Lithium ion secondary battery

Abstract

To provide a secondary battery with high capacity and less deterioration, or provide a novel power storage device.SOLUTION: A secondary battery has a positive electrode and a negative electrode. The negative electrode has a first active material, a second active material, and a graphene compound. At least a part of a surface of the first active material has a region covered with the second active material. At least a part of a surface of the second active material and the surface of the first active material has a region covered with the graphene compound. The first active material has graphite, and the second active material has silicon. A capacity of the positive electrode is 50% or more and less than 100% of a capacity of the negative electrode.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Relates to an electrode and a method for manufacturing the same. Or, relates to an active material included in the electrode and a method for manufacturing the same. Or, relates to a secondary battery and a method for manufacturing the same. Or, relates to a moving body including a vehicle or the like having the secondary battery, as well as a portable information terminal, an electronic device, and the like.

[0002] One aspect of the present invention relates to an article, a method, or a manufacturing method. Or, the present invention relates to a process, a machine, a manufacture, or a composition of matter. One aspect of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, an electronic device, or a manufacturing method thereof.

[0003] In the present specification, the electronic device generally refers to all devices having a power storage device, and all electro-optical devices having a power storage device, information terminal devices having a power storage device, and the like are electronic devices.

[0004] In the present specification, the power storage device generally refers to an element and a device having a power storage function. For example, it includes power storage devices (also referred to as secondary batteries) such as lithium-ion secondary batteries, lithium-ion capacitors, and electric double layer capacitors.

Background Art

[0005] In recent years, various power storage devices such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries have been actively developed. In particular, lithium-ion secondary batteries with high output and high energy density are essential in modern information societies as a source of rechargeable energy, and their demand has rapidly expanded along with the development of the semiconductor industry. They are used in portable information terminals such as mobile phones, smartphones, or notebook computers, portable music players, digital cameras, medical devices, or next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV).

Prior Art Documents

Patent Document

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] Secondary batteries used in mobile bodies such as electric vehicles and hybrid vehicles need to have increased capacity in order to extend the driving range.

[0008] In addition, in portable terminals and the like, power consumption is increasing with the addition of multifunctions. Also, secondary batteries used in portable terminals and the like are required to be miniaturized and lightweight. Therefore, there is also a demand for higher capacity in secondary batteries used in portable terminals.

[0009] In addition to its stability, it is important for a secondary battery to have a high capacity. Alloy-based materials such as silicon-based materials have a high capacity and are promising as active materials for secondary batteries. However, alloy-based materials with a high charge-discharge capacity have problems such as pulverization and shedding of the active material due to volume changes during charge and discharge, and sufficient cycle characteristics have not been obtained.

[0010] To improve the problems of the alloy-based materials as described above, the compounding of an alloy-based material and graphite or a carbonaceous material has been studied. Patent Document 1 describes a composite material in which a coating layer made of carbon is formed on the surface of a porous particle nucleus formed by bonding silicon-containing particles and carbon-containing particles. Patent Document 2 describes composite particles containing silicon (Si), lithium fluoride (LiF), and a carbon material. However, in none of the above documents has the problem of pulverization and shedding of the active material due to the expansion of the alloy-based material during charge and discharge been fully solved.

[0011] The electrodes of a secondary battery are composed of materials such as an active material, a conductive material, and a binder, for example. The higher the proportion of the material that contributes to the charge and discharge capacity, such as the active material, the higher the capacity of the secondary battery can be increased. By having a conductive material in the electrode, the conductivity of the electrode can be increased and excellent output characteristics can be obtained. Further, in the charge and discharge of the secondary battery, when the active material repeatedly expands and contracts, the active material may collapse and the conductive path may be blocked in the electrode. In such a case, by having a conductive material and a binder in the electrode, the collapse of the active material and the blocking of the conductive path can be suppressed. On the other hand, by using a conductive material and a binder, the proportion of the active material decreases, so the capacity of the secondary battery may decrease.

[0012] One aspect of the present invention is to provide an electrode having excellent characteristics. Or, one aspect of the present invention is to provide an active material having excellent characteristics. Or, one aspect of the present invention is to provide a novel electrode.

[0013] Or, one aspect of the present invention is to provide a mechanically strong negative electrode. Or, one aspect of the present invention is to provide a mechanically strong positive electrode. Or, one aspect of the present invention is to provide a negative electrode with a high capacity. Or, one aspect of the present invention is to provide a positive electrode with a high capacity. Or, one aspect of the present invention is to provide a negative electrode with less deterioration. Or, one aspect of the present invention is to provide a positive electrode with less deterioration.

[0014] Or, one aspect of the present invention is to provide a secondary battery with less deterioration. Or, one aspect of the present invention is to provide a highly safe secondary battery. Or, one aspect of the present invention is to provide a secondary battery with a high energy density. Or, one aspect of the present invention is to provide a novel secondary battery.

[0015] Note that the description of these problems does not prevent the existence of other problems. Note that one aspect of the present invention does not need to solve all of these problems. Note that it is possible to extract other problems from the description of the specification, drawings, and claims.

Means for Solving the Problems

[0016] One aspect of the present invention has a positive electrode and a negative electrode. The negative electrode has a first active material, a second active material, and a graphene compound. At least a part of the surface of the first active material has a region covered by the second active material. The surface of the second active material and at least a part of the surface of the first active material have regions covered by the graphene compound. The first active material has graphite, and the second active material has silicon. The capacity of the positive electrode is 50% or more and less than 100% with respect to the capacity of the negative electrode. It is a secondary battery.

[0017] Also, one aspect of the present invention has a positive electrode and a negative electrode. The negative electrode has a first active material, a second active material, and a graphene compound. At least a part of the surface of the first active material has a region covered by the second active material. The surface of the second active material and at least a part of the surface of the first active material have regions covered by the graphene compound. The first active material has graphite, and the second active material has silicon. In the fully charged state, the second active material has Si-Si bonds. It is a secondary battery.

[0018] Also, one aspect of the present invention has a positive electrode, a negative electrode, and an electrolyte. The negative electrode has a first active material, a second active material, and a graphene compound. At least a part of the surface of the first active material has a region covered by the second active material. The surface of the second active material and at least a part of the surface of the first active material have regions covered by the graphene compound. The first active material has graphite, and the second active material has silicon. The capacity of the positive electrode is 50% or more and less than 100% with respect to the capacity of the negative electrode, and the electrolyte has an ionic liquid. It is a secondary battery.

[0019] Also, one aspect of the present invention is a secondary battery having a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode has a first active material, a second active material, and a graphene compound, at least a part of the surface of the first active material has a region covered by the second active material, the surface of the second active material and at least a part of the surface of the first active material have regions covered by the graphene compound, the first active material has graphite, the second active material has silicon, in a fully charged state, the second active material has Si—Si bonds, and the electrolyte has an ionic liquid.

[0020] In the secondary battery according to any one of the above, it is desirable that the ionic liquid has 2 mol / L or more of LiFSI and EMI-FSI.

[0021] In the secondary battery according to any one of the above, the positive electrode has lithium cobaltate having magnesium, fluorine, aluminum, and nickel, and it is desirable that the lithium cobaltate has a region where the concentration of any one or more selected from magnesium, fluorine, and aluminum is maximum in the surface layer portion.

[0022] In the secondary battery according to any one of the above, it is desirable that the first active material has graphite with a particle diameter of 5 μm or more, and the second active material has silicon with a particle diameter of 250 nm or less.

[0023] One aspect of the present invention is a vehicle having the secondary battery according to any one of the above.

[0024] One aspect of the present invention is a power storage system having the secondary battery according to any one of the above.

[0025] One aspect of the present invention is an electronic device having the secondary battery according to any one of the above.

Advantages of the Invention

[0026] According to one aspect of the present invention, an active material having excellent characteristics can be provided. Further, an electrode having excellent characteristics can be provided. Also, according to one aspect of the present invention, a novel electrode can be provided.

[0027] Further, according to one aspect of the present invention, a mechanically robust negative electrode can be provided. Also, according to one aspect of the present invention, a mechanically robust positive electrode can be provided. Further, according to one aspect of the present invention, a negative electrode with a high capacity can be provided. Also, according to one aspect of the present invention, a positive electrode with a high capacity can be provided. Further, according to one aspect of the present invention, a negative electrode with less degradation can be provided. Also, according to one aspect of the present invention, a positive electrode with less degradation can be provided.

[0028] Further, according to one aspect of the present invention, a secondary battery with less degradation can be provided. Also, according to one aspect of the present invention, a highly safe secondary battery can be provided. Further, according to one aspect of the present invention, a secondary battery with a high energy density can be provided. Also, according to one aspect of the present invention, a novel secondary battery can be provided.

[0029] Note that the description of these effects does not prevent the existence of other effects. Note that one aspect of the present invention does not necessarily have to have all of these effects. Note that other effects will become apparent from the descriptions in the specification, drawings, claims, etc., and it is possible to extract these other effects from the descriptions in the specification, drawings, claims, etc.

Brief Description of the Drawings

[0030]

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MODE FOR CARRYING OUT THE INVENTION

[0031] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be easily understood by those skilled in the art that the form and details thereof can be variously changed. Further, the present invention is not to be construed as being limited to the description of the embodiments shown below.

[0032] In the drawings, the size, layer thickness, or area may be exaggerated for clarity. Therefore, it is not necessarily limited to that scale.

[0033] In this specification and the like, ordinal numbers such as first, second, etc. are used for convenience and do not indicate the process order or the stacking order. Therefore, for example, "first" can be appropriately replaced with "second" or "third" and so on for explanation. Also, the ordinal numbers described in this specification and the like may not match the ordinal numbers used to identify an aspect of the present invention.

[0034] In this specification and the like, the term "particle" is not limited to referring only to a spherical shape (circular cross-sectional shape), and the cross-sectional shape of each individual particle may be an ellipse, rectangle, trapezoid, triangle, rounded square, asymmetric shape, etc., and furthermore, each individual particle may be amorphous.

[0035] (Embodiment 1) In this embodiment, an example of a secondary battery according to one aspect of the present invention will be described.

[0036] [Configuration Example of Secondary Battery] A secondary battery having a positive electrode, a negative electrode, and an electrolyte will be described below.

[0037] FIG. 1A is a schematic cross-sectional view showing the inside of a secondary battery according to one aspect of the present invention. The negative electrode 570a, the positive electrode 570b, and the electrolyte 576 shown in FIG. 1A can be applied to a coin-type secondary battery, a cylindrical secondary battery, a laminate-type secondary battery, etc. shown in the embodiments described later. The negative electrode 570a includes at least a negative electrode current collector 571a and a negative electrode active material layer 572a formed in contact with the negative electrode current collector 571a. The positive electrode 570b includes at least a positive electrode current collector 571b and a positive electrode active material layer 572b formed in contact with the positive electrode current collector 571b. FIG. 1B is an enlarged view of the region surrounded by the broken line C in FIG. 1A. FIG. 1C is a diagram for explaining the capacity ratio of the negative electrode 570a and the positive electrode 570b in the region surrounded by the broken lines A and B in FIG. 1A. The secondary battery may have a separator between the negative electrode 570a and the positive electrode 570b.

[0038] [Capacity Ratio of Negative Electrode and Positive Electrode] The negative electrode characteristic curve 560a and the positive electrode characteristic curve 560b shown in FIGS. 1C, 2A, 2B, and 2C are characteristic curves showing the relationship between the capacity and the potential of the negative electrode active material layer 572a and the positive electrode active material layer 572b, which are opposite to each other and have the same area, of the negative electrode 570a and the positive electrode 570b in the region surrounded by the broken lines A and B in FIG. 1A.

[0039] In the negative electrode characteristic curve 560a of FIG. 1C, the capacitance C1 is the total capacitance that the negative electrode 570a can be charged and discharged. The total capacitance that the negative electrode 570a can be charged and discharged means, for example, preparing a half cell having the negative electrode 570a and lithium metal, performing constant current discharge (0.2C, lower limit voltage 0.01V), then performing constant voltage discharge (lower limit current density 0.02C), and then performing constant current charge (0.2C, upper limit voltage 1V), and refers to the charge capacitance. Further, in the positive electrode characteristic curve 560b of FIG. 1C, the capacitance C2 is the capacitance of the positive electrode in the fully charged state of the secondary battery. In this specification, the fully charged state of the secondary battery means, for example, the charged state in which the rated capacitance defined in JIS C8711 (2013) is obtained.

[0040] The capacitance ratio of the negative electrode 570a and the positive electrode 570b in the secondary battery is the capacitance of the positive electrode 570b shown in % when the capacitance of the negative electrode 570a is 100% in the negative electrode 570a and the positive electrode 570b having the same area. For example, as shown in FIG. 2A, when the capacitance of the negative electrode 570a and the capacitance of the positive electrode 570b are equal, the capacitance ratio of the negative electrode 570a and the positive electrode 570b is 100%.

[0041] Next, the case where the capacitance ratio of the negative electrode 570a and the positive electrode 570b is lower than 100% will be described with reference to FIG. 1C. The case where the capacitance ratio is lower than 100% indicates that the total capacitance that the negative electrode 570a can be charged and discharged is larger than the capacitance that the positive electrode 570b can be charged and discharged. In this case, the capacitance C1 of the negative electrode 570a shown in FIG. 1C becomes a value larger than the capacitance C2 of the positive electrode 570b.

[0042] As described above, when the capacitance ratio is lower than 100%, an excess capacitance is generated in the capacitance C1 of the negative electrode 570a, but there is an advantage that unintentional lithium ion precipitation in the negative electrode 570a is easily suppressed. Further, in the secondary battery having the negative electrode 570a of one aspect of the present invention described later, when the capacitance ratio is preferably 50% or more and less than 100%, more preferably 70% or more and less than 90%, a secondary battery having a high charge and discharge capacitance and good charge and discharge cycle characteristics can be obtained.

[0043] Next, the voltage of the secondary battery will be described. The voltage of the secondary battery can be considered as the difference between the positive electrode potential and the negative electrode potential. For example, the voltage of the secondary battery when the capacity ratio of the negative electrode 570a to the positive electrode 570b is 100% is shown as ΔVa in FIG. 2A. Also, the case where the capacity ratio is lower than 100% is shown as ΔVb in FIG. 2B. As shown in FIG. 2B, when the capacity ratio is lower than 100%, since the utilization potential range of the negative electrode 570a is used in a higher region, the voltage of the secondary battery decreases.

[0044] Next, FIG. 2C shows an example in which the secondary battery voltage does not decrease even when the capacity ratio of the negative electrode 570a to the positive electrode 570b is lower than 100%. Here, it is shown that ΔVa and ΔVc shown in FIG. 2C have the same voltage value. In FIG. 2B, the utilization potential range of the positive electrode 570b is the same as the utilization potential range of the positive electrode 570b in FIG. 2A, and in this case, the secondary battery voltage ΔVb is smaller than ΔVa as described above. As shown in FIG. 2C here, when the utilization potential range of the positive electrode 570b is expanded to a high potential, the secondary battery voltage ΔVc becomes as high as ΔVa.

[0045] As shown in FIG. 2C, it is possible to obtain a secondary battery in which the voltage does not decrease even when the capacity ratio of the negative electrode 570a to the positive electrode 570b is lower than 100%. In this case, since the positive electrode 570b is exposed to a relatively high potential, the positive electrode 570b needs to have high resistance to charge and discharge at a high potential. The positive electrode active material 100 shown in one aspect of the present invention can have a stable crystal structure in a charged state at a high potential, and thus is suitable as the active material of the positive electrode 570b. Details of the positive electrode active material 100 will be described later.

[0046] [Negative electrode] Figure 1B is an enlarged view of the region surrounded by the dashed line C in Figure 1A. As shown in Figure 1B, the negative electrode active material layer 572a includes a first active material 581, a second active material 582, a graphene compound 583 as a material having a sheet-like shape, and an electrolyte 576. Figure 3A is a schematic diagram showing a state in which the graphene compound 583 contacts the first active material 581 so as to cover, wrap, or cling to the second active material 582 located on the surface of the first active material 581. The graphene compound 583 included in the negative electrode 570a preferably functions as a conductive material, for example. In one aspect of the present invention, since the conductive material can cling to the active material by hydrogen bonding, an electrode with high conductivity can be realized.

[0047] Various materials can be used as the first active material 581 and the second active material 582. When particles having a surface layer portion that is a particle of one aspect of the present invention, particles having a functional group containing oxygen or fluorine, or particles having a region terminated by a functional group containing oxygen or a fluorine atom on the surface are used as the first active material 581 and the second active material 582, the affinity between the first active material 581 and the second active material 582 and the graphene compound 583 is improved, and as shown in Figures 1B and 3A, the graphene compound 583 can contact the first active material 581 so as to cover, wrap, or cling to the second active material 582 located on the surface of the first active material 581. Since the graphene compound 583 can cling to the first active material 581 and the second active material 582, an electrode with high conductivity can be realized. The state of clinging contact can also be described as being in close contact rather than in point contact. It can also be described as contacting along the surface of the particle. It can also be described as being in surface contact with a plurality of particles. Materials that can be used as the first active material 581 and the second active material 582 will be described later.

[0048] Regarding the case of using an active material with a large volume change during charge and discharge as the second active material 582, it will be described with reference to FIGS. 3B and 3C. FIG. 3B shows the first active material 581, the second active material 582, and the graphene compound 583 as a material having a sheet-like shape, and shows that the graphene compound 583 is in contact with the first active material 581 so as to cover, wrap, or cling to the second active material 582 located on the surface of the first active material 581. The second active material 582 is located between the first active material 581 and the graphene compound 583, and it can also be said that the graphene compound 583 is in contact with the first active material 581 and the second active material 582. FIG. 3C shows the case where the volume of the second active material 582 shown in FIG. 3B increases due to charging or discharging. Since the graphene compound 583 is in contact with the first active material 581 so as to cover, wrap, or cling to the second active material 582 located on the surface of the first active material 581, even when the volume of the second active material 582 increases due to charging or discharging, the electrical contact between the second active material 582 and the first active material 581 can be maintained. Also, the collapse of the electrode can be suppressed.

[0049] When the graphene compound 583 is in contact with active materials such as the first active material 581 and the second active material 582 so as to cling to them, the contact area between the graphene compound 583 and the active materials increases, and the conductivity of electrons moving through the graphene compound 583 is improved. Also, when the volume of the active material changes significantly due to charge and discharge, by having the graphene compound 583 in contact with the active material so as to cling to it, it is possible to effectively prevent the active material from falling off, and these effects can obtain more remarkable effects when in contact so as to cling tightly. Here, the graphene compound 583 desirably has pores of a size that allows Li ions to pass through, and has a large number of pores to such an extent that it does not interfere with the electron conductivity of the graphene compound 583.

[0050] In addition to the graphene compound 583, the negative electrode active material layer 572a can include carbon-based materials such as carbon black, graphite, carbon fiber, and fullerene. As the carbon black, for example, acetylene black (AB) can be used. As the graphite, for example, natural graphite, artificial graphite such as mesocarbon microbeads, etc. can be used. These carbon-based materials have high conductivity and can function as conductive materials in the active material layer. Note that these carbon-based materials may also function as active materials.

[0051] As the carbon fiber, for example, carbon fibers such as mesophase pitch-based carbon fiber and isotropic pitch-based carbon fiber can be used. Also, as the carbon fiber, carbon nanofibers or carbon nanotubes can be used. Carbon nanotubes can be produced, for example, by a vapor phase growth method.

[0052] The active material layer may also include metal powders such as copper, nickel, aluminum, silver, and gold, or metal fibers, conductive ceramic materials, etc. as conductive materials.

[0053] The content of the conductive material with respect to the total amount of the solid content of the active material layer is preferably 0.5 wt% or more and 10 wt% or less, and more preferably 0.5 wt% or more and 5 wt% or less.

[0054] Unlike granular conductive materials such as carbon black that make point contact with the active material, the graphene compound enables surface contact with low contact resistance, so it can improve the electrical conductivity between the granular active material and the graphene compound with a smaller amount than ordinary conductive materials. Therefore, the ratio of the active material in the active material layer can be increased. Thereby, the discharge capacity of the secondary battery can be increased.

[0055] Also, since the graphene compound of one aspect of the present invention has excellent lithium permeability, the charge and discharge rate of the secondary battery can be increased.

[0056] Particulate carbon-containing compounds such as carbon black and graphite, and fibrous carbon-containing compounds such as carbon nanotubes are likely to enter minute spaces. The minute spaces refer to, for example, the regions between a plurality of active materials. By using in combination a carbon-containing compound that is likely to enter minute spaces and a sheet-like carbon-containing compound such as graphene that can impart conductivity over a plurality of particles, the density of the electrode can be increased and an excellent conductive path can be formed. Further, since the secondary battery has the electrolyte 576 of one aspect of the present invention, the operating stability of the secondary battery can be enhanced. That is, the secondary battery of one aspect of the present invention can have both a high energy density and stability, and is effective as a secondary battery for vehicle-mounted use. When the number of secondary batteries is increased and the weight of the vehicle increases, the energy required to move the vehicle increases, so the cruising range also becomes shorter. By using a high-density secondary battery, even if the weight of the secondary battery mounted on the vehicle is the same, that is, even if the total weight of the vehicle is the same, the cruising range can be lengthened.

[0057] Further, when the secondary battery of the vehicle has a high capacity, a large amount of power is required for charging, so it is desirable to complete charging in a short time. Further, since charging under high-rate charging conditions is performed in so-called regenerative charging in which power is temporarily generated when the vehicle brakes and the power is charged, good rate characteristics are required for the vehicle secondary battery.

[0058] By using the electrolyte 576 of one aspect of the present invention, a vehicle-mounted secondary battery having a wide operating temperature range can be obtained.

[0059] Further, since the secondary battery of one aspect of the present invention has a high energy density, it can be miniaturized, and since it has high conductivity, rapid charging is also possible. Therefore, the configuration of the secondary battery of one aspect of the present invention is also effective in a portable information terminal.

[0060] The negative electrode active material layer 572a preferably has a binder (not shown). The binder binds or fixes, for example, the electrolyte 576 and the active material. The binder can also bind or fix the electrolyte 576 and the carbon-based material, the active material and the carbon-based material, a plurality of active materials, a plurality of carbon-based materials, etc.

[0061] As the binder, it is preferable to use materials such as polystyrene, methyl polyacrylate, polymethyl methacrylate (polymethyl acrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, nitrocellulose, etc.

[0062] Polyimide has very excellent thermal, mechanical, and chemical stability properties. Also, when polyimide is used as the binder, a dehydration reaction and a cyclization (imidization) reaction are carried out. These reactions can be carried out, for example, by heat treatment. In the electrode of one aspect of the present invention, when graphene having a functional group containing oxygen as the graphene compound and polyimide as the binder are used, the reduction of the graphene compound can also be carried out by the heat treatment, and the process can be simplified. Also, since it has excellent heat resistance, for example, the heat treatment can be carried out at a heating temperature of 200 °C or higher. By carrying out the heat treatment at a heating temperature of 200 °C or higher, the reduction reaction of the graphene compound can be sufficiently carried out, and the conductivity of the electrode can be further increased.

[0063] A fluoropolymer, which is a polymer material having fluorine, specifically polyvinylidene fluoride (PVDF), etc. can be used. PVDF is a resin having a melting point in the range of 134 °C or higher and 169 °C or lower, and is a material having excellent thermal stability.

[0064] Also, as the binder, it is preferable to use rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, etc. Also, fluororubber can be used as the binder.

[0065] Also, as the binder, it is preferable to use, for example, water-soluble polymers. As the water-soluble polymer, for example, polysaccharides can be used. As the polysaccharides, cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, regenerated cellulose, or starch can be used. Also, it is more preferable to use these water-soluble polymers in combination with the aforementioned rubber materials.

[0066] The binder may be used in combination of a plurality of the above.

[0067] In addition, the graphene compound 583 has flexibility and can wrap around the first active material 581 and the second active material 582 like natto. Also, for example, the first active material 581 and the second active material 582 can be likened to soybeans, and the graphene compound 583 can be likened to a sticky component, such as polyglutamic acid, respectively. By disposing the graphene compound 583 across materials such as the electrolyte 576, a plurality of active materials, and a plurality of carbon-based materials included in the negative electrode active material layer 572a, not only a good conductive path can be formed in the negative electrode active material layer 572a, but these materials can be bound or fixed using the graphene compound 583. Also, for example, a three-dimensional network structure, a structure in which polygons are arranged, such as a honeycomb structure in which hexagons are arranged in a matrix, is formed by a plurality of graphene compounds 583, and materials such as the electrolyte 576, a plurality of active materials, and a plurality of carbon-based materials are arranged in the network, whereby the graphene compound 583 forms a three-dimensional conductive path and the dropout of the electrolyte 576 from the current collector can be suppressed. Also, in the structure in which the above-mentioned polygons are arranged, polygons having different numbers of sides may be mixed and arranged. Therefore, the graphene compound 583 may function as a conductive material and also as a binder in the negative electrode active material layer 572a. The graphene compound 583 has holes of 9-membered rings or more and does not inhibit the movement of Li ions even when covering the active material, and thus is particularly preferable as a conductive material used for the negative electrode active material layer 572a.

[0068] [Negative electrode active material] The first active material 581 and the second active material 582 can have various shapes, such as a rounded shape and a shape having corners. Also, in the cross-section of the electrode, the first active material 581 and the second active material 582 can have various cross-sectional shapes, such as a circle, an ellipse, a figure having a curve, and a polygon. For example, as an example in FIGS. 1B and 3A, an example in which the cross-sections of the first active material 581 and the second active material 582 have a rounded shape is shown, but the cross-sections of the first active material 581 and the second active material 582 may have corners. Also, a part may be rounded and a part may have corners.

[0069] An example of the negative electrode active material will be described below.

[0070] As the negative electrode active material, silicon can be used. It is preferable that the negative electrode 570a uses particles having silicon as the second active material 582.

[0071] In addition, as the negative electrode active material included in the second active material 582, a metal or a compound having one or more elements selected from tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium can be used. Examples of alloy compounds using such elements include, for example, Mg 2 Si, Mg 2 Ge, Mg 2 Sn, SnS 2 , V 2 Sn 3 , FeSn 2 , CoSn 2 , Ni 3 Sn 2 , Cu 6 Sn 5 , Ag 3 , Ag 3 , Sb, Ni 2 , MnSb, CeSb 3 , LaSn 3 , La 3 , Co 2 Sn 7 , CoSb 3 , InSb, SbSn, and the like.

[0072] Alternatively, materials with reduced resistance may be used by adding phosphorus, arsenic, boron, aluminum, gallium, etc. as impurity elements to silicon. Also, a silicon material pre-doped with lithium may be used. Examples of pre-doping methods include mixing lithium fluoride, lithium carbonate, etc. with silicon and annealing, mechanical alloying of lithium metal and silicon, etc. Further, after forming a first electrode using silicon as an active material, it may be combined with a second electrode such as lithium metal and lithium may be doped into the silicon contained in the first electrode through a charge-discharge reaction. Thereafter, a secondary battery may be fabricated by combining an electrode serving as a counter electrode (for example, a positive electrode with respect to a pre-doped negative electrode) using the doped first electrode.

[0073] For example, nano-silicon particles can be used as the second active material 582. The average diameter of the nano-silicon particles is, for example, preferably 5 nm or more and less than 1 μm, more preferably 10 nm or more and 300 nm or less, still more preferably 10 nm or more and 100 nm or less.

[0074] The nano-silicon particles may have a spherical form, a flattened spherical form, or a rectangular parallelepiped form with rounded corners. The size (particle diameter) of the nano-silicon particles is, for example, preferably 5 nm or more and less than 1 μm, more preferably 10 nm or more and 300 nm or less, still more preferably 10 nm or more and 100 nm or less, as D50 of laser diffraction particle size distribution measurement. Here, D50 is the particle diameter when the integrated amount occupies 50% in the integrated particle amount curve of the particle size distribution measurement result, that is, the median. The measurement of the particle size is not limited to laser diffraction particle size distribution measurement, and the major axis of the particle cross-section may be measured by analysis such as SEM or TEM.

[0075] The nano-silicon particles preferably have amorphous silicon. Also, the nano-silicon particles preferably have polycrystalline silicon. The nano-silicon particles preferably have amorphous silicon and polycrystalline silicon. Further, the nano-silicon particles may have a crystalline region and an amorphous region.

[0076] As a material having silicon, for example, SiO x (where x is preferably less than 2, more preferably 0.5 or more and 1.6 or less) can be used.

