JP6459479B2 - Negative electrode for electric device and electric device using the same - Google Patents

Description

  The present invention relates to a negative electrode for an electric device and an electric device using the same. The negative electrode for an electric device and the electric device using the same according to the present invention are used as, for example, a driving power source or 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. It is done.

  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, 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.

International Publication No. 2006/129415 Pamphlet

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

  Then, an object of this invention is to provide the means which can improve the cycling durability of electric devices, 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, a negative electrode active material composed of a silicon-containing alloy having a predetermined structure and composition is used, and as a conductive assistant, a spherical conductive assistant having an aspect ratio of less than 10 and a fibrous conductive assistant having an aspect ratio of 10 to 1,000. By using the above in combination, the inventors have found that the above problems can be solved, and have completed the present invention.

  That is, this invention relates to the negative electrode for electric devices which has a collector and the negative electrode active material layer arrange | positioned on the surface of the said collector, the negative electrode active material containing a conductive support agent, and a binder. At this time, the negative electrode active material has a structure in which a silicide phase containing a silicide of a transition metal is dispersed in a matrix phase containing amorphous or low crystalline silicon as a main component. ):

(In the above chemical formula (1),
A is an inevitable impurity,
M is one or more transition metal elements,
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. )
It consists of a silicon containing alloy which has a composition represented by these. The negative electrode active material is 2θ = 37 to 45 with respect to the diffraction peak intensity A of the (111) plane of Si in the range of 2θ = 24 to 33 ° in the X-ray diffraction measurement using the CuKα1 line of the silicon-containing alloy. It is characterized in that the value (B / A) of the diffraction peak intensity B of the transition metal silicide in the range of 0 is 0.41 or more. Further, the conductive auxiliary agent is also characterized in that it includes a spherical conductive auxiliary agent having an aspect ratio of less than 10 and a fibrous conductive auxiliary agent having an aspect ratio of 10 to 1,000.

According to the present invention, when the value of B / A is within the above-described range, the amorphous-crystal phase transition (crystallization to Li ₁₅ Si ₄ ) occurs when Si and Li are alloyed. It 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. Furthermore, by using a combination of a spherical conductive assistant having an aspect ratio of less than 10 and a fibrous conductive assistant having an aspect ratio of 10 to 1000 as the conductive assistant, the electronic conductivity between the negative electrode active materials is improved. The strength of the negative electrode active material layer can be improved. As a result of such combined action, the negative electrode according to the present invention has a useful effect of having high cycle durability.

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. 3 is a diffraction spectrum obtained by X-ray diffraction analysis of the silicon-containing alloy (negative electrode active material) powder obtained in Reference Example 1. 4 is a diffraction spectrum obtained by X-ray diffraction analysis of the silicon-containing alloy (negative electrode active material) powder obtained in Reference Example 2. 4 is a diffraction spectrum obtained by X-ray diffraction analysis of the silicon-containing alloy (negative electrode active material) powder obtained in Reference Example 3. 6 is a diffraction spectrum obtained by X-ray diffraction analysis of the silicon-containing alloy (negative electrode active material) powder obtained in Reference Example 4. 3 is a diffraction spectrum obtained by X-ray diffraction analysis of the silicon-containing alloy (negative electrode active material) powder obtained in Comparative Reference Example 1. It is a graph showing the relationship between content of the spherical conductive support agent with respect to the total amount of the spherical conductive support agent and fibrous conductive support agent in the negative electrode obtained by each Example and the comparative example, and the discharge capacity maintenance factor of a battery.

  Hereinafter, embodiments of an anode 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 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 the negative electrode for an electric device according to the present invention, and a lithium ion secondary battery using the same, the voltage of the cell (single cell layer) is large. 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 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 obtained by replacing some of these transition metals 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 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 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, 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.

  In general, nickel (Ni), cobalt (Co), and manganese (Mn) are known to contribute to capacity and output characteristics from the viewpoint of improving the purity of materials and improving 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 preferable 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 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 fluororubber (VDF-PFP-TFE fluororubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluororubber (VDF-PFMVE-TFE fluororubber), 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 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 active material layer 15 can include a conductive additive.

(Conductive aid)
The conductive assistant 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 additive used for the positive electrode active material layer 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 in the active material layer used for the positive electrode active material layer is 1% by mass or more, more preferably 3% by mass or more, and further preferably 5%, based on the total amount of the positive electrode active material layer. It is the range of mass% or more. In addition, the content of the conductive additive mixed into the positive electrode 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 positive electrode active material layer. It is a range. By defining the compounding ratio (content) of the conductive additive in the positive electrode active material layer within the above range, the electronic conductivity of the positive electrode active material itself is low and the electrode resistance can be reduced by the amount of the conductive additive. Expressed. 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.

