Lithium ion secondary battery

Abstract

To provide a negative electrode with smaller deterioration, provide a novel negative electrode, provide a power storage device with smaller deterioration, or provide a novel power storage device.SOLUTION: An electrode has silicon, graphite, and a graphene compound. A silicon particle with a particle diameter of 1 μm or less adheres to a graphite particle whose particle diameter is 10 times or more of that of the silicon particle. The graphene compound is in contact with the graphite particle so as to cover the silicon particle.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 method for manufacturing them.

[0003] In this 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 this 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, for 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 increase in functionality. 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] In order 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 core 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 agent, and a binder. 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 agent in the electrode, the conductivity of the electrode can be enhanced, and excellent output characteristics can be obtained. Also, during the charge and discharge of the secondary battery, when the active material repeatedly expands and contracts, peeling of the active material, interruption of the conductive path, etc. may occur in the electrode. In such a case, by having a conductive agent and a binder in the electrode, peeling of the active material and interruption of the conductive path can be suppressed. On the other hand, by using a conductive agent 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 aims to provide an electrode having excellent characteristics. Or, one aspect of the present invention aims to provide an active material having excellent characteristics. Or, one aspect of the present invention aims to provide a novel electrode.

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

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

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

Means for Solving the Problems

[0016] An electrode according to one aspect of the present invention has a material having a particulate and sheet-like shape, the particles having first particles and second particles, the first particles and the material having a sheet-like shape being larger than the particle size of the second particles, and having a region in which the second particles are located between the first particles and the material having a sheet-like shape, and a region in which the first particles and the material having a sheet-like shape are in contact with each other.

[0017] Also, an electrode according to one aspect of the present invention has a material having a particulate and sheet-like shape, the particles having first particles and second particles, the first particles and the material having a sheet-like shape being larger than the particle size of the second particles, and the material having a sheet-like shape having a region in contact with the first particles so as to cover, wrap, or cling to the second particles located on the surface of the first particles.

[0018] The material having a sheet-like shape has a first region, and the first region is preferably terminated by hydrogen atoms. The first region is, for example, a region composed of one atom capable of bonding with hydrogen and a hydrogen atom bonded to the atom. Alternatively, the first region is, for example, a region having a plurality of atoms capable of bonding with hydrogen.

[0019] The hydrogen atoms of the first region and the oxygen atoms of the functional groups terminating the surfaces of the first particles or the second particles can form hydrogen bonds.

[0020] The material having a sheet-like shape curves towards the particles due to intermolecular forces and can wrap around the particles by hydrogen bonding. Note that the material having a sheet-like shape preferably has a plurality of regions terminated by hydrogen atoms on the sheet surface.

[0021] Alternatively, the first region may be terminated by a functional group having oxygen. Examples of the functional group having oxygen include a hydroxy group, an epoxy group, a carboxyl group, etc. The hydrogen atoms of the hydroxy group and the carboxyl group, etc. can form hydrogen bonds with the oxygen atoms of the functional group terminating the particles. Also, the oxygen atoms of the hydroxy group, the epoxy group, and the carboxyl group can form hydrogen bonds with the hydrogen atoms of the functional group terminating the particles.

[0022] Also, when the material having a sheet-like shape has a second region terminated by fluorine atoms, the fluorine atoms of the second region and the hydrogen atoms of the functional group terminating the particles can form hydrogen bonds. As a result, the material having a sheet-like shape can more easily wrap around the particles.

[0023] Also, the first region may have holes formed on the sheet surface. The holes are composed of, for example, a plurality of atoms bonded in a ring shape and an atom terminating the plurality of atoms. Also, the plurality of atoms may be terminated by a functional group.

[0024] The particles included in the electrode according to one embodiment of the present invention preferably function as an active material, for example. As the particles included in the electrode according to one embodiment of the present invention, a material that functions as an active material can be used. Alternatively, the particles included in the electrode according to one embodiment of the present invention preferably have, for example, a material that functions as an active material. Also, the material having a sheet-like shape included in the electrode according to one embodiment of the present invention preferably functions as a conductive agent, for example. In one embodiment of the present invention, since the conductive agent can wrap around the active material by hydrogen bonding, an electrode with high conductivity can be realized.

