ratio of Mn, d represents the atomic ratio of Co, and x represents the atomic ratio of M. Represents. From the viewpoint of cycle characteristics, it is preferable that 0.4 ≦ b ≦ 0.6 in the above general formula. 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 above general formula. 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 above general formula, b, c and d are 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31, 0.19 ≦ d ≦ 0.26. Is preferable from the viewpoint of improving the balance between capacity and life characteristics. For example, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ is LiCoO ₂ , LiMn ₂ O ₄ , LiNi _1/3 Mn _1/3 Co _1/3 O _2, etc. 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, from the viewpoint of capacity and output characteristics, a lithium-transition metal composite oxide is used as the positive electrode active material. 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 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 may contain 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 Copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene Fluororesin such as copolymer (ECTFE), polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluorine Rubber (VDF-HFP-TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-teto Fluoroethylene fluoro rubber (VDF-PFP-TFE fluoro rubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluoro rubber (VDF-PFMVE-TFE fluoro rubber), vinylidene fluoride-chlorotrifluoroethylene Vinylidene fluoride-based fluororubbers such as epoxy-based fluororubbers (VDF-CTFE-based fluororubbers), and epoxy resins. 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 can bind the active material, but it is preferably 0.5 to 15% by mass with respect to the active material layer. More preferably, it is 1 to 10% by mass.

The positive electrode (positive electrode active material layer) can be applied 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 is made of a silicon-containing alloy. The silicon-containing alloy as the negative electrode active material is characterized in that its oxygen content is 0.5 to 20% by mass. By using the silicon-containing alloy having such a structure as the negative electrode active material, amorphous-crystal phase transition (crystallization to Li ₁₅ Si ₄ ) when Si and Li are alloyed is suppressed. Thereby, the expansion | contraction and shrinkage | contraction of the silicon containing alloy which comprises the negative electrode active material in the charging / discharging process of an electrical device are suppressed. As a result, cycle durability of an electric device using the negative electrode active material can be improved.

In addition, the negative electrode active material according to the present embodiment is not particularly limited with respect to other configurations (structure structure, etc.) as long as it is made of a silicon-containing alloy that satisfies the above-mentioned rules. However, from the viewpoint of excellent capacity characteristics and cycle durability as a negative electrode active material, a transition metal silicide is contained in a matrix containing amorphous or low crystalline silicon (preferably containing this as a main component). It is preferably made of a silicon-containing alloy having a structure in which phases are dispersed and oxygen (O) atoms are contained in a dispersed state in the matrix. Therefore, in the following, the case where the silicon-containing alloy has such a structure will be described as an example, but the present invention is not limited to this as described above.

The silicon-containing alloy constituting the negative electrode active material in a preferred embodiment of the present invention first comprises a parent phase mainly composed of amorphous or low crystalline silicon. As described above, when the silicon constituting the parent phase is amorphous or has low crystallinity, an electric device having a high capacity and excellent cycle durability can be provided.

The parent phase constituting the silicon-containing alloy is a phase containing silicon as a main component, and is preferably a Si single phase (phase consisting of only Si). This parent phase (phase containing Si as a main component) 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 electrochemically reacts with Li. It is a possible phase. In the case of the Si single phase, it is possible to occlude and release a large amount of Li per weight and per volume. However, since Si has poor electron conductivity, the parent phase may contain a small amount of additive elements such as phosphorus and boron, transition metals, and the like. In addition, it is preferable that this parent phase (phase containing Si as a main component) is made amorphousr than a silicide phase described later. With such a configuration, the negative electrode active material (silicon-containing alloy) can have a higher capacity. Whether or not the parent phase is more amorphous than the silicide phase can be confirmed by electron beam diffraction analysis. Specifically, according to the electron diffraction analysis, a net pattern (lattice spot) of a two-dimensional dot arrangement is obtained for a single crystal phase, and a Debye-Scherrer ring (diffraction ring) is obtained for a polycrystalline phase, A halo pattern is obtained for the amorphous phase. By using this, the above confirmation becomes possible.

On the other hand, the silicon-containing alloy constituting the negative electrode active material in the present embodiment also includes a silicide phase containing a transition metal silicide (also referred to as silicide) dispersed in the parent phase in addition to the parent phase. It is out. This silicide phase contains a transition metal silicide (eg, TiSi ₂ ), so that it has excellent affinity with the parent phase, and can particularly suppress cracking at the crystal interface due to volume expansion during charging. Furthermore, the silicide phase is superior in terms of electron conductivity and hardness compared to the parent phase. For this reason, the silicide phase plays a role of improving the low electron conductivity of the parent phase and maintaining the shape of the active material against the stress during expansion.