  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 has a structure in which a silicide phase containing a transition metal silicide is dispersed in a parent phase mainly composed of amorphous or low crystalline silicon, and has a predetermined structure. It consists of a silicon-containing alloy having a composition.

  As described above, the silicon-containing alloy constituting the negative electrode active material in the present embodiment first includes 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 silicon-containing alloy constituting the negative electrode active material has a composition represented by the following chemical formula (1).

  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 silicon-containing 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. During 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, to maintain the function (high capacity) as an active material, and to improve the cycle life. By selecting such an additive element, a silicon-containing alloy negative electrode active material having 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 represented by the following formula (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).

  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% by 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.

  And 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 this embodiment, the x, y, and z are represented by the following formula (7):

It is preferable to satisfy.

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

  In the X-ray diffraction measurement using CuKα1 ray, the silicon-containing alloy that constitutes the negative electrode active material in the present embodiment is 2θ = for the diffraction peak intensity A of the (111) plane of Si in the range of 2θ = 24 to 33 °. It is characterized in that the value (B / A) of the diffraction peak intensity B of the transition metal silicide in the range of 37 to 45 ° is 0.41 or more. The value of this ratio (B / A) is preferably 0.89 or more, more preferably 2.55 or more, and particularly preferably 7.07 or more. In the present application, the X-ray diffraction analysis for calculating the intensity ratio of the diffraction peaks is performed using the method described in the column of Examples described later.

  Here, the diffraction peak intensity A of the (111) plane of Si in the range of 2θ = 24 to 33 ° can be obtained as follows (see FIG. 3A corresponding to the result of Reference Example 1 described later). .

  First, in the diffraction spectrum obtained by the X-ray diffraction analysis, a point where the perpendicular and the diffraction spectrum at 2θ = 24 ° intersect is defined as a. Similarly, let b be the point where the perpendicular at 2θ = 33 ° and the X-ray diffraction spectrum intersect. Here, a line segment ab is defined as a base line, and a point at which a perpendicular line at the diffraction peak (2θ = about 28.5 °) of the Si (111) plane intersects the base line is defined as c. Then, the diffraction peak intensity A of the Si (111) plane is obtained as the length of the line segment cd connecting the vertex d and the point c of the diffraction peak (2θ = about 28.5 °) of the Si (111) plane. be able to.

Similarly, the diffraction peak intensity B of the transition metal silicide in the range of 2θ = 37 to 45 ° can be obtained as follows. Hereinafter, the case where the silicide of the transition metal is TiSi ₂ will be described as an example.

First, in the diffraction spectrum obtained by X-ray diffraction analysis, let e be the point where the perpendicular and diffraction spectrum at 2θ = 37 ° intersect. Similarly, let f be the point where the perpendicular at 2θ = 45 ° and the X-ray diffraction spectrum intersect. Here, the line segment ef is the base line, and g is the point where the perpendicular line at the TiSi ₂ diffraction peak (2θ = about 39 °) and the base line intersect. Then, the diffraction peak intensity B of TiSi ₂ can be obtained as the length of the line segment gh connecting the vertex h of the diffraction peak of TiSi ₂ (2θ = about 39 °) and the point g.

  Here, specific values of the diffraction peak intensity A of the Si (111) plane and the diffraction peak intensity B of the transition metal silicide are not particularly limited, but the diffraction peak intensity A of the Si (111) plane is not particularly limited. Is preferably 6000 to 25000 (cps), more preferably 6000 to 15000. The diffraction peak intensity B of the transition metal silicide is preferably 9000 to 46000 (cps), more preferably 25,000 to 46000 (cps). By controlling A and B to values within these ranges, there is an advantage that the above-described diffraction peak intensity ratio (B / A) can be easily achieved.

  Although the particle diameter of the silicon-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.

(Method for producing negative electrode active material)
There is no particular limitation on the method for producing the negative electrode active material for an electrical device according to the present embodiment, and conventionally known knowledge can be referred to as appropriate. In this application, the value of the intensity ratio B / A of the diffraction peak by X-ray diffraction analysis is As an example of a manufacturing method for achieving the above-described range, a manufacturing method having the following steps is provided.