[0077] As a material having silicon, for example, a form having a plurality of crystal grains in one particle can be used. For example, a form having one or more silicon crystal grains in one particle can be used. Further, the one particle may have silicon oxide around the silicon crystal grains. Further, the silicon oxide may be amorphous. It may be a particle in which the graphene compound 583 is attached to the secondary particles of silicon.

[0078] Further, the compound having silicon is, for example, Li 2 SiO 3 and Li 4 SiO 4 can have. Li 2 SiO 3 and Li 4 SiO 4 may each have crystallinity or may be amorphous.

[0079] Analysis of the compound having silicon can be performed using NMR, XRD, Raman spectroscopy, SEM, TEM, EDX, etc.

[0080] The first active material 581 included in the negative electrode 570a preferably has graphite.

[0081] The first active material 581 is more preferably a material with a small volume change accompanying charge and discharge.

[0082] As the volume change of the first active material 581 accompanying charge or discharge, when the minimum volume in charge or discharge is 1, the maximum volume in charge or discharge is preferably 2 or less, more preferably 1.5 or less, and even more preferably 1.1 or less.

[0083] The particle size of the first active material 581 is preferably larger than that of the second active material 582.

[0084] For example, in laser diffraction particle size distribution measurement, the D50 of the first active material 581 is preferably 1.5 times or more and less than 1000 times that of the second active material 582, more preferably 2 times or more and 500 times or less, and even more preferably 10 times or more and 100 times or less. Here, D50 is the particle size when the integrated amount occupies 50% in the integrated particle amount curve of the particle size distribution measurement result, that is, the median. Note that the measurement of the particle size is not limited to laser diffraction particle size distribution measurement, and the diameter of the particle cross-section may be measured by analysis such as SEM or TEM.

[0085] Also, as the first active material 581, for example, carbon-based materials such as graphite, graphitizable carbon, non-graphitizable carbon, carbon nanotubes, carbon black, and graphene compound 583, which have a small volume change accompanying charge and discharge, can be used.

[0086] Also, as the first active material 581, for example, oxides having one or more elements selected from titanium, niobium, tungsten, and molybdenum can be used.

[0087] As the first active material 581, a plurality of the above-mentioned metals, materials, compounds, etc. can be used in combination.

[0088] As the first active material 581, for example, SnO, SnO 2 , titanium dioxide (TiO 2 ), lithium titanate (Li 4 Ti 5 O 12 ), lithium-graphite intercalation compound (Li x C 6 ), niobium pentoxide (Nb 2 O 5 ), tungsten oxide (WO 2 ), molybdenum oxide (MoO 2 ) and other oxides can be used.

[0089] Also, a material in which a conversion reaction occurs can be used as the first active material 581. For example, transition metal oxides that do not undergo an alloying reaction with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may be used as the first active material 581. As materials in which a conversion reaction occurs, further, Fe 2 O 3 , CuO, Cu 2 O, RuO 2 , Cr 2 O 3 and other oxides, CoS 0.89 , NiS, CuS and other sulfides, Zn 3 N 2 , Cu 3 N, Ge 3 N 4 and other nitrides, NiP 2 , FeP 2 , CoP 3 and other phosphides, FeF 3 , BiF 3 and other fluorides can be mentioned. Note that since the potential of the above fluorides is high, they may be used as a positive electrode material.

[0090] [Calculation 1 of negative electrode] Regarding the case where graphite is used as the first active material 581 and silicon is used as the second active material 582 for the negative electrode 570a of one aspect of the present invention, first-principles calculations were performed on the lithium diffusion coefficients in the first active material 581 and the second active material 582.

[0091] Figure 4A shows a model of the crystal structure used for the calculation of graphite (Li 0.25 C 6 ), and Figure 4B shows a model of the crystal structure used for the calculation of silicon (Li 1.25 Si).

[0092] The first-principles electronic state calculation package VASP was used for the calculation. Regarding the specific calculation conditions, the conditions shown in Table 1 were used.

[0093]

Table 1

[0094] Regarding the crystal structure models shown in FIGS. 4A and 4B, at each temperature, after the volume relaxation calculation, MD (molecular dynamics) calculation was performed under the condition of constant volume. The MD calculation was carried out in multiple steps, and the diffusion coefficient was derived from the relationship between the displacement amount of lithium and the elapsed time at each step.

[0095] The calculation results shown in FIGS. 4A, 4B, and Table 1 are shown in FIG. 5. As a result of the calculation, it was shown that the diffusion coefficient of lithium is higher in graphite than in silicon.

[0096] Also, regarding the relationship between the redox potentials of graphite and silicon, it is known that graphite is 0.05 V (vs. Li) and Si is 0.4 V (vs. Li). The redox potential is correlated with the voltage at which charging (lithium uptake) starts. Considering the priority of lithium insertion during charging, it is considered that lithium is preferentially taken into Si with a higher redox potential.

[0097] Combining and inferring these, the calculation results of the diffusion coefficient shown in FIG. 5 and the relationship of the redox potential, it is speculated that at the initial stage of charging, lithium is preferentially taken into silicon due to the difference in redox potential. However, as charging progresses, due to the difference in the lithium uptake rate, lithium uptake into graphite with a larger diffusion coefficient (higher uptake rate) may be gradually prioritized. Therefore, when capacity limitation is imposed on the negative electrode 570a of one aspect of the present invention, it is speculated that the graphite of the first active material 581 takes in lithium up to near the theoretical capacity of graphite, and the silicon of the second active material 582 takes in the excess lithium. That is, in the negative electrode 570a of one aspect of the present invention, when capacity limitation is imposed, the graphite of the first active material 581 is preferentially used for charge and discharge rather than the silicon of the second active material 582, and the effect of capacity limitation may mainly affect the silicon of the second active material 582.

[0098] [Calculation of Negative Electrode 2] FIG. 6A shows a lithium-free silicon crystal, and FIGS. 6B and 6C are diagrams showing the structure in a state where silicon is charged (state alloyed with Li).

[0099] FIG. 6B shows the structure at Li / Si = 1.714, and it can be seen that Si-Si bonds remain in the structure. On the other hand, in the crystal structure at Li / Si = 4.4, which is the limit value at the theoretical capacity shown in FIG. 6C, it can be seen that there are no Si-Si bonds in the structure because the Li ratio has increased. It is known that silicon undergoes crystal structure collapse, amorphization, and thinning during repeated charge and discharge. However, for example, in the fully charged state of a secondary battery, if the Si-Si bonds shown in FIG. 6B remain, it is highly likely that the structure will be maintained to some extent even after repeated charge and discharge. Preferably, when used at a lithium ratio (molar ratio) of Li / Si = 1.714 or less shown in FIG. 6B, it may exhibit good charge-discharge cycle characteristics.

[0100] [Capacity Limitation of Negative Electrode] The negative electrode 570a of one aspect of the present invention is preferably used as a secondary battery with a capacity less than the theoretical capacities of the first active material 581 and the second active material 582. As a capacity limitation of the negative electrode 570a, for example, when the capacity ratio is preferably 50% or more and less than 100%, more preferably 70% or more and less than 90% of the theoretical capacities of the first active material 581 and the second active material 582, a secondary battery with a high charge-discharge capacity and good charge-discharge cycle characteristics can be obtained, so it is preferable.

[0101] [Method for Producing Negative Electrode] FIG. 7 is a flowchart showing an example of a method for producing the negative electrode 570a of one aspect of the present invention.

[0102] First, in step S61, particles having silicon are prepared as the second active material 582. As the particles having silicon, for example, the particles described as the second active material 582 above can be used.

[0103] In step S62, a solvent is prepared. As the solvent, for example, any one or a mixture of two or more of water, methanol, ethanol, acetone, tetrahydrofuran (THF), dimethylformamide (DMF), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO) can be used.

[0104] Next, in step S63, the particles having silicon prepared in step S61 and the solvent prepared in step S62 are mixed, in step S64, the mixture is recovered, and in step S65, mixture E-1 is obtained. For the mixing, a kneader or the like can be used. As the kneader, for example, a planetary mixer or the like can be used.

[0105] Next, in step S72, as the first active material 581, particles having graphite are prepared. As the particles having graphite, for example, the particles described as the first active material 581 above can be used.

[0106] Next, in step S73, mixture E-1 and the particles having graphite prepared in step S72 are mixed, in step S74, the mixture is recovered, and in step S75, mixture E-2 is obtained. For the mixing, a kneader or the like can be used. As the kneader, for example, a planetary mixer or the like can be used.

[0107] Next, in step S80, a graphene compound 583 is prepared.

[0108] Next, in step S81, mixture E-2 and the graphene compound 583 prepared in step S80 are mixed, and in step S82, the mixture is recovered. It is preferable that the recovered mixture is in a high-viscosity state. Due to the high viscosity of the mixture, in the next step S83, solid kneading (kneading at high viscosity) can be performed.

[0109] Next, kneading is performed in step S83. The kneading can be performed using, for example, a spatula. By performing the kneading, a mixture with excellent dispersibility of the graphene compound 583 in which the particles having silicon and the graphene compound 583 are well mixed can be formed.

[0110] Next, in step S84, a solvent is added to the kneaded mixture and mixing is performed. For the mixing, for example, a kneader or the like can be used. The mixture obtained by the mixing is recovered in step S85.

[0111] It is preferable to repeat the steps of step S83 to step S85 n times for the mixture recovered in step S85. n is, for example, a natural number of 2 or more and 10 or less. Further, in the step of step S83, when the mixture is in a dry state, it is preferable to add a solvent. On the other hand, if too much solvent is added, the viscosity decreases and the effect of kneading decreases.

[0112] After repeating steps S83 to S85 n times, mixture E-3 is obtained (step S86).

[0113] Next, in step S87, a binder is prepared. As the binder, the materials described above can be used, and it is particularly preferable to use polyimide. In step S87, there may be a case where a precursor of the material used as the binder is prepared. For example, a precursor of polyimide is prepared.

[0114] Next, in step S88, mixture E-3 and the binder prepared in step S87 are mixed. Next, in step S89, the viscosity is adjusted. Specifically, for example, a solvent of the same type as the solvent prepared in step S62 is prepared and added to the mixture obtained in step S88. By adjusting the viscosity, for example, the thickness, density, etc. of the electrode obtained in step S97 may be adjusted.

[0115] Next, a solvent is added to the mixture whose viscosity was adjusted in step S89, mixed in step S90, recovered in step S91, to obtain mixture E-4 (step S92). The mixture E-4 obtained in step S92 is called, for example, a slurry.

[0116] Next, a current collector is prepared in step S93.

[0117] Next, in step S94, mixture E-4 is coated on the current collector prepared in step S93. For coating, a slot die method, gravure, blade method, and a method combining them, etc. can be used. Also, a continuous coater or the like may be used for coating.

[0118] Next, in step S95, first heating is performed. By the first heating, the solvent volatilizes. The first heating is preferably performed in a temperature range of 40°C or higher and 200°C or lower, more preferably 50°C or higher and 150°C or lower. Note that the first heating may be referred to as drying.

[0119] The first heating can be performed, for example, by heat treatment on a hot plate in an air atmosphere under conditions of 30°C or higher and 70°C or lower for 10 minutes or more, and then, for example, by heat treatment in a reduced pressure environment under conditions of room temperature or higher and 100°C or lower for 1 hour or more and 10 hours or less.

[0120] Alternatively, heat treatment may be performed using a drying oven or the like. When using a drying oven, for example, heat treatment may be performed at a temperature of 30°C or higher and 120°C or lower for 30 seconds or more and 2 hours or less.

[0121] Or the temperature may be increased stepwise. For example, after heat treatment at 60°C or lower for 10 minutes or less, heat treatment may be further performed at a temperature of 65°C or higher for 1 minute or more.

[0122] Next, in step S96, the second heating is performed. When polyimide is used as the binder, it is preferable that a cyclization addition reaction of the polyimide occurs due to the second heating. Further, a dehydration reaction of the polyimide may occur due to the second heating. Alternatively, a dehydration reaction of the polyimide may occur due to the first heating. Further, a cyclization reaction of the polyimide may occur during the first heating. Further, it is preferable that a reduction reaction of the graphene compound 583 occurs during the second heating. Note that the second heating may be referred to as imidization heat treatment, reduction heat treatment, or thermal reduction treatment.

[0123] Note that by performing a pressing process before the second heating, it is possible to increase the electrode density without degrading the battery characteristics. Therefore, it is preferable to perform a pressing process before step S96.

[0124] The second heating is preferably performed in a temperature range of 150°C or higher and 500°C or lower, more preferably 200°C or higher and 450°C or lower.

[0125] The second heating may be performed, for example, under a reduced pressure environment of 10 Pa or less, or in an inert atmosphere such as nitrogen or argon, under the conditions of 200°C or higher and 450°C or lower, and 1 hour or longer and 10 hours or shorter.

[0126] In step S97, a negative electrode 570a provided with an active material layer on a current collector is obtained.

[0127] The thickness of the thus formed active material layer is, for example, preferably 5 μm or more and 300 μm or less, more preferably 10 μm or more and 150 μm or less. Also, the active material loading amount of the active material layer is, for example, preferably 2 mg / cm 2 or more and 50 mg / cm 2 or less.

[0128] The active material layer may be formed on both sides of the current collector, or may be formed on only one side. Alternatively, it may partially have regions where the active material layer is formed on both sides.

[0129] After the solvent is volatilized from the active material layer, pressing may be performed by a compression method such as a roll press method or a flat press method. Heat may be applied during pressing.

[0130] [Positive electrode] The positive electrode 570b includes at least a positive electrode current collector 571b and a positive electrode active material layer 572b formed in contact with the positive electrode current collector 571b. Details of the positive electrode 570b will be described in the following embodiments.

[0131] [Conductive material] The conductive material, also called a conductivity-imparting agent or a conductive auxiliary agent, is a carbon material. By adhering a conductive agent between a plurality of active materials, the plurality of active materials are electrically connected to each other, enhancing conductivity. Note that the term "adhere" does not only refer to the physical close contact between the active material and the conductive agent, but also includes cases where a covalent bond is formed, cases where they are bonded by van der Waals forces, cases where a part of the surface of the active material is covered by the conductive agent, cases where the conductive agent fits into the surface irregularities of the active material, and cases where they are electrically connected even if they are not in contact with each other.

[0132] As the conductive material, for example, any one or two or more of carbon black such as acetylene black and furnace black, graphite such as artificial graphite and natural graphite, carbon fibers such as carbon nanofibers and carbon nanotubes, and graphene compound 583 can be used.

[0133] As the positive electrode 570b of the secondary battery, a binder (resin) is mixed to fix the positive electrode current collector 571b such as a metal foil and the active material. The binder is also called a binding agent. The binder is a polymer material. If a large amount of binder is included, the proportion of the active material in the positive electrode active material layer 572b decreases, and the discharge capacity of the secondary battery becomes small. Therefore, the amount of the binder is mixed to a minimum.

[0134] Since graphene has electrically, mechanically, or chemically amazing properties, it is a carbon material that is expected to be applied in various fields such as field-effect transistors and solar cells using graphene.

[0135] Also, carbon fibers can be used as conductive materials. For example, carbon fibers such as mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers can be used. Also, as carbon fibers, carbon nanofibers or carbon nanotubes etc. can be used. Carbon nanotubes can be produced by, for example, a vapor growth method.

[0136] [Graphene compound] In this specification etc., the graphene compound 583 includes graphene, multi-layer graphene, multi-graphene, graphene oxide, multi-layer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multi-layer graphene oxide, reduced multi-graphene oxide, graphene quantum dots, etc. The graphene compound 583 refers to something that has carbon, has a flat plate shape, sheet shape, etc., and has a two-dimensional structure formed by carbon six-membered rings. The two-dimensional structure formed by the carbon six-membered rings may be called a carbon sheet. The graphene compound 583 may have a functional group containing oxygen. Also, the graphene compound 583 preferably has a bent shape. Also, the graphene compound 583 may be rounded and be like a carbon nanofiber.

[0137] In this specification etc., graphene oxide refers to, for example, something that has carbon and oxygen, has a sheet shape, and has a functional group, particularly an epoxy group, carboxyl group, or hydroxy group.

[0138] As used in this specification and the like, reduced graphene oxide refers to, for example, a material that contains carbon and oxygen, has a sheet-like shape, and has a two-dimensional structure formed by carbon six-membered rings. It may also be referred to as a carbon sheet. Reduced graphene oxide can function alone, or multiple sheets may be stacked. Reduced graphene oxide preferably has a portion where the carbon concentration is greater than 80 atomic% and the oxygen concentration is 2 atomic% or more and 15 atomic% or less. By setting the carbon concentration and oxygen concentration in this way, it can function as a highly conductive material even in small amounts. Also, reduced graphene oxide preferably has an intensity ratio G / D of the G band and the D band in the Raman spectrum of 1 or more. Reduced graphene oxide with such an intensity ratio can function as a highly conductive material even in small amounts.

[0139] When reducing graphene oxide, pores may be formed in the reduced graphene oxide.

[0140] Also, as the graphene compound, a material in which the ends of graphene are terminated with fluorine may be used.

[0141] In the longitudinal section of the active material layer, sheet-like graphene compounds 583 are dispersed approximately uniformly in the internal region of the active material layer. Since the plurality of graphene compounds are formed so as to partially cover the plurality of granular active materials or adhere onto the surfaces of the plurality of granular active materials, they are in surface contact with each other.

[0142] Here, when the plurality of graphene compounds 583 are bonded to each other, a network-like graphene compound sheet (hereinafter referred to as a graphene compound net or a graphene net) can be formed. When the active material is covered with the graphene net, the graphene net can also function as a binder that binds the active materials together. Therefore, the amount of the binder can be reduced or it can be not used, so that the ratio of the active material in the electrode volume and the electrode weight can be improved. That is, the charge-discharge capacity of the secondary battery can be increased.

[0143] Here, it is preferable to use graphene oxide as the graphene compound 583, mix it with the active material to form a layer that becomes the active material layer, and then reduce the graphene oxide. That is, it is preferable that the completed active material layer has reduced graphene oxide. When forming the active material layer having the graphene compound 583, by using graphene oxide with extremely high dispersibility in a polar solvent, the graphene compound 583 can be dispersed substantially uniformly in the internal region of the active material layer.

[0144] In the active material layer produced by applying a dispersion liquid in which graphene oxide is substantially uniformly dispersed in a solvent onto a current collector, removing the solvent by volatilization, and then reducing the graphene oxide, the graphene compounds 583 possessed by the active material layer partially overlap. In this way, the reduced graphene oxide is dispersed to the extent of surface contact with each other, so that a three-dimensional conductive path can be formed. Note that the reduction of graphene oxide may be performed, for example, by heat treatment or by using a reducing agent.

[0145] Further, by covering the surface of the active material with a graphene compound in advance to form a conductive film on the surface of the active material, and further electrically connecting between the active materials with a graphene compound, a conductive path can also be formed.

[0146] The graphene compound 583 according to one aspect of the present invention preferably has pores in a part of the carbon sheet. In the graphene compound 583 according to one aspect of the present invention, by providing pores through which carrier ions such as lithium ions can pass in a part of the carbon sheet, insertion and desorption of carrier ions become easier on the surface of the active material covered with the graphene compound 583, and the rate characteristics of the secondary battery can be improved. The pores provided in a part of the carbon sheet may be called voids, defects, or gaps.

[0147] The graphene compound 583 according to one aspect of the present invention preferably has pores formed by a plurality of carbon atoms and one or more fluorine atoms. Further, the plurality of carbon atoms are preferably bonded in a cyclic manner, and one or more of the plurality of carbon atoms bonded in a cyclic manner are preferably terminated by the fluorine atoms. Fluorine has a high electronegativity and is likely to carry a negative charge. When a positively charged lithium ion approaches, an interaction occurs, the energy becomes stable, and the barrier energy for the lithium ion to pass through the pores can be lowered. Therefore, since the pores of the graphene compound 583 have fluorine, lithium ions can easily pass through even small pores, and a graphene compound 583 having excellent conductivity can be realized. Also, one or more of the plurality of carbon atoms bonded in a cyclic manner may be terminated by hydrogen.

[0148] Figures 8A and 8B show an example of the structure of the graphene compound 583 having pores. The graphene compound 583 having pores shown in Figures 8A and 8B is also referred to as graphene having pores or reduced graphene having pores.

[0149] The structure shown in Figure 8A has a 22-membered ring, and 8 of the carbons constituting the 22-membered ring are each terminated by hydrogen. Also, in the graphene compound 583, it can be said that two connected 6-membered rings are removed, and the carbons that were bonded to the removed 6-membered rings are terminated by hydrogen.

[0150] The structure shown in Figure 8B has a 22-membered ring, and among 8 of the carbons constituting the 22-membered ring, 6 carbons are terminated by hydrogen and 2 carbons are terminated by fluorine. Also, in the graphene compound 583, it can be said that two connected 6-membered rings are removed, and the carbons that were bonded to the removed 6-membered rings are terminated by hydrogen or fluorine.

[0151] Silicon terminated with a hydroxy group is considered to have a strong interaction with the graphene compound 583 having pores because a hydrogen bond is formed between the hydrogen of the hydroxy group on the silicon surface and the hydrogen atom or fluorine atom of the graphene compound 583.

[0152] Since the graphene compound 583 has fluorine in addition to hydrogen, in addition to the hydrogen bond between the oxygen atom of the hydroxy group and the hydrogen atom of the graphene compound 583, a hydrogen bond is also formed between the hydrogen atom of the hydroxy group and the fluorine atom of the graphene compound 583, and it is considered that the interaction between the particles having silicon and the graphene compound 583 becomes stronger and more stable.

[0153] When the graphene compound 583 has pores, for example, it may be possible to observe a spectrum based on the characteristics caused by the pores by Raman spectroscopic mapping measurement. Also, it may be possible to observe the bonds, functional groups, etc. constituting the pores by ToF-SIMS. Further, it may be possible to analyze the vicinity of the pores, the periphery of the pores, etc. by TEM observation.

[0154] [Binder] In this specification and the like, the binder refers to a polymer compound that is mixed only for binding an active material, a conductive material, etc. onto a current collector. For example, rubber materials such as polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, butadiene rubber, ethylene-propylene-diene copolymer, fluororubber, polystyrene, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, ethylene propylene diene polymer and other materials.

[0155] Since the lithium ion conductive polymer is a high molecular compound, it can be well mixed and used in the active material layer to bind the active material and the conductive material onto the current collector. Therefore, an electrode can be fabricated without using a binder. A binder is a material that does not contribute to the charge and discharge reaction. Therefore, the less the binder, the more materials that contribute to the charge and discharge such as the active material and the electrolyte can be increased. Therefore, a secondary battery with improved discharge capacity, cycle characteristics, etc. can be obtained.

[0156] In order to make the electrolyte 576 an electrolyte layer without or with very little organic solvent, it is preferably sufficiently dried. In this specification etc., when the weight change of the electrolyte layer when dried under reduced pressure at 90 °C for 1 hour is within 5%, it is considered to be sufficiently dried.

[0157] For the identification of materials such as the lithium ion conductive polymer, lithium salt, binder, and additive contained in the secondary battery, for example, nuclear magnetic resonance (NMR) can be used. Also, the analysis results of Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), time-of-flight secondary ion mass spectrometry (TOF-SIMS), gas chromatography mass spectrometry (GC / MS), pyrolysis gas chromatography mass spectrometry (Py-GC / MS), liquid chromatography mass spectrometry (LC / MS), etc. may be used as materials for judgment. It is preferable to suspend the active material layer in a solvent, separate the active material and other materials, and then subject them to analysis such as NMR.

[0158] Also, in each of the above configurations, a solid electrolyte material may be further included in the negative electrode 570a to improve the flame retardancy. It is preferable to use an oxide-based solid electrolyte as the solid electrolyte material.

[0159] Examples of the oxide-based solid electrolyte include LiPON, Li 2 O, Li 2 CO 3 、Li 2 MoO 4 、Li 3 PO 4 、Li 3 VO 4 、Li4 SiO 4 , LLT (La 2 / 3-x Li 3x TiO 3 ), LLZ (Li 7 La 3 Zr 2 O 12 ) and other lithium composite oxides and lithium oxide materials can be mentioned.

[0160] LLZ is a garnet-type oxide containing Li, La, and Zr, and may also be a compound containing Al, Ga, or Ta.

[0161] In addition, a polymer solid electrolyte such as PEO (polyethylene oxide) formed by a coating method or the like may be used. Since such a polymer solid electrolyte can also function as a binder, when using a polymer solid electrolyte, the components of the electrode can be reduced and the manufacturing cost can also be reduced.

[0162] [Current collector] As the positive electrode current collector 571b and the negative electrode current collector 571a, metals such as stainless steel, gold, platinum, zinc, iron, copper, aluminum, titanium, and alloys thereof, materials with high conductivity and that do not alloy with carrier ions such as lithium can be used. In addition, an aluminum alloy added with elements for improving heat resistance such as silicon, titanium, neodymium, scandium, molybdenum can be used. Also, it may be formed of a metal element that reacts with silicon to form a silicide. Examples of the metal element that reacts with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, etc. The current collector can appropriately use shapes such as sheet-like, net-like, punching metal-like, expanded metal-like. It is preferable to use a current collector with a thickness of 10 μm or more and 30 μm or less.

[0163] Note that it is preferable to use a material for the negative electrode current collector 571a that does not alloy with carrier ions such as lithium.

[0164] As a current collector, a titanium compound may be provided by laminating it on the above-described metal element. As the titanium compound, for example, titanium nitride, titanium oxide, titanium oxynitride (TiO x N y where 0 < x < 2 and 0 < y < 1), and one selected from titanium oxides in which a part of oxygen is substituted with nitrogen, or two or more of them may be mixed or laminated and used. Among them, titanium nitride is particularly preferable because it has high conductivity and a high function of suppressing oxidation. By providing the titanium compound on the surface of the current collector, for example, the reaction between the material of the active material layer formed on the current collector and the metal is suppressed. When the active material layer contains a compound having oxygen, the oxidation reaction between the metal element and oxygen can be suppressed. For example, when aluminum is used as the current collector and the active material layer is formed using graphene oxide described later, there is concern about the oxidation reaction between the oxygen of graphene oxide and aluminum. In such a case, by providing a titanium compound on aluminum, the oxidation reaction between the current collector and graphene oxide can be suppressed.

[0165] [Separator] A separator is disposed between the positive electrode 570b and the negative electrode 570a. As the separator, for example, those formed of fibers having cellulose such as paper, non-woven fabric, glass fiber, ceramics, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, polyurethane, etc. can be used. The separator is preferably processed into a bag shape and disposed so as to wrap either the positive electrode 570b or the negative electrode 570a.

[0166] The separator is a porous material having pores with a diameter of about 20 nm, preferably pores with a diameter of 6.5 nm or more, and more preferably pores with a diameter of at least 2 nm. In the case of the semi-solid secondary battery described above, the separator can also be omitted.

[0167] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic-based material, a fluorine-based material, a polyamide-based material, or a mixture thereof. As the ceramic-based material, for example, aluminum oxide particles, silicon oxide particles, etc. can be used. As the fluorine-based material, for example, PVDF, polytetrafluoroethylene, etc. can be used. As the polyamide-based material, for example, nylon, aramid (meta-aramid, para-aramid), etc. can be used.

[0168] Coating with a ceramic-based material improves oxidation resistance, suppresses deterioration of the separator during high-voltage charge and discharge, and can improve the reliability of the secondary battery. Also, coating with a fluorine-based material makes it easier for the separator and the electrode to adhere, and can improve the output characteristics. Coating with a polyamide-based material, especially aramid, improves heat resistance and can improve the safety of the secondary battery.

[0169] For example, a mixed material of aluminum oxide and aramid may be coated on both sides of a polypropylene film. Also, a mixed material of aluminum oxide and aramid may be coated on the surface of the polypropylene film that contacts the positive electrode 570b, and a fluorine-based material may be coated on the surface that contacts the negative electrode 570a.

[0170] Using a separator with a multilayer structure can maintain the safety of the secondary battery even if the overall thickness of the separator is thin, so the capacity per unit volume of the secondary battery can be increased.

[0171] [Electrolyte] When a liquid electrolyte 576 is used in a secondary battery, for example, as the electrolyte 576, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc., can be used alone, or two or more of these can be used in any combination and ratio.

