WO2016098215A1

WO2016098215A1 - Electrical device

Info

Publication number: WO2016098215A1
Application number: PCT/JP2014/083481
Authority: WO
Inventors: 渡邉　学; 智裕蕪木; 洋一吉岡; 寛和小松; 千葉　啓貴; 山本　伸司
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
Also published as: JP6380553B2; JPWO2016098215A1

Abstract

[Problem] To provide a means that makes achieving sufficient cycle durability possible, while taking sufficient advantage of the high capacity properties characteristic of solid-solution positive electrode materials, in an electrical device such as a lithium-ion secondary battery having a positive electrode using a solid-solution positive electrode active material. [Solution] As the Si-containing alloy to be contained in the negative electrode active material layer, the present invention uses an alloy which has a prescribed composition and a structure obtained by dispersing a silicide phase containing a transition metal silicide in a parent phase having amorphous or low-crystalline silicon as the principal component thereof, and also has prescribed peak intensity characteristics when measured using X-ray diffraction. As the solid-solution positive electrode active material to be included in the positive electrode active material layer, the present invention uses a solid-solution positive electrode active material having a substituent element such as Ti.

Description

Electrical device

The present invention relates to an electrical device. The electric device according to the present invention is used, for example, as a secondary battery, a capacitor or the like as a driving power source or auxiliary power source for motors of vehicles such as electric vehicles, fuel cell vehicles, and hybrid electric vehicles.

In recent years, a reduction in the amount of carbon dioxide has been strongly desired in order to cope with global warming. 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-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, 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.

Here, when a negative electrode as described in International Publication No. 2006/129415 is combined with a positive electrode using a solid solution positive electrode active material having high capacity characteristics, the negative electrode also has a high capacity, so the solid solution positive electrode active material It is possible to make use of the high capacity characteristics that are characteristic of the above, and it is possible to realize an excellent capacity profile as a cell. However, according to the study by the present inventors, it has been found that there is a problem that sufficient cycle durability cannot be obtained by the combination of these positive and negative electrodes.

Therefore, the present invention provides sufficient cycle durability while fully utilizing the high capacity characteristics that are characteristic of a solid solution cathode active material in an electrical device such as a lithium ion secondary battery having a cathode using a solid solution cathode active material. An object is to provide means that can be realized.

The present inventors have conducted intensive research to solve the above problems. As a result, the inventors have found that the above problem can be solved by using a combination of a negative electrode containing a predetermined Si-containing alloy as a negative electrode active material and a positive electrode containing a predetermined solid solution positive electrode active material, and completed the present invention. I came to let you.

That is, the present invention includes a positive electrode in which a positive electrode active material layer including a positive electrode active material is formed on the surface of a positive electrode current collector, and a negative electrode active material layer including a negative electrode active material on the surface of the negative electrode current collector. The present invention relates to an electric device having a power generation element including a negative electrode and a separator.

The negative electrode active material layer has the following formula (1):

In the above formula (1), α represents the weight percent of each component in the negative electrode active material layer, and 40 <α ≦ 98.
The negative electrode active material represented by these is contained. The positive electrode active material layer has the following formula (2):

In the above formula (2), e represents the weight percent of each component in the positive electrode active material layer, and 80 ≦ e ≦ 98.
The positive electrode active material represented by these is contained.

In this case, the Si-containing alloy has a structure in which a silicide phase containing a silicide of a transition metal is dispersed in a parent phase mainly composed of amorphous or low crystalline silicon. I):

In the above chemical formula (I),
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. )
In the X-ray diffraction measurement using the CuKα1 line of the Si-containing alloy, 2θ = 37 with respect to 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 ˜45 ° is 0.41 or more.

The solid solution positive electrode active material has the following formula (3):

In the above formula (3), X is at least one selected from the group consisting of Ti, Zr and Nb, and 0.01 ≦ e ≦ 0.4, a + b + c + d + e = 1.5, 0.1 ≦ d ≦ 0.4, 1.1 ≦ [a + b + c + e] ≦ 1.4, and z represents the number of oxygen satisfying the valence,
It is characterized in that it consists of a solid solution having a composition represented by:

1 is a schematic cross-sectional view showing the basic configuration of a non-aqueous electrolyte lithium ion secondary battery that is not a flat type (stacked type) bipolar type, which is an embodiment of the electrical device according to the present invention. It is a perspective view showing the appearance of a flat lithium ion secondary battery which is a typical embodiment of an electric device according to the present invention. It is a chart which shows the X-ray-diffraction pattern of the solid solution positive electrode active material C0 which does not contain Ti. 2 is a chart showing an X-ray diffraction pattern of the solid solution positive electrode active material C1 obtained in Example 1. FIG. It is the diffraction spectrum obtained by the X-ray-diffraction analysis about Si containing alloy (negative electrode active material) powder used for negative electrode A1 produced in the Example. It is the diffraction spectrum obtained by the X ray diffraction analysis about Si containing alloy (negative electrode active material) powder used for negative electrode A2 produced in the Example. It is the diffraction spectrum obtained by the X-ray diffraction analysis about Si containing alloy (negative electrode active material) powder used for negative electrode A3 produced in the Example. It is the diffraction spectrum obtained by the X ray diffraction analysis about Si containing alloy (negative electrode active material) powder used for negative electrode A4 produced in the Example. It is the diffraction spectrum obtained by the X-ray-diffraction analysis about Si containing alloy (negative electrode active material) powder used for negative electrode A5 produced in the Example.

According to one aspect of the present invention, a positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on the surface of a positive electrode current collector;
A negative electrode in which a negative electrode active material layer containing a negative electrode active material is formed on the surface of the negative electrode current collector;
A separator;
An electrical device having a power generation element comprising:
The negative electrode active material layer has the following formula (1):

In the above formula (1), α represents the weight percent of each component in the negative electrode active material layer, and 40 <α ≦ 98.
Containing a negative electrode active material represented by
The positive electrode active material layer has the following formula (2):

In the above formula (2), e represents the weight percent of each component in the positive electrode active material layer, and 80 ≦ e ≦ 98.
A positive electrode active material represented by
In this case, the Si-containing alloy has a structure in which a silicide phase containing a silicide of a transition metal is dispersed in a parent phase mainly composed of amorphous or low crystalline silicon. I):

In the above chemical formula (I), 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.
In the X-ray diffraction measurement using the CuKα1 line of the Si-containing alloy, 2θ = 37 with respect to the diffraction peak intensity A of the (111) plane of Si in the range of 2θ = 24 to 33 °. The value (B / A) of the diffraction peak intensity B of the transition metal silicide in the range of ˜45 ° is 0.41 or more,
And the said solid solution positive electrode active material is following formula (3):

In the above formula (3), X is at least one selected from the group consisting of Ti, Zr and Nb, and 0.01 ≦ e ≦ 0.4, a + b + c + d + e = 1.5, 0.1 ≦ d ≦ 0.4, 1.1 ≦ [a + b + c + e] ≦ 1.4, and z represents the number of oxygen satisfying the valence,
An electrical device comprising a solid solution having a composition represented by: According to the present invention having such a configuration, when the value of B / A in the negative electrode active material (Si-containing alloy) is a value within the above-described range, an amorphous state when Si and Li are alloyed is obtained. Crystal phase transition (crystallization to Li ₁₅ Si ₄ ) is suppressed. Thereby, the expansion | contraction and shrinkage | contraction of the Si containing alloy which comprises the negative electrode active material in the charge / discharge process of an electrical device are suppressed. As a result, the electrical device according to the present invention can realize sufficient cycle durability while fully utilizing the high capacity characteristics that are characteristic of the solid solution positive electrode active material.

Hereinafter, the basic configuration of the electric device according to the present invention will be described. In the present embodiment, a lithium ion secondary battery will be described as an example of an electric device.

First, in the lithium ion secondary battery using the electric device according to the present invention, the voltage of the cell (single cell layer) is large, and high energy density and high output density can be achieved. Therefore, 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.

When the lithium ion secondary battery is distinguished by its 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, a non-bipolar (internal parallel connection type) lithium ion secondary battery will be described very simply with reference to the drawings as an example of the lithium ion secondary battery of the present embodiment. However, the technical scope of the electric device according to the present invention and the lithium ion secondary battery according to 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 13 is disposed on both surfaces of the positive electrode current collector 11, the electrolyte layer 17, and the negative electrode active material layer 15 is disposed on both surfaces of the negative electrode current collector 12. 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 13 and the negative electrode active material layer 15 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 13 on the outermost layer located on both outermost layers of the power generating element 21 is provided with the positive electrode active material layer 13 only on one side, but the active material layer 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 11 and the negative electrode current collector 12 are attached to a positive electrode current collector plate 25 and a negative electrode current collector plate 27 that are electrically connected to the respective electrodes (positive electrode and negative electrode), and are sandwiched between end portions of the laminate sheet 29. Thus, it has a structure led out of the laminate sheet 29. The positive electrode current collector plate 25 and the negative electrode current collector plate 27 are ultrasonically welded to the positive electrode current collector 11 and the negative electrode current collector 12 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 according to this embodiment is characterized by the configuration of the positive electrode and the negative electrode. Hereinafter, main components of the battery including the positive electrode and the negative electrode will be described.