[0025] Further, it is preferable that the first particles included in the electrode according to one aspect of the present invention function as a first active material and the second particles function as a second active material. The first particles are preferably, for example, an active material with a small volume change associated with charge and discharge, and preferably have a particle diameter that is 10 times or more that of the second particles. Further, the sheet-shaped material included in the electrode according to one aspect of the present invention preferably functions as a conductive agent, for example. In one aspect of the present invention, since the sheet-shaped material can contact the first particles so as to cover, wrap, or cling to the second particles located on the surface of the first particles, an electrode with high conductivity can be realized.

[0026] Further, by clinging to the active material, the sheet-shaped material can prevent the peeling of the active material in the electrode. Further, the sheet-shaped material can also cling to a plurality of active materials. When a material with a large volume change during charge and discharge, such as silicon, is used as the active material, the adhesion between the active material and the conductive agent, between a plurality of active materials, etc. gradually weakens due to repeated charge and discharge, which may cause peeling of the active material in the electrode. In one aspect of the present invention, when silicon is used as the second particles, since the second particles located on the surface of the first particles with a small volume change associated with charge and discharge can contact the first particles so as to cover, wrap, or cling to them, peeling of the active material in the electrode can be suppressed even during repeated charge and discharge, and an electrode with stable characteristics and high reliability can be realized. Silicon has a very high theoretical capacity of 4000 mAh / g or more and can increase the energy density of the secondary battery. By using an active material with a small volume change associated with charge and discharge as the first particles and a material with silicon as the second particles according to one aspect of the present invention, a secondary battery with a high energy density and stable characteristics even during repeated charge and discharge and high reliability can be realized.

[0027] The second particle of one embodiment of the present invention has a silicon atom terminated by a hydroxy group. Or, the particle of one embodiment of the present invention has silicon, and at least a part of the surface is terminated by a hydroxy group. Or, the particle of one embodiment of the present invention is a silicon compound in which at least a part of the surface is terminated by a hydroxy group. Or, the particle of one embodiment of the present invention is silicon in which at least a part of the surface is terminated by a hydroxy group.

[0028] Or, it is preferable that the first particle of one embodiment of the present invention has a first material, and the second particle has a second material.

[0029] In the above configuration, it is preferable that the first material is one or more selected from graphite, graphitizable carbon, non-graphitizable carbon, carbon nanotubes, carbon black, and graphene.

[0030] In the above configuration, it is preferable that the second material has a metal or a compound having one or more elements selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium.

[0031] As the material having a sheet-like shape, it is preferable to use a graphene compound. As the graphene compound, for example, it is preferable to use graphene in which carbon atoms in the sheet plane are terminated by atoms or functional groups other than carbon.

[0032] Graphene has a structure in which the edges are terminated by hydrogen. Also, the sheet of graphene has a two-dimensional structure formed by carbon six-membered rings. When a defect or a hole is formed in the two-dimensional structure, the carbon atoms in the vicinity of the defect or the carbon atoms constituting the hole may be terminated by various functional groups or atoms such as hydrogen atoms and fluorine atoms.

[0033] In one aspect of the present invention, defects or pores are formed in graphene, and the carbon atoms near the defects or the carbon atoms constituting the pores are terminated with hydrogen atoms, fluorine atoms, functional groups having hydrogen atoms or fluorine atoms, functional groups having oxygen, etc., whereby graphene can be wrapped around the particles of the electrode. Note that the defects or pores formed in graphene are preferably in an amount such that the conductivity of the entire graphene is not significantly impaired. Here, constituting the pores refers to, for example, atoms at the opening periphery, atoms at the opening end, etc.

[0034] The graphene compound of one aspect of the present invention has pores formed by polycyclic rings of 7-membered rings or more, preferably 18-membered rings or more, more preferably 22-membered rings or more, composed of carbon. Also, one of the carbon atoms of the polycyclic ring is terminated with a hydrogen atom. Further, in one aspect of the present invention, one of the carbon atoms of the polycyclic ring is terminated with a hydrogen atom, and another one is terminated with a fluorine atom. Also, in one aspect of the present invention, among the carbon atoms of the polycyclic ring, the number of carbon atoms terminated with fluorine is less than 40% of the number of carbon atoms terminated with hydrogen atoms.