A plurality of phases may exist in the silicide phase. For example, _two or more phases (for example, MSi ₂ and MSi) having different composition ratios between the transition metal element M and Si may exist. Moreover, two or more phases may exist by including a silicide with different transition metal elements. Here, the type of transition metal contained in the silicide phase is not particularly limited, but is preferably at least one selected from the group consisting of Ti, Zr, Ni, Cu, and Fe, and more preferably Ti or Zr. Yes, particularly preferably Ti. These elements exhibit higher electronic conductivity and higher strength than silicides of other elements when silicides are formed. In particular, TiSi ₂ which is silicide when the transition metal element is Ti is preferable because it exhibits very excellent electron conductivity.

In particular, when the transition metal element M is Si and 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% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass is the TiSi ₂ phase.

The size of the silicide phase is not particularly limited, but in a preferred embodiment, the size of the silicide phase is 50 nm or less. With such a configuration, the negative electrode active material (silicon-containing alloy) can have a higher capacity.

In the present invention, the composition of the silicon-containing alloy constituting the negative electrode active material is not particularly limited, but from the viewpoint of excellent capacity characteristics and cycle durability, a composition represented by the following chemical formula (1) is used as a composition other than oxygen. It is preferable to have it.

In the above chemical formula (1), A is an inevitable impurity, M is one or more transition metal elements, and x, y, z, and a represent mass% values, where 0 <X <100, 0 ≦ y <100, 0 <z <100, and 0 ≦ a <0.5, and x + y + z + a = 100.

As is clear from the chemical formula (1), the silicon-containing alloy (having the composition of Si _x Sn _y M _z A _a ) according to a preferred embodiment of the present invention is a binary system of Si and M (transition metal). (When y = 0) or a ternary system of Si, Sn and M (transition metal) (when y> 0). Among these, a ternary system of Si, Sn, and M (transition metal) is more preferable from the viewpoint of cycle durability. 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 the present embodiment, particularly preferably, Ti is selected as an additive element (M; transition metal) to the negative electrode active material (silicon-containing alloy), and Sn is added as a second additive element as necessary. In alloying, the cycle life can be improved by 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). Therefore, according to a preferred embodiment of the present invention, in the composition represented by the chemical formula (1), M is preferably titanium (Ti), and M is a ternary system of Si—Sn—Ti containing titanium. More preferably.

Here, in the case of Li alloying, the amorphous-crystal phase transition is suppressed because, in the Si material, when Si and Li are alloyed, the amorphous state transitions to the crystalline state and a large volume change (about 4 times) occurs. This is because the particles themselves are broken and the function as an active material is lost. Therefore, by suppressing the amorphous-crystal phase transition, it is possible to suppress the collapse of the particles themselves, maintain the function as the active material (high capacity), and improve the cycle life. By selecting such an additive element, a Si alloy negative electrode active material having a high capacity and high cycle durability can be provided.

In the composition of the chemical formula (1), the composition ratio z of the transition metal M (particularly Ti) is preferably 7 <z <100, more preferably 10 <z <100, and 15 <z <100. It is more preferable that 20 ≦ z <100. By setting the composition ratio z of the transition metal M (particularly Ti) within such a range, the cycle characteristics can be further improved.

More preferably, the x, y, and z in the chemical formula (1) are the following formulas (1) or (2):

It is preferable to satisfy. When the content of each component is within the above range, an initial discharge capacity exceeding 1000 Ah / g can be obtained, and the cycle life can also exceed 90% (50 cycles).

In addition, from the viewpoint of further improving the above characteristics of the negative electrode active material, the content of the transition metal M (particularly Ti) is preferably in the range of more than 7 mass%. That is, the x, y, and z are represented by the following formula (3) or (4):

It is preferable to satisfy. As a result, the cycle characteristics can be further improved.

From the viewpoint of ensuring better cycle durability, the x, y, and z are represented by the following formula (5) or (6):

It is preferable to satisfy.

From the viewpoint of initial discharge capacity and cycle durability, in the negative electrode active material of the present embodiment, the x, y, and z are expressed by the following formula (7):

It is preferable to satisfy.