[0172] Also, as the solvent of the electrolyte 576, by using one or more ionic liquids (room temperature molten salts) that are flame-retardant and have low volatility, even if the internal region temperature of the secondary battery rises due to internal region short circuit or overcharging, etc., rupture or ignition of the secondary battery can be prevented. An ionic liquid consists of a cation and an anion, and contains an organic cation and an anion. Examples of the organic cation include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of the anion include monovalent amide-based anions, monovalent methide-based anions, fluorosulfonic acid anions, perfluoroalkylsulfonic acid anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, or perfluoroalkylphosphate anions, etc.

[0173] In particular, in the secondary battery according to one aspect of the present invention, when silicon is used as the second active material 582 included in the negative electrode 570a, it is preferable to use a liquid electrolyte 576 containing an ionic liquid.

[0174] The secondary battery according to one aspect of the present invention has, for example, any one or two or more of alkali metal ions such as lithium ions, sodium ions, and potassium ions, and alkaline earth metal ions such as calcium ions, strontium ions, barium ions, beryllium ions, and magnesium ions as carrier ions.

[0175] When using lithium ions as carrier ions, for example, the electrolyte contains a lithium salt. As the lithium salt, for example, LiPF 6 、LiClO 4 、LiAsF 6 、LiBF 4 、LiAlCl 4 、LiSCN、LiBr、LiI、Li 2 SO 4 、Li 2 B 10 Cl 10 、Li 2 B 12 Cl 12 、LiCF 3 SO 3 、LiC 4 F 9 SO 3 、LiC(CF 3 SO 2 ) 3 、LiC(C 2 F 5 SO 2 ) 3 、LiN(CF 3 SO 2 ) 2 、LiN(C 4 F 9 SO 2 )(CF 3 SO 2 )、LiN(C 2 F 5 SO 2 ) 2 etc. can be used.

[0176] Furthermore, the electrolyte preferably contains fluorine. As the electrolyte containing fluorine, for example, an electrolyte having one or more kinds of fluorinated cyclic carbonates and lithium ions can be used. The fluorinated cyclic carbonate can improve the nonflammability and enhance the safety of the lithium ion secondary battery.

[0177] As the fluorinated cyclic carbonate, ethylene carbonate fluoride, for example, monofluoroethylene carbonate (fluoroethylene carbonate, FEC, F1EC), difluoroethylene carbonate (DFEC, F2EC), trifluoroethylene carbonate (F3EC), tetrafluoroethylene carbonate (F4EC), etc. can be used. Note that DFEC has isomers such as cis-4,5 and trans-4,5. As the electrolyte, it is important for operating at low temperature to solvate lithium ions using one or more kinds of fluorinated cyclic carbonates and transport them in the electrolyte contained in the electrode during charge and discharge. When the fluorinated cyclic carbonate contributes to the transport of lithium ions during charge and discharge instead of being a small amount of additive, operation at low temperature becomes possible. In the secondary battery, lithium ions move in lumps of several or more up to about several tens.

[0178] By using a fluorinated cyclic carbonate as an electrolyte, the energy required for desolvation when solvated lithium ions in the electrolyte contained in the electrode enter the active material particles is reduced. If this desolvation energy can be reduced, lithium ions can be more easily inserted into or desorbed from the active material particles even in the low temperature range. Although lithium ions may move while remaining in a solvated state, a hopping phenomenon may occur in which the coordinating solvent molecules are replaced. When lithium ions are more easily desolvated, movement due to the hopping phenomenon becomes easier, and in some cases, the movement of lithium ions becomes easier. There is a concern that the degradation of the secondary battery may occur due to the decomposition products of the electrolyte adhering to the surface of the active material during the charge and discharge of the secondary battery. However, when the electrolyte contains fluorine, the electrolyte is slippery, and the decomposition products of the electrolyte are less likely to adhere to the surface of the active material. Therefore, the degradation of the secondary battery can be suppressed.

[0179] Multiple solvated lithium ions may form clusters in the electrolyte and move within the negative electrode 570a, between the positive electrode 570b and the negative electrode 570a, within the positive electrode 570b, and so on.

[0180] In this specification, an electrolyte is a general term including solid, liquid, or semi-solid materials and the like.

[0181] Interfaces existing in a secondary battery, such as the interface between an active material and an electrolyte, are prone to deterioration. In the secondary battery according to one aspect of the present invention, by having an electrolyte containing fluorine, it is possible to prevent deterioration that may occur at the interface between the active material and the electrolyte, typically the alteration of the electrolyte or the increase in the viscosity of the electrolyte. Further, a binder or a graphene compound may be wrapped around or held with respect to the electrolyte containing fluorine. By adopting such a configuration, it is possible to maintain a state where the viscosity of the electrolyte is reduced, in other words, a state where the electrolyte is smooth, and the reliability of the secondary battery can be improved. DFEC in which two fluorines are bonded and F4EC in which four fluorines are bonded have lower viscosities, are smoother, and have weaker coordination bonds with lithium compared to FEC in which one fluorine is bonded. Therefore, it is possible to reduce the adhesion of decomposition products with high viscosity to the active material particles. When decomposition products with high viscosity adhere to or wrap around the active material particles, it becomes difficult for lithium ions to move at the interface of the active material particles. The electrolyte containing fluorine alleviates the formation of decomposition products formed on the surface of the active material (positive electrode active material or negative electrode active material) by solvation. Further, by using an electrolyte containing fluorine, it is possible to prevent the generation and growth of dendrites by preventing the adhesion of decomposition products.

[0182] Another feature is to use an electrolyte containing fluorine as a main component, and the electrolyte containing fluorine is 5% by volume or more, 10% by volume or more, preferably 30% by volume or more and 100% by volume or less.

[0183] In this specification, the main component of the electrolyte means that it is 5% by volume or more of the entire electrolyte of the secondary battery. Further, 5% by volume or more of the entire electrolyte of the secondary battery here refers to the ratio occupied by the entire electrolyte measured during the manufacture of the secondary battery. Further, when disassembling the secondary battery after fabrication, it is difficult to quantify the ratio of each of the plurality of types of electrolytes, but it is possible to determine whether a certain type of organic compound is 5% by volume or more of the entire electrolyte.

[0184] By using an electrolyte containing fluorine, a secondary battery that can operate within a wide temperature range, specifically from -40°C to 150°C, preferably from -40°C to 85°C, can be realized.

[0185] In addition, additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), lithium bis(oxalate) borate (LiBOB), and dinitrile compounds such as succinonitrile and adiponitrile may be added to the electrolyte. The concentration of the additive may be, for example, 0.1% by volume or more and less than 5% by volume based on the entire electrolyte.

[0186] In addition to the above, the electrolyte may have one or more aprotic organic solvents such as γ-butyrolactone, acetonitrile, dimethoxyethane, and tetrahydrofuran.

[0187] Moreover, by having a polymer material that gels the electrolyte, the safety against leakage and the like is enhanced. Representative examples of the polymer material that gels include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide-based gel, polypropylene oxide-based gel, and gels of fluorine-based polymers.

[0188] As the polymer material, for example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing them can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. In addition, the formed polymer may have a porous shape.

[0189] In addition, although the above configuration shows an example of a secondary battery using a liquid electrolyte, it is not particularly limited. For example, semi-solid batteries and all-solid batteries can also be fabricated.

[0190] In the case of a secondary battery using a liquid electrolyte or a semi-solid battery in this specification and the like, the layer disposed between the positive electrode 570b and the negative electrode 570a shall be referred to as an electrolyte layer. The electrolyte layer of the semi-solid battery can be said to be a layer formed by film formation and can be distinguished from the liquid electrolyte layer.

[0191] In this specification and the like, a semi-solid battery refers to a battery having a semi-solid material in at least one of the electrolyte layer, the positive electrode 570b, and the negative electrode 570a. The semi-solid here does not mean that the ratio of the solid material is 50%. The semi-solid means having some properties close to those of a liquid such as flexibility while having properties of a solid such as small volume change. As long as these properties are satisfied, it may be a single material or a plurality of materials. For example, it may be a liquid material infiltrated into a porous solid material.

[0192] In this specification and the like, a polymer electrolyte secondary battery refers to a secondary battery having a polymer in the electrolyte layer between the positive electrode 570b and the negative electrode 570a. The polymer electrolyte secondary battery includes a dry (or true) polymer electrolyte battery and a polymer gel electrolyte battery.

[0193] The electrolyte 576 has a lithium ion conductive polymer and a lithium salt.

[0194] In this specification and the like, a lithium ion conductive polymer is a polymer having conductivity of cations such as lithium. More specifically, it is a polymer compound having a polar group capable of coordinating cations. As the polar group, it is preferably having an ether group, an ester group, a nitrile group, a carbonyl group, a siloxane, or the like.

[0195] As the lithium ion conductive polymer, for example, polyethylene oxide (PEO), a derivative having polyethylene oxide as the main chain, polypropylene oxide, polyacrylate ester, polymethacrylate ester, polysiloxane, polyphosphazene, or the like can be used.

[0196] The lithium ion conductive polymer may be branched or crosslinked. It may also be a copolymer. The molecular weight is preferably, for example, 10,000 or more, and more preferably 100,000 or more.

[0197] The lithium ion conductive polymer allows lithium ions to move while changing the polar groups that interact through the segmental motion (also referred to as segment motion) of the polymer chain. For example, in the case of PEO, lithium ions move while changing the oxygen that interacts through the segmental motion of the ether chain. When the temperature is close to or higher than the melting point or softening point of the lithium ion conductive polymer, the crystalline region dissolves and the amorphous region increases, and the motion of the ether chain becomes active, so the ionic conductivity increases. Therefore, when using PEO as the lithium ion conductive polymer, it is preferable to perform charge and discharge at 60 °C or higher.

[0198] According to the Shannon ionic radius (Shannon et al., Acta A 32 (1976) 751.), the radius of the monovalent lithium ion is 0.0590 nm in the case of 4 coordination, 0.076 nm in the case of 6 coordination, and 0.092 nm in the case of 8 coordination. The radius of the divalent oxygen ion is 0.135 nm in the case of 2 coordination, 0.136 nm in the case of 3 coordination, 0.138 nm in the case of 4 coordination, 0.140 nm in the case of 6 coordination, and 0.142 nm in the case of 8 coordination. The distance between the polar groups of adjacent lithium ion conductive polymer chains is preferably not less than the distance at which lithium ions and the anions of the polar groups can stably exist while maintaining the ionic radius as described above. And it is preferably a distance at which sufficient interaction occurs between the lithium ion and the polar group. However, as described above, since segmental motion occurs, it is not always necessary to maintain a constant distance. It is sufficient that the distance is appropriate when the lithium ions pass through.

[0199] As the lithium salt, for example, a compound having at least one of phosphorus, fluorine, nitrogen, sulfur, oxygen, chlorine, arsenic, boron, aluminum, bromine, and iodine together with lithium can be used. For example, LiPF 6, LiN(FSO 2 ) 2 (lithium bis(fluorosulfonyl)imide, LiFSI), LiClO 4 , LiAsF 6 , LiBF 4 , LiAlCl 4 , LiSCN, LiBr, LiI, Li 2 SO 4 , Li 2 B 10 Cl 10 , Li 2 B 12 Cl 12 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiC(CF 3 SO 2 ) 3 , LiC(C 2 F 5 SO 2 ) 3 , LiN(CF 3 SO 2 ) 2 (lithium bis(trifluoromethanesulfonyl)imide, LiTFSA), LiN(C 4 F 9 SO 2 )(CF 3 SO 2 ), LiN(C 2 F 5 SO 2 ) 2 , lithium salts such as lithium bis(oxalate) borate (LiBOB) can be used singly or in any combination and ratio of two or more of these.

[0200] In particular, when using LiFSI, the low-temperature characteristics are good, which is preferable. Also, LiFSI and LiTFSA are LiPF 6It is less likely to react with water compared to the like. Therefore, it becomes easier to control the dew point when fabricating an electrode and an electrolyte layer using LiFSI. For example, it can be handled not only in an inert atmosphere such as argon from which moisture has been excluded as much as possible and a dry room with controlled dew point, but also in a normal atmospheric atmosphere. Therefore, it is preferable as productivity is improved. Also, it is particularly preferable to use a highly dissociative and plasticizing Li salt such as LiFSI and LiTFSA because it can be used in a wide temperature range when using lithium conduction utilizing the segmental motion of the ether chain segment.

[0201] By having no or very little organic solvent, a secondary battery that is less likely to catch fire or ignite can be obtained, and the safety is improved, which is preferable.

[0202] [Outer package] As the outer package of the secondary battery, for example, a metal material such as aluminum and a resin material can be used. Also, a film-shaped outer package can be used. As the film, for example, a metal thin film excellent in flexibility such as aluminum, stainless steel, copper, nickel, etc. is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc., and further an insulating synthetic resin film such as a polyamide-based resin or a polyester-based resin is provided as the outer surface of the outer package on the metal thin film. A three-layer structure film can be used. Also, it is preferable to use a fluororesin film as the film. The fluororesin film has high stability against acids, alkalis, organic solvents, etc., suppresses side reactions, corrosion, etc. associated with the reaction of the secondary battery, etc., and an excellent secondary battery can be realized. Examples of the fluororesin film include PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxyalkane: copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether), FEP (perfluoroethylene propylene copolymer: copolymer of tetrafluoroethylene and hexafluoropropylene), ETFE (ethylene tetrafluoroethylene copolymer: copolymer of tetrafluoroethylene and ethylene), etc.

[0203] This embodiment can be used in appropriate combination with other embodiments.

[0204] (Embodiment 2) In this embodiment, the positive electrode and the positive electrode active material composite of one aspect of the present invention will be described.

[0205] An example of the positive electrode 570b of one aspect of the present invention is shown in FIG. 9. The positive electrode 570b has a positive electrode current collector 571b and a positive electrode active material layer 572b. The positive electrode active material layer 572b has a positive electrode active material composite 100z. As the positive electrode active material composite 100z, for example, as shown in FIGS. 10A1 and 10A2, it has a first active material 100x and a second active material 100y capable of occluding and releasing carrier ions. In FIG. 9, an example using a graphene compound 102 and carbon black 103 as the conductive material is shown. However, when the positive electrode active material composite 100z has sufficient electron conductivity, the conductive material may not be used in the positive electrode active material layer 572b. Also, the type of the conductive material is not limited to the example shown in FIG. 9, and only carbon fibers such as a graphene compound, carbon black, or carbon nanotubes may be used, or carbon fibers such as carbon nanotubes and carbon black may be used in combination. Although not shown in FIG. 9, the positive electrode active material layer 572b preferably has a binder. As the binder, a polymer material such as polyvinylidene fluoride and Li(FSI)(SN) 2 and other molecular crystal electrolytes can be used.

[0206] Further, the positive electrode active material composite 100z is arranged in a state capable of exchanging electrons with the positive electrode current collector 571b. That is, the positive electrode active material composite 100z has a configuration in electrical contact with the positive electrode current collector 571b. An undercoat layer may be provided on the positive electrode current collector 571b. In this case, the positive electrode active material composite 100z has a configuration in electrical contact with the positive electrode current collector 571b through the undercoat layer. Also, the positive electrode active material composite 100z may have a configuration in electrical contact with the positive electrode current collector 571b through a conductive material.

[0207] Note that the density of the positive electrode active material layer 572b is preferably 3.0 g / cm3 More preferably, it is 3.5 g / cm 3 or more, still more preferably 3.8 g / cm 3 or more. Therefore, in order to increase the density of the positive electrode active material layer 572b, pressing treatment may be performed. However, when performing the pressing treatment, it is desirable to appropriately set the conditions of the pressing treatment so as not to damage the structures of the first active material 100x and the positive electrode active material composite 100z described later.

[0208] [Positive Electrode Active Material Composite] Figs. 10A1 to 10C2 are schematic cross-sectional views for explaining the positive electrode active material composite 100z.

[0209] Figs. 10A1 and 10A2 are diagrams for explaining the positive electrode active material composite 100z having the first active material 100x that functions as a positive electrode active material and the second active material 100y that covers at least a part of the first active material 100x. In Fig. 10A1, a configuration in which one first active material 100x is covered with the second active material 100y is shown, but the present invention is not limited thereto, and a configuration in which a plurality of first active materials 100x are covered with the second active material 100y may be employed.

[0210] For example, as shown in FIG. 10A2, at least a part of the first active material 100xa and the first active material 100xb may be configured to be covered by the second active material 100y. In FIG. 10A2, a case where at least a part of the first active material 100xa and the first active material 100xb are in contact is shown, but the first active material 100xa and the first active material 100xb may not be in direct contact. When at least a part, preferably substantially the whole, of the particle surface of the particulate first active material 100x that functions as a positive electrode active material is covered by the second active material 100y, the region where the first active material 100x is in direct contact with the electrolyte 576 decreases, and at a high voltage charging state, the desorption of the transition metal element and / or oxygen from the first active material 100x can be suppressed, so that the capacity degradation due to repeated charge and discharge can be suppressed. Further, by being covered with the second active material 100y that is electrochemically stable even at a high temperature and a high voltage charging state, the secondary battery using the positive electrode active material composite 100z of one aspect of the present invention can obtain effects such as improved stability at a high temperature and improved fire resistance.

[0211] FIGS. 10B1 and 10B2 are diagrams for explaining a positive electrode active material composite 100z having a first active material 100x that functions as a positive electrode active material and a glass 101 that covers at least a part of the first active material 100x. In FIG. 10B1, a configuration in which one first active material 100x is covered by the glass 101 is shown, but the present invention is not limited thereto, and a configuration in which a plurality of first active materials 100x are covered by the glass 101 may be employed.

[0212] For example, as shown in FIG. 10B2, at least a part of the first active material 100xa and the first active material 100xb may be covered with glass 101. In FIG. 10B2, a case where at least a part of the first active material 100xa and the first active material 100xb are in contact is shown, but the first active material 100xa and the first active material 100xb may not be in direct contact. When at least a part, preferably substantially the whole, of the particle surface of the particulate first active material 100x that functions as a positive electrode active material is covered with glass 101, the region where the first active material 100x is in direct contact with the electrolyte 576 decreases, and at a high voltage charging state, the desorption of transition metal elements and / or oxygen from the first active material 100x can be suppressed, so that the capacity degradation due to repeated charge and discharge can be suppressed. Further, by being covered with the electrochemically stable glass 101 even at a high temperature and a high voltage charging state, the secondary battery using the positive electrode active material composite 100z of one aspect of the present invention can obtain effects such as improved stability at a high temperature and improved fire resistance.

[0213] FIGS. 10C1 and 10C2 are diagrams for explaining a positive electrode active material composite 100z having a first active material 100x that functions as a positive electrode active material and a second active material 100y that is in contact with the first active material 100x via glass 101 that covers at least a part of the first active material 100x. In FIG. 10C1, a configuration in which one first active material 100x is covered with glass 101 is shown, but the present invention is not limited thereto, and a configuration in which a plurality of first active materials 100x are covered with glass 101 may be used.

[0214] For example, as shown in FIG. 10C2, at least a part of the first active material 100xa and the first active material 100xb may be covered with glass 101. In FIG. 10C2, a case where at least a part of the first active material 100xa and the first active material 100xb are in contact is shown, but the first active material 100xa and the first active material 100xb may not be in direct contact. In a positive electrode active material composite 100z having a second active material 100y that is in contact with the first active material 100x via glass 101 in a state where at least a part, preferably substantially the whole, of the particle surface of the particulate first active material 100x that functions as a positive electrode active material is covered with glass 101, the region where the first active material 100x is in direct contact with the electrolyte 576 is reduced, and desorption of transition metal elements and / or oxygen from the first active material 100x can be suppressed in a high voltage charged state, so that a decrease in capacity due to repeated charge and discharge can be suppressed. Further, by being covered with the electrochemically stable glass 101 even in a high temperature and high voltage state and the second active material 100y that is stable even in a high charge voltage state, a secondary battery using the positive electrode active material composite 100z of one aspect of the present invention can obtain effects such as improved stability at high temperature and improved fire resistance.

[0215] In the positive electrode active material composite 100z shown in FIGS. 10A1 to 10C2, as the first active material 100x, lithium cobaltate having magnesium and fluorine, lithium cobaltate having magnesium, fluorine, aluminum, and nickel, and nickel-cobalt-manganese lithium oxide having a molar ratio such as nickel:cobalt:manganese = 8:1:1 and nickel:cobalt:manganese = 9:0.5:0.5, etc., materials excellent in stability in a high voltage charged state are used, whereby the durability and stability of the above-described positive electrode active material composite 100z in high voltage charging can be further improved. Further, the heat resistance and / or fire resistance of a secondary battery using the above-described positive electrode active material composite 100z can be further improved.

[0216] Lithium cobaltate having magnesium, fluorine, aluminum, and nickel has a characteristic that it has a large amount of magnesium, fluorine, or aluminum in the surface layer portion of the positive electrode active material, and nickel is widely distributed throughout the particles, and the charge-discharge cycle characteristics at high voltage are remarkably excellent. Therefore, it is a particularly preferable material as the first active material 100x. When the surface layer portion of the positive electrode active material has a large amount of magnesium, fluorine, or aluminum, for example, in the line analysis of STEM-EDX, the characteristic X-ray count number derived from magnesium, fluorine, or aluminum has a location where the maximum value is obtained in the surface layer portion. Here, the surface layer portion refers to a region up to about 10 nm from the surface of the positive electrode active material. Note that the crack portion of the positive electrode active material also has a surface layer portion, and the crack portion generated before the addition step of magnesium, fluorine, or aluminum in the production of the positive electrode active material has a surface layer portion having a large amount of magnesium, fluorine, or aluminum.

[0217] The positive electrode active material composite 100z as shown in FIGS. 10A1 and 10A2 is obtained by a composite treatment using at least the first active material 100x and the second active material 100y. As the composite treatment, for example, a composite treatment by mechanical energy such as a mechanochemical method, a mechanofusion method, and a ball mill method, a composite treatment by a liquid phase reaction such as a coprecipitation method, a hydrothermal method, and a sol-gel method, and a composite treatment by a gas phase reaction such as a barrel sputtering method, an ALD (Atomic Layer Deposition) method, a vapor deposition method, and a CVD (Chemical Vapor Deposition) method, any one or more of these composite treatments can be used. Further, in the composite treatment, it is preferable to perform heat treatment one or more times. Note that in this specification, the composite treatment may be referred to as a surface coating treatment or a coating treatment.

[0218] In addition, the positive electrode active material composite 100z as shown in FIGS. 10B1 and 10B2 is obtained by a composite treatment using at least the first active material 100x and glass 101. As the composite treatment, for example, a composite treatment by mechanical energy such as a mechanochemical method, a mechanofusion method, and a ball milling method, a composite treatment by a liquid phase reaction such as a coprecipitation method, a hydrothermal method, and a sol-gel method, and a composite treatment by a gas phase reaction such as a barrel sputtering method, an ALD method, a vapor deposition method, and a CVD method, any one or more of these composite treatments can be used. Further, in the composite treatment, it is preferable to perform heat treatment once or a plurality of times.

[0219] In addition, the positive electrode active material composite 100z as shown in FIGS. 10C1 and 10C2 is obtained by a composite treatment using at least the first active material 100x, the second active material 100y, and glass 101. As the composite treatment, for example, a composite treatment by mechanical energy such as a mechanochemical method, a mechanofusion method, and a ball milling method, a composite treatment by a liquid phase reaction such as a coprecipitation method, a hydrothermal method, and a sol-gel method, and a composite treatment by a gas phase reaction such as a barrel sputtering method, an ALD method, a vapor deposition method, and a CVD method, any one or more of these composite treatments can be used. Further, in the composite treatment, it is preferable to perform heat treatment once or a plurality of times.

[0220] As described above, in the positive electrode active material composite 100z according to one embodiment of the present invention, since the first active material 100x and the electrolyte 576 do not contact each other, deterioration of the first active material 100x caused by the electrolyte is suppressed. Such deterioration may be caused by defects occurring in the first active material 100x. For example, there are defects called pits. A pit refers to a region in which several layers of the main components of the first active material 100x, such as cobalt and oxygen, are missing in a charge-discharge cycle test. For example, cobalt may be eluted into the electrolyte. Pits may progress in a charge-discharge cycle test, and the pits may progress in the direction of the inside of the active material. Note that the opening shape of the pit is not circular but has a shape like a groove with depth. By adopting a configuration in which the electrolyte 576 and the first active material 100x do not contact each other, generation and progression of the above-described defects, particularly pits, can be suppressed.

[0221] When the positive electrode active material composite 100z has a second active material 100y that contacts the first active material 100x via the glass 101, it can be said that the positive electrode active material composite 100z has a double structure in the surface layer portion. However, the positive electrode active material composite 100z according to one embodiment of the present invention is not limited to the case where the glass 101 and the second active material 100y have a double structure. As another example of the positive electrode active material composite 100z according to one embodiment of the present invention, a glass active material mixed layer having the glass 101 and the second active material 100y may have a structure that covers at least a part of the surface of the first active material 100x.

[0222] Further, as the positive electrode active material composite 100z according to one embodiment of the present invention, the graphene compound 102 may be included in the surface layer portion or the glass active material mixed layer of the positive electrode active material composite 100z. Here, instead of the graphene compound 102, carbon fibers such as carbon black or carbon nanotubes may be used.

[0223] As the glass 101, a material having an amorphous portion can be used. Examples of the material having an amorphous portion include SiO 2 , SiO, Al 2 O 3 , TiO 2 , Li 4 SiO4 , Li 3 PO 4 , Li 2 S, SiS 2 , B 2 S 3 , GeS 4 , AgI, Ag 2 , O, Li 2 , O, P 2 O 5 , B 2 O 3 , and V 2 O 5 A material having one or more selected from the like, Li 7 P 3 S 11 , or Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 < x < 2, 0 < y < 3, etc.) can be used. The material having an amorphous part can be used in an entirely amorphous state or in a state of a crystallized glass (also called glass ceramics) in which a part is crystallized. It is desirable that the glass 101 has lithium ion conductivity. Lithium ion conductivity can also be said to have lithium ion diffusivity and lithium ion penetrability. Further, the glass 101 preferably has a melting point of 800°C or lower, more preferably 500°C or lower. Further, it is preferable that the glass 101 has electronic conductivity. Further, the glass 101 preferably has a softening point of 800°C or lower. For example, Li 2 O - B 2 O 3 -SiO 2 -based glass can be used.

[0224] Although it is desirable that the glass 101 has electronic conductivity, when the electronic conductivity of the glass 101 is low, a carbon fiber conductive material such as a graphene compound, carbon black, or carbon nanotube can be mixed with the glass 101 to impart electronic conductivity to the glass 101.

[0225] In addition, at least a part of the surface of the positive electrode active material composite 100z may have a structure covered with a graphene compound. Preferably, a structure in which 80% or more of the particle surface of the positive electrode active material composite 100z and / or the aggregate having the positive electrode active material composite 100z is covered with a graphene compound is preferred. The graphene compound will be described later.

[0226] Further, the positive electrode active material composite 100z preferably has a structure covered with a molecular crystal electrolyte. The molecular crystal electrolyte can function as a binder for the positive electrode active material layer 572b. The molecular crystal electrolyte is preferably a material having high ionic conductivity, and the positive electrode active material composite 100z covered with the molecular crystal electrolyte can exchange carrier ions with the electrolyte 576.

[0227] [Positive Electrode Active Material] As the first active material 100x, a composite oxide represented by LiM1O having a layered rock salt type crystal structure 2 (M1 is one or more selected from Fe, Ni, Co, Mn) can be used. Further, as the first active material 100x, LiM1O 2It is possible to use a composite oxide represented by to which an additive element X is added. As the additive element X contained in the first active material 100x, it is preferable to use one or more selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. These elements may stabilize the crystal structure of the first active material 100x. That is, the first active material 100x may include lithium cobaltate having magnesium and fluorine, lithium cobaltate having magnesium, fluorine, aluminum, and nickel, lithium cobaltate having magnesium, fluorine, and titanium, lithium nickel-cobaltate having magnesium and fluorine, lithium cobalt-aluminate having magnesium and fluorine, lithium nickel-cobalt-aluminate, lithium nickel-cobalt-aluminate having magnesium and fluorine, lithium nickel-cobalt-manganate having magnesium and fluorine, and the like. In addition, as the transition metal ratio of lithium nickel-cobalt-manganate, a high nickel ratio is preferable. For example, materials having a molar ratio of nickel:cobalt:manganese = 8:1:1 or nickel:cobalt:manganese = 9:0.5:0.5 are preferable. Further, as the above lithium nickel-cobalt-manganate, it is preferable to have lithium nickel-cobalt-manganate having calcium.