<Active material layer>
The active material layers (13, 15) contain an active material, and further contain other additives as necessary.

[Positive electrode active material layer]
The positive electrode active material layer 13 includes at least a positive electrode active material (also referred to as “solid solution positive electrode active material” in the present specification) made of a solid solution material.

(Solid solution positive electrode active material)
A solid solution positive electrode active material consists of a solid solution which has a composition represented by following formula (3).

In the formula (3), X is at least one selected from the group consisting of Ti, Zr and Nb, and 0.01 ≦ e ≦ 0.4, a + b + c + d + e = 1.5, 0.1 ≦ d ≦ 0 .4, 1.1 ≦ [a + b + c + e] ≦ 1.4, and z represents the number of oxygens satisfying the valence.

Further, this solid solution positive electrode active material was measured at 20-23 °, 35-40 ° (101), 42-45 ° (104) and 64-65 (108) / 65-66 (X-ray diffraction (XRD) measurement). 110) preferably has a diffraction peak indicating a rock salt type layered structure. At this time, in order to surely obtain the effect of improving the cycle characteristics, those having substantially no peak attributed to other than the diffraction peak of the rock salt type layered structure are preferable. More preferably, one having three diffraction peaks at 35-40 ° (101) and one diffraction peak at 42-45 ° (104) is suitable. However, as long as it belongs to a diffraction peak of a rock salt type layered structure, it does not necessarily have to be counted as three and one peak, respectively. The X-ray diffraction measurement shall employ the measurement method described in the examples described later. In addition, the notation of 64-65 (108) / 65-66 (110) has two peaks close to 64-65 and 65-66. Depending on the composition, one peak is broadly separated without being clearly separated. It is meant to include.

The solid solution positive electrode active material having the composition represented by the composition formula (3) preferably has a plurality of specific diffraction peaks in the X-ray diffraction (XRD) measurement. The solid solution positive electrode active material having the above composition formula is a solid solution system of Li ₂ MnO ₃ and LiMnO _2. Of the plurality of diffraction peaks specified above, the diffraction peak at 20-23 ° is characteristic of Li ₂ MnO ₃ . Superlattice diffraction peak. Also, the diffraction peaks of 36.5-37.5 ° (101), 44-45 ° (104) and 64-65 (108) / 65-66 (110) are usually in the rock salt type layered structure of LiMnO _2. It is characteristic. Further, in the present embodiment, it is preferable that three diffraction peaks at 35-40 ° (101) and one diffraction peak at 42-45 ° (104) are present as a part of diffraction peaks showing a rock salt type layered structure. It is preferable that the solid solution positive electrode active material of the present embodiment does not include those having a peak other than a diffraction peak showing a rock salt type layered structure, for example, other peaks derived from impurities or the like, in these angular ranges. When such other peaks exist, it means that a structure other than the rock salt type layered structure is included in the positive electrode active material. If the structure other than the rock salt type layered structure is not included, the effect of improving the cycle characteristics can be surely obtained.

In the solid solution positive electrode active material according to the present embodiment, at least one of Ti, Zr, and Nb is dissolved in a transition metal layer made of Ni, Co, and Mn by substituting Mn ⁴⁺ to form a rock salt type It is considered that a layered structure is formed. Since at least one kind of Ti, Zr and Nb is dissolved, the crystal structure is stabilized, so that it is considered that elution of transition metals including Mn is suppressed during charging and discharging. As a result, even if charging / discharging is repeated, a reduction in battery capacity can be prevented, and excellent cycle characteristics can be achieved. In addition, battery performance itself and durability can be improved. When the rock salt type layered structure is changed by elution of Mn, a spinel phase is usually formed, and the diffraction peak in the X-ray diffraction (XRD) measurement of the positive electrode active material represents the spinel phase. In the spinel phase, diffraction peaks appear at 35-36 ° (101) and 42.5-43.5 ° (104). In the solid solution positive electrode active material according to the present embodiment, it is considered that a spinel phase is not formed even after repeated charge and discharge, and a rock salt type layered structure is maintained. However, the present embodiment is not limited to the above consideration.

Furthermore, it is preferable that the diffraction peak showing the rock salt type layered structure in this embodiment is shifted to the low angle side. That is, the solid solution positive electrode active material according to the present embodiment is 20-23 °, 35.5-36.5 ° (101), 43.5-44.5 ° (104) in X-ray diffraction (XRD) measurement. And preferably have diffraction peaks at 64-65 (108) / 65-66 (110). The shift of the diffraction peak to the lower angle side indicates that Ti and the like are more solid-dissolved in the positive electrode active material and substitutes Mn, which is considered to have a greater effect of suppressing Mn elution.

Furthermore, when Ti or the like substitutes Mn ⁴⁺ in the transition metal layer of the positive electrode active material and solid-dissolves, the covalent bond between the substitution element and oxygen becomes stronger, and the oxygen in the crystal lattice accompanying the oxidation of the transition metal becomes stronger. Separation can also be reduced. As a result, generation of oxygen gas can be suppressed and oxygen defects in the crystal structure can be reduced.

Here, in the composition formula (3), a + b + c + e satisfies 1.1 ≦ [a + b + c + e] ≦ 1.4. Generally, nickel (Ni), cobalt (Co), and manganese (Mn) are known to contribute to capacity characteristics and output characteristics from the viewpoint of improving the purity of the material and improving the electronic conductivity. Ti or the like partially substitutes Mn in the crystal lattice. When 1.1 ≦ [a + b + c + e] ≦ 1.2, each element can be optimized and the capacity and output characteristics can be further improved. Therefore, when a positive electrode active material that satisfies this relationship is used in an electrical device such as a lithium ion secondary battery, it exhibits excellent initial charge / discharge efficiency while maintaining a high capacity by maintaining a high reversible capacity. It becomes possible.

In the composition formula (3), the values of a, b, and c are not particularly limited as long as the relationship of a + b + c + d + e = 1.5 and 1.1 ≦ [a + b + c + e] ≦ 1.4 is satisfied. However, a is preferably 0 <a <1.5, and more preferably 0.1 ≦ a ≦ 0.75. When a is in the above range, a secondary battery having a better capacity retention rate can be obtained. When a is not a ≦ 0.75, the crystal structure is not stabilized because nickel is contained in the positive electrode active material within the above range d on condition that nickel (Ni) is divalent. There is. On the other hand, when a ≦ 0.75, the crystal structure of the positive electrode active material tends to be a rock salt type layered structure.

Furthermore, in the composition formula (3), b is preferably 0 <b <1.5, and more preferably 0.2 ≦ b ≦ 0.9. When b is in the above range, an electric device having a better capacity retention rate can be obtained. However, when b does not satisfy b ≦ 0.9, manganese is contained in the positive electrode active material within the above range d, provided that manganese is tetravalent, and nickel (Ni ), The crystal structure may not be stabilized. On the other hand, when b ≦ 0.9, the crystal structure of the positive electrode active material tends to be a rock salt type layered structure.

In the composition formula (3), c is preferably 0 ≦ c <1.5. However, when c is not c ≦ 0.6, nickel and manganese are contained in the positive electrode active material within the above range d on condition that cobalt is trivalent. Further, cobalt (Co) is contained in the positive electrode active material within the above range d on condition that nickel (Ni) is divalent and manganese (Mn) is tetravalent. Therefore, the crystal structure of the positive electrode active material may not be stabilized. On the other hand, when c ≦ 0.6, the crystal structure of the positive electrode active material tends to be a rock salt type layered structure.

In the composition formula (3), a + b + c + d + e = 1.5. By satisfying this formula, the crystal structure of the positive electrode active material can be stabilized.

In the composition formula (3), 0.1 ≦ d ≦ 0.4. When d is not 0.1 ≦ d ≦ 0.4, the crystal structure of the positive electrode active material may not be stabilized. On the contrary, when d is 0.1 ≦ d ≦ 0.4, the positive electrode active material tends to have a rock salt type layered structure. The range of d is more preferably 0.15 ≦ d ≦ 0.35. When d is 0.1 or more, the composition is less likely to be close to Li ₂ MnO ₃ and charge / discharge is facilitated, which is preferable.