[0035] The graphene compound of one aspect of the present invention has pores, and the pores are composed of a plurality of carbon atoms bonded in a ring and atoms or functional groups etc. that terminate the plurality of carbon atoms. One or more of the plurality of carbon atoms bonded in a ring may be substituted with elements of Group 13 such as boron, elements of Group 15 such as nitrogen, and elements of Group 16 such as oxygen.

[0036] In the graphene compound of one aspect of the present invention, it is preferable that carbon atoms other than the edges are terminated with hydrogen atoms, fluorine atoms, functional groups having hydrogen atoms or fluorine atoms, functional groups having oxygen, etc. Also, for example, in the graphene compound of one aspect of the present invention, it is preferable that carbon atoms are terminated with hydrogen atoms, fluorine atoms, functional groups having hydrogen atoms or fluorine atoms, functional groups having oxygen, etc. near the center of the graphene plane.

[0037] One aspect of the present invention has a first active material, a second active material, and a graphene compound. The first active material has silicon with a particle size of 1 μm or less. The second active material has graphite larger than the first active material. The first active material is located on the surface of the second active material. The graphene compound is an electrode in contact with the first active material and the second active material.

[0038] In the electrode according to any one of the above, it is preferable that the graphene compound is in contact with the second active material so as to cover the first active material.

[0039] In the electrode according to any one of the above, it is preferable that the graphene compound is in contact with the second active material so as to wrap around the first active material.

[0040] In the electrode according to any one of the above, it is preferable that the first active material is located between the second active material and the graphene compound.

[0041] In the electrode according to any one of the above, it is preferable that the size of the second active material is 10 times or more the size of the first active material.

[0042] In the electrode according to any one of the above, it is preferable that the silicon has amorphous silicon.

[0043] In the electrode according to any one of the above, the graphene compound has pores and has a plurality of carbon atoms and one or more hydrogen atoms. Each of the one or more hydrogen atoms terminates one of the plurality of carbon atoms, and it is preferable that the pores are formed by the plurality of carbon atoms and the one or more hydrogen atoms.

[0044] Or, one aspect of the present invention is a secondary battery having the electrode according to any one of the above and an electrolyte.

[0045] Or, one aspect of the present invention is a moving body having the secondary battery according to any one of the above.

[0046] Alternatively, one aspect of the present invention is an electronic device having the secondary battery described in any one of the above.

[0047] Further, one aspect of the present invention includes a first step of mixing silicon and a solvent to produce a first mixture, a second step of mixing the first mixture and graphite to produce a second mixture, a third step of mixing the second mixture and a graphene compound to produce a third mixture, a fourth step of mixing the third mixture, a polyimide precursor, and a solvent to produce a fourth mixture, a fifth step of coating the fourth mixture on a metal foil, a sixth step of drying the fourth mixture, and a seventh step of heating the fourth mixture to produce an electrode, wherein the heating is performed in a reduced-pressure environment, and the graphene compound is reduced and the polyimide precursor is imidized by the heating, which is a method for producing an electrode for a lithium-ion secondary battery.

[0048] In the above configuration, the graphene compound preferably has graphene oxide, and the graphite is preferably 10 times or more the size of the silicon.

Advantages of the Invention

[0049] According to one aspect of the present invention, an electrode having excellent characteristics can be provided. Alternatively, according to one aspect of the present invention, a novel electrode can be provided.

[0050] Further, according to one aspect of the present invention, a mechanically strong negative electrode can be provided. Also, according to one aspect of the present invention, a strong positive electrode 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. 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.

[0051] Moreover, according to one aspect of the present invention, a secondary battery with less degradation can be provided. Moreover, according to one aspect of the present invention, a highly safe secondary battery can be provided. Moreover, according to one aspect of the present invention, a secondary battery with a high energy density can be provided. Moreover, according to one aspect of the present invention, a novel secondary battery can be provided.

[0052] Note that the description of these effects does not preclude 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 be 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

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MODE FOR CARRYING OUT THE INVENTION

[0054] 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 construed as being limited to the description of the embodiments shown below.