[0228] Further, as the first active material 100x, secondary particles of a composite oxide represented by LiM1O 2 (where M1 is one or more selected from Fe, Ni, Co, and Mn) coated with a metal oxide may be used. As the metal oxide, oxides of one or more metals selected from Al, Ti, Nb, Zr, La, and Li can be used. For example, LiM1O 2(M1 is one or more selected from Fe, Ni, Co, and Mn) The secondary particles of the composite oxide represented by can be used as the first active material 100x with the metal oxide-coated composite oxide coated with aluminum oxide. For example, nickel: cobalt: manganese = 8:1:1, nickel: cobalt: manganese = 9:0.5:0.5 molar ratio of lithium nickel-cobalt-manganese composite oxide secondary particles can be used with the metal oxide-coated composite oxide coated with aluminum oxide. Here, the coating layer is preferably thin, for example, 1 nm or more and 200 nm or less, more preferably 1 nm or more and 100 nm or less. Further, as the above lithium nickel-cobalt-manganese composite oxide, it is preferable to have lithium nickel-cobalt-manganese composite oxide having calcium.

[0229] As the first active material 100x, the positive electrode active material 100 described in the following embodiments can be used.

[0230] As the second active material 100y, oxides and LiM2PO having an olivine-type crystal structure 4 (M2 is one or more selected from Fe, Ni, Co, and Mn) One or more of them can be used. Examples of the oxide include aluminum oxide, zirconium oxide, hafnium oxide, and niobium oxide. Further, LiM2PO 4 Examples of include LiFePO 4 , LiNiPO 4 , LiCoPO 4 , LiMnPO 4 , LiFe a Ni b PO 4 , LiFe a Co b PO 4 , LiFe a Mn b PO 4 , LiNi a Co b PO 4 , LiNi a Mn b PO 4 (a + b is 1 or less, 0 < a < 1, 0 < b < 1), LiFe c Nid Co e PO 4 、LiFe c Ni d Mn e PO 4 、LiNi c Co d Mn e PO 4 (c + d + e is 1 or less, 0 < c < 1, 0 < d < 1, 0 < e < 1), LiFe f Ni g Co h Mn i PO 4 (f + g + h + i is 1 or less, 0 < f < 1, 0 < g < 1, 0 < h < 1, 0 < i < 1), etc. Also, the particle surface of the second active material 100y may have a carbon coating layer.

[0231] As the conductive material, for example, any one or two or more of carbon black such as acetylene black and furnace black, graphite such as artificial graphite and natural graphite, carbon fibers such as carbon nanofibers and carbon nanotubes, and graphene compounds can be used.

[0232] This embodiment can be used in appropriate combination with other embodiments.

[0233] (Embodiment 3) In this embodiment, an anode active material of one aspect of the present invention will be described with reference to FIGS. 11 to 17.

[0234] In addition, in this specification and the like, crystal planes and directions are indicated by Miller indices. In crystallography, the notation for crystal planes and directions has a bar above the numbers, but in this specification and the like, due to the constraints of the application notation, instead of putting a bar above the numbers, a -(minus sign) may be attached before the numbers for expression. Also, individual orientations indicating directions within a crystal are represented by [], collective orientations indicating all equivalent directions are represented by <>, individual planes indicating crystal planes are represented by (), and collective planes having equivalent symmetries are represented by {}. In addition, for the Miller indices of trigonal and hexagonal crystals including R-3m, (hkil) may be used in addition to (hkl). Here, i is -(h + k).

[0235] In addition, in this specification and the like, the layered rock salt-type crystal structure of the composite oxide containing lithium and transition metals refers to a crystal structure having a rock salt-type ion arrangement in which cations and anions are alternately arranged, and in which transition metals and lithium are regularly arranged to form a two-dimensional plane, so that two-dimensional diffusion of lithium is possible. Note that there may be defects such as deficiencies of cations or anions. Also, strictly speaking, the layered rock salt-type crystal structure may be a structure in which the lattice of the rock salt-type crystal is distorted.

[0236] In addition, in this specification and the like, the rock salt-type crystal structure refers to a structure in which cations and anions are alternately arranged. Note that there may be deficiencies of cations or anions in a part of the crystal structure.

[0237] In addition, in this specification and the like, the theoretical capacity of the positive electrode active material refers to the amount of electricity when all the insertable and removable lithium in the positive electrode active material has been removed. For example, the theoretical capacity of LiFePO 4 is 170 mAh / g, the theoretical capacity of LiCoO 2 is 274 mAh / g, the theoretical capacity of LiNiO 2 is 275 mAh / g, and the theoretical capacity of LiMn 2 O 4 is 148 mAh / g.

[0238] Also, the degree to which insertable and removable lithium remains in the positive electrode active material is represented by x in the composition formula. For example, Li x CoO2 x in it, or Li x MO 2 is indicated by x in it. Li in this specification x CoO 2 is appropriately Li x MO 2 can be read as. x can be called the occupancy rate. In the case of the positive electrode active material in the secondary battery, x = (theoretical capacity - charged capacity) / theoretical capacity may be used. For example, when a secondary battery using LiCoO 2 as the positive electrode active material is charged to 219.2 mAh / g, Li 0.2 CoO 2 or x = 0.2 can be said. Li x CoO 2 When x in it is small, for example, it means 0.1 < x ≤ 0.24.

[0239] When lithium cobaltate approximately satisfies the stoichiometric ratio, it is LiCoO 2 and the occupancy rate of Li in the lithium site is x = 1. Also, the secondary battery after the discharge is completed is also LiCoO 2 and it can be said that x = 1. Here, the completion of the discharge means, for example, a state where the voltage becomes 2.5 V (versus lithium counter electrode) or less at a current of 100 mA / g. In a lithium-ion secondary battery, when the occupancy rate of lithium in the lithium site becomes x = 1 and no more lithium can enter, the voltage drops rapidly. At this time, it can be said that the discharge is completed. Generally, in a lithium-ion secondary battery using LiCoO 2 , since the discharge voltage drops rapidly until the discharge voltage reaches 2.5 V, it is assumed that the discharge is completed under the above conditions.

[0240] Also, in this specification and the like, the depth of charge when all the lithium that can be inserted and removed from the positive electrode active material is inserted is sometimes referred to as 0, and the depth of charge when all the insertable and removable lithium in the positive electrode active material is removed is sometimes referred to as 1.

[0241] [Positive Electrode Active Material] The positive electrode active material of one aspect of the present invention will be described with reference to FIGS. 11 to 15.

[0242] FIG. 11A is a schematic top view of the positive electrode active material 100 according to one aspect of the present invention. A schematic cross-sectional view taken along A-B in FIG. 11A is shown in FIG. 11B.

[0243] <Elements Contained and Distribution> The positive electrode active material 100 contains lithium, a transition metal, oxygen, and an additive element X. The positive electrode active material 100 is LiM1O 2 (where M1 is one or more selected from Fe, Ni, Co, and Mn), and it may be said that the additive element X is added to the composite oxide represented thereby.

[0244] As the transition metal contained in the positive electrode active material 100, it is preferable to use a metal that can form a layered rock salt type composite oxide belonging to the space group R-3m together with lithium. For example, at least one of manganese, cobalt, and nickel can be used. That is, only cobalt, only nickel, two kinds of cobalt and manganese, or two kinds of cobalt and nickel, or three kinds of cobalt, manganese, and nickel can be used as the transition metal contained in the positive electrode active material 100. That is, the positive electrode active material 100 can have a composite oxide containing lithium and a transition metal, such as lithium cobaltate, lithium nickelate, lithium cobaltate in which a part of cobalt is substituted with manganese, lithium cobaltate in which a part of cobalt is substituted with nickel, lithium nickel-manganese-cobaltate, etc. Having nickel in addition to cobalt as the transition metal may be preferable because the crystal structure may become more stable in the charged state at high voltage.

[0245] As the additive element X included in the positive electrode active material 100, it is preferable to use one or more selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. These elements may stabilize the crystal structure of the positive electrode active material 100. That is, the positive electrode active material 100 may include lithium cobaltate having magnesium and fluorine, lithium cobaltate having magnesium, fluorine, and titanium, lithium nickel-cobaltate having magnesium and fluorine, lithium cobalt-aluminate having magnesium and fluorine, lithium nickel-cobalt-aluminate, lithium nickel-cobalt-aluminate having magnesium and fluorine, lithium nickel-manganese-cobaltate having magnesium and fluorine, and the like. In this specification and the like, the additive element X may be referred to by replacing it with a mixture, a part of a raw material, or the like.

[0246] As shown in FIG. 11B, the positive electrode active material 100 has a surface layer portion 100a and an interior 100b. It is preferable that the surface layer portion 100a has a higher concentration of the additive element X than the interior 100b. Also, as shown by gradation in FIG. 11B, it is preferable that the additive element X has a concentration gradient that increases from the interior toward the surface. In this specification and the like, the surface layer portion 100a refers to a region from the surface of the positive electrode active material 100 to about 10 nm. A surface generated by a crack and / or a fissure may also be referred to as the surface, and as shown in FIG. 11C, a region from the surface to about 10 nm is referred to as the surface layer portion 100c. Also, a region deeper than the surface layer portion 100a and the surface layer portion 100c of the positive electrode active material 100 is defined as the interior 100b. When the positive electrode active material 100 forms a positive electrode active material composite 100z, it is desirable that the surface generated by a crack is also covered with the glass 101.

[0247] In the positive electrode active material 100 according to one aspect of the present invention, even when lithium is removed from the positive electrode active material 100 by charging, the surface layer portion 100a with a high concentration of the additive element X, that is, the outer peripheral portion of the particles, is reinforced so that the layered structure composed of octahedrons of cobalt and oxygen does not break.

[0248] Further, the concentration gradient of the additive element X preferably exists uniformly throughout the surface layer portion 100a of the positive electrode active material 100. This is because even if there is reinforcement in a part of the surface layer portion 100a, if there is a non-reinforced part, stress may concentrate in the non-reinforced part, which is not preferable. When stress concentrates in a part of the particles, defects such as cracks may occur therefrom, leading to cracking of the positive electrode active material and a decrease in charge and discharge capacity.

[0249] Magnesium is divalent and is more stable in the lithium site than in the transition metal site in the layered rock salt type crystal structure, so it easily enters the lithium site. By having magnesium present in the lithium site of the surface layer portion 100a at an appropriate concentration, it is possible to easily maintain the layered rock salt type crystal structure. Also, since magnesium has a strong binding force with oxygen, it is possible to suppress the detachment of oxygen around magnesium. Magnesium is preferable as long as it is at an appropriate concentration and does not adversely affect the insertion and detachment of lithium during charge and discharge. However, if it is excessive, there is a risk of adversely affecting the insertion and detachment of lithium.

[0250] Aluminum is trivalent and can exist in the transition metal site in the layered rock salt type crystal structure. Aluminum can suppress the elution of the surrounding cobalt. Also, since aluminum has a strong binding force with oxygen, it is possible to suppress the detachment of oxygen around aluminum. Therefore, when the additive element X includes aluminum, the positive electrode active material 100 can be made such that the crystal structure is not easily broken even when charge and discharge are repeated.

[0251] Fluorine is a monovalent anion. When a part of oxygen is replaced by fluorine in the surface layer portion 100a, the lithium detachment energy becomes smaller. This is because the change in the valence of cobalt ions accompanying lithium detachment is from trivalent to tetravalent when there is no fluorine, and from divalent to trivalent when there is fluorine, due to the different redox potentials. Therefore, when a part of oxygen is replaced by fluorine in the surface layer portion 100a of the positive electrode active material 100, it can be said that the detachment and insertion of lithium ions near fluorine occur smoothly. Therefore, when used in a secondary battery, it is preferable because the charge-discharge characteristics, rate characteristics, etc. are improved.

[0252] Titanium oxide is known to have super hydrophilicity. Therefore, by using the positive electrode active material 100 having titanium oxide in the surface layer portion 100a, the wettability with respect to a highly polar solvent may be improved. When used as a secondary battery, the contact at the interface between the positive electrode active material 100 and a highly polar electrolyte may be improved, and there is a possibility of suppressing an increase in resistance. In this specification, etc., the electrolyte corresponds to a liquid electrolyte.

[0253] As the charging voltage of the secondary battery increases, the voltage of the positive electrode generally increases. The positive electrode active material of one aspect of the present invention has a stable crystal structure even at a high voltage. Since the crystal structure of the positive electrode active material is stable in the charged state, it is possible to suppress a decrease in capacity accompanying repeated charge and discharge.

[0254] In addition, a short circuit in the secondary battery not only causes problems in the charging operation and / or discharging operation of the secondary battery, but also may cause heat generation and ignition. In order to realize a safe secondary battery, it is preferable that the short circuit current is suppressed even at a high charging voltage. The positive electrode active material 100 of one aspect of the present invention suppresses the short circuit current even at a high charging voltage. Therefore, it is possible to obtain a secondary battery that achieves both high capacity and safety.

[0255] A secondary battery using the positive electrode active material 100 of one aspect of the present invention preferably simultaneously satisfies high capacity, excellent charge-discharge cycle characteristics, and safety.

[0256] The concentration gradient of the added element X can be evaluated, for example, using energy dispersive X-ray spectroscopy (EDX). Among EDX measurements, when measuring while scanning within a region and evaluating the region two-dimensionally, it may be called EDX surface analysis. Also, from the surface analysis of EDX, when extracting data of a linear region and evaluating the distribution of atomic concentration within the positive electrode active material particles, it may be called line analysis.

[0257] By EDX surface analysis (for example, elemental mapping), the concentration of the added element X in the surface layer portion 100a, the interior 100b, near the crystal grain boundaries, etc. of the positive electrode active material 100 can be quantitatively analyzed. Also, by EDX line analysis, the distribution of the concentration of the added element X can be analyzed.

[0258] When performing EDX line analysis on the positive electrode active material 100, the peak of the magnesium concentration (the position where the concentration becomes the maximum value) in the surface layer portion 100a preferably exists up to a depth of 3 nm from the surface of the positive electrode active material 100 toward the center, more preferably up to a depth of 1 nm, and even more preferably up to a depth of 0.5 nm.

[0259] Also, the distribution of fluorine possessed by the positive electrode active material 100 preferably overlaps with the distribution of magnesium. Therefore, when performing EDX line analysis, the peak of the fluorine concentration (the position where the concentration becomes the maximum value) in the surface layer portion 100a preferably exists up to a depth of 3 nm from the surface of the positive electrode active material 100 toward the center, more preferably up to a depth of 1 nm, and even more preferably up to a depth of 0.5 nm.

[0260] Note that not all of the additive elements X need to have the same concentration distribution. For example, when the positive electrode active material 100 has aluminum as the additive element X, it preferably has a distribution slightly different from that of magnesium and fluorine. For example, when EDX line analysis is performed, the peak of the magnesium concentration (the position where the concentration reaches the maximum value) is preferably closer to the surface than the peak of the aluminum concentration (the position where the concentration reaches the maximum value) in the surface layer portion 100a. For example, the peak of the aluminum concentration preferably exists at a depth of 0.5 nm or more and 20 nm or less from the surface of the positive electrode active material 100 toward the center, and more preferably exists at a depth of 1 nm or more and 5 nm or less.

[0261] When line analysis or surface analysis is performed on the positive electrode active material 100, the ratio (X / M1) of the additive element X to the transition metal M1 in the vicinity of the grain boundary is preferably 0.020 or more and 0.50 or less. More preferably, it is 0.025 or more and 0.30 or less. Even more preferably, it is 0.030 or more and 0.20 or less. For example, when the additive element X is magnesium and the transition metal M1 is cobalt, the ratio (Mg / Co) of the number of atoms of magnesium to cobalt is preferably 0.020 or more and 0.50 or less. More preferably, it is 0.025 or more and 0.30 or less. Even more preferably, it is 0.030 or more and 0.20 or less.

[0262] As described above, if the additive element X contained in the positive electrode active material 100 is excessive, it may have an adverse effect on the insertion and extraction of lithium. Also, when used as a secondary battery, it may cause an increase in resistance, a decrease in capacity, etc. On the other hand, if it is insufficient, it may not be distributed throughout the surface layer portion 100a, and the effect of maintaining the crystal structure may become insufficient. Thus, the additive element X is adjusted to an appropriate concentration in the positive electrode active material 100.

[0263] Therefore, for example, the positive electrode active material 100 may have a region where the excessive additive element X is unevenly distributed. Due to the existence of such a region, the excessive additive element X is removed from other regions, and an appropriate concentration of the additive element X can be achieved in most of the interior and surface layer of the positive electrode active material 100. By achieving an appropriate concentration of the additive element X in most of the interior and surface layer of the positive electrode active material 100, an increase in resistance, a decrease in capacity, etc. when used as a secondary battery can be suppressed. The ability to suppress an increase in the resistance of the secondary battery is an extremely favorable characteristic particularly in high-rate charge and discharge.

[0264] In addition, in the positive electrode active material 100 having a region where the excessive additive element X is unevenly distributed, it is allowed to mix the additive element X to some extent excessively in the manufacturing process. Therefore, the margin in production becomes wider, which is preferable.

[0265] In this specification etc., uneven distribution means that the concentration of a certain element is different between a certain region A and a certain region B. It may also be referred to as segregation, precipitation, non-uniformity, bias, high concentration or low concentration, etc.

[0266] <Crystal structure> Materials having a layered rock salt type crystal structure such as lithium cobalt oxide (LiCoO 2 ) are known to have a high discharge capacity and be excellent as a positive electrode active material for secondary batteries. Examples of materials having a layered rock salt type crystal structure include composite oxides represented by LiM1O 2 (M1 is one or more selected from Fe, Ni, Co, Mn).

[0267] It is known that the Jahn-Teller effect in transition metal compounds varies in strength depending on the number of electrons in the d orbitals of the transition metal.

[0268] In compounds having nickel, distortion may easily occur due to the Jahn-Teller effect. Therefore, when charge and discharge are performed at a high voltage in LiNiO 2 , there is a concern that the crystal structure may collapse due to distortion. LiCoO 2It is suggested that the influence of the Jahn-Teller effect is small, and it may be preferable when the charging and discharging resistance at high voltage is more excellent.

[0269] Using FIGS. 12 to 17, the structure of the positive electrode active material will be described. FIGS. 12 to 17 describe the case where cobalt is used as the transition metal included in the positive electrode active material.

[0270] <Conventional positive electrode active material> The positive electrode active material shown in FIG. 14 is lithium cobalt oxide (LiCoO 2 , LCO) to which halogen and magnesium are not added. The lithium cobalt oxide shown in FIG. 14 has a crystal structure that changes depending on the depth of charge. In other words, when expressed as LixCoO 2 , the crystal structure changes according to the occupancy x of lithium in the lithium site.

[0271] As shown in FIG. 14, lithium cobalt oxide in the state of x = 1 (discharged state) has a region having a crystal structure of space group R-3m, and CoO 2 layers are present in three layers in the unit cell. Therefore, this crystal structure may be referred to as an O3-type crystal structure. Note that the CoO 2 layer refers to a structure in which an octahedral structure in which oxygen is six-coordinated to cobalt is continuous in the plane direction in a state of sharing edges.

[0272] Also, when x = 0, it has a crystal structure of space group P-3m1, and CoO 2 layers are present in one layer in the unit cell. Therefore, this crystal structure may be referred to as an O1-type crystal structure.

[0273] Also, lithium cobalt oxide when x is about 0.12 has a crystal structure of space group R-3m. This structure is a structure of CoO 2 such as P-3m1 (O1), and LiCoO 2It can also be said that it has a structure in which they are alternately laminated. Therefore, this crystal structure may be referred to as the H1-3 type crystal structure. Note that since unevenness may occur in the actual insertion and extraction of lithium, the H1-3 type crystal structure is experimentally observed from about x = 0.25. In reality, the H1-3 type crystal structure has twice as many cobalt atoms per unit cell as other structures. However, in this specification including FIG. 14, for the sake of easy comparison with other structures, the c-axis of the H1-3 type crystal structure will be shown in a figure with half of the unit cell.

[0274] As an example, the H1-3 type crystal structure can express the coordinates of cobalt and oxygen in the unit cell as Co(0, 0, 0.42150 ± 0.00016), O 1 (0, 0, 0.27671 ± 0.00045), O 2 (0, 0, 0.11535 ± 0.00045). O 1 and O 2 are oxygen atoms respectively. Thus, the H1-3 type crystal structure is represented by a unit cell using one cobalt and two oxygens. On the other hand, as will be described later, the O3' type crystal structure of one aspect of the present invention is preferably represented by a unit cell using one cobalt and one oxygen. This indicates that the symmetry between cobalt and oxygen is different between the O3' type crystal structure and the H1-3 type structure, and the change from the O3 structure in the O3' type crystal structure is smaller than that in the H1-3 type structure. The choice of which unit cell is more preferable for representing the crystal structure of the positive electrode active material may be made, for example, so that the value of GOF (goodness of fit) is smaller in the Rietveld analysis of the XRD pattern.

[0275] When high-voltage charging such that the charging voltage becomes 4.6 V or more based on the redox potential of lithium metal, or deep charging such that x = 0.24 or less, and discharging are repeated, lithium cobaltate repeats a change in crystal structure (that is, a non-equilibrium phase change) between the H1-3 type crystal structure and the R-3m (O3) structure in the discharged state.

[0276] However, the shift of these two crystal structures in the CoO 2 layer is large. As shown by the dotted line and double arrows in FIG. 14, in the H1-3 type crystal structure, the CoO 2 layer is significantly shifted from R-3m (O3). Such dynamic structural changes can have an adverse effect on the stability of the crystal structure.

[0277] Furthermore, the volume difference is also large. When compared per the same number of cobalt atoms, the volume difference between the H1-3 type crystal structure and the O3 type crystal structure in the discharged state is more than 3.0%.

[0278] In addition, the structure in which the CoO 2 layers such as P-3m1 (O1) in the H1-3 type crystal structure are continuous is likely to be unstable.

[0279] Therefore, when repeatedly charging and discharging at high voltage, the crystal structure of lithium cobaltate collapses. The collapse of the crystal structure causes deterioration of the cycle characteristics. This is presumably because when the crystal structure collapses, the sites where lithium can stably exist decrease, and the insertion and extraction of lithium become difficult.

[0280] <Positive electrode active material of one aspect of the present invention> <Inside> The positive electrode active material 100 of one aspect of the present invention can reduce the shift of the CoO 2 layer during repeated high-voltage charging and discharging. Furthermore, the volume change can be reduced. Therefore, the positive electrode active material of one aspect of the present invention can achieve excellent cycle characteristics. In addition, the positive electrode active material of one aspect of the present invention can adopt a stable crystal structure in the high-voltage charged state. Therefore, when the positive electrode active material of one aspect of the present invention holds a high-voltage charged state, short circuits may be less likely to occur. In such cases, the safety is further improved, which is preferable.

[0281] In the positive electrode active material of one aspect of the present invention, the change in the crystal structure and the volume difference when compared per the same number of transition metal atoms are small in the fully discharged state and the state charged at high voltage.

[0282] The crystal structures of the positive electrode active material 100 before and after charge and discharge are shown in FIG. 12. The positive electrode active material 100 is a composite oxide having lithium, cobalt as a transition metal, and oxygen. In addition to the above, it is preferable to have magnesium as the additive element X. Further, it is preferable to have a halogen such as fluorine or chlorine as the additive element X.

[0283] The crystal structure at x = 1 (discharged state) in FIG. 12 is the same R-3m (O3) as in FIG. 14. On the other hand, the positive electrode active material 100 according to one aspect of the present invention has crystals having a structure different from the H1-3 type crystal structure in the case of a fully charged state of charge depth. This structure belongs to the space group R-3m, and ions such as cobalt and magnesium occupy the oxygen six-coordinate positions. Also, the symmetry of the CoO 2 layer is the same as that of the O3 type. Therefore, this structure is referred to as an O3'-type crystal structure in this specification and the like. In the diagram of the O3'-type crystal structure shown in FIG. 12, the display of lithium is omitted in order to explain the symmetry of cobalt atoms and oxygen atoms, but actually, there is lithium, for example, 20 atomic% or less with respect to cobalt between the CoO 2 layers.

[0284] In the O3'-type crystal structure, light elements such as lithium may occupy the oxygen four-coordinate positions.

[0285] Also, the O3'-type crystal structure can be said to be a crystal structure similar to the CdCl 2 type crystal structure although it has lithium randomly between the layers. This crystal structure similar to the CdCl 2 type is close to the crystal structure when lithium nickelate is charged to a charge depth of 0.94 (Li 0.06 NiO 2 ), but it is known that pure lithium cobaltate or a layered rock salt type positive electrode active material containing a large amount of cobalt usually does not take this crystal structure.

[0286] In the positive electrode active material 100 according to one aspect of the present invention, when charged at a high voltage and a large amount of lithium is detached, the change in the crystal structure is suppressed more than that of the conventional positive electrode active material. For example, as shown by the dotted line in FIG. 12, in these crystal structures, CoO 2 There is almost no shift of the layer.

[0287] More specifically, the positive electrode active material 100 according to one aspect of the present invention has high structural stability even when the charging voltage is high. For example, in the conventional positive electrode active material, there is a region of charging voltage that can maintain the crystal structure of R-3m(O3) even at a charging voltage that results in an H1-3 type crystal structure, for example, a voltage of about 4.6 V based on the potential of lithium metal. Further, there is a region where an O3' type crystal structure can be adopted even in a region where the charging voltage is increased, for example, at a voltage of about 4.65 V to 4.7 V based on the potential of lithium metal. When the charging voltage is further increased, an H1-3 type crystal may be observed. In addition, when graphite is used as the negative electrode active material in a secondary battery, for example, there is a region of charging voltage that can maintain the crystal structure of R-3m(O3) even when the voltage of the secondary battery is 4.3 V or more and 4.5 V or less. Further, there is a region where an O3' type crystal structure can be adopted even in a region where the charging voltage is increased, for example, at a voltage of 4.35 V or more and 4.55 V or less based on the potential of lithium metal.

[0288] Therefore, in the positive electrode active material 100 according to one aspect of the present invention, the crystal structure is less likely to collapse even when charging and discharging are repeated at a high voltage.

[0289] In addition, in the positive electrode active material 100, the difference in volume per unit cell between the O3 type crystal structure with x = 1 and the O3' type crystal structure with x = 0.2 is 2.5% or less, more specifically 2.2% or less.

[0290] The O3' type crystal structure can be represented by the coordinates of cobalt and oxygen in the unit cell as Co(0,0,0.5), O(0,0,x), within the range of 0.20 ≤ x ≤ 0.25.

[0291] CoO 2The additive element X, such as magnesium, which is randomly and thinly present between the layers, that is, in the lithium sites, is CoO 2 has the effect of suppressing the layer shift. Therefore, CoO 2 When magnesium is present between the layers, it is likely to have an O3' type crystal structure. Therefore, magnesium is distributed in at least a part of the surface layer of the positive electrode active material 100 of one aspect of the present invention, and it is preferably distributed throughout the surface layer of the positive electrode active material 100. Further, in order to distribute magnesium throughout the surface layer of the positive electrode active material 100, it is preferable to perform heat treatment in the manufacturing process of the positive electrode active material 100 of one aspect of the present invention.

[0292] However, if the temperature of the heat treatment is too high, cation mixing occurs and the additive element X, such as magnesium, is more likely to enter the cobalt site. Magnesium present in the cobalt site has no effect of maintaining the R-3m structure in the high-voltage charged state. Further, if the temperature of the heat treatment is too high, there are concerns about adverse effects such as cobalt being reduced to divalent and lithium evaporating.

[0293] Therefore, it is preferable to add a halogen compound such as a fluorine compound to lithium cobaltate before the heat treatment for distributing magnesium throughout the surface layer of the positive electrode active material 100. Adding a halogen compound causes a melting point drop of lithium cobaltate. By lowering the melting point, it becomes easy to distribute magnesium throughout the surface layer of the positive electrode active material 100 at a temperature at which cation mixing is less likely to occur. Further, if a fluorine compound is present, it can be expected that the corrosion resistance against hydrofluoric acid generated by the decomposition of the electrolytic solution is improved.