  First, a step of 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. The intensity ratio (B / A) of the diffraction peak can be controlled by adjusting the composition ratio between silicon (Si) and titanium (Ti) in the raw material. For example, when the composition ratio of Ti to Si is increased, the strength ratio (B / A) can be increased.

  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.

  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.

  In the manufacturing method according to this embodiment, the alloying process described above is performed. Thereby, it can be set as the structure which consists of a mother phase / silicide phase as mentioned 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, still more preferably 36 hours or more, still more preferably 42 hours or more, and particularly preferably 48 hours. That's it. As described above, the diffraction peak intensity ratio (B / A) can also be increased by increasing the time required for the alloying treatment. 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 above-described method is usually performed in a dry atmosphere, but the particle size distribution after the alloying treatment 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.

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%.

  Furthermore, the negative electrode active material layer 13 includes a conductive additive.

(Conductive aid)
The negative electrode active material layer includes, as conductive assistants, spherical conductive assistants having an aspect ratio of less than 10 and fibrous conductive assistants having an aspect ratio of 10 to 1,000.

  A conductive support agent is mix | blended in order to improve the electroconductivity of an active material layer. At this time, the spherical conductive additive having an aspect ratio of less than 10 is filled in minute voids between the negative electrode active material particles, and ensures a certain level of strength in the entire negative electrode active material layer. However, it is difficult to obtain a certain strength or higher because the spherical conductive auxiliary agent alone cannot exist so as to cover the periphery of the negative electrode active material particles.

  In addition, the spherical conductive auxiliary agent is filled in minute gaps between the negative electrode active material particles, but since the spherical conductive auxiliary agent alone cannot exist so as to surround the negative electrode active material particles, It is difficult to form a conductive path. Therefore, sufficient conductivity cannot be obtained in the negative electrode active material layer, and as a result, the capacity of the battery tends to decrease, and high cycle durability is difficult to obtain.

  On the other hand, the fibrous conductive additive having an aspect ratio of 10 to 1000 is present so as to cover the surface of the negative electrode active material particles, but cannot fill the minute gaps between the negative electrode active material particles. It is difficult to form a stable conductive path only with the agent. Moreover, since it is difficult for only the fibrous conductive auxiliary agent to enter the minute gaps between the negative electrode active material particles, it is difficult to give sufficient strength to the negative electrode active material layer due to the generation of voids. As a result, the capacity of the battery tends to decrease, and high cycle durability is difficult to obtain.

  However, by using the spherical conductive aid and the fibrous conductive aid in combination, the spherical conductive aid is mainly filled in the fine gaps between the negative electrode active material particles, and the fibrous conductive aid is used as the spherical conductive aid. It arrange | positions so that the surface of negative electrode active material particles may be covered except the part with which the adjuvant was filled. As a result, the strength of the negative electrode active material layer can be improved as a whole. In addition, since both long-distance and short-distance conductive paths can be secured, the electron conductivity can be improved. Thus, it is thought that charge and discharge progress stably and lead to improvement in cycle durability by improving the strength and electronic conductivity of the active material layer.

  Here, the particle size and shape of the particulate conductive aid are not particularly limited as long as the aspect ratio (major axis / minor axis) is less than 10.

  The average particle diameter of the particulate conductive auxiliary agent is, for example, 23 to 48 nm, and preferably 35 to 45 nm. Moreover, although the aspect ratio of a particulate-form conductive support agent is so good that it approaches 1, it is preferable that it is 1-5, for example, and it is more preferable that it is 1-2. If it is the said range, the effect of this invention can be acquired more notably.

  Examples of the particulate conductive aid include carbon black such as acetylene black, ketjen black (furnace black), channel black, thermal black and the like, and graphite (graphite) such as natural graphite and artificial graphite. However, it is not limited to these.

  On the other hand, as long as the fibrous conductive additive has an aspect ratio (fiber length / fiber diameter) of 10 to 1000, the shape such as the fiber diameter and the fiber length is not particularly limited. In the present invention, the fiber diameter is preferably 1 to 300 nm, and more preferably 1 to 50 nm. Moreover, it is preferable that fiber length is 0.1-100 micrometers, and it is more preferable that it is 5-50 micrometers. The aspect ratio is preferably 20 to 1000. If it is the said range, the effect of this invention can be acquired more notably.

  As the fibrous conductive additive, for example, carbon fiber (carbon fiber) such as gas phase method carbon fiber or liquid phase method carbon fiber (carbon nanotube (CNT), graphite fiber, etc.) and carbon nanofiber can be used. The carbon fiber can be synthesized by a liquid phase method or a gas phase method.