[0055] Also, in the drawings, sizes, layer thicknesses, or regions may be exaggerated for clarity. Therefore, they are not necessarily limited to that scale.

[0056] Also, 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 lamination order. Therefore, for example, "the first" can be appropriately replaced with "the second" or "the third" etc. for explanation. Also, the ordinal numbers described in this specification and the like may not match the ordinal numbers used to specify an aspect of the present invention.

[0057] (Embodiment 1) In this embodiment, an electrode, an active material, a conductive agent, etc. of an aspect of the present invention will be described.

[0058] <An example of an electrode> FIG. 1A is a cross-sectional schematic view showing an electrode of an aspect of the present invention. The electrode 570 shown in FIG. 1A can be applied to the positive electrode and / or negative electrode of a secondary battery. The electrode 570 includes at least a current collector 571 and an active material layer 572 formed in contact with the current collector 571.

[0059] FIG. 1B is an enlarged view of the region surrounded by the dashed line in FIG. 1A. As shown in FIG. 1B, the active material layer 572 has a first particle 581, a second particle 582, a graphene compound 583, and an electrolyte 584. The graphene compound 583 has a sheet-like shape. FIG. 1C is a schematic diagram showing the state in which the graphene compound 583 contacts the first particle 581 so as to cover, wrap, or cling to the second particle 582 located on the surface of the first particle 581. As the first particle 581 and the second particle 582, a material that functions as an active material can be used. Alternatively, at least the second particle 582 preferably has a material that functions as an active material. Further, the graphene compound 583 included in the electrode 570 preferably functions as a conductive agent. In one aspect of the present invention, when the graphene compound 583 is used as a conductive material, it can cling to the active material by hydrogen bonding, so that an electrode with high conductivity can be realized.

[0060] As the first particle 581 and the second particle 582, various materials can be used. When using the particles of one aspect of the present invention as the first particle 581 and the second particle 582, as shown in FIGS. 1B and 1C, the affinity between the first particle 581 and the second particle 582 and the graphene compound 583 is improved, and as shown in FIGS. 1B and 1C, the graphene compound 583 can contact the first particle 581 so as to cover, wrap, or cling to the second particle 582 located on the surface of the first particle 581. As the particles of one aspect of the present invention, for example, particles having a functional group containing oxygen or fluorine in the surface layer portion, or particles having a region terminated by a functional group containing oxygen or a fluorine atom on the surface can be used. Since the graphene compound 583 can cling to the first particle 581 and the second particle 582, a highly conductive electrode can be realized. The state of contacting in a clinging manner can also be described as contacting closely rather than contacting at a point. It can also be described as contacting along the particle surface. It can also be described as being in surface contact with a plurality of particles. The materials that can be used as the first particle 581 and the second particle 582 will be described later.

[0061] The case of using an active material with a large volume change during charge and discharge as the second particle 582 will be described with reference to FIG. 2. The first particle 581, the second particle 582, and the graphene compound 583 as a material having a sheet-like shape are provided. The state where the graphene compound 583 contacts the first particle 581 so as to cover, wrap, or cling to the second particle 582 located on the surface of the first particle 581 is shown in FIG. 2A. It can also be said that the second particle 582 is located between the first particle 581 and the graphene compound 583, and the graphene compound 583 is in contact with the first particle 581 and the second particle 582. FIG. 2B shows the case where the volume of the second particle 582 shown in FIG. 2A increases due to charging or discharging. Since the graphene compound 583 contacts the first particle 581 so as to cover, wrap, or cling to the second particle 582 located on the surface of the first particle 581, even when the volume of the second particle 582 increases due to charging or discharging, the electrical contact between the second particle 582 and the first particle 581 can be maintained. In addition, peeling of the active material of the electrode can be suppressed.

[0062] When the graphene compound 583 contacts the active materials such as the first particle 581 and the second particle 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. Further, when the volume of the active material changes greatly due to charge and discharge, by having the graphene compound 583 contact the active material so as to cling to it, it is possible to effectively prevent the active material from falling off. These effects can obtain more remarkable effects when contacting so as to cling tightly. Here, the graphene compound 583 desirably has pores of a size that allows Li ions to pass through, and the number of pores is large enough not to interfere with the electron conductivity of the graphene compound 583.