[0294] Note that when the magnesium concentration is increased to a value equal to or higher than a desired value, the effect on the stabilization of the crystal structure may become small. This is presumably because magnesium enters not only the lithium sites but also the cobalt sites. The number of magnesium atoms in the cathode active material according to one embodiment of the present invention is preferably 0.001 times or more and 0.1 times or less, more preferably more than 0.01 times and less than 0.04 times, and even more preferably about 0.02 times the number of atoms of a transition metal such as cobalt. The magnesium concentration shown here may be, for example, a value obtained by performing elemental analysis of the entire cathode active material using ICP-MS or the like, or may be based on the value of the raw material formulation in the process of producing 100 of the cathode active material.

[0295] One or more metals selected from, for example, nickel, aluminum, manganese, titanium, vanadium, and chromium may be added to lithium cobaltate as a metal other than cobalt (hereinafter referred to as additive element X). In particular, it is preferable to add one or more of nickel and aluminum. Manganese, titanium, vanadium, and chromium may be stable in the tetravalent state and may contribute highly to structural stability. By adding additive element X, the crystal structure may become more stable in the charged state at high voltage. Here, in the cathode active material according to one embodiment of the present invention, additive element X is preferably added at a concentration that does not significantly change the crystallinity of lithium cobaltate. For example, it is preferably an amount that does not exhibit the above-described Jahn-Teller effect or the like.

[0296] Transition metals such as nickel and manganese and aluminum preferably exist in the cobalt sites, but a part thereof may exist in the lithium sites. Magnesium preferably exists in the lithium sites. A part of oxygen may be substituted with fluorine.

[0297] As the magnesium concentration of the positive electrode active material in one aspect of the present invention increases, the capacity of the positive electrode active material may decrease. For example, as a factor, it is conceivable that the amount of lithium contributing to charge and discharge may decrease due to magnesium entering the lithium site. When the positive electrode active material in one aspect of the present invention has nickel in addition to magnesium as the additive element X, the charge-discharge cycle characteristics may be improved. Also, when the positive electrode active material in one aspect of the present invention has aluminum in addition to magnesium as the additive element X, the charge-discharge cycle characteristics may be improved. Further, by using the positive electrode active material in one aspect of the present invention having magnesium, nickel, and aluminum as the additive element X, the charge-discharge cycle characteristics may be improved.

[0298] Hereinafter, the concentration of the elements of the positive electrode active material in one aspect of the present invention having magnesium, nickel, and aluminum as the additive element X will be examined.

[0299] The number of nickel atoms in the positive electrode active material in one aspect of the present invention is preferably 10% or less, more preferably 7.5% or less, still more preferably 0.05% or more and 4% or less, and particularly preferably 0.1% or more and 2% or less of the number of cobalt atoms. The nickel concentration shown here may be, for example, a value obtained by performing elemental analysis of the entire positive electrode active material using ICP-MS or the like, or may be based on the value of the raw material formulation in the process of manufacturing the positive electrode active material.

[0300] When the state of being charged at a high voltage is maintained for a long time, there is a risk that the constituent elements of the positive electrode active material will elute into the electrolyte and the crystal structure will collapse. However, having nickel in the above ratio may suppress the elution of the constituent elements from 100 of the positive electrode active material.

[0301] The number of aluminum atoms in the positive electrode active material of one embodiment of the present invention is preferably 0.05% or more and 4% or less, more preferably 0.1% or more and 2% or less of the number of cobalt atoms. The aluminum concentration shown here may be a value obtained by performing elemental analysis of the entire positive electrode active material using, for example, ICP-MS or the like, or may be based on the value of the raw material formulation in the process of producing the positive electrode active material.

[0302] Further, in the positive electrode active material having the additive element X of one embodiment of the present invention, it is preferable to use phosphorus as the additive element X. Further, it is more preferable that the positive electrode active material of one embodiment of the present invention has a compound containing phosphorus and oxygen.

[0303] When the positive electrode active material of one embodiment of the present invention has a compound containing phosphorus as the additive element X, short circuits may be less likely to occur when a charged state at high temperature and high voltage is maintained for a long time.

[0304] When the positive electrode active material of one embodiment of the present invention has phosphorus as the additive element X, hydrogen fluoride generated by the decomposition of the electrolytic solution may react with phosphorus, and the hydrogen fluoride concentration in the electrolytic solution may decrease.

[0305] When the electrolytic solution has LiPF as a lithium salt 6 hydrogen fluoride may be generated by hydrolysis. Further, hydrogen fluoride may also be generated by the reaction between PVDF used as a component of the positive electrode and an alkali. By reducing the hydrogen fluoride concentration in the electrolytic solution, corrosion of the current collector and / or peeling of the film may be suppressed. Further, a decrease in adhesiveness due to gelation and / or insolubilization of PVDF may be suppressed.

[0306] When the positive electrode active material 100 of one embodiment of the present invention has phosphorus and magnesium as additive elements X, the stability in a high-voltage charged state is extremely high. When having phosphorus and magnesium as additive elements X, the number of phosphorus atoms is preferably 1% or more and 20% or less, more preferably 2% or more and 10% or less, still more preferably 3% or more and 8% or less of the number of cobalt atoms. In addition, the number of magnesium atoms is preferably 0.1% or more and 10% or less, more preferably 0.5% or more and 5% or less, still more preferably 0.7% or more and 4% or less of the number of cobalt atoms. The concentrations of phosphorus and magnesium shown here may be values obtained by performing elemental analysis of the entire positive electrode active material 100 using, for example, ICP-MS or the like, or may be based on the values of the raw material formulation in the process of manufacturing the positive electrode active material 100.

[0307] When the positive electrode active material 100 has cracks, the progress of the cracks may be suppressed by the presence of phosphorus, more specifically, a compound containing, for example, phosphorus and oxygen, inside thereof.

[0308] In FIG. 12, the symmetry of oxygen atoms is slightly different between the O3-type crystal structure and the O3'-type crystal structure. Specifically, in the O3-type crystal structure, oxygen atoms are aligned along the dotted line, whereas the oxygen atoms in the O3'-type crystal structure are not strictly aligned. This is because in the O3'-type crystal structure, as lithium decreases, tetravalent cobalt increases, the Jahn-Teller distortion becomes large, and the octahedral structure of CoO 6 is distorted. In addition, as lithium decreases, the repulsion between oxygen atoms in the CoO 2 layer also becomes stronger, which also has an impact.

[0309] <Surface layer portion 100a> Magnesium is preferably distributed throughout the surface layer portion of the positive electrode active material 100 of one embodiment of the present invention. In addition to this, the magnesium concentration in the surface layer portion 100a is preferably higher than the overall average. For example, it is preferable that the magnesium concentration in the surface layer portion 100a measured by XPS or the like is higher than the overall average magnesium concentration measured by ICP-MS or the like.

[0310] Further, when the positive electrode active material 100 of one aspect of the present invention has one or more metals selected from elements other than cobalt, such as nickel, aluminum, manganese, iron, and chromium, it is preferable that the concentration in the vicinity of the particle surface of the metal is higher than the overall average. For example, it is preferable that the concentration of the element other than cobalt in the surface layer portion 100a measured by XPS or the like is higher than the concentration of the element in the overall average measured by ICP-MS or the like.

[0311] The surface layer portion of the positive electrode active material 100 is, so to speak, all crystal defects, and since lithium is removed from the surface during charging, it is a portion where the lithium concentration is likely to be lower than that of the inside. Therefore, it is likely to become unstable and the crystal structure is likely to collapse. If the magnesium concentration in the surface layer portion 100a is high, the change in the crystal structure can be more effectively suppressed. Further, if the magnesium concentration in the surface layer portion 100a is high, it can also be expected that the corrosion resistance against hydrofluoric acid generated by the decomposition of the electrolytic solution is improved.

[0312] Also, for a halogen such as fluorine, it is preferable that the concentration in the surface layer portion 100a of the positive electrode active material 100 of one aspect of the present invention is higher than the overall average. The presence of the halogen in the surface layer portion 100a, which is the region in contact with the electrolytic solution, can effectively improve the corrosion resistance against hydrofluoric acid.

[0313] Thus, it is preferable that the surface layer portion 100a of the positive electrode active material 100 of one aspect of the present invention has a composition different from that of the inside, in which the concentration of additive elements such as magnesium and fluorine is higher than that of the inside 100b. Further, it is preferable that the composition has a crystal structure stable at room temperature. Therefore, the surface layer portion 100a may have a crystal structure different from that of the inside 100b. For example, at least a part of the surface layer portion 100a of the positive electrode active material 100 of one aspect of the present invention may have a rock salt-type crystal structure. Further, when the surface layer portion 100a and the inside 100b have different crystal structures, it is preferable that the crystal orientations of the surface layer portion 100a and the inside 100b are substantially the same.

[0314] The anions of the layered rock salt type crystal and the rock salt type crystal adopt a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that the anions of the O3’ type crystal also adopt a cubic close-packed structure. In this specification and the like, when the A layer, B layer, and C layer having anions are stacked in a structure where they are offset from each other like ABCABC, it shall be called a cubic close-packed structure. Therefore, the anions do not necessarily have to be a strict cubic lattice. At the same time, since real crystals always have defects, the analysis results do not necessarily have to be in accordance with the theory. For example, in FFT (Fast Fourier Transform) such as electron diffraction or TEM image, spots may appear at positions slightly different from the theoretical positions. For example, if the orientation with respect to the theoretical position is 5 degrees or less, or 2.5 degrees or less, it can be said that it adopts a cubic close-packed structure.

[0315] When the layered rock salt type crystal and the rock salt type crystal are in contact, there is a crystal plane where the orientations of the cubic close-packed structures composed of anions are aligned.

[0316] Or, it can also be explained as follows. The anions on the (111) plane of the cubic crystal structure have a triangular arrangement. The layered rock salt type has a space group of R-3m and a rhombohedral structure, but is generally represented by a composite hexagonal lattice for easy understanding of the structure, and the (0001) plane of the layered rock salt type has a hexagonal lattice. The triangular lattice of the cubic crystal (111) has the same atomic arrangement as the hexagonal lattice of the (0001) plane of the layered rock salt type. The fact that the lattices of the two are consistent can be said that the orientations of the cubic close-packed structures are aligned.

[0317] However, since the space groups of the layered rock salt type crystal and the O3’ type crystal are R-3m, which are different from the space group Fm-3m (the space group of a general rock salt type crystal) and Fd-3m (the space group of a rock salt type crystal having the simplest symmetry) of the rock salt type crystal, the Miller indices of the crystal planes satisfying the above conditions are different between the layered rock salt type crystal and the O3’ type crystal and the rock salt type crystal. In this specification, in the layered rock salt type crystal, the O3’ type crystal, and the rock salt type crystal, when the orientations of the cubic close-packed structures composed of anions are aligned, it may be said that the crystal orientations are generally in agreement.

[0318] The approximate alignment of the crystal orientations of the two regions can be determined from TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope) images, ABF-STEM (annular bright-field scanning transmission electron microscope) images, electron diffraction, FFT of TEM images, etc. X-ray diffraction (XRD), neutron diffraction, etc. can also be used as materials for determination.

[0319] Fig. 16 shows an example of a TEM image in which the orientations of the layered rock-salt type crystal LRS and the rock-salt type crystal RS are approximately aligned. In TEM images, STEM images, HAADF-STEM images, ABF-STEM images, etc., images reflecting the crystal structure can be obtained.

[0320] For example, in high-resolution images of TEM, etc., contrast derived from crystal planes can be obtained. Due to the diffraction and interference of the electron beam, for example, when the electron beam is incident perpendicular to the c-axis of the composite hexagonal lattice of the layered rock-salt type, the contrast derived from the (0003) plane is obtained as a repetition of bright lines and dark lines. Therefore, when a repetition of bright lines and dark lines is observed in the TEM image, and the angle between the bright lines (for example, L shown in Fig. 16 RS and L LRS ) is 5 degrees or less, or 2.5 degrees or less, it can be determined that the crystal planes are approximately aligned, that is, the crystal orientations are approximately aligned. Similarly, when the angle between the dark lines is 5 degrees or less, or 2.5 degrees or less, it can be determined that the crystal orientations are approximately aligned.

[0321] In the HAADF-STEM image, contrast corresponding to the atomic number is obtained, and elements with a larger atomic number are observed brighter. For example, in the case of layered rock-salt type lithium cobaltate belonging to the space group R-3m, since cobalt (atomic number 27) has the largest atomic number, the electron beam is strongly scattered at the positions of cobalt atoms, and the arrangement of cobalt atoms is observed as a sequence of bright lines or points with strong luminance. Therefore, when observing lithium cobaltate having a layered rock-salt type crystal structure perpendicular to the c-axis, the arrangement of cobalt atoms is observed as a sequence of bright lines or points perpendicular to the c-axis, and the arrangements of lithium atoms and oxygen atoms are observed as dark lines or regions with low luminance. The same applies to the case where lithium cobaltate has fluorine (atomic number 9) and magnesium (atomic number 12) as additive elements.

[0322] Therefore, in the HAADF-STEM image, if the repetition of bright lines and dark lines is observed in two regions with different crystal structures and the angle between the bright lines is 5 degrees or less, or 2.5 degrees or less, it can be determined that the atomic arrangements are generally in agreement, that is, the crystal orientations are generally in agreement. Similarly, if the angle between the dark lines is 5 degrees or less, or 2.5 degrees or less, it can be determined that the crystal orientations are generally in agreement.

[0323] In ABF-STEM, elements with a smaller atomic number are observed brighter, but since it is the same as HAADF-STEM in that contrast corresponding to the atomic number is obtained, the crystal orientation can be determined in the same manner as in the HAADF-STEM image.

[0324] Fig. 17A shows an example of a STEM image in which the orientations of the layered rock-salt type crystal LRS and the rock-salt type crystal RS are generally in agreement. The FFT of the region of the rock-salt type crystal RS is shown in Fig. 17B, and the FFT of the region of the layered rock-salt type crystal LRS is shown in Fig. 17C. The literature values are shown on the left and the measured values are shown on the right in Figs. 17B and 17C. The spots marked with O are the 0th order diffractions.

[0325] The spot marked with A in Fig. 17B is derived from the 11-1 reflection of the cubic crystal. The spot marked with A in Fig. 17C is derived from the 0003 reflection of the layered rock salt type. Here, it can be seen that the straight line passing through AO in Fig. 17B and the straight line passing through AO in Fig. 17C are approximately parallel. That is, from Fig. 17B and Fig. 17C, it can be seen that the orientation of the 11-1 reflection of the cubic crystal and the orientation of the 0003 reflection of the layered rock salt type are approximately the same. The so-called approximate coincidence and approximate parallel here mean that the angle is 5 degrees or less, or 2.5 degrees or less.

[0326] In this way, in FFT and electron diffraction, when the orientations of the layered rock salt type crystal and the rock salt type crystal are approximately the same, the <0003> orientation of the layered rock salt type or an equivalent plane orientation, and the <11-1> orientation of the rock salt type or an equivalent plane orientation, may be approximately the same. At this time, it is preferable that these reciprocal lattice points are spot-shaped, that is, not continuous with other reciprocal lattice points. The reciprocal lattice points being spot-shaped and not continuous with other reciprocal lattice points means high crystallinity.

[0327] Also, when the orientation of the 11-1 reflection of the cubic crystal and the orientation of the 0003 reflection of the layered rock salt type are approximately the same as described above, depending on the incident orientation of the electron beam, spots not derived from the 0003 reflection of the layered rock salt type may be observed in a reciprocal lattice space different from the orientation of the 0003 reflection of the layered rock salt type. For example, the spot marked with B in Fig. 17C is derived from the 10-14 reflection of the layered rock salt type. This is at an angle of 52° or more and 56° or less from the orientation of the reciprocal lattice point (A in Fig. 17C) derived from the 0003 reflection of the layered rock salt type (that is, ∠AOB is 52° or more and 56° or less), and may be observed at a location where d is 0.19 nm or more and 0.21 nm or less. Note that this index is an example and does not necessarily have to match this. For example, reciprocal lattice points equivalent to 0003 and 1014 may also be used.

[0328] In the reciprocal lattice space different from the orientation where the cubic 11-1 is observed, spots not derived from the cubic 11-1 may be observed. For example, the spot labeled B in Fig. 17B is derived from the 200 reflection of the cubic crystal. This means that diffraction spots may be observed at positions where the angle is between 54° and 56° (i.e., ∠AOB is between 54° and 56°) from the orientation of the reflection derived from the cubic 11-1 (A in Fig. 17B). Note that this index is just an example and does not necessarily have to match exactly. For example, it may be an equivalent reciprocal lattice point to 11-1 and 200.

[0329] Note that for layered rock salt type cathode active materials such as lithium cobaltate, the (0003) plane and equivalent planes, as well as the (10-14) plane and equivalent planes, are known to easily appear as crystal planes. Therefore, by observing the shape of the cathode active material well with SEM or the like, it is possible to thin the observation sample with FIB or the like so that the (0003) plane is easily observable, for example, in TEM or the like with the electron beam incident along [1-210]. When it is desired to judge the coincidence of crystal orientation, it is preferable to thin the sample so that the (0003) plane of the layered rock salt type is easily observable.

[0330] However, if the surface layer portion 100a consists only of MgO or has only a structure in which MgO and CoO(II) are solid-solved, the insertion and extraction of lithium will become difficult. Therefore, the surface layer portion 100a must have at least cobalt, and also have lithium in the discharged state, and have a path for the insertion and extraction of lithium. Also, it is preferable that the concentration of cobalt is higher than that of magnesium.

[0331] Also, the additive element X is preferably located in the surface layer portion 100a of the particles of the cathode active material 100 of one aspect of the present invention. For example, the cathode active material 100 of one aspect of the present invention may be covered with a film having the additive element X.

[0332] <grain boundary> The additive element X contained in the cathode active material 100 of one aspect of the present invention may be randomly and thinly present inside, but it is more preferable that a part of it is segregated at the grain boundaries.

[0333] In other words, it is preferable that the concentration of the additive element X at the grain boundaries of the positive electrode active material 100 and in the vicinity thereof in one aspect of the present invention is also higher than that in other regions inside.

[0334] Grain boundaries can be considered as plane defects. Therefore, similar to the particle surface, they tend to become unstable and the change of the crystal structure easily starts. Therefore, if the concentration of the additive element X at the grain boundaries and in the vicinity thereof is high, the change of the crystal structure can be suppressed more effectively.

[0335] Further, when the concentration of the additive element X at the grain boundaries and in the vicinity thereof is high, even when cracks occur along the grain boundaries of the particles of the positive electrode active material 100 in one aspect of the present invention, the concentration of the additive element X becomes high in the vicinity of the surface generated by the cracks. Therefore, the corrosion resistance against hydrofluoric acid can be enhanced even in the positive electrode active material after cracks occur.

[0336] In this specification etc., the vicinity of the grain boundaries shall mean the region up to about 10 nm from the grain boundaries.

[0337] <Particle size> If the particle size of the positive electrode active material 100 in one aspect of the present invention is too large, there are problems such as difficulty in lithium diffusion or the surface of the active material layer becoming too rough when coated on the current collector. On the other hand, if it is too small, there are also problems such as difficulty in supporting the active material layer during coating on the current collector and excessive progress of the reaction with the electrolytic solution. Therefore, the average particle size (D50: also referred to as the median diameter) is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less.

[0338] <Analysis method> Whether a certain positive electrode active material is the positive electrode active material 100 of one aspect of the present invention that exhibits an O3'-type crystal structure when charged at a high voltage can be determined by analyzing the positively charged electrode using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. In particular, XRD can analyze the symmetry of transition metals such as cobalt in the positive electrode active material with high resolution, can compare the high crystallinity and crystal orientation, can analyze the periodic lattice strain and crystallite size, and can obtain sufficient accuracy even when measuring the positive electrode obtained by disassembling the secondary battery as it is. Therefore, it is preferable in this regard.

[0339] The positive electrode active material 100 of one aspect of the present invention has the characteristic that there is little change in the crystal structure between the state of being charged at a high voltage and the discharged state as described above. A material in which a crystal structure with a large change from the discharged state occupies 50 wt% or more in the state of being charged at a high voltage is not preferable because it cannot withstand the charge and discharge at a high voltage. It should be noted that simply adding an additive element may not result in the desired crystal structure. For example, even if they are common in that they are lithium cobaltate having magnesium and fluorine, there are cases where the O3'-type crystal structure is 60 wt% or more and cases where the H1-3 type crystal structure occupies 50 wt% or more in the state of being charged at a high voltage. Also, at a predetermined voltage, the O3'-type crystal structure may become almost 100 wt%, and further, when the predetermined voltage is increased, the H1-3 type crystal structure may occur. Therefore, in order to determine whether it is the positive electrode active material 100 of one aspect of the present invention, analysis of the crystal structure including XRD is necessary.

[0340] However, the positive electrode active material in the charged state or discharged state may change its crystal structure when exposed to the atmosphere. For example, it may change from the O3'-type crystal structure to the H1-3 type crystal structure. Therefore, it is preferable to handle all samples in an inert atmosphere such as an argon atmosphere.

[0341] <Charging method> To determine whether a certain composite oxide is the cathode active material 100 of one embodiment of the present invention, high-voltage charging can be carried out, for example, by fabricating a coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) with a lithium counter electrode and then charging it.

[0342] More specifically, for the cathode, a slurry obtained by mixing a cathode active material, a conductive material, and a binder can be used, which is coated on an aluminum foil cathode current collector.

[0343] Lithium metal can be used for the counter electrode. When a material other than lithium metal is used for the counter electrode, the potential of the secondary battery is different from the potential of the cathode. Unless otherwise specified, the voltage and potential in this specification and the like refer to the potential of the cathode.

[0344] As the electrolyte in the electrolytic solution, 1 mol / L lithium hexafluorophosphate (LiPF 6 ) can be used. For the electrolytic solution, a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of EC:DEC = 3:7 and vinylene carbonate (VC) at 2 wt% can be used.

[0345] A 25-μm-thick polypropylene can be used for the separator.

[0346] For the cathode can and the anode can, those made of stainless steel (SUS) can be used.

[0347] The coin cell fabricated under the above conditions is charged at a constant current of 4.6 V and 0.5 C, and then charged at a constant voltage until the current value reaches 0.01 C. Here, 1 C is taken as 137 mA / g, and the temperature is 25°C. After charging in this way, if the coin cell is disassembled in a glove box under an argon atmosphere to take out the cathode, a cathode active material charged at a high voltage can be obtained. When performing various analyses thereafter, it is preferable to seal it in an argon atmosphere to suppress the reaction with external components. For example, XRD can be carried out by enclosing it in a sealed container under an argon atmosphere.

[0348] <xrd> The ideal powder XRD patterns for the O3’-type crystal structure and the CuKα1 line calculated from the model of the H1-3-type crystal structure are shown in FIGS. 13 and 15. Also, for comparison, LiCoO with x = 1 2 (O3) and CoO with x = 0 2 (O1) are also shown for the ideal XRD patterns calculated from the crystal structures. Note that LiCoO 2 (O3) and CoO 2 (O1) patterns were created using Reflex Powder Diffraction, one of the modules of Materials Studio (BIOVIA), from the crystal structure information obtained from the ICSD (Inorganic Crystal Structure Database). The range of 2θ was set from 15° to 75°, Step size = 0.01, wavelength λ1 = 1.540562×10 -10 m, λ2 was not set, and the Monochromator was set to single. The crystal structure pattern of the O3’-type crystal structure was estimated from the XRD pattern of the cathode active material of one aspect of the present invention, and was fitted using TOPAS ver.3 (crystal structure analysis software manufactured by Bruker), and the XRD pattern was created in the same manner as the others.

[0349] As shown in FIG. 13, in the O3’-type crystal structure, diffraction peaks appear at 2θ = 19.30 ± 0.20° (19.10° or more and 19.50° or less) and 2θ = 45.55 ± 0.10° (45.45° or more and 45.65° or less). More specifically, sharp diffraction peaks appear at 2θ = 19.30 ± 0.10° (19.20° or more and 19.40° or less) and 2θ = 45.55 ± 0.05° (45.50° or more and 45.60° or less). However, as shown in FIG. 15, in the H1-3-type crystal structure and CoO 2 (P-3m1, O1), peaks do not appear at these positions. Therefore, it can be said that the appearance of peaks at 2θ = 19.30 ± 0.20° and 2θ = 45.55 ± 0.10° in the state of being charged at a high voltage is a characteristic of the cathode active material 100 of one aspect of the present invention.

[0350] It can also be said that the crystal structure at x = 1 and the crystal structure in the high-voltage charged state have similar positions where the diffraction peaks of XRD appear. More specifically, it can be said that for two or more, more preferably three or more of the main diffraction peaks of both, the difference in the positions where the peaks appear is 2θ = 0.7° or less, more preferably 2θ = 0.5° or less.

[0351] Note that the positive electrode active material 100 of one aspect of the present invention has an O3'-type crystal structure when charged at a high voltage, but not all of the positive electrode active material 100 needs to have an O3'-type crystal structure. It may contain other crystal structures or a part thereof may be amorphous. However, when Rietveld analysis is performed on the XRD pattern, it is preferably 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more of the O3'-type crystal structure. If the O3'-type crystal structure is 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more, a positive electrode active material with excellent cycle characteristics can be obtained.

[0352] Also, even after 100 cycles or more of charge and discharge from the start of measurement, when Rietveld analysis is performed, it is preferably 35 wt% or more, more preferably 40 wt% or more, and even more preferably 43 wt% or more of the O3'-type crystal structure.

[0353] Also, the crystallite size of the O3'-type crystal structure of the particles of the positive electrode active material only decreases to about 1 / 10 of that of LiCoO 2 (O3) in the discharged state. Therefore, even under the same XRD measurement conditions as the positive electrode before charge and discharge, a clear peak of the O3'-type crystal structure can be confirmed in the high-voltage charged state. On the other hand, in the case of simple LiCoO 2 , even if a part has a structure similar to the O3'-type crystal structure, the crystallite size becomes small and the peak becomes broad and small. The crystallite size can be obtained from the half-width of the XRD peak.

[0354] In the cathode active material according to one embodiment of the present invention, as described above, it is preferable that the influence of the Jahn-Teller effect is small. The cathode active material according to one embodiment of the present invention preferably has a layered rock salt-type crystal structure and mainly contains cobalt as a transition metal. Further, in the cathode active material according to one embodiment of the present invention, within a range where the influence of the Jahn-Teller effect is small, in addition to cobalt, it may have the above-described additive element X.

[0355] When considering the preferable range of the lattice constant, in the cathode active material according to one embodiment of the present invention, in the layered rock salt-type crystal structure of the particles of the cathode active material in a state where charge and discharge are not performed or in a discharged state, which can be estimated from the XRD pattern, the lattice constant of the a-axis is 2.814×10 -10 m and larger than 2.817×10 -10 m, and the lattice constant of the c-axis is larger than 14.05×10 -10 m and smaller than 14.07×10 -10 m. It was found that this is preferable. The state where charge and discharge are not performed may be, for example, the powder state before manufacturing the cathode of the secondary battery.

[0356] Alternatively, in the layered rock salt-type crystal structure of the particles of the cathode active material in a state where charge and discharge are not performed or in a discharged state, the value obtained by dividing the lattice constant of the a-axis by the lattice constant of the c-axis (a-axis / c-axis) is preferably larger than 0.20000 and smaller than 0.20049.

[0357] Alternatively, in the layered rock salt-type crystal structure of the particles of the cathode active material in a state where charge and discharge are not performed or in a discharged state, when XRD analysis is performed, the first peak may be observed at 2θ of 18.50° or more and 19.30° or less, and the second peak may be observed at 2θ of 38.00° or more and 38.80° or less.

[0358] Note that the peaks appearing in the powder XRD pattern reflect the crystal structure of the interior 100b of the cathode active material 100, which occupies the majority of the volume of the cathode active material 100. The crystal structure of the surface layer portion 100a and the like can be analyzed by electron diffraction or the like of the cross section of the cathode active material 100.

[0359] <xps> In X-ray photoelectron spectroscopy (XPS), since it is possible to analyze the region from the surface to a depth of about 2 to 8 nm (usually about 5 nm), the concentration of each element can be quantitatively analyzed for about half of the surface layer portion 100a. Also, if narrow scan analysis is performed, the bonding state of the element can be analyzed. The quantitative accuracy of XPS is often about ±1 atomic %, and the detection limit is about 1 atomic % depending on the element.

[0360] When performing XPS analysis, for example, monochromatized aluminum can be used as the X-ray source. Also, the take-off angle can be, for example, 45°.