In the composition formula (3), 0.01 ≦ e ≦ 0.4. When e is not 0.01 ≦ e ≦ 0.4, the element cannot be uniformly dissolved in the crystal structure, and the crystal structure cannot be stabilized. On the other hand, if e is 0.01 ≦ e ≦ 0.4, at least one of Ti, Zr, and Nb can sufficiently substitute Mn ^{4+ so} that elution is suppressed. More preferably, e satisfies 0.02 ≦ e ≦ 0.3, more preferably 0.025 ≦ e ≦ 0.25, and particularly preferably 0.03 ≦ e ≦ 0.2.

The ionic radius of each element is Mn ⁴⁺ 0.54０．５, Mn ⁴⁺ 0.54Å, Ti ⁴⁺ 0.61Å, Zr ⁴⁺ 0.72Å, Nb ⁵⁺ 0.64Å, and Ti, Zr and Nb are larger than Mn. ing. Therefore, as Mn ⁴⁺ in the positive electrode active material is replaced with Ti or the like, the crystal lattice expands, and the diffraction peak indicating the rock salt type layered structure shifts to a lower angle side. On the contrary, if the diffraction peak is shifted to a lower angle side, the substitution amount of Mn ⁴⁺ such as Ti is larger, and the crystal structure is easily stabilized. That is, elution of Mn at the time of charging / discharging is further suppressed, and the capacity reduction of the electric device can be more effectively prevented.

The specific surface area of the positive electrode active material is preferably 0.2 to 0.6 m ² / g, and more preferably 0.25 to 0.5 m ² / g. A specific surface area of 0.2 m ² / g or more is preferable because sufficient battery output can be obtained. On the other hand, it is preferable that the specific surface area is 0.6 m ² / g or less because elution of manganese can be further suppressed. In addition, in this specification, the value measured by the method of an Example shall be employ | adopted as the value of a specific surface area unless there is particular notice.

The average particle diameter of the positive electrode active material is preferably 10 to 20 μm, and more preferably 12 to 18 μm. It is preferable that the average particle size is 10 μm or more because elution of manganese can be suppressed. On the other hand, when the average particle size is 20 μm or less, it is preferable that foil breakage, clogging, and the like can be suppressed in the application step to the current collector during the production of the positive electrode. The average particle diameter is measured by a laser diffraction / scattering particle size distribution measuring device. The average particle diameter can be measured, for example, using a particle size distribution analyzer (model LA-920) manufactured by Horiba.

The solid solution positive electrode active material as described above can be prepared, for example, by the following method. That is, a first step of mixing at least one citrate of Ti, Zr and Nb with an organic acid salt of a transition metal having a melting point of 100 ° C. to 350 ° C., and a mixture obtained in the first step at 100 ° C. A second step of melting at ˜350 ° C., a third step of pyrolyzing the melt obtained in the second step at a temperature higher than the melting point, and a second step of firing the pyrolyzate obtained in the third step. 4 steps. Hereinafter, each step will be described.

First Step In the first step, at least one citrate of Ti, Zr and Nb and an organic acid salt of a transition metal having a melting point of 100 ° C. to 350 ° C. are mixed. At least one citrate of Ti, Zr and Nb is preferably mixed in the form of an aqueous citric acid complex solution. The aqueous solution of at least one kind of citrate complex of Ti, Zr and Nb is not limited to the following, but it can be preferably prepared as follows.

That is, anhydrous citric acid is dissolved in an organic solvent such as acetone, and at least one alkoxide of Ti, Zr and Nb is added to the solution. At this time, the molar ratio of at least one of Ti, Zr and Nb to citric acid is preferably (at least one of Ti, Zr and Nb) / citric acid being 1/1 to 1/2. When alkoxide is added, precipitation occurs in the solution, and the precipitate is filtered with suction. Next, water is added to the resulting precipitate, and the mixture is stirred and heated to 50 to 60 ° C. to dissolve. The amount of water is appropriately added so that the concentration of the aqueous citric acid complex is 1 to 10% by mass in terms of at least one of Ti, Zr and Nb. This aqueous solution is allowed to stand for one day, and the precipitate is filtered to obtain an aqueous solution of at least one citrate complex of Ti, Zr and Nb as a filtrate.

As at least one alkoxide of Ti, Zr and Nb, titanium tetraisopropoxide, zirconium tetraisopropoxide, niobium isopropoxide, titanium ethoxide, titanium n-propoxide, titanium butoxide, zirconium ethoxide, zirconium n- Examples thereof include propoxide, zirconium butoxide, niobium ethoxide, and niobium butoxide.

Next, an organic acid salt of a transition metal having a melting point of 100 ° C. to 350 ° C. is added to the obtained aqueous solution of at least one kind of citric acid complex of Ti, Zr and Nb to obtain a mixture. The organic acid salt of transition metal having a melting point of 100 ° C. to 350 ° C. preferably includes nickel acetate, manganese acetate, cobalt acetate, manganese citrate and the like.

Preferably, an alkali metal organic acid salt is further mixed with the above-described aqueous solution of at least one kind of citric acid complex of Ti, Zr and Nb. Preferred examples of the organic acid salt of alkali metal include lithium acetate and lithium citrate. It is preferable to mix an alkali metal organic acid salt at this stage because the production method is simple.

Second Step The mixture obtained in the first step is melted at 100 to 350 ° C., preferably 200 to 300 ° C.

Third Step The heated melt (slurry) obtained in the second step is pyrolyzed at a temperature equal to or higher than the melting point of the organic acid salt of the transition metal used in the first step to obtain a pyrolyzate that is a dry powder. When the melting points of the organic acid salts of a plurality of transition metals are different from each other, they are thermally decomposed at a temperature higher than the highest melting point. More specifically, the melt can be heated and sprayed at 200 to 600 ° C., more preferably 200 to 400 ° C., with a spray device.

Fourth Step The pyrolyzate obtained in the third step is calcined at 600 to 1200 ° C., more preferably 800 to 1100 ° C., for 5 to 20 hours, preferably 10 to 15 hours. Temporary baking may be performed before baking, in which case the temporary baking may be performed at 200 to 700 ° C., more preferably 300 to 600 ° C. for 1 to 10 hours, more preferably 2 to 6 hours. Thus, the positive electrode active material of this embodiment is obtained.

In some cases, a positive electrode active material other than the solid solution positive electrode active material described above may be used in combination. In this case, preferably, a lithium-transition metal composite oxide is used in combination as the positive electrode active material from the viewpoint of capacity and output characteristics. Of course, other positive electrode active materials may be used. When the optimum particle size is different for expressing the unique effect of each active material, the optimum particle size may be blended and used for expressing each unique effect. It is not always necessary to make the particle diameter uniform.

The average particle diameter of the positive electrode active material contained in the positive electrode active material layer 13 is not particularly limited, but is preferably 1 to 30 μm and 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.

As described above, the positive electrode active material layer contains a positive electrode active material (solid solution positive electrode active material) represented by the following formula (2).

In the formula (2), e represents mass% of each component in the positive electrode active material layer, and 80 ≦ e ≦ 98.

As is clear from the formula (2), the content of the solid solution positive electrode active material in the positive electrode active material layer is essential to be 80 to 98% by mass, but preferably 84 to 98% by mass.

The positive electrode active material layer preferably contains a binder and a conductive aid in addition to the solid solution positive electrode active material described above. Further, if necessary, it further contains other additives such as an electrolyte (polymer matrix, ion-conductive polymer, electrolyte solution, etc.) and a lithium salt for increasing the ion conductivity.

(Binder)
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, polyacrylonitrile, polyimide, polyamide, cellulose, carboxymethyl cellulose (CMC) and its salts, 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 hydrogenated product thereof Thermoplastic polymers such as products, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (F P), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE) ), Fluororesin such as polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene fluororubber (VDF-HFP fluoropolymer), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluororubber (VDF-HFP) -TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene Fluorine rubber (VDF-PFP-TFE fluorine rubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluorine rubber (VDF-PFMVE-TFE fluorine rubber), vinylidene fluoride-chlorotrifluoroethylene fluorine Examples thereof include vinylidene fluoride type fluoro rubber such as rubber (VDF-CTFE type fluoro rubber), epoxy resin and the like. These binders may be used independently and may use 2 or more types together.

The binder content in the positive electrode active material layer is preferably 1 to 10% by mass, more preferably 1 to 8% by mass.