[0063] Here, an example using the graphene compound 583 as the material having a sheet-like shape is shown. However, the material having a sheet-like shape is not limited to the graphene compound 583, and other materials with a high electron conductivity having a sheet-like shape may be used.

[0064] In addition to the graphene compound 583, the active material layer 572 can have carbon-based materials such as carbon black, graphite, carbon fiber, fullerene, etc. As the carbon black, for example, acetylene black (AB) etc. 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 agents in the active material layer. Incidentally, these carbon-based materials may also function as active materials.

[0065] As the carbon fiber, for example, carbon fibers such as mesophase pitch-based carbon fiber, isotropic pitch-based carbon fiber, etc. can be used. Also, as the carbon fiber, carbon nanofibers or carbon nanotubes etc. can be used. Carbon nanotubes can be produced, for example, by a vapor phase growth method.

[0066] Moreover, the active material layer may have metal powders such as copper, nickel, aluminum, silver, gold, etc., or metal fibers, conductive ceramic materials, etc. as conductive agents.

[0067] The content of the conductive aid 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.

[0068] Different from granular conductive materials such as carbon black that are in point contact with the active material, the graphene compound 583 enables a surface contact with low contact resistance. Therefore, the electrical conductivity between the granular active material and the graphene compound 583 can be improved with a smaller amount than that of ordinary conductive materials. Thus, 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.

[0069] In addition, since the graphene compound 583 of one embodiment of the present invention has excellent lithium permeability, the charge-discharge rate of the secondary battery can be increased.

[0070] Particulate carbon-containing compounds such as carbon black and graphite, and fibrous carbon-containing compounds such as carbon nanotubes easily enter minute spaces. The minute spaces refer to, for example, regions between a plurality of active materials. By combining a carbon-containing compound that easily enters 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 of one embodiment of the present invention, the operating stability of the secondary battery can be enhanced. That is, the secondary battery of one embodiment of the present invention can have both high energy density and stability, and is effective as an in-vehicle secondary battery. 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 extended.

[0071] In addition, 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, during so-called regenerative charging in which power is temporarily generated when the brakes of the vehicle are applied and the power is charged, charging is performed under high-rate charging conditions, so good rate characteristics are required for the in-vehicle secondary battery.

[0072] By using the electrolyte of one embodiment of the present invention, an in-vehicle secondary battery having a wide operating temperature range can be obtained.

[0073] In addition, since the secondary battery of one embodiment 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 embodiment of the present invention is also effective in a portable information terminal.

[0074] The active material layer 572 preferably has a binder (not shown). The binder binds or fixes, for example, an electrolyte and an active material. The binder can also bind or fix an electrolyte and a carbon-based material, an active material and a carbon-based material, a plurality of active materials, a plurality of carbon-based materials, etc.

[0075] As the binder, it is preferable to use materials such as polystyrene, methyl polyacrylate, methyl polymethacrylate (polymethyl methacrylate, 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.

[0076] Polyimide has very excellent thermal, mechanical, and chemical stability properties. Also, when polyimide is used as the binder, a dehydration reaction and a cyclization (imidation) 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, heat treatment can be carried out at a heating temperature of 200°C or higher. By carrying out 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.

[0077] 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.

[0078] 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, and ethylene-propylene-diene copolymer. Further, fluororubber can be used as the binder.

[0079] Also, as the binder, it is preferable to use, for example, a water-soluble polymer. 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, and regenerated cellulose, or starch can be used. Further, it is more preferable to use these water-soluble polymers in combination with the aforementioned rubber materials.

[0080] The binder may be used in combination of a plurality of the above.

[0081] In addition, the graphene compound 583 is flexible and has flexibility, and can wrap around the second particle 582 like natto. Also, for example, the second particle 582 can be likened to soybeans, and the graphene compound 583 can be likened to a sticky component such as polyglutamic acid. By arranging the graphene compound 583 across materials such as the electrolyte included in the active material layer 572, a plurality of active materials such as the second particle 582, and a plurality of carbon-based materials, not only a good conductive path can be formed within the active material layer 572, 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 an electrolyte, a plurality of active materials, and a plurality of carbon-based materials are arranged in the network, so that the graphene compound 583 forms a three-dimensional conductive path and can suppress the dropout of the electrolyte from the current collector. Also, in the structure in which the above polygons are arranged, polygons having different numbers of sides may be mixed and arranged. Therefore, the graphene compound 583 may function as a conductive agent and may also function as a binder in the active material layer 572.