[0361] Also, when XPS analysis is performed on the positive electrode active material 100 of one aspect of the present invention, the peak indicating the binding energy between fluorine and other elements is preferably 682 eV or more and less than 685 eV, and more preferably about 684.3 eV. This is a value different from both 685 eV, which is the binding energy of lithium fluoride, and 686 eV, which is the binding energy of magnesium fluoride. That is, when the positive electrode active material 100 of one aspect of the present invention contains fluorine, it is preferably a bond other than lithium fluoride and magnesium fluoride.

[0362] Furthermore, when XPS analysis is performed on the positive electrode active material 100 of one aspect of the present invention, the peak indicating the binding energy between magnesium and other elements is preferably 1302 eV or more and less than 1304 eV, and more preferably about 1303 eV. This is a value different from 1305 eV, which is the binding energy of magnesium fluoride, and is a value close to the binding energy of magnesium oxide. That is, when the positive electrode active material 100 of one aspect of the present invention contains magnesium, it is preferably a bond other than magnesium fluoride.

[0363] Additive element X, which is preferably present in a large amount in the surface layer portion 100a, such as magnesium and aluminum, preferably has a concentration measured by XPS or the like higher than the concentration measured by ICP-MS (inductively coupled plasma mass spectrometry) or GD-MS (glow discharge mass spectrometry).

[0364] When magnesium and aluminum are analyzed using TEM-EDX after exposing their cross-sections by processing, it is preferable that the concentration in the surface layer portion 100a is higher than the concentration in the interior 100b. The processing can be performed, for example, by FIB.

[0365] In the analysis by XPS (X-ray photoelectron spectroscopy), the atomic number of magnesium is preferably 0.4 times or more and 1.5 times or less the atomic number of cobalt. On the other hand, the ratio of the atomic number of magnesium Mg / Co by ICP-MS analysis is preferably 0.001 or more and 0.06 or less.

[0366] On the other hand, nickel contained in the transition metal is preferably not unevenly distributed in the surface layer portion 100a but is distributed throughout the entire positive electrode active material 100. However, this is not the case when there is a region where the aforementioned excessive additive element X is unevenly distributed.

[0367] <Surface roughness and specific surface area> The positive electrode active material 100 according to one aspect of the present invention preferably has a smooth surface with few irregularities. The smooth surface with few irregularities is one factor indicating that the distribution of the additive element X in the surface layer portion 100a is good. In the production process of the positive electrode active material 100, when initial heating is performed on lithium cobaltate or lithium nickel-cobalt-manganese oxide before adding the additive element X, the charge-discharge cycle characteristics at high voltage are remarkably excellent, so it is particularly preferable as the positive electrode active material 100.

[0368] In addition, since the surface of the positive electrode active material 100 is smooth and has few irregularities, the stability on the surface of the positive electrode active material 100 is improved, and the generation of pits may be suppressed.

[0369] The smoothness of the surface and the low irregularities can be determined, for example, from the cross-sectional SEM image or cross-sectional TEM image of the positive electrode active material 100, the specific surface area of the positive electrode active material 100, etc.

[0370] For example, as follows, the smoothness of the surface can be quantified from the cross-sectional SEM image of the positive electrode active material 100.

[0371] First, the positive electrode active material 100 is processed by FIB or the like to expose the cross section. At this time, it is preferable to cover the positive electrode active material 100 with a protective film, a protective agent, etc. Next, an SEM image of the interface between the protective film or the like and the positive electrode active material 100 is taken. Noise processing is performed on the SEM image with image processing software. For example, after performing Gaussian blur (σ = 2), binarization is performed. Further, interface extraction is performed with image processing software. Further, the interface line between the protective film or the like and the positive electrode active material 100 is selected with a magic hand tool or the like, and the data is extracted into spreadsheet software or the like. Using the functions of spreadsheet software or the like, correction is performed from the regression curve (quadratic regression), a parameter for calculating roughness is obtained from the data after slope correction, and the root mean square (RMS) surface roughness with the standard deviation calculated is obtained. Further, this surface roughness is the surface roughness of the positive electrode active material at least at 400 nm on the outer periphery of the particles.

[0372] On the particle surface of the positive electrode active material 100 of the present embodiment, the root mean square (RMS) surface roughness, which is an index of roughness, is preferably 10 nm or less, less than 3 nm, preferably less than 1 nm, and more preferably less than 0.5 nm.

[0373] Note that the image processing software for performing noise processing, interface extraction, etc. is not particularly limited, but for example, "ImageJ" can be used. Also, the spreadsheet software or the like is not particularly limited, but for example, Microsoft Office Excel can be used.

[0374] Also, for example, the actual specific surface area A measured by the gas adsorption method by the constant volume method R and the ideal specific surface area A i From the ratio with [something], the smoothness of the surface of the positive electrode active material 100 can be quantified.

[0375] Ideal specific surface area A i is calculated and obtained assuming that the diameter of all particles is the same as D50, the weight is the same, and the shape is an ideal sphere.

[0376] The median diameter D50 can be measured by a particle size distribution meter using the laser diffraction / scattering method or the like. The specific surface area can be measured by a specific surface area measuring device using, for example, the gas adsorption method by the constant volume method.

[0377] The positive electrode active material 100 according to one aspect of the present invention has an ideal specific surface area A obtained from the median diameter D50 i and the actual specific surface area A R The ratio A R / A i is preferably 1 or more and 2 or less.

[0378] The content of this embodiment can be freely combined with the content of other embodiments.

[0379] (Embodiment 4) In this embodiment, examples of the shapes of a plurality of types of secondary batteries having a positive electrode or a negative electrode manufactured by the manufacturing method described in the previous embodiment will be described.

[0380] [Coin-type secondary battery] An example of a coin-type secondary battery will be described. FIG. 18A is an exploded perspective view of a coin-type (single-layer flat type) secondary battery, FIG. 18B is an external view, and FIG. 18C is a cross-sectional view thereof. The coin-type secondary battery is mainly used for small electronic devices. In this specification and the like, the coin-type battery includes a button-type battery.

[0381] In FIG. 18A, for clarity, it is a schematic diagram so that the overlap (vertical relationship and positional relationship) of the members can be understood. Therefore, FIGS. 18A and 18B are not completely corresponding diagrams that match exactly.

[0382] In FIG. 18A, a positive electrode 304, a separator 310, a negative electrode 307, a spacer 322, and a washer 312 are stacked. These are sealed with a negative electrode can 302 and a positive electrode can 301. Note that in FIG. 18A, a gasket for sealing is not shown. The spacer 322 and the washer 312 are used to protect the inside or fix the position inside the can when the positive electrode can 301 and the negative electrode can 302 are crimped. The spacer 322 and the washer 312 are made of stainless steel or an insulating material.

[0383] A positive electrode 304 has a laminated structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305.

[0384] To prevent short - circuit between the positive electrode and the negative electrode, a separator 310 and a ring - shaped insulator 313 are respectively arranged so as to cover the side surface and the upper surface of the positive electrode 304. The separator 310 has a larger planar area than the positive electrode 304.

[0385] FIG. 18B is a perspective view of a completed coin - type secondary battery.

[0386] In a coin - type secondary battery 300, a positive electrode can 301 that also serves as a positive electrode terminal and a negative electrode can 302 that also serves as a negative electrode terminal are insulated and sealed with a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed of a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact therewith. The negative electrode 307 is formed of a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact therewith. Also, the negative electrode 307 is not limited to a laminated structure, and a lithium metal foil or an alloy foil of lithium and aluminum may be used.

[0387] Note that for the positive electrode 304 and the negative electrode 307 used in the coin - type secondary battery 300, the active material layer may be formed only on one side.

[0388] For the positive electrode can 301 and the negative electrode can 302, metals such as nickel, aluminum, titanium, etc. that are corrosion-resistant to the electrolyte, or alloys thereof, and alloys of these with other metals (such as stainless steel, etc.) can be used. Also, in order to prevent corrosion by the electrolyte, etc., it is preferable to coat nickel, aluminum, etc. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307 respectively.

[0389] These negative electrode 307, positive electrode 304, and separator 310 are immersed in the electrolyte solution. As shown in FIG. 18C, with the positive electrode can 301 facing downwards, the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are laminated in this order, and the positive electrode can 301 and the negative electrode can 302 are crimped via the gasket 303 to manufacture the coin-shaped secondary battery 300.

[0390] By having the above configuration, a coin-type secondary battery 300 with high capacity, high charge-discharge capacity, and excellent cycle characteristics can be obtained. In addition, when making a secondary battery having a solid electrolyte layer between the negative electrode 307 and the positive electrode 304, the separator 310 can be made unnecessary.

[0391] [Cylindrical secondary battery] Examples of the cylindrical secondary battery will be described with reference to FIGS. 19A and 19B. FIG. 19B is a diagram schematically showing a cross-section of the cylindrical secondary battery. As shown in FIGS. 19A and 19B, the cylindrical secondary battery 616 has a positive electrode cap (battery lid) 601 on the upper surface and a battery can (outer can) 602 on the side surface and the bottom surface. The positive electrode cap 601 and the battery can (outer can) 602 are insulated by a gasket (insulating packing) 610.

[0392] Inside the hollow cylindrical battery can 602, a battery element is provided in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 interposed therebetween. Although not shown, the battery element is wound around a central axis. One end of the battery can 602 is closed and the other end is open. For the battery can 602, metals such as nickel, aluminum, and titanium that are corrosion-resistant to the electrolytic solution, or alloys thereof, and alloys of these with other metals (for example, stainless steel, etc.) can be used. Further, in order to prevent corrosion by the electrolytic solution, it is preferable to coat the battery can 602 with nickel, aluminum, etc. Inside the battery can 602, the battery element around which the positive electrode, negative electrode, and separator are wound is sandwiched between a pair of opposing insulating plates 608 and 609. Further, a non-aqueous electrolytic solution (not shown) is injected into the interior of the battery can 602 in which the battery element is provided. As the non-aqueous electrolytic solution, the same one as that used for a coin-type secondary battery can be used.

[0393] Since the positive and negative electrodes used in the cylindrical storage battery are wound, it is preferable to form the active material on both sides of the current collector. Although secondary battery 616 in which the height of the cylinder is larger than the diameter of the cylinder is shown in FIGS. 19A to 19D, it is not limited thereto. A secondary battery in which the diameter of the cylinder is larger than the height of the cylinder may also be used. With such a configuration, for example, miniaturization of the secondary battery can be achieved.

[0394] By using the negative electrode 570a obtained in the above-described embodiment as the negative electrode 606, a cylindrical secondary battery 616 having a high capacity, a high charge / discharge capacity, and excellent cycle characteristics can be obtained. Further, by using the positive electrode active material composite 100z obtained in the above-described embodiment as the positive electrode 604, a cylindrical secondary battery 616 having a high capacity, a high charge / discharge capacity, and excellent cycle characteristics can be obtained.

[0395] A positive electrode terminal (positive current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative current collector lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be made of a metal material such as aluminum. The positive electrode terminal 603 is resistance-welded to the safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC element (Positive Temperature Coefficient) 611. The safety valve mechanism 613 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery rises above a predetermined threshold value. Also, the PTC element 611 is a thermal sensing resistance element whose resistance increases when the temperature rises, and it limits the current amount due to the increase in resistance to prevent abnormal heat generation. For the PTC element, barium titanate (BaTiO 3 )-based semiconductor ceramics or the like can be used.

[0396] FIG. 19C shows an example of a power storage system 615. The power storage system 615 has a plurality of secondary batteries 616. The positive electrodes of the respective secondary batteries are in contact with and electrically connected to a conductor 624 separated by an insulator 625. The conductor 624 is electrically connected to a control circuit 620 via a wiring 623. Also, the negative electrodes of the respective secondary batteries are electrically connected to the control circuit 620 via a wiring 626. As the control circuit 620, a protection circuit or the like that prevents overcharging or over-discharging can be applied.

[0397] FIG. 19D shows an example of a power storage system 615. The power storage system 615 has a plurality of secondary batteries 616, and the plurality of secondary batteries 616 are sandwiched between a conductive plate 628 and a conductive plate 614. The plurality of secondary batteries 616 are electrically connected to the conductive plate 628 and the conductive plate 614 by a wiring 627. The plurality of secondary batteries 616 may be connected in parallel or in series. By configuring a power storage system 615 having a plurality of secondary batteries 616, a large amount of power can be extracted.

[0398] A plurality of secondary batteries 616 may be connected in parallel and then further connected in series.

[0399] A temperature control device may be provided between the plurality of secondary batteries 616. When the secondary battery 616 is overheated, it can be cooled by the temperature control device, and when the secondary battery 616 is too cold, it can be heated by the temperature control device. Therefore, the performance of the power storage system 615 is less affected by the outside air temperature.

[0400] Also, in FIG. 19D, the power storage system 615 is electrically connected to the control circuit 620 via the wiring 621 and the wiring 622. The wiring 621 is electrically connected to the positive electrodes of the plurality of secondary batteries 616 via the conductive plate 628, and the wiring 622 is electrically connected to the negative electrodes of the plurality of secondary batteries 616 via the conductive plate 614.

[0401] [Other Structural Examples of Secondary Batteries] Structural examples of secondary batteries will be described with reference to FIGS. 20 and 21.

[0402] The secondary battery 913 shown in FIG. 20A has a wound body 950 in which a terminal 951 and a terminal 952 are provided inside a housing 930. The wound body 950 is immersed in the electrolytic solution inside the housing 930. The terminal 952 is in contact with the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. In FIG. 20A, for the sake of convenience, the housing 930 is shown separately, but actually, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. As the housing 930, a metal material (for example, aluminum or the like) or a resin material can be used.

[0403] Note that, as shown in FIG. 20B, the housing 930 shown in FIG. 20A may be formed of a plurality of materials. For example, the secondary battery 913 shown in FIG. 20B has a housing 930a and a housing 930b bonded together, and a wound body 950 is provided in the region surrounded by the housing 930a and the housing 930b.

[0404] As the housing 930a, an insulating material such as an organic resin can be used. In particular, by using a material such as an organic resin on the surface where the antenna is formed, shielding of the electric field by the secondary battery 913 can be suppressed. If the shielding of the electric field by the housing 930a is small, an antenna may be provided inside the housing 930a. As the housing 930b, for example, a metal material can be used.

[0405] Furthermore, the structure of the wound body 950 is shown in FIG. 20C. The wound body 950 includes a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body obtained by winding a laminated sheet in which the negative electrode 931 and the positive electrode 932 overlap with each other with the separator 933 interposed therebetween. Note that a plurality of laminations of the negative electrode 931, the positive electrode 932, and the separator 933 may be further stacked.

[0406] Also, a secondary battery 913 having a wound body 950a as shown in FIGS. 21A to 21C may be used. The wound body 950a shown in FIG. 21A includes a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 has a negative electrode active material layer 931a. The positive electrode 932 has a positive electrode active material layer 932a.

[0407] By using the negative electrode 570a obtained in the above-described embodiment as the negative electrode 606, a cylindrical secondary battery 616 having a high capacity, a high charge / discharge capacity, and excellent cycle characteristics can be obtained. Also, by using the positive electrode active material composite 100z obtained in the above-described embodiment as the positive electrode 932, a secondary battery 913 having a high capacity, a high charge / discharge capacity, and excellent cycle characteristics can be obtained.

[0408] The separator 933 has a width wider than that of the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap with the negative electrode active material layer 931a and the positive electrode active material layer 932a. It is preferable from the viewpoint of safety that the width of the negative electrode active material layer 931a is wider than that of the positive electrode active material layer 932a. Also, a wound body 950a having such a shape is preferable in terms of safety and productivity.

[0409] As shown in FIG. 21B, the negative electrode is electrically connected to terminal 951. Terminal 951 is electrically connected to terminal 911a. Also, the positive electrode is electrically connected to terminal 952. Terminal 952 is electrically connected to terminal 911b.

[0410] As shown in FIG. 21C, the housing 930 covers the wound body 950a and the electrolytic solution, forming the secondary battery 913. It is preferable to provide a safety valve, an overcurrent protection element, etc. in the housing 930. The safety valve is a valve that opens when the internal pressure of the housing 930 reaches a predetermined internal pressure to prevent battery rupture.

[0411] As shown in FIG. 21B, the secondary battery 913 may have a plurality of wound bodies 950a. By using a plurality of wound bodies 950a, a secondary battery 913 with a larger charge / discharge capacity can be obtained. Other elements of the secondary battery 913 shown in FIGS. 21A and 21B can be referred to the description of the secondary battery 913 shown in FIGS. 20A to 20C.

[0412] <Laminated secondary battery> Next, an example of a laminated secondary battery is shown in FIGS. 22A and 22B as an example of an external view. FIGS. 22A and 22B include a positive electrode 503, a negative electrode 506, a separator 507, an exterior body 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0413] FIG. 23A shows an external view of the positive electrode 503 and the negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and the positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. Also, the positive electrode 503 has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as a tab region). The negative electrode 506 has a negative electrode current collector 504, and the negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. Also, the negative electrode 506 has a region where the negative electrode current collector 504 is partially exposed, that is, a tab region. The area and shape of the tab regions of the positive electrode and the negative electrode are not limited to the example shown in FIG. 23A.

[0414] <Manufacturing method of laminated secondary battery> Here, an example of a method for manufacturing a laminated secondary battery whose external view is shown in FIG. 22A will be described with reference to FIGS. 23B and 23C.

[0415] First, the negative electrode 506, the separator 507, and the positive electrode 503 are laminated. FIG. 23B shows the laminated negative electrode 506, separator 507, and positive electrode 503. Here, an example is shown in which five sets of negative electrodes and four sets of positive electrodes are used. It can also be called a laminate composed of a negative electrode, a separator, and a positive electrode. Next, the tabs of the positive electrode 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For the joining, for example, ultrasonic welding or the like may be used. Similarly, the tabs of the negative electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0416] Next, the negative electrode 506, the separator 507, and the positive electrode 503 are arranged on the exterior body 509.

[0417] Next, as shown in FIG. 23C, the exterior body 509 is bent at the portion indicated by the broken line. Then, the outer peripheral portion of the exterior body 509 is joined. For the joining, for example, thermocompression bonding or the like may be used. At this time, a region that is not joined (hereinafter referred to as an inlet) is provided in a part (or one side) of the exterior body 509 so that an electrolytic solution can be introduced later.

[0418] Next, the electrolytic solution is introduced into the interior of the exterior body 509 through the inlet provided in the exterior body 509. The introduction of the electrolytic solution is preferably performed under a reduced-pressure atmosphere or an inert atmosphere. Finally, the inlet is joined. In this way, the laminated secondary battery 500 can be manufactured.

[0419] By using the negative electrode 570a obtained in the above-described embodiment as the negative electrode 606, a cylindrical secondary battery 616 with high capacity, high charge-discharge capacity, and excellent cycle characteristics can be obtained. Also, by using the positive electrode active material composite 100z obtained in the above-described embodiment as the positive electrode 503, a secondary battery 500 with high capacity, high charge-discharge capacity, and excellent cycle characteristics can be obtained.

[0420] [Example of Battery Pack] An example of a secondary battery pack according to one aspect of the present invention capable of wireless charging using an antenna will be described with reference to FIGS. 24A to 24C.

[0421] FIG. 24A is a view showing the appearance of the secondary battery pack 531, which has a thin rectangular parallelepiped shape (which can also be called a thick flat plate shape). FIG. 24B is a view for explaining the configuration of the secondary battery pack 531. The secondary battery pack 531 includes a circuit board 540 and a secondary battery 513. A label 529 is attached to the secondary battery 513. The circuit board 540 is fixed by a seal 515. The secondary battery pack 531 also has an antenna 517.

[0422] The interior of the secondary battery 513 may have a structure having a wound body or a structure having a laminate.

[0423] In the secondary battery pack 531, for example, as shown in FIG. 24B, a control circuit 590 is provided on the circuit board 540. The circuit board 540 is electrically connected to a terminal 514. The circuit board 540 is also electrically connected to the antenna 517, one of the positive and negative leads 551 of the secondary battery 513, and the other of the positive and negative leads 552.

[0424] Alternatively, as shown in FIG. 24C, it may have a circuit system 590a provided on the circuit board 540 and a circuit system 590b electrically connected to the circuit board 540 via a terminal 514.

[0425] Note that the antenna 517 is not limited to a coil shape, and may be, for example, linear or plate-shaped. Further, antennas such as a planar antenna, an aperture antenna, a traveling wave antenna, an EH antenna, a magnetic field antenna, and a dielectric antenna may be used. Alternatively, the antenna 517 may be a flat plate-shaped conductor. This flat plate-shaped conductor can function as one of the conductors for electric field coupling. That is, the antenna 517 may function as one of the two conductors of the capacitor. Thereby, power can be exchanged not only by an electromagnetic field and a magnetic field but also by an electric field.

[0426] The secondary battery pack 531 has a layer 519 between the antenna 517 and the secondary battery 513. The layer 519 has a function of, for example, shielding the electromagnetic field by the secondary battery 513. As the layer 519, for example, a magnetic material can be used.

[0427] The content of the present embodiment can be freely combined with the content of other embodiments.

[0428] (Embodiment 5) In the present embodiment, an example of manufacturing an all-solid-state battery using the positive electrode active material composite 100z obtained in the above-described embodiment is shown.

[0429] As shown in FIG. 25A, a secondary battery 400 according to one aspect of the present invention has a positive electrode 410, a solid electrolyte layer 420, and a negative electrode 430.

[0430] The positive electrode 410 has a positive electrode current collector 413 and a positive electrode active material layer 414. The positive electrode active material layer 414 has a positive electrode active material 411 and a solid electrolyte 421. The positive electrode active material 411 uses the positive electrode active material composite 100z obtained in the above-described embodiment. Further, the positive electrode active material layer 414 may have a conductive material and a binder.

[0431] The solid electrolyte layer 420 has a solid electrolyte 421. The solid electrolyte layer 420 is located between the positive electrode 410 and the negative electrode 430 and is a region that has neither the positive electrode active material 411 nor the negative electrode active material 431.

[0432] The negative electrode 430 has a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 has a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also have a conductive material and a binder. When metallic lithium is used as the negative electrode active material 431, since it is not necessary to make it into particles, as shown in Fig. 25B, the negative electrode 430 having no solid electrolyte 421 can be used. When metallic lithium is used for the negative electrode 430, it is preferable because the energy density of the secondary battery 400 can be improved.

[0433] As the solid electrolyte 421 included in the solid electrolyte layer 420, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, or the like can be used.

[0434] The sulfide-based solid electrolytes include thio-LISICON-based (Li 10 GeP 2 S 12 、Li 3.25 Ge 0.25 P 0.75 S 4 etc.), sulfide glasses (70Li 2 S·30P 2 S 5 、30Li 2 S·26B 2 S 3 ·44LiI、63Li 2 S·36SiS 2 ·1Li 3 PO 4 、57Li 2 S·38SiS 2 ·5Li 4 SiO 4 、50Li 2 S·50GeS 2 etc.), and sulfide crystallized glasses (Li 7 P 3 S 11 、Li 3.25 P 0.95 S 4 etc.). The sulfide-based solid electrolytes have advantages such as having materials with high conductivity, being synthesizable at low temperatures, and being relatively soft so that the conductive path is easily maintained even after charge and discharge.

[0435] Oxide-based solid electrolytes include materials having a perovskite crystal structure (La 2 / 3-x Li 3x TiO 3 etc.), materials having a NASICON crystal structure (Li 1-Y Al Y Ti 2-Y (PO 4 ) 3 etc.), materials having a garnet crystal structure (Li 7 La 3 Zr 2 O 12 etc.), materials having a LISICON crystal structure (Li 14 ZnGe 4 O 16 etc.), LLZO (Li 7 La 3 Zr 2 O 12 ), oxide glasses (Li 3 PO 4 -Li 4 SiO 4 、50Li 4 SiO 4 ·50Li 3 BO 3 etc.), oxide crystallized glasses (Li 1.07 Al 0.69 Ti 1.46 (PO 4 ) 3 、Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 etc.). Oxide-based solid electrolytes have the advantage of being stable in the atmosphere.

[0436] Halide-based solid electrolytes include LiAlCl 4 、Li 3 InBr 6 、LiF, LiCl, LiBr, LiI, etc. Also, composite materials in which these halide-based solid electrolytes are filled in the pores of porous aluminum oxide or porous silica can be used as solid electrolytes.

[0437] Further, different solid electrolytes may be mixed and used.

[0438] Among them, Li having a NASICON-type crystal structure 1-x Al x Ti 2-x (PO 4 ) 3 (0 < x < 1) (hereinafter referred to as LATP) contains elements such as aluminum and titanium that the positive electrode active material used in the secondary battery 400 of one aspect of the present invention may have. Therefore, a synergistic effect can be expected for improving cycle characteristics, which is preferable. In addition, an improvement in productivity due to reduction of processes can also be expected. In this specification and the like, the NASICON-type crystal structure refers to a structure in which MO 2 (XO 4 ) 3 (M: transition metal, X: S, P, As, Mo, W, etc.) in a compound represented by, in which MO 6 octahedra and XO 4 tetrahedra share vertices and are three-dimensionally arranged.

[0439] 〔Shape of the exterior body and the secondary battery〕 For the exterior body of the secondary battery 400 of one aspect of the present invention, those of various materials and shapes can be used, but it preferably has a function of pressing the positive electrode, the solid electrolyte layer, and the negative electrode.

[0440] For example, FIG. 26 is an example of a cell for evaluating materials of an all-solid-state battery.

[0441] FIG. 26A is a schematic cross-sectional view of the evaluation cell. The evaluation cell has a lower member 761, an upper member 762, and fixing screws or wing nuts 764 for fixing them. By rotating the pressing screw 763, the electrode plate 753 is pressed to fix the evaluation material. An insulator 766 is provided between the lower member 761 and the upper member 762 made of a stainless steel material. An O-ring 765 for sealing is provided between the upper member 762 and the pressing screw 763.

[0442] The evaluation material is placed on the electrode plate 751, surrounded by the insulating tube 752 around it, and is being pressed by the electrode plate 753 from above. A perspective view of the periphery of this evaluation material enlarged is shown in Fig. 26B.

[0443] As an example of the evaluation material, a stack of a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c is shown, and a cross-sectional view is shown in Fig. 26C. In Figs. 26A to 26C, the same reference numerals are used for the same parts.

[0444] The electrode plate 751 and the lower member 761 that are electrically connected to the positive electrode 750a can be said to correspond to the positive electrode terminal. The electrode plate 753 and the upper member 762 that are electrically connected to the negative electrode 750c can be said to correspond to the negative electrode terminal. Electrical resistance and the like can be measured while applying pressure to the evaluation material through the electrode plate 751 and the electrode plate 753.

[0445] Also, for the exterior body of the secondary battery according to one aspect of the present invention, it is preferable to use a package with excellent airtightness. For example, a ceramic package or a resin package can be used. Also, when sealing the exterior body, it is preferable to perform it in an atmosphere that blocks the outside air and is sealed, for example, inside a glove box.

[0446] Fig. 27A shows a perspective view of a secondary battery according to one aspect of the present invention having an exterior body and a shape different from Fig. 26. The secondary battery in Fig. 27A has external electrodes 771 and 772 and is sealed with an exterior body having a plurality of package members.

[0447] An example of a cross-section cut along the dashed line in Fig. 27A is shown in Fig. 27B. The laminate having the positive electrode 750a, the solid electrolyte layer 750b, and the negative electrode 750c is surrounded and sealed by a package member 770a provided with an electrode layer 773a on a flat plate, a frame-shaped package member 770b, and a package member 770c provided with an electrode layer 773b on a flat plate. For the package members 770a, 770b, and 770c, an insulating material, for example, a resin material and ceramic can be used.

[0448] The external electrode 771 is electrically connected to the positive electrode 750a via the electrode layer 773a and functions as a positive electrode terminal. Also, the external electrode 772 is electrically connected to the negative electrode 750c via the electrode layer 773b and functions as a negative electrode terminal.

[0449] By using the positive electrode active material composite 100z obtained in the above-described embodiment, it is possible to realize an all-solid-state secondary battery having a high energy density and good output characteristics.

[0450] The content of this embodiment can be appropriately combined with the content of other embodiments.

[0451] (Embodiment 6) This embodiment is an example different from FIG. 19D which is a cylindrical secondary battery. An example of applying it to an electric vehicle (EV) is shown using FIG. 28C.

[0452] In the electric vehicle, first batteries 1301a and 1301b are installed as main driving secondary batteries, and a second battery 1311 that supplies power to an inverter 1312 that starts a motor 1304 is installed. The second battery 1311 is also called a cranking battery (also called a starter battery). The second battery 1311 only needs to be able to output high power, and a large capacity is not so necessary, and the capacity of the second battery 1311 is smaller compared to the first batteries 1301a and 1301b.