(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 assistant include carbon black such as ketjen black and acetylene black. 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 in the positive electrode active material layer is preferably 1 to 10% by mass, more preferably 1 to 8% by mass. By defining the blending ratio (content) of the conductive assistant within the above range, the following effects are exhibited. That is, the electron conductivity can be sufficiently ensured without hindering the electrode reaction, the decrease in the energy density due to the decrease in the electrode density can be suppressed, and as a result, the energy density can be improved due to the increase in the electrode density. It is.

(Other ingredients)
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.

Examples of the ion conductive polymer include polyethylene oxide (PEO) and polypropylene oxide (PPO) polymers.

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 15 essentially contains a Si-containing alloy as a negative electrode active material.

(Si-containing alloy)
In the present embodiment, the Si-containing alloy as 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 having a predetermined composition.

As described above, the Si-containing alloy constituting the negative electrode active material in the present embodiment is first provided with a parent phase mainly composed of amorphous or amorphous 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 have a higher electron 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 (I).

In the above chemical formula (I), 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 apparent from the chemical formula (I), 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 (I), 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 (I), 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 (I) 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).

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% 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.

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 the present embodiment has a 2θ = value corresponding to the diffraction peak intensity A on the (111) plane of Si in the range of 2θ = 24 to 33 ° in the X-ray diffraction measurement using CuKα1 ray. 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 (corresponding to the result of the negative electrode A1 manufactured in an example described later). See FIG. 5A).

First, in the diffraction spectrum obtained by X-ray diffraction analysis, a point where a perpendicular line at 2θ = 24 ° and the diffraction spectrum 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 25000 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.

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

(Method for producing negative electrode active material)
There is no particular limitation on the method for producing the negative electrode active material (Si-containing alloy) according to this embodiment, and conventionally known knowledge can be referred to as appropriate, but in this application, the intensity ratio B / A of the diffraction peak by X-ray diffraction analysis is As an example of a manufacturing method for setting the value within 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. 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 24 hours or longer, a negative electrode active material (Si-containing alloy) capable of exhibiting desired cycle durability can be obtained. The alloying treatment time is preferably 30 hours or more, more preferably 36 hours or more, still more preferably 42 hours or more, and particularly preferably 48 hours or more. 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 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.

The negative electrode active material layer contains a negative electrode active material represented by the following formula (1).

In the formula (1), α represents the weight percent of each component in the negative electrode active material layer, and 40 <α ≦ 98.

As is clear from the formula (1), the content of the negative electrode active material made of the Si-containing alloy in the negative electrode active material layer is more than 40 mass% and 98 mass% or less.

In the present embodiment, the negative electrode active material layer preferably contains a binder and a conductive additive in addition to the negative electrode active material described above. Further, if necessary, it further contains other additives such as an electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.) and a lithium salt for increasing the ion conductivity. About these specific types and preferable contents in the negative electrode active material layer, the above-described embodiments in the column of the description of the positive electrode active material layer can be similarly adopted, and thus detailed description thereof is omitted here.

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, 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 preferable 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 weight.

<Separator (electrolyte layer)>
The separator has a function of holding an electrolyte and ensuring lithium ion conductivity between the positive electrode and the negative electrode, and a function as a partition wall between the positive electrode and the negative electrode.

Examples of the form of the separator include a separator made of a porous sheet made of a polymer or fiber that absorbs and holds the electrolyte and a nonwoven fabric separator.

As the separator of the porous sheet made of polymer or fiber, for example, a microporous (microporous film) can be used. Specific examples of the porous sheet made of the polymer or fiber include polyolefins such as polyethylene (PE) and polypropylene (PP); a laminate in which a plurality of these are laminated (for example, three layers of PP / PE / PP) And a microporous (microporous membrane) separator made of a hydrocarbon resin such as polyimide, aramid, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), glass fiber, and the like.

The thickness of the microporous (microporous membrane) separator cannot be uniquely defined because it varies depending on the intended use. For example, in applications such as secondary batteries for driving motors such as electric vehicles (EV), hybrid electric vehicles (HEV), and fuel cell vehicles (FCV), it is 4 to 60 μm in a single layer or multiple layers. Is desirable. The fine pore diameter of the microporous (microporous membrane) separator is desirably 1 μm or less (usually a pore diameter of about several tens of nm).

As the nonwoven fabric separator, cotton, rayon, acetate, nylon, polyester; polyolefins such as PP and PE; conventionally known ones such as polyimide and aramid are used alone or in combination. The bulk density of the nonwoven fabric is not particularly limited as long as sufficient battery characteristics can be obtained by the impregnated polymer gel electrolyte. Furthermore, the thickness of the nonwoven fabric separator may be the same as that of the electrolyte layer, and is preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

Also, as described above, the separator includes an electrolyte. The electrolyte is not particularly limited as long as it can exhibit such a function, but a liquid electrolyte or a gel polymer electrolyte is used. By using the gel polymer electrolyte, the distance between the electrodes is stabilized, the occurrence of polarization is suppressed, and the durability (cycle characteristics) is improved.

The liquid electrolyte functions as a lithium ion carrier. The liquid electrolyte constituting the electrolytic solution layer has a form in which a lithium salt as a supporting salt is dissolved in an organic solvent as a plasticizer. Examples of the organic solvent used include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate. As the lithium _{_{_{_{salt, Li (CF 3 SO 2)}}}} 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiClO 4, LiAsF 6, LiTaF such 6, LiCF ₃ SO ₃ A compound that can be added to the active material layer of the electrode can be similarly employed. The liquid electrolyte may further contain additives other than the components described above. Specific examples of such compounds include, for example, vinylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate, phenyl vinylene carbonate, diphenyl vinylene carbonate, ethyl vinylene carbonate, diethyl vinylene carbonate, vinyl ethylene carbonate, 1,2-divinyl ethylene carbonate. 1-methyl-1-vinylethylene carbonate, 1-methyl-2-vinylethylene carbonate, 1-ethyl-1-vinylethylene carbonate, 1-ethyl-2-vinylethylene carbonate, vinyl vinylene carbonate, allyl ethylene carbonate, vinyl Oxymethyl ethylene carbonate, allyloxymethyl ethylene carbonate, acryloxymethyl ethylene carbonate, methacrylate Oxy methylethylene carbonate, ethynyl ethylene carbonate, propargyl carbonate, ethynyloxy methylethylene carbonate, propargyloxy ethylene carbonate, methylene carbonate, etc. 1,1-dimethyl-2-methylene-ethylene carbonate. Among these, vinylene carbonate, methyl vinylene carbonate, and vinyl ethylene carbonate are preferable, and vinylene carbonate and vinyl ethylene carbonate are more preferable. These cyclic carbonates may be used alone or in combination of two or more.

The gel polymer electrolyte has a configuration in which the above liquid electrolyte is injected into a matrix polymer (host 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 the ion conductivity between the layers is easily cut off. Examples of the ion conductive polymer used as the matrix polymer (host polymer) include polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylidene fluoride-hexafluoropropylene ( PVdF-HEP), poly (methyl methacrylate (PMMA), and copolymers thereof.

The matrix polymer of gel 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.

Further, the separator is preferably a separator in which a heat-resistant insulating layer is laminated on a porous substrate (a separator with a heat-resistant insulating layer). The heat resistant insulating layer is a ceramic layer containing inorganic particles and a binder. As the separator with a heat-resistant insulating layer, a highly heat-resistant separator having a melting point or a heat softening point of 150 ° C. or higher, preferably 200 ° C. or higher is used. By having the heat-resistant insulating layer, the internal stress of the separator that increases when the temperature rises is relieved, so that the effect of suppressing thermal shrinkage can be obtained. As a result, it is possible to prevent the induction of a short circuit between the electrodes of the battery, so that the battery configuration is unlikely to deteriorate in performance due to a temperature rise. Moreover, by having a heat-resistant insulating layer, the mechanical strength of the separator with a heat-resistant insulating layer is improved, and it is difficult for the separator to break. Furthermore, the separator is less likely to curl in the battery manufacturing process due to the effect of suppressing thermal shrinkage and high mechanical strength.

The inorganic particles in the heat resistant insulating layer contribute to the mechanical strength and heat shrinkage suppressing effect of the heat resistant insulating layer. The material used as the inorganic particles is not particularly limited. Examples thereof include silicon, aluminum, zirconium, titanium oxides (SiO ₂ , Al ₂ O ₃ , ZrO ₂ , TiO ₂ ), hydroxides and nitrides, and composites thereof. These inorganic particles may be derived from mineral resources such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine and mica, or may be artificially produced. Moreover, only 1 type may be used individually for these inorganic particles, and 2 or more types may be used together. Of these, silica (SiO ₂ ) or alumina (Al ₂ O ₃ ) is preferably used, and alumina (Al ₂ O ₃ ) is more preferably used from the viewpoint of cost.