Note that, as described above, A is an impurity (unavoidable impurity) other than the above three components derived from the raw materials and the manufacturing method. The a is 0 ≦ a <0.5, and preferably 0 ≦ a <0.1.

The silicon-containing alloy constituting the negative electrode active material in this embodiment is characterized in that its oxygen content is 0.5 to 20% by mass. The value of the oxygen content is preferably 0.7 to 20% by mass, more preferably 0.9 to 18% by mass. When the value of the oxygen content is within such a range, a negative electrode active material having even better cycle durability can be provided. In the present application, the measurement of the value of the oxygen content is performed using the method described in the column of Examples described later. Here, when the oxygen content is less than 0.5% by mass, sufficient cycle durability cannot be obtained. Further, when the oxygen content is more than 20 masses, although the cycle durability is excellent, the ratio of the oxygen amount to the whole active material increases, and the energy density (mAh / g) of the active material may be reduced. .

In the silicon-containing alloy having the structure according to the above-described preferred embodiment (matrix-silicide phase mixed phase), the oxygen (O) atom includes a parent phase (amorphous or low crystalline silicon (preferably It is preferably contained in a dispersed state in the phase) which is the main component. By adopting such a configuration, a negative electrode active material that is further excellent in cycle durability can be provided.

Here, conventionally, a SiO-based material in which Si nanoparticles are highly dispersed in SiO ₂ particles is known as a negative electrode active material having excellent capacity characteristics. However, according to the study by the present inventors, it has been found that in the case of such a conventional SiO-based material, an active material having excellent characteristics cannot be realized unless the oxygen content is made larger than 20% by mass. . On the other hand, according to the negative electrode active material according to the present invention, by using a negative electrode active material made of a silicon-containing alloy, even when the oxygen content is smaller than that of a conventional negative electrode active material, good characteristics are obtained. It becomes possible to express.

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

Here, as a result of further studies by the present inventors, in the negative electrode active material comprising the silicon-containing alloy according to the present invention, at least a part of oxygen atoms contained in the alloy is bonded to silicon atoms (Si—O It was found to be included). It has also been found that when the silicon atoms contained in the alloy are bonded to oxygen atoms at a certain ratio or higher, a negative electrode active material for an electric device that is further excellent in cycle durability can be provided. Specifically, for a negative electrode active material (silicon-containing alloy) that has never been charged / discharged (this is also referred to as an “uncharged / discharged state” in this specification), Raman measured for the silicon-containing alloy is used. When the peak area due to the Si—O bond in the spectrum is S ₁ (Si—O) and the peak area due to the Si—Si bond is S ₂ (Si—Si), S ₁ (Si—O) / ( When the value of S ₁ (Si—O) + S ₂ (Si—Si)) (also simply referred to as “peak area ratio” in this specification) is 0.06 to 0.40, the negative electrode active material was used. It has been found that the cycle durability of electrical devices can be further improved. This value is more preferably 0.12 to 0.40, and still more preferably 0.20 to 0.35.

Here, the outline of the calculation method of the peak area ratio is as follows. First, the Raman spectrum measured for the silicon-containing alloy is separated into five peaks. More particularly ^{^{^{^{900cm -1, 700cm -1, 500cm -1}}}} , 450cm -1, assuming peaks respectively at the position of 300 cm ^-1, changing the size of each peak. Then, curve fitting is performed so as to be closest to the spectrum obtained by measurement when these five peaks are combined. After that, the peak area appearing at 300 cm ⁻¹ when closest to the spectrum obtained by measurement is S ₁ (Si—O), and the peak area appearing at 450 cm ⁻¹ is S ₂ (Si—Si). The ratio value is calculated as the peak area ratio. A more specific method for calculating the peak area ratio will be described in Examples described later.