  The aspect ratio and particle diameter of the particulate conductive aid and the fibrous conductive aid are the average values of the particles observed in several to several tens of fields using an observation means such as a transmission electron microscope (TEM). The calculated value shall be adopted.

  In the negative electrode of the present embodiment, the content of the spherical conductive additive relative to the total amount of the spherical conductive additive and the fibrous conductive additive ((mass of spherical conductive additive / (mass of spherical conductive additive + fibrous The mass of the conductive aid) × 100)) is not particularly limited, but is preferably 25 to 80% by mass, and more preferably 40 to 60% by mass. When the amount is in the above range, the spherical conductive auxiliary agent sufficiently fills the gaps between the active material particles, and the fibrous conductive auxiliary agent is suitable for effectively reinforcing the surroundings. Therefore, the electron conductivity in the negative electrode active material layer is further improved, and the strength of the negative electrode active material layer is further increased, so that more excellent cycle durability can be obtained.

  The content of the conductive auxiliary agent mixed into the negative electrode active material layer is such that the total amount of the spherical conductive auxiliary agent and the fibrous conductive auxiliary agent is, for example, 1% by mass or more with respect to the total amount of the negative electrode active material layer. Is 3% by mass or more, more preferably 5% by mass or more. In addition, the content of the conductive auxiliary agent mixed into the negative electrode active material layer is such that the total amount of the spherical conductive auxiliary agent and the fibrous conductive auxiliary agent is, for example, 15% by mass or less with respect to the total amount of the negative electrode active material layer, More preferably, it is 10 mass% or less, More preferably, it is the range of 7 mass% or less. By defining the blending ratio (content) of the conductive assistant within the above range, the following effects are exhibited. 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. .

(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 an electrolyte salt (lithium salt), an ion conductive polymer, and the like as necessary.

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.

  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>
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, 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 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 for lithium ion secondary batteries and the lithium ion secondary battery of this embodiment are suitably used as a large-capacity power source for electric vehicles, hybrid electric vehicles, fuel cell vehicles, hybrid fuel cell vehicles, and the like. can do. 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.

  First, as a reference example, performance evaluation was performed on the silicon-containing alloy represented by the above chemical formula (1) constituting the negative electrode active material for an electric device according to the present invention.

(Reference Example 1)
[Manufacture of silicon-containing alloys]
A silicon-containing alloy (Si ₈₀ Sn ₁₀ Ti ₁₀ ) (unit: mass%, the same applies hereinafter) 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 were charged into a zirconia pulverized pot and alloyed at 600 rpm for 24 hours (alloying treatment). ), And then pulverization was performed at 400 rpm for 1 hour. In addition, the average particle diameter of the obtained silicon-containing alloy (negative electrode active material) powder was 0.3 μm.

[Production of negative electrode]
80 parts by mass of the silicon-containing alloy (Si ₈₀ Sn ₁₀ Ti ₁₀ ) 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.

(Reference 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 Reference Example 1 described above except that the composition of the silicon-containing alloy was changed to Si ₇₀ Sn ₁₅ Ti ₁₅ . In addition, the average particle diameter of the obtained silicon-containing alloy (negative electrode active material) powder was 0.3 μm.

(Reference Example 3)
The same method as in Reference Example 1 described above, except that the composition of the silicon-containing alloy was changed to Si ₅₉ Sn ₂₂ Ti ₁₉ and the time for the alloying treatment in producing the silicon-containing alloy was changed to 25 hours. Thus, a negative electrode active material, a negative electrode, and a lithium ion secondary battery (coin cell) were produced. In addition, the average particle diameter of the obtained silicon-containing alloy (negative electrode active material) powder was 0.3 μm.

(Reference 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 Reference Example 3 described above, except that the alloying treatment time for producing the silicon-containing alloy was changed to 50 hours. Produced. In addition, the average particle diameter of the obtained silicon-containing alloy (negative electrode active material) powder was 0.3 μm.

(Comparative Reference Example 1)
A negative electrode active material, a negative electrode, and a lithium ion secondary battery (coin cell) were produced in the same manner as in Reference Example 1 described above except that the composition of the silicon-containing alloy was changed to Si ₉₀ Ti ₁₀ . In addition, the average particle diameter of the obtained silicon-containing alloy (negative electrode active material) powder was 0.3 μm.