The basis weight of the heat-resistant particles is not particularly limited, but is preferably 5 to 15 g / m ² . If it is this range, sufficient ion conductivity will be acquired and it is preferable at the point which maintains heat resistant strength.

The binder in the heat-resistant insulating layer has a role of adhering the inorganic particles and the inorganic particles to the resin porous substrate layer. By the binder, the heat resistant insulating layer is stably formed, and peeling between the porous substrate layer and the heat resistant insulating layer is prevented.

The binder used for the heat-resistant insulating layer is not particularly limited. For example, carboxymethyl cellulose (CMC), polyacrylonitrile, cellulose, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), isoprene rubber A compound such as butadiene rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), or methyl acrylate can be used as the binder. Of these, carboxymethylcellulose (CMC), methyl acrylate, or polyvinylidene fluoride (PVDF) is preferably used. As for these compounds, only 1 type may be used independently and 2 or more types may be used together.

The binder content in the heat-resistant insulating layer is preferably 2 to 20% by weight with respect to 100% by weight of the heat-resistant insulating layer. When the binder content is 2% by weight or more, the peel strength between the heat-resistant insulating layer and the porous substrate layer can be increased, and the vibration resistance of the separator can be improved. On the other hand, when the binder content is 20% by weight or less, the gap between the inorganic particles is appropriately maintained, so that sufficient lithium ion conductivity can be ensured.

The thermal contraction rate of the separator with a heat-resistant insulating layer is preferably 10% or less for both MD and TD after holding for 1 hour at 150 ° C. and ² gf / cm ² . By using such a material having high heat resistance, it is possible to effectively prevent the separator from contracting even if the positive electrode heat generation amount increases and the battery internal temperature reaches 150 ° C. As a result, it is possible to prevent the induction of a short circuit between the electrodes of the battery, so that the battery configuration is unlikely to deteriorate in performance due to a temperature rise.

<Current collector plate (tab)>
In a lithium ion secondary battery, a current collector plate (tab) electrically connected to a current collector is taken out of a laminate film as an exterior material for the purpose of taking out current outside the battery.

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. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. Note that the same material may be used for the positive electrode current collector plate (positive electrode tab) and the negative electrode current collector plate (negative electrode tab), or different materials may be used.

Also, the

tabs

58 and 59 shown in FIG. 2 are not particularly limited. The positive electrode tab 58 and the negative electrode tab 59 may be drawn out from the same side, or the positive electrode tab 58 and the negative electrode tab 59 may be divided into a plurality of parts and taken out from each side, as shown in FIG. It is not limited to. Further, in a wound type lithium ion battery, instead of a tab, for example, a terminal may be formed using a cylindrical can (metal can).

<Seal part>
The seal portion is a member unique to the serially stacked battery and has a function of preventing leakage of the electrolyte layer. In addition to this, it is possible to prevent current collectors adjacent in the battery from coming into contact with each other and a short circuit due to a slight unevenness at the end of the laminated electrode.

The constituent material of the seal part is not particularly limited, but polyolefin resin such as polyethylene and polypropylene, epoxy resin, rubber, polyimide and the like can be used. Among these, it is preferable to use a polyolefin resin from the viewpoints of corrosion resistance, chemical resistance, film-forming property, economy, and the like.

<Positive terminal lead and negative terminal lead>
As a material for the negative electrode and the positive electrode terminal lead, a lead used in a known laminated secondary battery can be used. In addition, the parts removed from the battery exterior material should be heat-insulating so that they do not affect products (for example, automobile parts, especially electronic devices) by touching peripheral devices or wiring and causing leakage. It is preferable to coat with a heat shrinkable tube or the like.

<Exterior material; Laminate film>
A conventionally known metal can case can be used as the exterior material. In addition, the power generation element 17 may be packed using a laminate film 22 as shown in FIG. The laminate film can be configured as a three-layer structure in which, for example, polypropylene, aluminum, and nylon are laminated in this order. By using such a laminate film, it is possible to easily open the exterior material, add the capacity recovery material, and reseal the exterior material.

<Method for producing lithium ion secondary battery>
The manufacturing method in particular of a lithium ion secondary battery is not restrict | limited, It can manufacture by a well-known method. Specifically, it includes (1) production of electrodes, (2) production of single cell layers, (3) production of power generation elements, and (4) production of stacked batteries. Hereinafter, although an example is given and demonstrated about the manufacturing method of a lithium ion secondary battery, it is not limited to this.

(1) Production of electrodes (positive electrode and negative electrode) The electrode (positive electrode or negative electrode) is prepared, for example, by preparing an active material slurry (positive electrode active material slurry or negative electrode active material slurry) and applying the active material slurry onto a current collector. It can be made by drying, then pressing. The active material slurry includes the above-described active material (positive electrode active material or negative electrode active material), a binder, a conductive additive, and a solvent.

The solvent is not particularly limited, and N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylformamide, cyclohexane, hexane, water and the like can be used.

The method for applying the active material slurry to the current collector is not particularly limited, and examples thereof include a screen printing method, a spray coating method, an electrostatic spray coating method, an ink jet method, and a doctor blade method.

The method for drying the coating film formed on the surface of the current collector is not particularly limited as long as at least a part of the solvent in the coating film is removed. An example of the drying method is heating. Drying conditions (drying time, drying temperature, etc.) can be appropriately set according to the volatilization rate of the solvent contained in the applied active material slurry, the coating amount of the active material slurry, and the like. A part of the solvent may remain. The remaining solvent can be removed by a press process described later.

The pressing means is not particularly limited, and for example, a calendar roll, a flat plate press, or the like can be used.

(2) Production of single cell layer The single cell layer can be produced by laminating the electrodes (positive electrode and negative electrode) produced in (1) via an electrolyte layer.

(3) Production of power generation element The power generation element can be produced by laminating the single cell layers in consideration of the output and capacity of the single cell layer, the output and capacity required for the battery, and the like.

(4) Manufacture of laminated battery As the structure of the battery, various shapes such as a rectangular shape, a paper shape, a laminated shape, a cylindrical shape, and a coin shape can be adopted. Further, the current collector and insulating plate of the component parts are not particularly limited, and may be selected according to the above shape. However, in the present embodiment, a stacked battery is preferable. In the stacked battery, a lead is joined to the current collector of the power generation element obtained above, and the positive electrode lead or the negative electrode lead is joined to the positive electrode tab or the negative electrode tab. A power generation element is placed in a laminate sheet so that the positive electrode tab and the negative electrode tab are exposed to the outside of the battery, and an electrolytic solution is injected with a liquid injector and then sealed in a vacuum to produce a stacked battery. sell.

(5) Activation treatment, etc. Further, in this embodiment, from the viewpoint of enhancing the performance and durability of the laminated battery obtained as described above, the initial charge treatment, gas removal treatment and activation treatment are further performed under the following conditions. Preferably it is done (see Example 1). In this case, the three sides of the laminate sheet (exterior material) are completely sealed in a rectangular shape by thermocompression when sealing in the production of the laminated battery of (4) so that the gas removal treatment can be performed. Stop (main sealing), and the remaining one side is temporarily sealed by thermocompression bonding. The remaining one side may be freely opened and closed by, for example, clip fastening, but from the viewpoint of mass production (production efficiency), it is preferable to temporarily seal the side by thermocompression bonding. In this case, it is only necessary to adjust the temperature and pressure for pressure bonding. When temporarily sealed by thermocompression, it can be opened by lightly applying force, and after degassing, it may be sealed again by thermocompression, or finally completely sealed by thermocompression ( Main sealing).

(First charging process)
The battery aging treatment is preferably performed as follows. At 25 ° C., a constant current charging method is used for 0.05 C for 4 hours (SOC approximately 20%). Next, after charging to 4.45 V at a 0.1 C rate at 25 ° C., the charging is stopped, and the state (SOC is about 70%) is maintained for about 2 days (48 hours).

(First (first) gas removal process)
Next, the following process is performed as the first (first) gas removal process. First, one side temporarily sealed by thermocompression bonding is opened, gas is removed at 10 ± 3 hPa for 5 minutes, and then thermocompression bonding is performed again to perform temporary sealing. Further, pressurization with a roller (surface pressure 0.5 ± 0.1 MPa) is performed, and the electrode and the separator are sufficiently adhered.

(Activation process)
Next, the following electrochemical pretreatment method is performed as an activation treatment method.