Further, as a result of investigations by the present inventors, it has been found that the peak area ratio of the silicon-containing alloy increases when charge / discharge treatment is performed on the negative electrode active material made of the silicon-containing alloy. On the other hand, the peak area ratio increases up to 1 to 3 charge / discharge cycles, but it hardly increases when it exceeds 3 times, and the value of the peak area ratio in the uncharged / discharged state is x, and charge / discharge is performed 3 times. Assuming that the value of the peak area ratio after the operation is y, it has been found that the value converges to a value that satisfies the relationship approximated by a linear function of y = 0.5x + 0.49. Therefore, another preferred embodiment of the negative electrode active material for an electrical device according to the present invention is the peak due to Si—O bond in the Raman spectrum measured in the complete discharge state after repeating the charge / discharge cycle three times for the silicon-containing alloy. Where S ₃ (Si—O) and the peak area due to the Si—Si bond is S ₄ (Si—Si), S ₃ (Si—O) / (S ₃ (Si—O) + S ₄ (Si—Si)) having a value of 0.52 to 0.69. This value is more preferably 0.55 to 0.68, and further preferably 0.55 to 0.66. Here, as described above, since the value (y) of the peak area ratio converges to a constant value when the charge / discharge cycle is performed three times or more, whether or not the negative electrode active material according to the preferred embodiment is determined. The determination can be applied regardless of whether or not the negative electrode active material for an electric device has been subjected to charge / discharge treatment before the measurement of the Raman spectrum. In addition, the “complete discharge state after repeating the charge / discharge cycle three times” in the present embodiment refers to a state in which the charge / discharge cycle is repeated three times and the discharge is completely performed at the end of the third cycle. Shall.

(Method for producing negative electrode active material)
Although there is no restriction | limiting in particular about the manufacturing method of the negative electrode active material for electrical devices which concerns on this embodiment, Although conventionally well-known knowledge can be referred suitably, in this application, the value of the oxygen content in the silicon-containing alloy as a negative electrode active material is mentioned above. As an example of a manufacturing method for achieving the above-described range, a manufacturing method having the following steps is provided.

First, a process for obtaining a mixed powder by mixing raw materials of a silicon-containing alloy is performed. In this step, in consideration of the composition of the obtained negative electrode active material (silicon-containing alloy), raw materials for the alloy are mixed. The raw material of the alloy is not particularly limited as long as the ratio of elements necessary as the negative electrode active material can be realized. For example, it is possible to use a single element constituting the negative electrode active material mixed in a target ratio, an alloy having a target element ratio, a solid solution, or an intermetallic compound. Usually, raw materials in a powder state are mixed. Thereby, the mixed powder which consists of a raw material is obtained.

Subsequently, an alloying process is performed on the mixed powder obtained above. Thereby, the silicon-containing alloy which can be used as a negative electrode active material for electric devices is obtained. And the value of oxygen content can be made into the value in the range mentioned above by performing this alloying process.

Examples of alloying methods include a solid phase method, a liquid phase method, and a gas phase method. For example, a mechanical alloy method, an arc plasma melting method, a casting method, a gas atomizing method, a liquid quenching method, an ion beam sputtering method, a vacuum method, and the like. Examples include vapor deposition, plating, and gas phase chemical reaction. Especially, it is preferable to perform an alloying process using a mechanical alloy method. It is preferable to perform the alloying process by the mechanical alloy method because the phase state can be easily controlled. Further, before the alloying treatment, a step of melting the raw material and a step of rapidly cooling and solidifying the molten material may be included. Furthermore, before performing the alloying treatment, a metal oxide such as TiO ₂ may be additionally added to the raw material powder, and the resulting mixed powder may be subjected to the alloying treatment.

In the manufacturing method according to the present embodiment, the above-described alloying treatment can be performed to obtain a structure composed of the parent phase / silicide phase as described above. In particular, when the alloying time is 12 hours or longer, a negative electrode active material (silicon-containing alloy) capable of exhibiting desired cycle durability can be obtained. The alloying treatment time is preferably 24 hours or more, more preferably 30 hours or more, further preferably 36 hours or more, particularly preferably 42 hours or more, and most preferably 48 hours or more. It is. Thus, by increasing the time required for the alloying treatment, the value of the oxygen content can be controlled to be increased. 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.

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

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 complex 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 to 100% by mass, more preferably 80 to 100% by mass, still more preferably 90 to 100% by mass, particularly preferably 95 to 100% by mass, and most preferably 100% by mass.

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

(Binder)
The binder is added for the purpose of 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.

The amount of the binder contained in the negative electrode active material layer is not particularly limited as long as it can bind the active material, but is preferably 0.5 to It is 20% by mass, more preferably 1 to 15% by 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 include 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 auxiliary agent A conductive auxiliary agent means the additive mix | blended in order to improve the electroconductivity of a positive electrode active material layer or a 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. . Commercially available TAB-2 (manufactured by Hosen Co., Ltd.) can be used as the conductive binder.

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 mixing ratio can be adjusted by appropriately referring to known knowledge about the non-aqueous solvent secondary battery.