[0453] The internal structure of the first battery 1301a may be a wound type shown in FIG. 20A or FIG. 21C, or may be a laminated type shown in FIG. 22A or FIG. 22B. Also, the first battery 1301a may use the all-solid-state battery of Embodiment 5. By using the all-solid-state battery of Embodiment 5 for the first battery 1301a, a high capacity can be achieved, safety can be improved, and miniaturization and weight reduction can be achieved.

[0454] In this embodiment, an example is shown in which the first batteries 1301a and 1301b are connected in parallel, but they may be connected in parallel with three or more. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack having a plurality of secondary batteries, a large amount of power can be extracted. The plurality of secondary batteries may be connected in parallel, may be connected in series, or may be further connected in series after being connected in parallel. The plurality of secondary batteries are also referred to as a battery pack.

[0455] Also, in an in-vehicle secondary battery, in order to cut off the power from a plurality of secondary batteries, it has a service plug or a circuit breaker that can cut off a high voltage without using tools, and is provided in the first battery 1301a.

[0456] Also, the power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but supplies power to 42V in-vehicle components (electric power steering 1307, heater 1308, defogger 1309, etc.) via the DCDC circuit 1306. Even when the rear wheels have a rear motor 1317, the first battery 1301a is used to rotate the rear motor 1317.

[0457] Also, the second battery 1311 supplies power to 14V in-vehicle components (audio 1313, power window 1314, lamps 1315, etc.) via the DCDC circuit 1310.

[0458] Also, the first battery 1301a will be described with reference to FIG. 28A.

[0459] FIG. 28A shows an example in which nine rectangular secondary batteries 1300 are used as one battery pack 1415. Also, the nine rectangular secondary batteries 1300 are connected in series, and one electrode is fixed by a fixing portion 1413 made of an insulator, and the other electrode is fixed by a fixing portion 1414 made of an insulator. In the present embodiment, an example of fixing by the fixing portions 1413 and 1414 is shown, but it may be configured to be housed in a battery housing box (also referred to as a casing). Since it is assumed that the vehicle is subjected to vibration or shaking from the outside (such as a road surface), it is preferable to fix a plurality of secondary batteries by the fixing portions 1413 and 1414 and the battery housing box or the like. Also, one electrode is electrically connected to the control circuit portion 1320 by a wiring 1421. Also, the other electrode is electrically connected to the control circuit portion 1320 by a wiring 1422.

[0460] Further, the control circuit portion 1320 may use a memory circuit including a transistor using an oxide semiconductor. A charge control circuit or a battery control system having a memory circuit including a transistor using an oxide semiconductor may be referred to as BTOS (Battery operating system, or Battery oxide semiconductor).

[0461] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, as the oxide, it is advisable to use a metal oxide such as an In-M-Zn oxide (the element M is one or more selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, or magnesium). In particular, the In-M-Zn oxide that can be applied as an oxide is preferably CAAC-OS (C-Axis Aligned Crystal Oxide Semiconductor) or CAC-OS (Cloud-Aligned Composite Oxide Semiconductor). Also, as the oxide, In-Ga oxide or In-Zn oxide may be used. CAAC-OS is an oxide semiconductor having a plurality of crystal regions, and the c-axis of the plurality of crystal regions is oriented in a specific direction. Note that the specific direction is the thickness direction of the CAAC-OS film, the normal direction of the surface on which the CAAC-OS film is formed, or the normal direction of the surface of the CAAC-OS film. Also, the crystal region is a region having periodicity in the atomic arrangement. Note that when the atomic arrangement is regarded as a lattice arrangement, the crystal region is also a region where the lattice arrangements are aligned. Furthermore, CAAC-OS has a region where a plurality of crystal regions are connected in the a-b plane direction, and this region may have strain. Note that the strain refers to a portion where the direction of the lattice arrangement changes between a region where the lattice arrangements are aligned and another region where the lattice arrangements are aligned in the region where the plurality of crystal regions are connected. That is, CAAC-OS is an oxide semiconductor with c-axis orientation and no obvious orientation in the a-b plane direction. Also, CAC-OS is, for example, a configuration of a material in which the elements constituting the metal oxide are unevenly distributed in a size of 0.5 nm or more and 10 nm or less, preferably 1 nm or more and 3 nm or less, or in the vicinity thereof. Note that hereinafter, in a metal oxide, a state in which one or more metal elements are unevenly distributed and the regions having the metal elements are mixed in a size of 0.5 nm or more and 10 nm or less, preferably 1 nm or more and 3 nm or less, or in the vicinity thereof is also referred to as a mosaic state or a patch state.

[0462] Furthermore, in CAC-OS, materials are separated into a first region and a second region, forming a mosaic pattern, and the first region has a structure distributed in the film (hereinafter also referred to as a cloud-like structure). That is, CAC-OS is a composite metal oxide having a structure in which the first region and the second region are mixed.

[0463] Here, the atomic number ratios of In, Ga, and Zn to the metal elements constituting CAC-OS in the In-Ga-Zn oxide are denoted as [In], [Ga], and [Zn], respectively. For example, in CAC-OS in the In-Ga-Zn oxide, the first region is a region where [In] is larger than [In] in the composition of the CAC-OS film. Also, the second region is a region where [Ga] is larger than [Ga] in the composition of the CAC-OS film. Or, for example, the first region is a region where [In] is larger than [In] in the second region and [Ga] is smaller than [Ga] in the second region. Also, the second region is a region where [Ga] is larger than [Ga] in the first region and [In] is smaller than [In] in the first region.

[0464] Specifically, the above-mentioned first region is a region mainly composed of indium oxide, indium zinc oxide, etc. Also, the above-mentioned second region is a region mainly composed of gallium oxide, gallium zinc oxide, etc. That is, the above-mentioned first region can be rephrased as a region mainly composed of In. Also, the above-mentioned second region can be rephrased as a region mainly composed of Ga.

[0465] Note that there may be cases where no clear boundary can be observed between the above-mentioned first region and the above-mentioned second region.

[0466] For example, in the case of CAC-OS in In-Ga-Zn oxide, it can be confirmed by EDX mapping obtained using energy dispersive X-ray spectroscopy (EDX) that the region mainly composed of In (the first region) and the region mainly composed of Ga (the second region) are unevenly distributed and have a mixed structure.

[0467] When CAC-OS is used in a transistor, the conductivity caused by the first region and the insulating property caused by the second region act complementarily, thereby enabling the function of switching (the function of turning on / off) to be imparted to CAC-OS. That is, CAC-OS has a conductive function in a part of the material and an insulating function in a part of the material, and has a function as a semiconductor in the whole material. By separating the conductive function and the insulating function, both functions can be enhanced to the maximum extent. Therefore, by using CAC-OS in a transistor, a high on-current (I on ), a high field-effect mobility (μ), and a good switching operation can be realized.

[0468] Oxide semiconductors have various structures and each has different characteristics. The oxide semiconductor according to one aspect of the present invention may have two or more of an amorphous oxide semiconductor, a polycrystalline oxide semiconductor, an a-like OS (amorphous-like Oxide Semiconductor), a CAC-OS, an nc-OS (nano crystalline Oxide Semiconductor), and a CAAC-OS.

[0469] In addition, since it can be used in a high-temperature environment, it is preferable that the control circuit unit 1320 uses a transistor using an oxide semiconductor. In order to simplify the process, the control circuit unit 1320 may be formed using a unipolar transistor. A transistor using an oxide semiconductor for the semiconductor layer has an operating ambient temperature range wider than that of a single-crystalline Si transistor, which is -40°C or higher and 150°C or lower, and even when the secondary battery overheats, the characteristic change is smaller than that of a single-crystalline Si transistor. The off-current of a transistor using an oxide semiconductor is below the measurement lower limit even at 150°C, while the off-current characteristic of a single-crystalline Si transistor has a large temperature dependence. For example, at 150°C, the off-current of a single-crystalline Si transistor increases, and the current on / off ratio does not become sufficiently large. The control circuit unit 1320 can improve safety. Further, by combining with a secondary battery using the positive electrode active material composite 100z obtained in the above-described embodiment for the positive electrode, a synergistic effect on safety can be obtained.

[0470] The control circuit unit 1320 using a memory circuit including a transistor using an oxide semiconductor can also function as an automatic control device for a secondary battery against causes of instability such as micro-shorts. Functions for eliminating the causes of instability of the secondary battery include prevention of overcharging, prevention of overcurrent, overheat control during charging, cell balance in a battery pack, prevention of over-discharge, remaining capacity meter, automatic control of charging voltage and current according to temperature, control of charging current according to degree of deterioration, detection of abnormal behavior of micro-shorts, prediction of abnormalities related to micro-shorts, etc. The control circuit unit 1320 has at least one of these functions. In addition, the automatic control device for the secondary battery can be miniaturized.

[0471] In addition, a micro-short refers to a minute short circuit inside the secondary battery, not to the state where the positive electrode and the negative electrode of the secondary battery are short-circuited and charging and discharging are impossible, but to the phenomenon where a slight short-circuit current flows through a minute short-circuit part. Since a large voltage change occurs even in a relatively short time and at a small location, the abnormal voltage value may affect subsequent estimations.

[0472] One of the causes of micro-short circuit is that due to multiple charge and discharge cycles, the uneven distribution of the positive electrode active material results in local current concentration between a part of the positive electrode and a part of the negative electrode, causing a part of the separator to malfunction or a micro short circuit to occur due to the generation of side reaction products from side reactions.

[0473] Also, not only can the control circuit unit 1320 detect micro short circuits, but it can also be said to detect the terminal voltage of the secondary battery and manage the charge and discharge state of the secondary battery. For example, in order to prevent overcharging, both the output transistor of the charging circuit and the cutoff switch can be turned off almost simultaneously.

[0474] Also, an example of the block diagram of the battery pack 1415 shown in FIG. 28A is shown in FIG. 28B.

[0475] The control circuit unit 1320 includes a switch unit 1324 including at least a switch for preventing overcharging and a switch for preventing over-discharging, a control circuit 1322 for controlling the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 has the upper limit voltage and the lower limit voltage of the secondary battery to be used set, and limits the input current from the outside and the output current to the outside. The range between the lower limit voltage and the upper limit voltage of the secondary battery is the recommended voltage range for use. When outside this range, the switch unit 1324 operates and functions as a protection circuit. Also, since the control circuit unit 1320 controls the switch unit 1324 to prevent over-discharging and overcharging, it can also be called a protection circuit. For example, when the control circuit 1322 detects a voltage that is likely to cause overcharging, the switch of the switch unit 1324 is turned off to cut off the current. Further, a PTC element may be provided in the charge and discharge path to provide a function of cutting off the current in response to an increase in temperature. Also, the control circuit unit 1320 has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0476] The switch section 1324 can be configured by combining an n-channel transistor and a p-channel transistor. The switch section 1324 is not limited to a switch having an Si transistor using single-crystalline silicon. For example, it may be formed of a power transistor having Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), GaO x (gallium oxide; x is a real number greater than 0), etc. Also, since a memory element using an OS transistor can be freely arranged by laminating it on a circuit using an Si transistor or the like, integration can be easily performed. Further, since an OS transistor can be manufactured using the same manufacturing equipment as an Si transistor, it can be manufactured at low cost. That is, a control circuit section 1320 using an OS transistor can be laminated on the switch section 1324 and integrated into one chip. Since the occupied volume of the control circuit section 1320 can be reduced, miniaturization is possible.

[0477] The first batteries 1301a and 1301b mainly supply power to in-vehicle devices of the 42V system (high voltage system), and the second battery 1311 supplies power to in-vehicle devices of the 14V system (low voltage system).

[0478] In the present embodiment, an example is shown in which a lithium-ion secondary battery is used for both the first battery 1301a and the second battery 1311. The second battery 1311 may use a lead-acid battery, a all-solid-state battery, or an electric double layer capacitor. For example, the all-solid-state battery of Embodiment 5 may be used. By using the all-solid-state battery of Embodiment 5 for the second battery 1311, a high capacity can be achieved, and miniaturization and weight reduction can be achieved.

[0479] In addition, the regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305 and is charged to the second battery 1311 via the motor controller 1303 and the control circuit unit 1321 from the battery controller 1302. Or it is charged to the first battery 1301a via the control circuit unit 1320 from the battery controller 1302. Or it is charged to the first battery 1301b via the control circuit unit 1320 from the battery controller 1302. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b can be rapidly charged.

[0480] The battery controller 1302 can set the charging voltage, charging current, etc. of the first batteries 1301a and 1301b. The battery controller 1302 can set the charging conditions according to the charging characteristics of the secondary battery to be used and perform rapid charging.

[0481] Also, although not shown, when connected to an external charger, the charger's plug or the charger's connection cable is electrically connected to the battery controller 1302. The power supplied from the external charger is used to charge the first batteries 1301a and 1301b via the battery controller 1302. Also, depending on the charger, a control circuit may be provided and in some cases, the functions of the battery controller 1302 may not be used, but it is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320 to prevent overcharging. Also, in some cases, the charger's plug or the charger's connection cable may be equipped with a control circuit. The control circuit unit 1320 may also be called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) provided in the electric vehicle. The CAN is one of the serial communication standards used as an in-vehicle LAN. Also, the ECU includes a microcomputer. Also, the ECU uses a CPU or a GPU.

[0482] External chargers installed in charging stands, etc. include 100V outlets, 200V outlets, three-phase 200V and 50kW, etc. It is also possible to receive power supply from external charging facilities by means of non-contact power supply and charge the battery.

[0483] When performing rapid charging, in order to charge in a short time, a secondary battery that can withstand charging at a high voltage is desired.

[0484] In addition, the secondary battery of the present embodiment described above uses the positive electrode active material composite 100z obtained in the previous embodiment. Furthermore, by using graphene as the conductive material and increasing the thickness of the electrode layer to increase the loading amount, it is possible to suppress a decrease in capacity and maintain a high capacity, and as a synergistic effect, a secondary battery with significantly improved electrical characteristics can be realized. In particular, it is effective for secondary batteries used in vehicles, and it is possible to provide a vehicle with a long cruising range, specifically, a vehicle with a single-charge driving range of 500 km or more, without increasing the ratio of the weight of the secondary battery to the total weight of the vehicle.

[0485] In particular, the secondary battery of the present embodiment described above can increase the operating voltage of the secondary battery by using the positive electrode active material composite 100z described in the previous embodiment, and as the charging voltage increases, the available capacity can be increased. In addition, by using the positive electrode active material composite 100z described in the previous embodiment for the positive electrode, it is possible to provide a secondary battery for vehicles with excellent cycle characteristics.

[0486] Next, an example of mounting a secondary battery, which is an aspect of the present invention, on a vehicle, typically a transport vehicle, will be described.

[0487] In addition, when the secondary battery shown in any one of FIGS. 19D, 21C, and 28A is mounted on a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV) can be realized. In addition, secondary batteries can also be mounted on transportation vehicles such as agricultural machinery, motorized bicycles including electric assist bicycles, motorcycles, electric wheelchairs, electric carts, small or large ships, submarines, aircraft such as fixed-wing aircraft and rotary-wing aircraft, rockets, artificial satellites, space exploration vehicles, and planetary exploration vehicles. The secondary battery according to one aspect of the present invention can be a high-capacity secondary battery. Therefore, the secondary battery according to one aspect of the present invention is suitable for miniaturization and weight reduction and can be preferably used in transportation vehicles.

[0488] In FIGS. 29A to 29D, a transportation vehicle is illustrated as an example of a moving body using one aspect of the present invention. The automobile 2001 shown in FIG. 29A is an electric vehicle that uses an electric motor as a power source for running. Or, it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as power sources for running. When mounting a secondary battery on a vehicle, an example of the secondary battery shown in Embodiment 4 is installed at one location or at a plurality of locations. The automobile 2001 shown in FIG. 29A has a battery pack 2200, and the battery pack has a secondary battery module in which a plurality of secondary batteries are connected. Further, it preferably has a charge control device electrically connected to the secondary battery module.

[0489] In addition, the automobile 2001 can be charged by receiving power supply from an external charging facility by a plug-in method, a non-contact power supply method, or the like to the secondary battery that the automobile 2001 has. At the time of charging, the charging method, the standard of the connector, etc. may be appropriately performed in a predetermined method such as CHAdeMO (registered trademark) or Combo. The secondary battery may be a charging station provided in a commercial facility or a household power source. For example, by plug-in technology, the power storage device mounted on the automobile 2001 can be charged by external power supply. Charging can be performed by converting AC power into DC power through a conversion device such as an AC-DC converter.

[0490] Further, although not shown, a power receiving device can be mounted on a vehicle, and power can be supplied and charged non - contactlessly from a power transmitting device on the ground. In the case of this non - contact power supply method, by incorporating a power transmitting device into a road or an outer wall, charging can be performed not only while the vehicle is stopped but also while it is running. Also, using this non - contact power supply method, power can be transmitted and received between two vehicles. Furthermore, a solar cell can be provided on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped and when it is running. For such non - contact power supply, an electromagnetic induction method or a magnetic resonance method can be used.

[0491] Figure 29B shows a large transport vehicle 2002 having an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 has, for example, four secondary batteries with a nominal voltage of 3.0V or more and 5.0V or less as a cell unit, and a maximum voltage of 170V with 48 cells connected in series. Since it has the same functions as those in Figure 29A except for the number of secondary batteries constituting the secondary battery module of the battery pack 2201, the description is omitted.

[0492] Figure 29C shows a large transport vehicle 2003 having an electrically controlled motor as an example. The secondary battery module of the transport vehicle 2003 has a maximum voltage of 600V with, for example, more than one hundred secondary batteries with a nominal voltage of 3.0V or more and 5.0V or less connected in series. By using the negative electrode 570a obtained in the above - mentioned embodiment as the negative electrode, a cylindrical secondary battery 616 with high capacity, high charge - discharge capacity, and excellent cycle characteristics can be obtained. Also, by using a secondary battery using the positive electrode active material composite 100z described in the above - mentioned embodiment as the positive electrode, a secondary battery with good rate characteristics and charge - discharge cycle characteristics can be manufactured, which can contribute to the high performance and long life of the transport vehicle 2003. Since it has the same functions as those in Figure 29A except for the number of secondary batteries constituting the secondary battery module of the battery pack 2202, the description is omitted.

[0493] Figure 29D shows an aircraft 2004 having an engine that burns fuel as an example. Since the aircraft 2004 shown in Figure 29D has wheels for takeoff and landing, it can be said to be a type of transport vehicle, and has a battery pack 2203 that constitutes a secondary battery module by connecting a plurality of secondary batteries and includes the secondary battery module and a charge control device.

[0494] The secondary battery module of the aircraft 2004 has a maximum voltage of 32V by connecting, for example, eight 4V secondary batteries in series. Since it has the same functions as those in Figure 29A except for the number of secondary batteries constituting the secondary battery module of the battery pack 2203 and the like, the description thereof is omitted.

[0495] The content of this embodiment can be appropriately combined with the content of other embodiments.

[0496] (Embodiment 7) In this embodiment, an example of mounting a secondary battery, which is one aspect of the present invention, on a building will be described with reference to Figures 30A and 30B.

[0497] The house shown in Figure 30A has a power storage device 2612 having a secondary battery, which is one aspect of the present invention, and a solar panel 2610. The power storage device 2612 is electrically connected via the solar panel 2610, wiring 2611, and the like. Also, the power storage device 2612 and a ground-mounted charging device 2604 may be electrically connected. The electric power obtained by the solar panel 2610 can be used to charge the power storage device 2612. Further, the electric power stored in the power storage device 2612 can be used to charge the secondary battery of the vehicle 2603 via the charging device 2604. The power storage device 2612 is preferably installed in the underfloor space. By installing it in the underfloor space, the space above the floor can be effectively utilized. Alternatively, the power storage device 2612 may be installed on the floor.

[0498] The power stored in the power storage device 2612 can also supply power to other electronic devices in the house. Therefore, even when power supply from the commercial power source cannot be received due to a power outage or the like, by using the power storage device 2612 according to one aspect of the present invention as an uninterruptible power supply, the electronic devices can be used.

[0499] FIG. 30B shows an example of a power storage device according to one aspect of the present invention. As shown in FIG. 30B, a power storage device 791 according to one aspect of the present invention is installed in the underfloor space 796 of the building 799. Further, a control circuit described in Embodiment 6 may be provided in the power storage device 791. Further, by using the negative electrode 570a obtained in the above-described embodiment as the negative electrode, a cylindrical secondary battery 616 having a high capacity, a high charge / discharge capacity, and excellent cycle characteristics can be obtained. Further, by using a secondary battery using the positive electrode active material composite 100z obtained in the above-described embodiment as the positive electrode for the power storage device 791, a long-life power storage device 791 can be obtained.

[0500] A control device 790 is installed in the power storage device 791, and the control device 790 is electrically connected to the distribution board 703, the power storage controller 705 (also referred to as a control device), the display 706, and the router 709 by wiring.

[0501] Power is sent from the commercial power source 701 to the distribution board 703 via the lead wire attachment portion 710. Further, power is sent to the distribution board 703 from the power storage device 791 and the commercial power source 701, and the distribution board 703 supplies the sent power to the general load 707 and the power storage system load 708 via an outlet (not shown).

[0502] The general load 707 is, for example, electrical devices such as a television and a personal computer, and the power storage system load 708 is, for example, electrical devices such as a microwave oven, a refrigerator, and an air conditioner.

[0503] The power storage controller 705 includes a measurement unit 711, a prediction unit 712, and a planning unit 713. The measurement unit 711 has a function of measuring the amount of power consumed by the general load 707 and the power storage system load 708 during one day (for example, from 0:00 to 24:00). Further, the measurement unit 711 may have a function of measuring the amount of power of the power storage device 791 and the amount of power supplied from the commercial power supply 701. Further, the prediction unit 712 has a function of predicting the required power consumption amount consumed by the general load 707 and the power storage system load 708 during the next day based on the amount of power consumed by the general load 707 and the power storage system load 708 during one day. Further, the planning unit 713 has a function of making a charge / discharge plan for the power storage device 791 based on the required power consumption amount predicted by the prediction unit 712.

[0504] The amount of power consumed by the general load 707 and the power storage system load 708 measured by the measurement unit 711 can be confirmed by the display 706. Further, it can also be confirmed in electrical devices such as a television and a personal computer via the router 709. Furthermore, it can also be confirmed by a portable electronic terminal such as a smartphone and a tablet via the router 709. Also, the required power consumption amount for each time period (or every hour) predicted by the prediction unit 712 can also be confirmed by the display 706, the electrical device, and the portable electronic terminal.

[0505] The content of this embodiment can be appropriately combined with the content of other embodiments.

[0506] (Embodiment 8) In this embodiment, an example of mounting a power storage device, which is one aspect of the present invention, on a two-wheeled vehicle or a bicycle is shown.

[0507] FIG. 31A is an example of an electric bicycle using a power storage device according to one aspect of the present invention. The power storage device according to one aspect of the present invention can be applied to the electric bicycle 8700 shown in FIG. 31A. The power storage device according to one aspect of the present invention has, for example, a plurality of storage batteries and a protection circuit.

[0508] The electric bicycle 8700 is equipped with a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists the driver. Also, the power storage device 8702 is portable and is shown in a state removed from the bicycle in Fig. 31B. Further, the power storage device 8702 incorporates a plurality of storage batteries 8701 that the power storage device of one aspect of the present invention has, and can display the remaining battery level and the like on a display unit 8703. Also, the power storage device 8702 has a control circuit 8704 capable of charging control or abnormality detection of the secondary battery shown as an example in Embodiment 6. The control circuit 8704 is electrically connected to the positive and negative electrodes of the storage battery 8701. Also, a small solid secondary battery shown in Figs. 27A and 27B may be provided in the control circuit 8704. By providing the small solid secondary battery shown in Figs. 27A and 27B in the control circuit 8704, it is also possible to supply power to retain data in the memory circuit of the control circuit 8704 for a long time. Also, by combining with a secondary battery using the positive electrode active material composite 100z obtained in the above-described embodiment as the positive electrode, a synergistic effect on safety can be obtained. The secondary battery using the positive electrode active material composite 100z obtained in the above-described embodiment as the positive electrode and the control circuit 8704 can greatly contribute to extinguishing accidents such as fires caused by the secondary battery.

[0509] Also, Fig. 31C is an example of a two-wheeled vehicle using a power storage device of one aspect of the present invention. The scooter 8600 shown in Fig. 31C includes a power storage device 8602, side mirrors 8601, and direction indicator lights 8603. The power storage device 8602 can supply electricity to the direction indicator lights 8603. Also, the power storage device 8602 in which a plurality of secondary batteries using the positive electrode active material composite 100z obtained in the above-described embodiment as the positive electrode are housed can have a high capacity and can contribute to miniaturization.

[0510] Also, the scooter 8600 shown in Fig. 31C can house the power storage device 8602 in an under-seat storage 8604. The power storage device 8602 can be housed in the under-seat storage 8604 even if the under-seat storage 8604 is small.

[0511] The content of this embodiment can be appropriately combined with the content of other embodiments.

[0512] (Embodiment 9) In this embodiment, an example of mounting a secondary battery, which is one aspect of the present invention, on an electronic device will be described. Examples of the electronic device on which the secondary battery is mounted include, for example, a television device (also referred to as a TV or a television receiver), a monitor for a computer, a digital camera, a digital video camera, a digital photo frame, a mobile phone (also referred to as a cellular phone or a mobile phone device), a portable game machine, a portable information terminal, an audio reproduction device, and a large game machine such as a pachinko machine. Examples of the portable information terminal include a notebook personal computer, a tablet terminal, an e-book terminal, and a mobile phone.

[0513] FIG. 32A shows an example of a mobile phone. The mobile phone 2100 includes, in addition to a display unit 2102 incorporated in a housing 2101, operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. Note that the mobile phone 2100 has a secondary battery 2107. By providing the secondary battery 2107 using the positive electrode active material composite 100z described in the above embodiments for the positive electrode, a high capacity can be achieved, and a configuration that can cope with space saving accompanying the miniaturization of the housing can be realized.

[0514] The mobile phone 2100 can execute various applications such as mobile phone calls, e-mails, text viewing and creation, music reproduction, Internet communication, and computer games.

[0515] In addition to time setting, the operation buttons 2103 can have various functions such as turning on and off the power, turning on and off wireless communication, executing and canceling the silent mode, and executing and canceling the power saving mode. For example, the functions of the operation buttons 2103 can be freely set by the operating system incorporated in the mobile phone 2100.

[0516] In addition, the mobile phone 2100 is capable of performing short-range wireless communication that complies with a communication standard. For example, it can also make hands-free calls by communicating with a wireless-capable headset.

[0517] The mobile phone 2100 is also provided with an external connection port 2104, and can directly exchange data with other information terminals via a connector. Charging can also be performed via the external connection port 2104. Note that the charging operation may also be performed by wireless power supply without using the external connection port 2104.

[0518] The mobile phone 2100 preferably has sensors. As sensors, for example, it is preferable to mount human body sensors such as fingerprint sensors, pulse sensors, body temperature sensors, touch sensors, pressure sensors, acceleration sensors, and the like.

[0519] Figure 32B shows an unmanned aerial vehicle 2300 having a plurality of rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 has a secondary battery 2301, a camera 2303, and an antenna (not shown), which are aspects of the present invention. The unmanned aerial vehicle 2300 can be remotely operated via the antenna. The secondary battery using the positive electrode active material composite 100z obtained in the above-described embodiment as the positive electrode has a high energy density and high safety, and thus can be safely used for a long time over a long period, and is suitable as the secondary battery mounted on the unmanned aerial vehicle 2300.

[0520] Figure 32C shows an example of a robot. The robot 6400 shown in Figure 32C includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a moving mechanism 6408, an arithmetic unit, and the like.

[0521] The microphone 6402 has a function of detecting the user's voice, environmental sounds, etc. Also, the speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.

[0522] The display unit 6405 has a function of displaying various information. The robot 6400 can display the information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. Also, the display unit 6405 may be a removable information terminal, and by installing it at a fixed position of the robot 6400, charging and data transfer are made possible.