First, the battery is charged at 25 ° C. by a constant current charging method until the voltage reaches 4.45 V at 0.1 C, and then discharged twice to 2.0 V at 0.1 C. Similarly, after charging at 25 ° C. to 4.55 V at 0.1 C by the constant current charging method, a cycle of discharging to 2.0 V at 0.1 C once is 4.65 V at 0.1 C. The battery is charged until it reaches 0, and then discharged once at 0.1 C to 2.0 V. Furthermore, a cycle of charging at 0.1 C to 4.75 V by a constant current charging method at 25 ° C. and then discharging to 0.1 V at 0.1 C may be performed once.

In this example, the constant current charging method is used as the activation processing method, and the electrochemical pretreatment method when the voltage is set as the termination condition is described as an example, but the charging method is a constant current constant voltage charging method. You may use. Further, as the termination condition, a charge amount or time may be used in addition to the voltage.

(Last (second) gas removal process)
Next, the following process is performed as the first (first) gas removal process. First, one side temporarily sealed by thermocompression bonding is opened, gas is removed at 10 ± 3 hPa for 5 minutes, and then thermocompression bonding is performed again to perform main sealing. Further, pressurization with a roller (surface pressure 0.5 ± 0.1 MPa) is performed, and the electrode and the separator are sufficiently adhered.

In the present embodiment, the performance and durability of the obtained battery can be improved by performing the initial charging process, the gas removal process, and the activation process described above.

[Battery]
The assembled battery is configured by connecting a plurality of batteries. Specifically, at least two or more are used, and are configured by serialization, parallelization, or both. Capacitance and voltage can be freely adjusted by paralleling in series.

It is also possible to form a small assembled battery that can be attached and detached by connecting a plurality of batteries in series or in parallel. Then, a plurality of small assembled batteries that can be attached and detached are connected in series or in parallel to provide a large capacity and large capacity suitable for vehicle drive power supplies and auxiliary power supplies that require high volume energy density and high volume output density. An assembled battery having an output can also be formed. How many batteries are connected to make an assembled battery, and how many small assembled batteries are stacked to make a large-capacity assembled battery depends on the battery capacity of the mounted vehicle (electric vehicle) It may be determined according to the output.

[vehicle]
The electric device of the present invention including the lithium ion secondary battery according to the present embodiment maintains a discharge capacity even when used for a long time, and has good cycle characteristics. Furthermore, the volume energy density is high. Vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles require higher capacity, larger size, and longer life than electric and portable electronic devices. . Therefore, the lithium ion secondary battery (electric device) can be suitably used as a vehicle power source, for example, as a vehicle driving power source or an auxiliary power source.

Specifically, a battery or an assembled battery formed by combining a plurality of these batteries can be mounted on the vehicle. In the present invention, since a battery having a long life with excellent long-term reliability and output characteristics can be configured, a plug-in hybrid electric vehicle having a long EV mileage or an electric vehicle having a long charge mileage can be formed by mounting such a battery. . For example, in the case of a car, a hybrid car, a fuel cell car, an electric car (four-wheeled vehicles (passenger cars, trucks, buses, commercial vehicles, light cars, etc.) This is because it can be used for motorcycles (including motorcycles) and tricycles) to provide a long-life and highly reliable automobile. However, the application is not limited to automobiles. For example, it can be applied to various power sources for moving vehicles such as other vehicles, for example, trains, and power sources for mounting such as uninterruptible power supplies. It is also possible to use as.

Hereinafter, although it demonstrates in detail using an Example and a comparative example, this invention is not necessarily limited only to the following Examples.

[Example 1]
(Solid solution positive electrode active material C1)
(Preparation of aqueous solution of titanium citrate complex)
60 g (0.3 mol) of anhydrous citric acid (molecular weight 192.12 g / mol) was added to 400 ml of acetone and heated to 60 ° C. to dissolve. Next, 56 g (0.2 mol) of titanium tetraisopropoxide (molecular weight 284.22 g / mol) was added to form a precipitate. This liquid was subjected to suction filtration to obtain a precipitate (light yellow).

H ₂ O (200 ml) was added to the precipitate and heated to 50-60 ° C. to dissolve. This solution was allowed to stand for 1 day or longer to precipitate insoluble matters, and then filtered to remove insoluble matters, thereby obtaining a titanium citrate complex aqueous solution. The Ti concentration was 5.0% by weight as TiO ₂ (molecular weight 79.87 g / mol).

(Preparation of solid solution positive electrode active material C1)
Li _1.5 [Ni _0.450 Mn _0.750 [Li] _0.20 Ti _0.10 ] O _z
15.97 g of titanium citrate complex aqueous solution (5.0 wt% as TiO ₂ ), 14.71 g of manganese acetate tetrahydrate (molecular weight 245.09 g / mol), nickel acetate tetrahydrate (molecular weight 248. 84 g / mol) 7.47 g and lithium acetate dihydrate (molecular weight 102.02 g / mol) 14.57 g were sequentially added. The obtained mixture was heated to 200 ° C. to 300 ° C. to melt and dissolve. Next, using a spray drying apparatus, the obtained melted solution (slurry) was sprayed by heating at 200 ° C. to 400 ° C. and dried. The obtained dry powder was vacuum-dried at 140 ° C. to 250 ° C. for 12 hours and then calcined at 450 ° C. for 12 hours. Thereafter, the main baking was performed at 900 ° C. for 12 hours.

The composition of the solid solution positive electrode active material C1 obtained as described above was as follows.
Composition formula: Li _1.5 [Ni _0.450 Mn _0.750 [Li] _0.20 Ti _0.10 ] O _z
a + b + c + d + e = 1.5, d = 0.20, a + b + c + e = 1.30, e = 0.10
(X-ray diffraction measurement)
The obtained solid solution positive electrode active material was evaluated for crystal structure and crystallinity by X-ray diffraction. Cu-Kα rays were used as the X-ray source, and the measurement conditions were a tube voltage of 40 KV, a tube current of 20 mA, a scanning speed of 2 ° / min, a divergence slit width of 0.5 °, and a light receiving slit width of 0.15 °.

FIG. 3 shows a positive electrode active material C0 having the following composition that does not contain Ti for comparison.
Composition formula: Li _1.5 [Ni _0.450 Mn _0.850 [Li] _0.20 Ti _0.00 ] O _z
The X-ray diffraction pattern of is shown. Further, FIG. 4 shows an X-ray diffraction pattern of the solid solution positive electrode active material C1.

3 and 4 show a peak attributed to the superlattice structure characteristic of the solid solution system at 20-23 °. Furthermore, in FIG. 4, the peaks at 36.5-37.5 (101) and 44-45 ° (104) and 64-65 ° (108) / 65-66 (110) are slightly shifted to the lower angle side. It was observed. Further, no diffraction peak attributed to the spinel phase was observed in any sample.

(Preparation of positive electrode C1 having a positive electrode active material layer formed on one side of a current collector)
(Composition of slurry for positive electrode)
The positive electrode slurry had the following composition.

Cathode active material: Ti-substituted solid solution cathode active material C1 obtained above 9.4 parts by weight Conductive aid: flake graphite 0.15 parts by weight Acetylene black 0.15 parts by weight Binder: Polyvinylidene fluoride (PVDF) 0 .3 parts by weight Solvent: 8.2 parts by weight of N-methyl-2-pyrrolidone (NMP).

When this composition is applied to the formula (2), e = 94, which satisfies the requirement of the formula (2).

(Production of positive electrode slurry)
A positive electrode slurry having the above composition was prepared as follows. First, 4.0 parts by weight of a solvent (NMP) is added to 2.0 parts by weight of a 20% binder solution obtained by dissolving a binder in a solvent (NMP) into a 50 ml disposable cup, and a stirring defoaming machine (spinning revolving mixer: Awatori) A binder diluted solution was prepared by stirring for 1 minute with Rentaro AR-100). Next, 0.4 parts by weight of a conductive additive, 9.2 parts by weight of a solid solution positive electrode active material C1, and 2.6 parts by weight of a solvent (NMP) are added to the binder dilution, and the mixture is stirred for 3 minutes with a stirring deaerator. Thus, a positive electrode slurry (solid content concentration 55% by weight) was obtained.

(Application and drying of positive electrode slurry)
The positive electrode slurry was applied to one side of an aluminum current collector with a thickness of 20 μm using an automatic coating apparatus (Doctor blade manufactured by Tester Sangyo: PI-1210 automatic coating apparatus). Subsequently, the current collector coated with the positive electrode slurry was dried on a hot plate (100 ° C. to 110 ° C., drying time 30 minutes), and the amount of NMP remaining in the positive electrode active material layer was 0.02 wt%. A sheet-like positive electrode was formed as follows.