The thickness of each active material layer (active material layer on one side of the current collector) is not particularly limited, and conventionally known knowledge about the battery can be appropriately referred to. As an example, the thickness of each active material layer is usually about 1 to 500 μm, preferably 2 to 100 μm, taking into consideration 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 are no particular restrictions on the materials that make up 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.

Also, 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 has a 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>
A liquid electrolyte or a polymer electrolyte can be used as the electrolyte constituting the electrolyte layer 17.

The liquid electrolyte has a form in which a lithium salt (electrolyte salt) is dissolved in an organic solvent. Examples of the organic solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), 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, polymer electrolytes are classified into gel electrolytes containing an electrolytic solution and intrinsic polymer electrolytes not containing an electrolytic solution.

The gel electrolyte has a configuration in which the above liquid electrolyte (electrolytic solution) is injected into a matrix polymer made of an ion conductive polymer. The use of a gel polymer electrolyte as the electrolyte is 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.

When the electrolyte layer is composed of a liquid electrolyte, a gel electrolyte, or an intrinsic polymer electrolyte, a separator may be used for the electrolyte layer. Specific 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 above matrix polymer, and does not contain 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 express 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 constituting the current collector plate is not particularly limited, and a known highly conductive material conventionally used as a current collector plate for a lithium ion secondary battery can be used. As 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.

∙ Use positive terminal lead and negative terminal lead as required. As the material of the positive terminal lead and the negative 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 wrapped 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 large vehicles such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles. It can be suitably used as a capacity power source. 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 present invention will be described in further detail using the following examples. However, the technical scope of the present invention is not limited only to the following examples.

(Example 1)
[Production of silicon-containing alloy (negative electrode active material)]
A silicon-containing alloy (Si ₅₉ Sn ₂₂ Ti ₁₉ ) (unit: mass%, hereinafter the same) was produced by a mechanical alloy method. Specifically, using a planetary ball mill device P-6 manufactured by Fricht, Germany, zirconia pulverized balls and alloy raw material powders are put into a zirconia pulverizing pot and alloyed at 600 rpm for 25 hours (alloying treatment). ), And then pulverization was performed at 400 rpm for 1 hour.

[Production of negative electrode]
80 parts by mass of the silicon-containing alloy (Si ₅₉ Sn ₂₂ Ti ₁₉ ) produced above as a negative electrode active material, 5 parts by mass of acetylene black as a conductive additive, and 15 parts by mass of polyamideimide as a binder are mixed. A negative electrode slurry was obtained by dispersing in N-methylpyrrolidone. Next, 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 the insulation between the positive electrode and the negative electrode, a gasket is attached, the following electrolyte is injected with a syringe, the spring and spacer are stacked, the upper side of the coin cell is overlapped and sealed by caulking. A lithium ion secondary battery was obtained.

In addition, as said electrolyte solution, hexafluorophosphoric acid which is lithium salt in the organic solvent which mixed ethylene carbonate (EC) and diethyl carbonate (DEC) in the ratio of EC: DEC = 1: 2 (volume ratio). lithium (LiPF ₆₎ was used dissolved at a concentration of 1 mol / L.

(Example 2)
A negative electrode active material, a negative electrode, and a lithium ion secondary battery (coin cell) were prepared in the same manner as in Example 1 except that the time for alloying treatment for producing the silicon-containing alloy was changed to 12.5 hours. ) Was produced.

(Example 3)
The same method as in Example 1 described above, except that the composition of the silicon-containing alloy was changed to Si ₆₀ Sn ₂₀ Ti ₂₀ and the time for alloying treatment for producing the silicon-containing alloy was changed to 36 hours. Thus, a negative electrode active material, a negative electrode, and a lithium ion secondary battery (coin cell) were produced.

Example 4
A negative electrode active material, a negative electrode, and a lithium ion secondary battery (coin cell) were prepared in the same manner as in Example 1 described above except that the time for alloying treatment for producing the silicon-containing alloy was changed to 50 hours. Produced.

(Example 5)
The same method as in Example 1 described above, except that the composition of the silicon-containing alloy was changed to Si ₇₀ Sn ₁₅ Ti ₁₅ and the time of alloying treatment for producing the silicon-containing alloy was changed to 24 hours. Thus, a negative electrode active material, a negative electrode, and a lithium ion secondary battery (coin cell) were produced.