[Analysis of the structure of the anode active material]
As a result of analyzing the structure of the negative electrode active material (silicon-containing alloy) produced in each of Reference Examples 1 to 4 and Comparative Reference Example 1 by electron diffraction, both of Reference Examples 1 to 4 and Comparative Reference Example 1 were silicided. A diffraction spot and a halo pattern showing the crystallinity of the phase (TiSi ₂ ) were observed, and it was confirmed that the amorphous Si phase as a parent phase had a textured structure in which a crystalline silicide phase was dispersed.

  Moreover, the crystal structure of the negative electrode active material (silicon-containing alloy) produced in each of Reference Examples 1 to 4 and Comparative Reference Example 1 was analyzed by an X-ray diffraction measurement method. The apparatus and conditions used for the X-ray diffraction measurement method are as follows.

Device name: X-ray diffractometer (SmartLab9kW) manufactured by Rigaku Corporation
Voltage / Current: 45kV / 200mA
X-ray wavelength: CuKα1
Here, the X-ray diffraction spectra acquired for the negative electrode active materials (silicon-containing alloys) of Reference Examples 1 to 4 and Comparative Reference Example 1 are shown in FIGS. 3A to 3E. Further, the value of diffraction peak intensity A of (111) plane of Si in the range of 2θ = 24 to 33 ° obtained from these X-ray diffraction spectra and the diffraction peak intensity of TiSi ₂ in the range of 2θ = 37 to 45 ° The value of B and the value of these ratios (B / A) are shown in Table 1 below. This X-ray diffraction analysis also confirmed that all Ti contained in the silicon-containing alloy was present as a silicide (TiSi ₂ ) phase.

[Evaluation of cycle durability]
Each of the lithium ion secondary batteries (coin cells) produced above 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 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 0.1 mA. 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. 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.

  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.

Example 1
[Manufacture of silicon-containing alloys]
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 raw material powder of an alloy are put into a zirconia pulverizing pot and alloyed at 600 rpm for 12.5 hours (alloy) ), And then pulverization was performed at 400 rpm for 1 hour. In addition, the average particle diameter of the obtained silicon-containing alloy (negative electrode active material) powder was 0.3 μm.

[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 and acetylene black (Super-P, particle diameter 40 nm, aspect ratio 1) as a spherical conductive auxiliary 3.75 masses Parts and carbon nanotubes (VGCF manufactured by Showa Denko KK: fiber diameter 150 nm, length 10 μm, aspect ratio 67) 1.25 parts by mass were added. At this time, the content of the spherical conductive additive relative to the total amount of the spherical conductive additive and the fibrous conductive additive ((mass of spherical conductive additive / (mass of spherical conductive additive + mass of fibrous conductive additive)) × 100) was 75% by mass. Next, 15 parts by mass of a polyimide as a binder was 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). Next, the obtained negative electrode slurry was uniformly applied to both surfaces of the negative electrode current collector made of copper foil so that the thickness of the negative electrode active material layer was 27 μm, and dried in vacuum at 300 ° C. for 1 hour, A negative electrode was 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: 1 (volume ratio). lithium (LiPF ₆₎ was used dissolved at a concentration of 1 mol / L.

(Example 2)
In the preparation of the negative electrode, except that the addition amount of acetylene black, which is a spherical conductive additive, is changed to 2.5 parts by mass, and the addition amount of carbon nanotube, which is a fibrous conductive additive, is changed to 2.5 parts by mass. A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1. Under the present circumstances, content of the spherical conductive support agent with respect to the total amount of a spherical conductive support agent and a fibrous conductive support agent was 50 mass%.

(Example 3)
In the preparation of the negative electrode, except that the addition amount of acetylene black, which is a spherical conductive additive, was changed to 1.25 parts by mass, and the addition amount of carbon nanotube, which is a fibrous conductive additive, was changed to 3.75 parts by mass. A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1. Under the present circumstances, content of the spherical conductive support agent with respect to the total amount of a spherical conductive support agent and a fibrous conductive support agent was 25 mass%.

(Comparative Example 1)
In the production of the negative electrode, 5 parts by mass of acetylene black, which is a spherical conductive aid, was used as the conductive aid (the content of the spherical conductive aid is 100% by mass with respect to the total amount of the spherical conductive aid and the fibrous conductive aid). ) A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 described above.