(Positive electrode press)
The sheet-like positive electrode was compression-molded with a roller press and cut to produce a positive electrode. At this time, the coating amount was adjusted in consideration of the discharge capacity of the positive electrode active material and the positive electrode slurry composition so that the discharge capacity of the positive electrode C1 was 5.55 mAh / cm ² (the same applies to the following negative electrodes C2 to C12). .

(Dry cathode)
Next, the drying process was performed in the vacuum drying furnace using the positive electrode produced in the said procedure. After the positive electrode was installed inside the drying furnace, the pressure in the room was reduced (100 mmHg (1.33 × 10 ⁴ Pa)) at room temperature (25 ° C.) to remove the air in the drying furnace. Subsequently, while flowing nitrogen gas (100 cm ³ / min), the temperature was raised to 120 ° C. at 10 ° C./min, the pressure was reduced again at 120 ° C., and nitrogen was maintained in the furnace for 12 hours. The temperature was lowered. In this way, a positive electrode C1 from which moisture on the positive electrode surface was removed was obtained.

(Preparation of negative electrode A1 in which an active material layer is formed on one side of the current collector foil)
(Manufacture of Si-containing alloys)
Si ₈₀ Sn ₁₀ Ti ₁₀ (unit: mass%, hereinafter the same) was used as the Si-containing alloy as the negative electrode active material. The Si-containing alloy 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 put 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. The average particle size of the obtained Si-containing alloy (negative electrode active material) powder was 0.3 μm.

(Composition of slurry for negative electrode)
The negative electrode slurry had the following composition.

Negative electrode active material: Si-containing alloy (Si ₈₀ Sn ₁₀ Ti ₁₀ ) 80 parts by weight Conductive auxiliary agent: SuperP 5 parts by weight Binder: Polyimide 15 parts by weight Solvent: N-methyl-2-pyrrolidone (NMP) Appropriate amount.

When this composition is applied to the formula (1), α = 80, which satisfies the requirement of the formula (1).

(Manufacture of negative electrode slurry)
A negative electrode slurry having the above composition was prepared as follows. First, a binder solution in which a binder was dissolved was added to a solvent (NMP), and the mixture was stirred for 1 minute with a stirring deaerator to prepare a binder diluted solution. A conductive additive, negative electrode active material powder, and a solvent (NMP) were added to the binder dilution, and the mixture was stirred for 3 minutes with a stirring deaerator to obtain a negative electrode slurry.

(Application and drying of slurry for negative electrode)
The negative electrode slurry was applied to one side of a 10 μm thick electrolytic copper current collector using an automatic coating apparatus. Subsequently, the current collector coated with the negative electrode slurry was dried on a hot plate (100 ° C. to 110 ° C., drying time 30 minutes), and the amount of NMP remaining in the negative electrode active material layer was 0.02 wt% or less. A sheet-like negative electrode was formed.

(Negative electrode press)
The obtained sheet-like negative electrode was compression-molded with a roller press and cut to prepare a negative electrode. At this time, the coating amount was adjusted in consideration of the discharge capacity of the negative electrode active material and the negative electrode slurry composition so that the discharge capacity of the negative electrode A1 was 5.83 mAh / cm ² (the same applies to the following negative electrodes A2 to A5). . When the surface of this negative electrode was observed, no cracks were observed.

(Dry electrode)
Next, the drying process was performed in the vacuum drying furnace using the negative electrode produced in the said procedure. After installing the negative electrode inside the drying furnace, the air in the drying furnace was removed under reduced pressure (100 mmHg (1.33 × 10 ⁴ Pa)) at room temperature (25 ° C.). Subsequently, while flowing nitrogen gas (100 cm ³ / min), the temperature was raised to 325 ° C. at 10 ° C./min, the pressure was reduced again at 325 ° C. and the nitrogen in the furnace was kept exhausted for 24 hours, The temperature was lowered. In this way, moisture on the surface of the negative electrode was removed to obtain a negative electrode A1.

[Capacity confirmation of positive electrode C1]
[Production of coin cell]
The positive electrode C1 obtained by the above (punching to a diameter of 15 mm) and a counter electrode made of a lithium foil (Honjo Metal Co., Ltd., diameter 16 mm, thickness 200 μm) are passed through a separator (diameter 17 mm, Cellguard Cellguard 2400). After facing each other, an electrolytic solution was injected to produce a CR2032-type coin cell.

As the above electrolyte solution, ethylene carbonate (EC) and diethyl carbonate (DEC) 1: in a mixed nonaqueous solvent were mixed at a volume ratio, the concentration of LiPF ₆ a (lithium hexafluorophosphate) 1M What was dissolved so that it might become was used.

Using a charge / discharge tester (HJ0501SM8A manufactured by Hokuto Denko Co., Ltd.), activation treatment was performed in a thermostatic chamber (PFU-3K manufactured by Espec Co., Ltd.) set at a temperature of 298K (25 ° C.).

[Activation processing]
After charging at 25 ° C. by a constant current charging method at 0.1 C until the voltage reached 4.45 V, a cycle of discharging to 0.1 V at 0.1 C was performed twice. Similarly, after charging at 25 ° C. to 4.55 V at 0.1 C by the constant current charging method, a cycle of discharging to 2.0 V at 0.1 C once is 4.65 V at 0.1 C. After being charged until it was, a cycle of discharging to 2.0 V at 0.1 C was performed once. Furthermore, the battery was charged at 25 ° C. by a constant current charging method until it reached 4.75 V at 0.1 C, and then discharged once to 2.0 V at 0.1 C.

[Production of laminate cell]
The positive electrode C1 obtained above was cut out so as to have an active material layer area of 2.5 cm in length and 2.0 cm in width, and the two current collectors faced each other, so that the uncoated surface (aluminum current collector) The current collector portion was spot welded together with the surface not coated with the foil slurry. This formed the positive electrode which has a positive electrode active material layer on both surfaces of the two-ply current collector foil with which the outer peripheral part was integrated by spot welding. Thereafter, an aluminum positive electrode tab (positive electrode current collector plate) was further welded to the current collector portion to form a positive electrode C11. That is, the positive electrode C11 has a configuration in which a positive electrode active material layer is formed on both surfaces of the current collector foil.

On the other hand, the negative electrode A1 obtained above was cut out so as to have an active material layer area of 2.7 cm in length and 2.2 cm in width, and then a negative electrode tab of electrolytic copper was further welded to the current collector portion to form a negative electrode A11. Formed. That is, the negative electrode A11 has a structure in which a negative electrode active material layer is formed on one surface of a current collector.

A porous polypropylene separator (S) (length 3.0 cm × width 2.5 cm, thickness 25 μm, porosity 55%) is sandwiched between the negative electrode A11 to which these tabs are welded and the positive electrode C11. A laminated power generation element was produced. The structure of the stacked type power generation element is the structure of negative electrode (single side) / separator / positive electrode (both sides) / separator / negative electrode (single side), that is, A11- (S) -C11- (S) -A11. The configuration. Next, both sides of the power generation element were sandwiched with an aluminum laminate film exterior material (length 3.5 cm × width 3.5 cm), and the above power generation element was accommodated by thermocompression sealing at three sides. After injecting an electrolyte solution of 0.8 cm ³ into this power generation element (in the case of the above five-layer structure, it becomes a two-cell structure and the amount of liquid injected per cell is 0.4 cm ³ ), the remaining one side is thermocompression bonded. Was temporarily sealed to prepare a laminated battery. In order to sufficiently infiltrate the electrolyte into the electrode pores, the electrolyte was held at 25 ° C. for 24 hours while being pressurized at a surface pressure of 0.5 Mpa.

In the preparation of the electrolytic solution, first, 1.0 M LiPF ₆ (electrolyte) was dissolved in a mixed solvent of 30% by volume of ethylene carbonate (EC) and 70% by volume of diethyl carbonate (DEC). Thereafter, lithium lithium fluorophosphate (LiPO ₂ F ₂ ) 1.8% by weight and methylenemethane disulfonic acid (MMDS) 1.5% by weight as lithium fluorophosphate acting as an additive were dissolved in an electrolytic solution. Used as.

In the following examples, a positive electrode and a negative electrode were produced according to Example 1. That is, a positive electrode and a negative electrode were produced in the same manner as in Example 1 described above except as otherwise noted below.

First, for the positive electrode, positive electrodes C2 to C12 were prepared in the same manner as the positive electrode C1, except that the composition of the solid solution positive electrode active material was changed as shown in Table 1 below.

(Negative electrode A2)
A negative electrode active material and a negative electrode were produced in the same manner as the negative electrode A1 described above, except that the composition of the Si-containing alloy (negative electrode active material) was changed to Si ₇₀ Sn ₁₅ Ti ₁₅ . The average particle size of the obtained Si-containing alloy (negative electrode active material) powder was 0.3 μm.