(Example 6)
A silicon-containing alloy (Si ₅₉ Sn ₂₂ Ti ₁₉ ) was produced by using a cooling rapid solidification method and a mechanical alloy method in combination. Specifically, first, using a cooling rapid solidification apparatus (manufactured by Nisshin Giken Co., Ltd.), the mother alloy having the composition of Si ₅₉ Sn ₂₂ Ti ₁₉ was melted under reduced pressure with argon substitution, and the injection pressure was 0.05 MPa. And sprayed onto a copper roll having a rotational speed of 3500 rpm to produce a flaky alloy. Then, using a planetary ball mill device P-6 manufactured by Fricht, Germany, the zirconia pulverized ball and the flaky alloy were put into a zirconia pulverized pot, and alloyed at 600 rpm for 3 hours (alloying treatment). The grinding process was carried out at 400 rpm for 1 hour.

Using the silicon-containing alloy (Si ₅₉ Sn ₂₂ Ti ₁₉ ) thus obtained, a negative electrode and a lithium ion secondary battery (coin cell) were produced in the same manner as in Example 1 described above.

(Example 7)
A negative electrode active material, a negative electrode, and a lithium ion secondary battery (coin cell) were prepared in the same manner as in Example 6 except that the alloying treatment time for producing the silicon-containing alloy was changed to 6 hours. Produced.

(Example 8)
A negative electrode active material, a negative electrode, and a lithium ion secondary battery (coin cell) were prepared in the same manner as in Example 6 except that the time for alloying treatment for producing the silicon-containing alloy was changed to 12.5 hours. ) Was produced.

Example 9
A silicon-containing alloy (Si ₆₀ Sn ₁₀ Ti ₃₀ ) was produced by a cooling and rapid solidification method. Specifically, using a cooling and rapid solidification apparatus (manufactured by Nisshin Giken Co., Ltd.), the mother alloy having the composition of Si ₆₀ Sn ₁₀ Ti ₃₀ is melted under reduced pressure substituted with argon and rotated at an injection pressure of 0.05 MPa. It sprayed on the copper roll of several 3500 rpm, and the flaky alloy was produced. Thereafter, using a planetary ball mill device P-6 manufactured by Fricht, Germany, the zirconia pulverized balls and the flaky alloy were charged into a zirconia pulverized pot, and the pulverization treatment was performed at 400 rpm for 1 hour.

Using the silicon-containing alloy (Si ₆₀ Sn ₁₀ Ti ₃₀ ) thus obtained, a negative electrode and a lithium ion secondary battery (coin cell) were produced in the same manner as in Example 1 described above.

(Example 10)
A silicon-containing alloy (Si ₅₉ Sn ₂₂ Ti ₁₉ ) was produced by using a cooling rapid solidification method and a mechanical alloy method in combination. Specifically, first, using a cooling rapid solidification apparatus (manufactured by Nisshin Giken Co., Ltd.), the mother alloy having the composition of Si ₆₂ Sn ₂₁ Ti ₁₈ was melted under reduced pressure with argon substitution, and the injection pressure was 0.05 MPa. And sprayed onto a copper roll having a rotational speed of 3500 rpm to produce a flaky alloy. Thereafter, using the planetary ball mill device P-6 manufactured by Fricht, Germany, the zirconia pulverized balls and the flaky alloy are introduced into the zirconia pulverized pot, and the metal composition based on the charged mass is Si ₅₉ Sn ₂₂ Ti _19. Thus, TiO ₂ was charged and alloyed at 600 rpm for 3 hours (alloying treatment), and then pulverized at 400 rpm for 1 hour.

(Comparative Example 1)
A silicon-containing alloy (Si ₇₀ Sn ₁₅ Ti ₁₅ ) was produced by a cooling and rapid solidification method. Specifically, first, using a cooling rapid solidification apparatus (manufactured by Nisshin Giken Co., Ltd.), the mother alloy having the composition of Si ₇₀ Sn ₁₅ Ti ₁₅ was melted under reduced pressure with argon substitution, and the injection pressure was 0.05 MPa. And sprayed onto a copper roll having a rotational speed of 3500 rpm to produce a flaky alloy. Thereafter, using a planetary ball mill device P-6 manufactured by Fricht, Germany, the zirconia pulverized balls and the flaky alloy were charged into a zirconia pulverized pot, and the pulverization treatment was performed at 400 rpm for 1 hour.