[Analysis of the structure of the anode active material]
As a result of analyzing the structure of the negative electrode active material (silicon-containing alloy) produced in Example 1 by an electron diffraction method, a diffraction spot and a halo pattern indicating the crystallinity of the silicide phase (TiSi ₂ ) were observed, which is the parent phase. It was confirmed that the amorphous Si phase has a structure in which crystalline silicide phases are dispersed.

  Further, the crystal structure of the negative electrode active material (silicon-containing alloy) produced in Example 1 was analyzed by an X-ray diffraction measurement method. The apparatus and conditions used for the X-ray diffraction measurement method are as follows.

Device name: X-ray diffractometer (SmartLab9kW) manufactured by Rigaku Corporation
Voltage / Current: 45kV / 200mA
X-ray wavelength: CuKα1
Here, the value of the diffraction peak intensity A on the (111) plane of Si in the range of 2θ = 24 to 33 ° obtained from the X-ray diffraction spectrum obtained for the negative electrode active material (silicon-containing alloy) of Example 1, and Table 2 below shows the value of the diffraction peak intensity B of TiSi ₂ in the range of 2θ = 37 to 45 °, and the value of these ratios (B / A). This X-ray diffraction analysis also confirmed that all Ti contained in the silicon-containing alloy was present as a silicide (TiSi ₂ ) phase.

[Aspect ratio of conductive additive]
The aspect ratio of the conductive additive is obtained by observing a scanning electron microscope (SEM) image, photographing about 10 fields of view, and calculating the average value, median value, standard deviation, and sample number of the observed particle length and diameter. Measured with.

[Evaluation of cycle durability]
Each lithium ion secondary battery produced above 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. Then, the ratio of the discharge capacity at the 50th cycle to the discharge capacity at the first cycle (discharge capacity retention rate [%]) was determined, together with the initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency, as shown in Table 3 below. Shown in Moreover, in FIG. 4, the relationship between content of the spherical conductive support agent with respect to the total amount of a spherical conductive support agent and a fibrous conductive support agent and a discharge capacity maintenance factor is shown.

  From the results shown in Tables 2 and 3 and FIG. 4, the lithium ion battery using the negative electrode according to the present invention is maintained at a high discharge capacity maintenance rate after 50 cycles and has excellent cycle durability. I know that there is.

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 (10)

A negative electrode for an electrical device comprising: a current collector; and a negative electrode active material layer including a negative electrode active material, a conductive additive, and a binder disposed on a surface of the current collector,
The negative electrode active material has a structure in which a silicide phase containing a silicide of titanium is dispersed in a parent phase mainly composed of amorphous or low crystalline silicon, and has the following chemical formula (1):
(In the above chemical formula (1),
A is an inevitable impurity,
M is titanium (Ti) ,
x, y, z, and a represent mass% values, where 0 ≦ a <0.5, x + y + z + a = 100, and satisfies the following formula (1) or (2). )
A silicon-containing alloy having a composition represented by:
In the X-ray diffraction measurement using CuKα1 line of the silicon-containing alloy, the silicon silicide of titanium in the range of 2θ = 37 to 45 ° with respect to the diffraction peak intensity A of the (111) plane of Si in the range of 2θ = 24 to 33 °. The value of the ratio of the diffraction peak intensity B of the compound (B / A) is 0.41 or more,
The negative electrode for electric devices in which the said conductive support agent contains the spherical conductive support agent whose aspect-ratio is less than 10, and the fibrous conductive support agent whose aspect-ratio is 10-1000. 2. The negative electrode for an electric device according to claim 1, wherein the content of the spherical conductive additive relative to the total amount of the spherical conductive additive and the fibrous conductive additive is 25 to 80% by mass. The negative electrode for an electric device according to claim 1 or 2, wherein the content of the spherical conductive additive relative to the total amount of the spherical conductive additive and the fibrous conductive additive is 40 to 60% by mass.   The negative electrode for an electric device according to any one of claims 1 to 3, wherein the B / A is 0.89 or more.   The negative electrode for an electric device according to claim 4, wherein the B / A is 2.55 or more.   The negative electrode for an electric device according to claim 5, wherein the B / A is 7.07 or more.   The negative electrode for an electric device according to claim 1, wherein the matrix phase is more amorphous than the silicide phase.   The negative electrode for an electric device according to claim 1, wherein the silicide phase has a size of 50 nm or less. The negative electrode for an electrical device according to any one of claims 1 to 8 , further satisfying 7 < z in the chemical formula (1). Obtained by using the negative electrode for an electric device according to any one of claims 1 to 9 electrical device.