[0523] The upper camera 6403 and the lower camera 6406 have a function of imaging the surroundings of the robot 6400. Also, the obstacle sensor 6407 can detect the presence or absence of obstacles in the traveling direction when the robot 6400 moves forward using the moving mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0524] The robot 6400 includes a secondary battery 6409 according to one aspect of the present invention and semiconductor devices or electronic components in its internal area. The secondary battery using the positive electrode active material composite 100z obtained in the above-described embodiment for the positive electrode has a high energy density and high safety, so it can be safely used for a long time over a long period, and is suitable as the secondary battery 6409 mounted on the robot 6400.

[0525] FIG. 32D shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 disposed on the upper surface of the housing 6301, a plurality of cameras 6303 disposed on the side surface, a brush 6304, operation buttons 6305, a secondary battery 6306, various sensors, etc. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, etc. The cleaning robot 6300 can move autonomously, detect dust 6310, and suck the dust from the suction port provided on the lower surface.

[0526] For example, the cleaning robot 6300 can analyze the image captured by the camera 6303 and determine the presence or absence of obstacles such as walls, furniture, or steps. Also, when an object that is likely to get caught in the brush 6304, such as wiring, is detected by image analysis, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 includes a secondary battery 6306 according to one aspect of the present invention and a semiconductor device or electronic components in its internal region. The secondary battery using the positive electrode active material composite 100z obtained in the above-described embodiment as the positive electrode has a high energy density and high safety, so it can be safely used for a long time over a long period, and is suitable as the secondary battery 6306 mounted on the cleaning robot 6300.

[0527] FIG. 33A shows an example of a wearable device. The wearable device uses a secondary battery as a power source. Also, when the user uses it in daily life or outdoors, in order to enhance the anti-foaming performance, water resistance performance, or dustproof performance, a wearable device that can perform not only wired charging with the connector part being exposed but also wireless charging is desired.

[0528] For example, a secondary battery according to one aspect of the present invention can be mounted on a glasses-type device 4000 as shown in FIG. 33A. The glasses-type device 4000 has a frame 4000a and a display unit 4000b. By mounting the secondary battery on the temple portion of the frame 4000a having a curvature, a lightweight glasses-type device 4000 with a good weight balance and a long continuous use time can be obtained. The secondary battery using the positive electrode active material composite 100z obtained in the above-described embodiment for the positive electrode has a high energy density and can realize a configuration capable of coping with space saving accompanying the miniaturization of the housing.

[0529] In addition, a secondary battery according to one aspect of the present invention can be mounted on a headset-type device 4001. The headset-type device 4001 has at least a microphone unit 4001a, a flexible pipe 4001b, and an earphone unit 4001c. The secondary battery can be provided inside the flexible pipe 4001b or inside the earphone unit 4001c. The secondary battery using the positive electrode active material composite 100z obtained in the above-described embodiment for the positive electrode has a high energy density and can realize a configuration capable of coping with space saving accompanying the miniaturization of the housing.

[0530] In addition, a secondary battery according to one aspect of the present invention can be mounted on a device 4002 that can be directly attached to the body. The secondary battery 4002b can be provided inside the thin housing 4002a of the device 4002. The secondary battery using the positive electrode active material composite 100z obtained in the above-described embodiment for the positive electrode has a high energy density and can realize a configuration capable of coping with space saving accompanying the miniaturization of the housing.

[0531] In addition, a secondary battery according to one aspect of the present invention can be mounted on a device 4003 that can be attached to clothing. The secondary battery 4003b can be provided inside the thin housing 4003a of the device 4003. The secondary battery using the positive electrode active material composite 100z obtained in the above-described embodiment for the positive electrode has a high energy density and can realize a configuration capable of coping with space saving accompanying the miniaturization of the housing.

[0532] In addition, a secondary battery according to one embodiment of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 has a belt portion 4006a and a wireless power feeding / receiving portion 4006b, and a secondary battery can be mounted in the internal region of the belt portion 4006a. The secondary battery using the positive electrode active material composite 100z obtained in the above-described embodiment for the positive electrode has a high energy density and can realize a configuration that can cope with space saving accompanying the miniaturization of the housing.

[0533] In addition, a secondary battery according to one embodiment of the present invention can be mounted on the wristwatch-type device 4005. The wristwatch-type device 4005 has a display portion 4005a and a belt portion 4005b, and a secondary battery can be provided in the display portion 4005a or the belt portion 4005b. The secondary battery using the positive electrode active material composite 100z obtained in the above-described embodiment for the positive electrode has a high energy density and can realize a configuration that can cope with space saving accompanying the miniaturization of the housing.

[0534] The display portion 4005a can display various information such as not only time but also incoming mails and calls.

[0535] In addition, since the wristwatch-type device 4005 is a wearable device of a type that is directly wound around the wrist, a sensor for measuring the user's pulse, blood pressure, etc. may be mounted. Data regarding the user's exercise amount and health can be accumulated to manage the health.

[0536] Fig. 33B shows a perspective view of the wristwatch-type device 4005 removed from the wrist.

[0537] In addition, a side view is shown in Fig. 33C. Fig. 33C shows a state in which a secondary battery 913 is built in the internal region. The secondary battery 913 is the secondary battery shown in Embodiment 4. The secondary battery 913 is provided at a position overlapping the display portion 4005a, and can have a high density and a high capacity, and is small and lightweight.

[0538] In the wristwatch-type device 4005, since it is required to be small and lightweight, by using the positive electrode active material composite 100z obtained in the above-described embodiment for the positive electrode of the secondary battery 913, a secondary battery 913 with a high energy density and small size can be obtained.

[0539] FIG. 33D shows an example of wireless earphones. Here, wireless earphones having a pair of main bodies 4100a and 4100b are illustrated, but they do not necessarily have to be a pair.

[0540] The main bodies 4100a and 4100b have a driver unit 4101, an antenna 4102, and a secondary battery 4103. They may have a display unit 4104. It is also preferable to have a substrate on which circuits such as an IC for wireless communication are mounted, a charging terminal, etc. They may also have a microphone.

[0541] The case 4110 has a secondary battery 4111. It is also preferable to have a substrate on which circuits such as a wireless IC and a charge control IC are mounted, and a charging terminal. It may also have a display unit, buttons, etc.

[0542] The main bodies 4100a and 4100b can communicate wirelessly with other electronic devices such as a smartphone. Thereby, sound data etc. sent from other electronic devices can be reproduced by the main bodies 4100a and 4100b. Also, if the main bodies 4100a and 4100b have a microphone, the sound acquired by the microphone can be sent to other electronic devices, and after being processed by the electronic devices, the sound data can be sent back to the main bodies 4100a and 4100b for reproduction. Thereby, for example, it can also be used as a translator.

[0543] In addition, charging can be performed from the secondary battery 4111 included in the case 4110 to the secondary battery 4103 included in the main body 4100a. As the secondary battery 4111 and the secondary battery 4103, a coin-type secondary battery, a cylindrical secondary battery, or the like of the previous embodiment can be used. The secondary battery obtained in the above-described embodiment has a high energy density, and by using it for the secondary battery 4103 and the secondary battery 4111, a configuration that can cope with space saving due to the miniaturization of the wireless earphone can be realized.

[0544] This embodiment can be implemented in appropriate combination with other embodiments.

Example

[0545] In this example, a negative electrode of one aspect of the present invention was fabricated, and the fabricated negative electrode was evaluated.

[0546] <Fabrication of negative electrode> A negative electrode was fabricated according to the flow shown in FIG. 7. As the particles having silicon, Aldrich-made nanosilicon particles were used. As the particles having graphite, artificial graphite particles MCMB-G10 manufactured by Linyi Gelon New Battery Materials were used. Graphene oxide was used as the graphene compound. A polyimide precursor manufactured by Toray Industries, Inc. was used as the polyimide.

[0547] As the negative electrode, electrode GS1 was fabricated. The weight ratio of the materials prepared in steps S61, S72, S80, and S87 in FIG. 7 was artificial graphite particles:nanosilicon particles:graphene oxide:polyimide precursor = 82.8:9.2:5:3 by weight. Note that the ratio of artificial graphite particles to nanosilicon particles is 9:1 by weight.

[0548] Nanosilicon particles and a solvent were prepared and mixed (steps S61, S62, S63 in FIG. 7). NMP was used as the solvent. The mixing was performed at 2000 rpm for 3 minutes using a rotation revolution mixer (Avatori Rentaro, manufactured by THINKY Corporation), and the mixture was recovered to obtain mixture E-1 (steps S64, S65 in FIG. 7).

[0549] Next, artificial graphite particles were prepared and mixed with mixture E-1 (steps S72 and S73 in FIG. 7). The mixing was carried out at 2000 rpm for 3 minutes using a rotating and revolving mixer, and then the mixture was recovered to obtain mixture E-2 (steps S74 and S75 in FIG. 7).

[0550] Next, mixture E-2 and the graphene compound were repeatedly mixed while adding a solvent. As the graphene compound, graphene oxide was prepared, and the mixing was carried out at 2000 rpm for 3 minutes using a rotating and revolving mixer, and then the mixture was recovered (steps S80, S81, and S82 in FIG. 7). Next, the recovered mixture was kneaded, and NMP was appropriately added, and the mixture was mixed at 2000 rpm for 3 minutes using a rotating and revolving mixer, and then the mixture was recovered (steps S83, S84, and step S85 in FIG. 7). Steps S83 to S85 were repeated 5 times to obtain mixture E-3 (step S86 in FIG. 7).

[0551] Next, mixture E-3 and the polyimide precursor were mixed (step S88 in FIG. 7). The mixing was carried out at 2000 rpm for 3 minutes using a rotating and revolving mixer. Then, NMP was prepared and added to the mixture to adjust the viscosity (step S89 in FIG. 7), and further mixing was carried out (2000 rpm for 3 minutes twice using a rotating and revolving mixer), and the mixture was recovered to obtain mixture E-4 as a slurry (steps S90, S91, and S92 in FIG. 7).

[0552] Next, a current collector was prepared, and mixture E-4 was coated (steps S93 and S94 in FIG. 7). As the current collector, a copper foil with a thickness of 18 μm was prepared, and mixture E-3 was used to coat mixture E-4 on the copper foil using a doctor blade with a gap thickness of 100 μm.

[0553] Next, the copper foil coated with mixture E-4 was first heated at 50° C. for 1 hour (step S95 in FIG. 7). Then, under reduced pressure, it was secondarily heated at 400° C. for 5 hours (step S96 in FIG. 7) to obtain an electrode. By heating, graphene oxide is reduced and the oxygen content decreases.

[0554] <sem> SEM observation of the surface of the fabricated electrode was carried out. The SEM used was S4800 manufactured by Hitachi High-Technologies. The acceleration voltage was set at 5 kV.

[0555] Figures 34A and 34B are observation images of the surface of electrode GS1. In the SEM images, the nanosilicon particles show relatively bright contrast.

[0556] Figure 34B is an enlarged image of the surface of electrode GS1. On the surface of graphite particles with a particle size of approximately 5 μm or more and 15 μm or less, a plurality of nanosilicon particles with a size of approximately 50 nm or more and 250 nm or less were present, and a region where these plurality of nanosilicon particles were covered with graphene (reduced graphene oxide) was observed. In other words, it can be said that electrode GS1 has a region where a mixed layer of nanosilicon particles and graphene covers the graphite particles.

[0557] <Fabrication of Coin Cell> Next, five CR2032 type (diameter 20 mm, height 3.2 mm) coin cells (also called coin-type secondary batteries) were fabricated using the fabricated electrode GS1 (GS-C1, GS-C2, GS-C3, GS-C4, GS-C5).

[0558] Lithium metal was used as the counter electrode. As the electrolyte, a mixture of lithium hexafluorophosphate (LiPF 6 ) and ethylene carbonate (EC) and diethyl carbonate (DEC) mixed at a volume ratio of EC:DEC = 3:7, with a concentration of 1 mol / L, was used.

[0559] A 25-μm-thick polypropylene separator was used as the separator.

[0560] Stainless steel (SUS)-formed positive and negative cans were used.

[0561] <Charge and Discharge Characteristics> The charge-discharge characteristics were evaluated using the five fabricated coin cells. Since lithium metal was used as the counter electrode, in the fabricated coin cells, electrode GS1 acts as the positive electrode, lithium is intercalated into the electrode during discharge, and lithium is released from the electrode during charging.

[0562] For the five fabricated coin cells, as the first charge-discharge, the discharge condition (lithium intercalation) was a constant current discharge (0.1C, lower limit voltage 0.01V) followed by a constant voltage discharge (lower limit current density 0.01C), and the charging condition (lithium deintercalation) was a constant current charge (0.1C, upper limit voltage 1V). Next, as the second charge-discharge, the discharge condition (lithium intercalation) was a constant current discharge (0.2C, lower limit voltage 0.01V) followed by a constant voltage discharge (lower limit current density 0.02C), and the charging condition (lithium deintercalation) was a constant current charge (0.2C, upper limit voltage 1V). Discharge and charge were performed at 25°C. Next, for the charge-discharge cycle tests after the third time, the discharge condition (lithium intercalation) was a constant current discharge (0.2C, lower limit voltage 0.01V) followed by a constant voltage discharge (lower limit current density 0.02C), and the charging condition (lithium deintercalation) was a constant current charge (0.2C, upper limit voltage 1V). Based on the second charge capacity, tests were conducted under different conditions with no capacity limit, 90% capacity limit, 80% capacity limit, 70% capacity limit, and 60% capacity limit. Discharge and charge were performed at 25°C.

[0563] Table 2 shows the maximum charge capacity and 30-cycle retention rate of coin cells GS-C1 to GS-C5. Also, the results of the charge-discharge cycle tests are shown in FIGS. 35A and 35B.

[0564]

Table 2

[0565] As shown in FIGS. 35A and 35B, in the coin cells (GS-C2 to GS-C5) with capacity limitation, the effect of suppressing the deterioration of the charge capacity in the charge-discharge cycle test was confirmed. Note that in GS-C2 to GS-C5, the capacity limitation was tested under different conditions of 60%, 70, 80%, and 90%, but from the perspective of the charge capacity retention rate shown in FIG. 35B, no significant difference was observed in GS-C2 to GS-C5.

[0566] Next, regarding the results of this experiment, in Embodiment 1, it will be discussed in combination with the contents shown in Calculation 1 of the negative electrode and Calculation 2 of the negative electrode.

[0567] Based on the content shown in Calculation 1 of the negative electrode in Embodiment 1, the alloying ratio (Li / Si) of silicon and lithium in GS-C1 to GS-C5 was calculated using Equation 1. The calculation results are shown in Table 3.

[0568] [Equation]

[0569] [Table 3]

[0570] As shown in Table 3, in GS-C1 with poor charge-discharge cycle characteristics, Li / Si was calculated to be 2.22. On the other hand, in GS-C2 with excellent charge-discharge cycle characteristics, Li / Si was 1.75, and it was found that this ratio was close to the structure shown in FIG. 6B (crystal structure at Li / Si = 1.714). Since the structure shown in FIG. 6B has Si-Si bonds, it is considered possible that charge-discharge occurred in GS-C2 to GS-C5 within the range where the Si-Si bonds were not lost, and this can be considered as a factor for obtaining good charge-discharge cycle efficiency. [Examples]

[0571] In this example, an evaluation of a coin cell fabricated using the electrode GS1 shown in Example 1 and an ionic liquid was performed.

[0572] <Fabrication of Coin Cell> Next, a CR2032 type (diameter 20 mm, height 3.2 mm) coin cell (also referred to as a coin-type secondary battery), (GS-C6), was fabricated using the fabricated electrode GS1.

[0573] Lithium metal was used as the counter electrode. As the electrolyte, EMI-FSI having LiFSI at a concentration of 2.15 mol / L was used.

[0574] As the separator, a 25-μm-thick polypropylene separator and a 260-μm-thick glass fiber separator were laminated and used.

[0575] For the positive electrode can and the negative electrode can, those made of stainless steel (SUS) were used.

[0576] <Charge-Discharge Characteristics> The charge-discharge characteristics of the fabricated coin cell GS-C6 were evaluated. Since lithium metal is used as the counter electrode, in the fabricated coin cell, the electrode GS1 acts as the positive electrode, lithium is occluded in the electrode during discharge, and lithium is released from the electrode during charging.

[0577] Regarding the fabricated coin cell GS-C6, for the first charge-discharge cycle, the discharge condition (lithium intercalation) was a constant current discharge (0.1C, lower limit voltage 0.01V) followed by a constant voltage discharge (lower limit current density 0.01C), and the charge condition (lithium deintercalation) was a constant current charge (0.1C, upper limit voltage 1V). Next, for the second charge-discharge cycle, the discharge condition (lithium intercalation) was a constant current discharge (0.2C, lower limit voltage 0.01V) followed by a constant voltage discharge (lower limit current density 0.02C), and the charge condition (lithium deintercalation) was a constant current charge (0.2C, upper limit voltage 1V). Next, for the charge-discharge cycle tests after the third cycle, the discharge condition (lithium intercalation) was a constant current discharge (0.2C, lower limit voltage 0.01V) followed by a constant voltage discharge (lower limit current density 0.02C), and the charge condition (lithium deintercalation) was a constant current charge (0.2C, upper limit voltage 1V), which was carried out under the condition of 80% of the capacity limit based on the second charge capacity. Discharge and charge were performed at 25°C.

[0578] The results of the charge-discharge cycle test of GS-C6, together with the results of GS-C2 and GS-C3, are shown in FIGS. 36A and 36B. The maximum charge capacity was 468 mAh / g, and the 30-cycle retention rate was 99.99%, which were very excellent characteristics. For GS-C6, the result of the calculation using Equation 1 was Li / Si = 1.40. FIGS. 37A and 37B show the curves of the third discharge (the first discharge under the capacity limit condition) of GS-C3 and GS-C6. FIG. 37B is an enlarged view of a part of FIG. 37A.

[0579] As shown in FIGS. 36A and 36B, GS-C6 has excellent charge-discharge cycle characteristics. In Embodiment 1, the relationship between the Li / Si ratio and the charge-discharge cycle characteristics was shown. Although the Li / Si = 1.40 of GS-C6 is a value between the Li / Si value of GS-C2 and the Li / Si value of GS-C3, in FIG. 36B, it shows a remarkable result that the charge-discharge cycle deterioration is 99.99%. Also, as shown in FIG. 37B, in GS-C6, the potential is 0.05 V or more even at the end of discharge (at the end of Li insertion), and it is considered possible that Li precipitation and reductive decomposition of the electrolyte are suppressed. Thus, by using the secondary battery having the negative electrode of one aspect of the present invention and the ionic liquid under the conditions of capacity limitation, an effect of remarkable characteristic improvement that could not be easily assumed was obtained.

Explanation of Symbols

[0580] 560a: Negative electrode characteristic curve, 560b: Positive electrode characteristic curve, 570a: Negative electrode, 570b: Positive electrode, 571a: Negative electrode current collector, 571b: Positive electrode current collector, 572a: Negative electrode active material layer, 572b: Positive electrode active material layer, 576: Electrolyte, 581: First active material, 582: Second active material, 583: Graphene compound< / sem> < / xps> < / xrd>

Claims

1. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The positive electrode has a positive electrode active material including lithium cobalt oxide, the positive electrode active material has magnesium, fluorine, aluminum, nickel, and oxygen on a surface side of the positive electrode active material, A part of the oxygen is replaced with fluorine, The positive electrode active material has an O3'-type crystal structure due to lithium being released in a charged state, The O3' type crystal structure is 50 wt % or more according to Rietveld analysis, The negative electrode includes a first negative electrode active material including silicon particles, a second negative electrode active material including graphite having a particle size larger than that of the silicon particles, and graphene or a graphene compound; the silicon particles are in contact with the graphite, and the graphene or graphene compound is in surface-to-surface contact with the first negative electrode active material and the second negative electrode active material; The silicon particles include silicon oxide, During charging, lithium released from the positive electrode is incorporated into the silicon particles of the negative electrode, resulting in a charge-discharge state. Lithium-ion secondary battery.

2. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The positive electrode has a positive electrode active material including lithium cobalt oxide, the positive electrode active material has magnesium, fluorine, aluminum, nickel, and oxygen on a surface side of the positive electrode active material, A part of the oxygen is replaced with fluorine, The positive electrode active material has an O3'-type crystal structure due to lithium being released in a charged state, The O3' type crystal structure is 50 wt % or more according to Rietveld analysis, the negative electrode includes a first negative electrode active material including a compound having silicon, a second negative electrode active material including graphite having a larger particle size than the compound having silicon, and a graphene compound; the silicon-containing compound is in contact with the graphite, and the graphene or graphene compound is in surface-to-surface contact with the first negative electrode active material and the second negative electrode active material; During charging, lithium released from the positive electrode is incorporated into the silicon-containing compound of the negative electrode, resulting in a charge-discharge state. Lithium-ion secondary battery.

3. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The positive electrode has a positive electrode active material including lithium cobalt oxide, the positive electrode active material has magnesium, fluorine, aluminum, nickel, and oxygen on a surface side of the positive electrode active material, A part of the oxygen is replaced with fluorine, The positive electrode active material has an O3'-type crystal structure due to lithium being released in a charged state, The O3' type crystal structure is 50 wt % or more according to Rietveld analysis, The negative electrode has a first negative electrode active material including SiOx (x is smaller than 2), a second negative electrode active material including graphite having a particle size larger than that of the SiOx, and graphene or a graphene compound; the SiOx is in contact with the graphite, and the graphene or the graphene compound is in surface-to-surface contact with the first negative electrode active material and the second negative electrode active material; During charging, lithium released from the positive electrode is incorporated into the SiOx of the negative electrode, resulting in a charge-discharge state. Lithium-ion secondary battery.

4. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The positive electrode has a positive electrode active material including lithium cobalt oxide, the positive electrode active material has magnesium, fluorine, aluminum, nickel, and oxygen on a surface side of the positive electrode active material, The positive electrode active material has an O3'-type crystal structure due to lithium being released in a charged state, The O3' type crystal structure is 50 wt % or more according to Rietveld analysis, The negative electrode includes a first negative electrode active material containing silicon particles, a second negative electrode active material having a particle size larger than that of the silicon particles, and graphene or a graphene compound; the first negative electrode active material is in contact with the second negative electrode active material, and the graphene or graphene compound is in contact with the first negative electrode active material and the second negative electrode active material, The silicon particles include silicon oxide, During charging, lithium released from the positive electrode is incorporated into the silicon particles of the negative electrode, resulting in a charge-discharge state. Lithium-ion secondary battery.

5. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The positive electrode has a positive electrode active material including lithium cobalt oxide, the positive electrode active material has magnesium, fluorine, aluminum, nickel, and oxygen on a surface side of the positive electrode active material, The positive electrode active material has an O3'-type crystal structure due to lithium being released in a charged state, The O3' type crystal structure is 50 wt % or more according to Rietveld analysis, the negative electrode includes a first negative electrode active material including a silicon-containing compound, a second negative electrode active material having a particle size larger than that of the silicon-containing compound, and graphene or a graphene compound; the first negative electrode active material is in contact with the second negative electrode active material in a covering, wrapping, or clinging manner, and the graphene or graphene compound is in contact with the first negative electrode active material and the second negative electrode active material in a covering, wrapping, or clinging manner, During charging, lithium released from the positive electrode is incorporated into the silicon-containing compound of the negative electrode, resulting in a charge-discharge state. Lithium-ion secondary battery.

6. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The positive electrode has a positive electrode active material including lithium cobalt oxide, the positive electrode active material has magnesium, fluorine, aluminum, nickel, and oxygen on a surface side of the positive electrode active material, The positive electrode active material has an O3'-type crystal structure due to lithium being released in a charged state, The O3' type crystal structure is 50 wt % or more according to Rietveld analysis, The negative electrode has a first negative electrode active material containing SiOx (x is smaller than 2), a second negative electrode active material having a particle size larger than that of the SiOx, and graphene or a graphene compound; the first negative electrode active material is in contact with the second negative electrode active material in a covering, wrapping, or clinging manner, and the graphene or graphene compound is in contact with the first negative electrode active material and the second negative electrode active material in a covering, wrapping, or clinging manner, During charging, lithium released from the positive electrode is incorporated into the SiOx of the negative electrode, resulting in a charge-discharge state. Lithium-ion secondary battery.

7. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The positive electrode has a positive electrode active material including lithium cobalt oxide, the positive electrode active material has magnesium, fluorine, aluminum, nickel, and oxygen on a surface side of the positive electrode active material, A part of the oxygen is replaced by fluorine. The positive electrode active material has an O3'-type crystal structure due to lithium being released in a charged state, The O3' type crystal structure is 50 wt % or more according to Rietveld analysis, the negative electrode includes a second negative electrode active material including graphite, a first negative electrode active material including silicon particles covering at least a portion of a surface of the second negative electrode active material, and a conductive assistant; During charging, lithium released from the positive electrode is incorporated into the silicon particles of the negative electrode, resulting in a charge-discharge state. Lithium-ion secondary battery.

8. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The positive electrode has a positive electrode active material including lithium cobalt oxide, the positive electrode active material has magnesium, fluorine, aluminum, nickel, and oxygen on a surface side of the positive electrode active material, A part of the oxygen is replaced with fluorine, The positive electrode active material has an O3'-type crystal structure due to lithium being released in a charged state, The O3' type crystal structure is 50 wt % or more according to Rietveld analysis, The negative electrode has a second negative electrode active material including graphite, a first negative electrode active material including SiOx (x is smaller than 2) covering at least a part of a surface of the second negative electrode active material, and a conductive assistant; During charging, lithium released from the positive electrode is incorporated into the SiOx of the negative electrode, resulting in a charge-discharge state. Lithium-ion secondary battery.

9. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The positive electrode has a positive electrode active material including lithium cobalt oxide, the positive electrode active material has magnesium, fluorine, aluminum, nickel, and oxygen on a surface side of the positive electrode active material, The positive electrode active material has an O3'-type crystal structure due to lithium being released in a charged state, the negative electrode includes a second negative electrode active material including graphite, a first negative electrode active material including silicon particles covering at least a portion of a surface of the second negative electrode active material, and a conductive assistant; During charging, lithium released from the positive electrode is incorporated into the silicon particles of the negative electrode, resulting in a charge-discharge state. Lithium-ion secondary battery.

10. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The positive electrode has a positive electrode active material including lithium cobalt oxide, the positive electrode active material has magnesium, fluorine, aluminum, nickel, and oxygen on a surface side of the positive electrode active material, The positive electrode active material has an O3'-type crystal structure due to lithium being released in a charged state, The negative electrode has a second negative electrode active material including graphite, a first negative electrode active material including SiOx (x is smaller than 2) covering at least a part of a surface of the second negative electrode active material, and a conductive assistant; During charging, lithium released from the positive electrode is incorporated into the SiOx of the negative electrode, resulting in a charge-discharge state. Lithium-ion secondary battery.

11. In claim 2 or claim 5, The silicon-containing compound is Li ２ SiO ３ , or Li ４ SiO ４ having Lithium-ion secondary battery.

12. In any one of claims 1 to 11, The first negative electrode active material has a particle size of 5 μm or more, The second negative electrode active material has a particle size of 250 nm or less. Lithium-ion secondary battery.

13. In any one of claims 1 to 12, The state of charge is a voltage of 4.65V to 4.7V relative to the potential of lithium metal. Lithium-ion secondary battery.

14. In any one of claims 1 to 13, The O3′ type crystal structure was found to be Diffraction peaks appear at 2θ = 19.30 ± 0.20 ° (19.10 ° or more and 19.50 ° or less) and 2θ = 45.55 ± 0.10 ° (45.45 ° or more and 45.65 ° or less). Lithium-ion secondary battery.

15. In any one of claims 1 to 14, The O3' type crystal structure is 60 wt% or more according to Rietveld analysis. Lithium-ion secondary battery.

16. In any one of claims 1 to 15, The O3' type crystal structure is 66 wt% or more according to Rietveld analysis. Lithium-ion secondary battery.

17. In any one of claims 1 to 16, The positive electrode has a positive electrode current collector, The positive electrode current collector comprises aluminum. Lithium-ion secondary battery.

18. In any one of claims 1 to 17, The negative electrode has a negative electrode current collector, The negative electrode current collector contains copper. Lithium-ion secondary battery.

19. In any one of claims 1 to 18, The first negative electrode active material is in contact with the second negative electrode active material so as to cover, wrap, or cling to the second negative electrode active material. Lithium-ion secondary battery.

20. In any one of claims 1 to 6, The graphene or graphene compound is in contact with the first negative electrode active material and the second negative electrode active material so as to cover, wrap, or cling to the first negative electrode active material and the second negative electrode active material. Lithium-ion secondary battery.

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