Using the silicon-containing alloy (Si ₇₀ Sn ₁₅ Ti ₁₅ ) thus obtained, a negative electrode and a lithium ion secondary battery (coin cell) were produced by the same method as in Example 1 described above.

(Comparative Example 2)
A negative electrode active material, a negative electrode, and a lithium ion secondary battery (coin cell) were produced in the same manner as in Comparative Example 1 except that the composition of the silicon-containing alloy was changed to Si ₆₀ Sn ₂₀ Ti ₂₀ .

[Analysis of negative electrode active material]
(Measurement of oxygen content)
The oxygen content in the negative electrode active material (silicon-containing alloy) produced in each of Examples 1 to 10 and Comparative Examples 1 and 2 was measured using an oxygen / nitrogen analyzer (EMGA-920, manufactured by Horiba, Ltd.). It was measured by an inert gas melting-non-dispersive infrared absorption method. The results are shown in Table 1 below.

(Measurement of peak area ratio)
For the negative electrode active materials (silicon-containing alloys) produced in Examples 1 to 10 and Comparative Examples 1 and 2, the peak area ratio (S ₁ (Si—O) / ( The value of S ₁ (Si—O) + S ₂ (Si—Si))) was measured.

<Cleaning of negative electrode active material>
About the sample for a Raman spectrum measurement in an uncharged / discharged state, it prepared by wash | cleaning the negative electrode active material produced in each Example and each comparative example with dimethyl carbonate (DMC).

<Raman spectrum measurement>
In order to measure the Raman spectrum, the sample powder obtained above was developed on a flat plate and analyzed. Measurement was carried out for each sample at four points, and the obtained Raman spectra were averaged. The measurement conditions were a 10 × objective lens, and a green laser with an excitation wavelength of 532 nm was used as incident light. Measurement range and 1550 cm ^-1 from 50 cm ^-1, was four times the number of integration. The equipment used is as follows.
Device name: Bruker Optics Microscopic Laser Raman SENTERRA
Here, the result of curve fitting (peak fitting) of the Raman spectrum measured for the silicon-containing alloy (negative electrode active material) produced in Example 4 is shown in FIG. Here, peaks of the circled numbers 2,500 cm ^-1 of the circled 1,700Cm ^-1 peaks 900 cm ^-1 peak of circled 3,450Cm ^-1 (peak of crystalline silicon) (the peak of amorphous silicon) Is the round numeral 4, and the peak at 300 cm ⁻¹ is the round numeral 5.

<Curve fitting>
Curve fitting was performed based on the data obtained by the Raman spectrum measurement. Curve fitting was performed based on Lorentz functions centered at five positions of 900 cm ⁻¹ , 700 cm ⁻¹ , 500 cm ⁻¹ , 450 cm ⁻¹ , and 300 cm ⁻¹ .

<Calculation of peak area ratio>
The peak area appearing at the circled number 5 (300 cm ⁻¹ ) is S ₁ (Si—O), and the peak at the circled number 3 (500 cm ⁻¹ ) is attributed to the Si—Si bond to calculate the peak area. The value of the peak area ratio (S ₁ (Si—O) / (S ₁ (Si—O) + S ₂ (Si—Si))) was determined. For example, referring to FIG. 3, when the peak areas of the circled numbers 3 and 5 are calculated, the peak area S ₁ (Si—O) of the circled numbers 5 is 1221 and the peak area S ₂ (Si—O) of the circled numbers 3 -Si) is 2309. Therefore, it is confirmed that the peak area ratio in Example 4 is 0.34.

<Calculation of peak area ratio after charge / discharge treatment>
The negative electrode active materials (silicon-containing alloys) obtained in Examples 1 to 4 were subjected to charge / discharge treatment three times, and then the same peak area ratio was measured as described above. Here, the conditions of the charge / discharge treatment are the conditions described in the column “Evaluation of cycle durability” described later, and the negative electrode active material is taken out in a completely discharged state after the three charge / discharge tests, and diethyl carbonate (DEC) is used. After washing, the Raman spectrum was measured and used for calculation of the peak area ratio.

The results obtained above (the values of the peak area ratio in the uncharged / discharged state for the negative electrode active materials of the examples and the comparative examples, and the peak area ratio after the third charge / discharge for the examples 1 to 4) Values) are shown in Table 1 below.