(Negative electrode A3)
The negative electrode A1 described above, except that the composition of the Si-containing alloy (negative electrode active material) was changed to Si ₅₉ Sn ₂₂ Ti ₁₉ and the time of alloying treatment for producing the silicon-containing alloy was changed to 25 hours. A negative electrode active material and a negative electrode were prepared in the same manner as described above. The average particle size of the obtained Si-containing alloy (negative electrode active material) powder was 0.3 μm.

(Negative electrode A4)
A negative electrode active material and a negative electrode were prepared by the same method as that of the negative electrode A3 described above, except that the time of alloying treatment for preparing the Si-containing alloy (negative electrode active material) was changed to 50 hours. The average particle size of the obtained Si-containing alloy (negative electrode active material) powder was 0.3 μm.

(Negative electrode A5)
A negative electrode active material and a negative electrode were prepared in the same manner as the negative electrode A1 described above, except that the composition of the Si-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 each of the negative electrode active materials (Si-containing alloys) used for the preparation of the negative electrodes A1 to A5 by the electron diffraction method, the crystallinity of the silicide phase (TiSi ₂ ) for any of the negative electrodes A1 to A5. A diffraction spot and a halo pattern were observed, and it was confirmed that the amorphous Si phase as a parent phase had a structure in which crystalline silicide phases were dispersed.

Further, the structure of each of the negative electrode active materials (Si-containing alloys) used for the production of the negative electrodes A1 to A5 described above 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, X-ray diffraction spectra obtained for the respective negative electrode active materials (Si-containing alloys) are shown in FIGS. 5A to 5E. Further, the diffraction peak intensity B of TiSi ₂ 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 ° obtained from these X-ray diffraction spectra. The ratio values (B / A) are shown in Tables 2 to 6 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.

Next, the positive electrodes C1 to C12 obtained above and the negative electrodes A1 to A5 obtained above were combined as shown in the following Tables 2 to 6 to produce a battery according to Example 1 (implementation). Examples 1 to 48 and comparative examples 1 to 12).

Thereafter, the power generation element of each battery obtained above was set on an evaluation cell mounting jig, and a positive electrode lead and a negative electrode lead were attached to each tab end of the power generation element, and a test was performed.

[Evaluation of battery characteristics]
The laminate type battery produced above was subjected to initial charge treatment and activation treatment under the following conditions, and performance was evaluated.

(First charging process)
The battery aging treatment was performed as follows. At 25 ° C., the battery was charged at a constant current charging method of 0.05 C for 4 hours (SOC approximately 20%). Next, after charging to 4.45 V at a 0.1 C rate at 25 ° C., the charging was stopped and the state (SOC about 70%) was maintained for about 2 days (48 hours).

(Gas removal treatment 1)
One side temporarily sealed by thermocompression bonding was opened, gas was removed at 10 ± 3 hPa for 5 minutes, and then thermocompression bonding was performed again to perform temporary sealing. Further, pressurization with a roller (surface pressure 0.5 ± 0.1 MPa) was performed, and the electrode and the separator were sufficiently adhered.

(Activation process)
After charging at 25 ° C. by a constant current charging method at 0.1 C until the voltage reached 4.45 V, a cycle of discharging to 0.1 V at 0.1 C was performed twice. Similarly, after charging at 25 ° C. to 4.55 V at 0.1 C by the constant current charging method, a cycle of discharging to 2.0 V at 0.1 C once is 4.65 V at 0.1 C. After being charged until it was, a cycle of discharging to 2.0 V at 0.1 C was performed once. Furthermore, the battery was charged at 25 ° C. by a constant current charging method until it reached 4.75 V at 0.1 C, and then discharged once to 2.0 V at 0.1 C.

(Gas removal process 2)
One side temporarily sealed by thermocompression bonding was opened, gas was removed at 10 ± 3 hPa for 5 minutes, and then thermocompression bonding was performed again to perform main sealing. Further, pressurization with a roller (surface pressure 0.5 ± 0.1 MPa) was performed, and the electrode and the separator were sufficiently adhered.

(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 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 100 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 100th cycle to the discharge capacity at the first cycle (discharge capacity retention rate [%]) are shown in Tables 2 to 6 below.

As is apparent from the results shown in Tables 2 to 6, the lithium ion secondary batteries of Examples 1 to 48, which are electrical devices according to the present invention, have excellent cycle characteristics (100 cycles) compared to Comparative Examples 1 to 12. It can be seen that the eye capacity retention ratio has been achieved.

10, 50 lithium ion secondary battery,
11 negative electrode current collector,
12 positive electrode current collector,
13 negative electrode active material layer,
15 positive electrode active material layer,
17 separator,
19 cell layer,
21, 57 power generation element,
25 negative current collector,
27 positive current collector,
29, 52 Battery exterior material,
58 positive electrode tab,
59 Negative electrode tab.

Claims

A positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on the surface of the positive electrode current collector;
A negative electrode in which a negative electrode active material layer containing a negative electrode active material is formed on the surface of the negative electrode current collector;
A separator;
An electrical device having a power generation element comprising:
The negative electrode active material layer has the following formula (1):

In the above formula (1), α represents the weight percent of each component in the negative electrode active material layer, and 40 <α ≦ 98.
Containing a negative electrode active material represented by
The positive electrode active material layer has the following formula (2):

In the above formula (2), e represents the weight percent of each component in the positive electrode active material layer, and 80 ≦ e ≦ 98.
A positive electrode active material represented by
In this case, the Si-containing alloy has a structure in which a silicide phase containing a silicide of a transition metal is dispersed in a parent phase mainly composed of amorphous or low crystalline silicon. I):

In the above chemical formula (I), 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.
In the X-ray diffraction measurement using the CuKα1 line of the Si-containing alloy, 2θ = 37 with respect to the diffraction peak intensity A of the (111) plane of Si in the range of 2θ = 24 to 33 °. The value (B / A) of the diffraction peak intensity B of the transition metal silicide in the range of ˜45 ° is 0.41 or more,
And the said solid solution positive electrode active material is following formula (3):

In the above formula (3), X is at least one selected from the group consisting of Ti, Zr and Nb, and 0.01 ≦ e ≦ 0.4, a + b + c + d + e = 1.5, 0.1 ≦ d ≦ 0.4, 1.1 ≦ [a + b + c + e] ≦ 1.4, and z represents the number of oxygen satisfying the valence,
An electrical device comprising a solid solution having a composition represented by:
The electric device according to claim 1, wherein the B / A is 0.89 or more.
The electric device according to claim 2, wherein the B / A is 2.55 or more.
The electric device according to claim 3, wherein the B / A is 7.07 or more.
5. The diffraction peak intensity A (cps) of Si (111) plane is 6000 to 25000, and the diffraction peak intensity B (cps) of transition metal silicide is 9000 to 46000. The electrical device according to item.
The diffraction peak intensity A (cps) of the Si (111) plane is 6000 to 15000, and the diffraction peak intensity B (cps) of the transition metal silicide is 25000 to 46000. The electrical device according to item.
The electric device according to any one of claims 1 to 6, wherein the matrix phase is more amorphous than the silicide phase.
The electric device according to any one of claims 1 to 7, wherein a size of the silicide phase is 50 nm or less.
The electric device according to any one of claims 1 to 8, wherein M is titanium (Ti) in the chemical formula (I).
10. The electrical device according to claim 1, wherein 7 <z <100 in the chemical formula (I).
The solid solution positive electrode active material has 20-23 °, 35-40 ° (101), 42-45 ° (104) and 64-65 (108) / 65-66 (110) in X-ray diffraction (XRD) measurement. The electric device according to any one of claims 1 to 10, which has a diffraction peak showing a rock salt type layered structure.
The solid solution positive electrode active material according to any one of claims 1 to 11, which has substantially no peak attributed to other than a diffraction peak of a rock salt type layered structure in X-ray diffraction (XRD) measurement. Electrical devices.
The solid solution positive electrode active material has three diffraction peaks at 35-40 ° (101) and one diffraction peak at 42-45 ° (104) in X-ray diffraction (XRD) measurement. The electrical device according to any one of 1 to 12.
The solid solution positive electrode active material was measured at 20-23 °, 35.5-36.5 ° (101), 43.5-44.5 ° (104) and 64-65 (108) in X-ray diffraction (XRD) measurement. The electrical device according to any one of claims 1 to 13, which has a diffraction peak at) / 65-66 (110).
The electrical device according to any one of claims 1 to 14, which is a lithium ion secondary battery.