[Evaluation of cycle durability]
Each lithium ion secondary battery (coin cell) produced in each of Examples 1 to 10 and Comparative Examples 1 and 2 was evaluated for cycle durability 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 set to the constant current / constant voltage mode in the charging process (referring to the Li insertion process to the evaluation electrode) in the thermostat set to the above evaluation temperature using a charge / discharge tester. The battery was charged from 2 V to 10 mV at 0.1 mA. Thereafter, in a discharge process (referring to a 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. The results of determining the ratio of the discharge capacity at the 50th cycle to the discharge capacity at the first cycle (discharge capacity retention rate [%]) are shown in Table 1 below. In Table 1, the alloy composition is shown as a composition other than oxygen.

From the results shown in Table 1, the lithium ion battery using the negative electrode active material according to the present invention is maintained at a high discharge capacity retention rate after 50 cycles, and has excellent cycle durability. Recognize. On the other hand, it can be seen that Comparative Examples 1 and 2 have poor cycle durability due to the low oxygen content. Further, in Example 10, since oxygen atoms are only contained in the form of TiO ₂ , although some oxygen is contained in the silicon-containing alloy, it is slightly cycled as compared with other examples. The result was inferior in durability.

Further, when examining the peak area ratio based on the Raman spectrum, the cycle durability (discharge capacity maintenance ratio) can be further improved when the value of the peak area ratio in the uncharged / discharged state is 0.06 to 0.40. It has been shown.

Incidentally, it shows a photograph obtained by EDX analysis (energy dispersive X-ray analysis) of the fabricated silicon-containing alloy in Example _{_{_{4 (Si 59 Sn 22 Ti 19}}} ) in FIG. 4. In FIG. 4, red indicates a site where Ti is present, green indicates a site where O is present, and blue indicates a site where Si is present. From the results shown in FIG. 4, it is confirmed that the oxygen (O) atoms contained in the obtained silicon-containing alloy are present at the same positions as the silicon (Si) atoms. From this, in the silicon-containing alloy obtained in this example, the transition phase (Ti) silicide phase is dispersed in the amorphous silicon (Si) matrix, and the oxygen (O) atom is It can be seen that it is dispersed in the matrix.

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

A negative electrode active material for electrical devices, comprising a silicon-containing alloy and having an oxygen content of 0.5 to 20% by mass.
2. The negative electrode active material for an electric device according to claim 1, wherein the oxygen content is 0.9 to 18% by mass.
The amorphous phase or the low crystalline silicon-containing matrix includes a structure in which a silicide phase of a transition metal is dispersed, and oxygen is contained in a dispersed state in the matrix. 2. The negative electrode active material for electrical devices according to 2.
The negative electrode active material for an electric device according to any one of claims 1 to 3, wherein the matrix phase is more amorphous than the silicide phase.
The silicon-containing alloy has the following chemical formula (1) as a composition other than oxygen:

(In the above chemical formula (1),
M is one or more transition metal elements,
A is an inevitable impurity,
x, y, z, and a represent mass% values, where 0 <x <100, 0 ≦ y <100, 0 <z <100, and 0 ≦ a <0.5, and x + y + z + a = 100. The negative electrode active material for an electric device according to any one of claims 1 to 4, which has a composition represented by:
The negative electrode active material for an electric device according to any one of claims 1 to 5,
It is in an uncharged / discharged state,
Oxygen contained in the silicon-containing alloy forms a Si-O bond,
When the peak area due to Si—O bond in the Raman spectrum measured for the silicon-containing alloy is S 1 (Si—O) and the peak area due to Si—Si bond is S 2 (Si—Si), S 1. A negative electrode active material for an electric device having a value of 1 (Si—O) / (S 1 (Si—O) + S 2 (Si—Si)) of 0.06 to 0.40.
The negative electrode active material for an electric device according to any one of claims 1 to 5,
Oxygen contained in the silicon-containing alloy forms a Si-O bond,
For the silicon-containing alloy, the peak area due to the Si—O bond in the Raman spectrum measured in the complete discharge state after repeating the charge / discharge cycle three times is S 3 (Si—O), and the peak due to the Si—Si bond. When the area is S 4 (Si—Si), the value of S 3 (Si—O) / (S 3 (Si—O) + S 4 (Si—Si)) is 0.52 to 0.69. , Negative electrode active material for electrical devices.
A negative electrode for electric devices, comprising the negative electrode active material for electric devices according to any one of claims 1 to 7.
An electric device comprising the negative electrode for an electric device according to claim 8.