[0082] The first particle 581 and the second particle 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 particle 581 and the second particle 582 can have various cross-sectional shapes such as a circle, an ellipse, a figure having a curve, and a polygon. For example, FIGS. 1B and 1C show an example in which the first particle 581 and the second cross-section of the particle 582 have a rounded shape as an example, but the cross-sections of the first particle 581 and the second particle 582 may have corners. Also, a part may be rounded and a part may have corners.

[0083] <graphene compound> In this specification and the like, the graphene compound includes graphene, multilayer graphene, multi-graphene, graphene oxide, multilayer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multi-graphene oxide, graphene quantum dots, etc. The graphene compound refers to a substance that contains carbon, has a flat or sheet-like shape, and has a two-dimensional structure formed by carbon six-membered rings. The two-dimensional structure formed by the carbon six-membered rings may also be referred to as a carbon sheet. The graphene compound may have a functional group containing oxygen. Also, the graphene compound preferably has a bent shape. Further, the graphene compound may be curled to be like a carbon nanofiber.

[0084] In this specification and the like, graphene oxide refers to, for example, a substance that contains carbon and oxygen, has a sheet-like shape, and has a functional group, particularly an epoxy group, a carboxy group, or a hydroxy group.

[0085] In this specification and the like, reduced graphene oxide refers to, for example, a substance that contains carbon and oxygen, has a sheet-like shape, and has a two-dimensional structure formed by carbon six-membered rings. It may be referred to as a carbon sheet. Reduced graphene oxide can function even as a single sheet, but 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 such carbon and oxygen concentrations, it can function as a highly conductive material even in a small amount. 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 a small amount.

[0086] When reducing graphene oxide, pores may be provided in the reduced graphene oxide in some cases.

[0087] Further, as the graphene compound, a material in which the ends of graphene are terminated with fluorine may be used.

[0088] In the longitudinal section of the active material layer, sheet-like graphene compounds are dispersed substantially 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.

[0089] Here, by bonding the plurality of graphene compounds 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 to each other. 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.

[0090] Here, it is preferable to use graphene oxide as the graphene compound, 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, by using graphene oxide having extremely high dispersibility in a polar solvent, the graphene compound can be dispersed substantially uniformly in the internal region of the active material layer.

[0091] In the active material layer produced by applying a dispersion liquid in which graphene oxide is dispersed substantially uniformly in a solvent onto a current collector, removing the solvent by volatilization, and then reducing the graphene oxide, the graphene compounds included in the active material layer partially overlap. Thus, the reduced graphene oxide is dispersed to such an extent that they are in 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.

[0092] In addition, by previously covering the surface of the active material with a graphene compound, a conductive film can be formed on the surface of the active material, and further, by electrically connecting between the active materials with the graphene compound, a conductive path can also be formed.

[0093] The graphene compound according to one aspect of the present invention preferably has pores in a part of the carbon sheet. In the graphene compound 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, 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.

[0094] The graphene compound according to one aspect of the present invention preferably has pores provided by a plurality of carbon atoms and one or more fluorine atoms. Further, the plurality of carbon atoms preferably bond in a cyclic manner, and one or more of the plurality of carbon atoms that bond in a cyclic manner are preferably terminated by the fluorine. Fluorine has a high electronegativity and easily carries 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 pore can be lowered. Therefore, since the pores of the graphene compound have fluorine, lithium ions can easily pass through even small pores, and a graphene compound having excellent conductivity can be realized. Also, one or more of the plurality of carbon atoms that bond in a cyclic manner may be terminated by hydrogen.

[0095] FIG. 3A and FIG. 3B show an example of the configuration of a graphene compound having pores.

[0096] The configuration shown in FIG. 3A has a 22-membered ring, and 8 of the carbons constituting the 22-membered ring are each terminated by hydrogen. Also, in the graphene, it can be said that it has a structure in which two connected 6-membered rings are removed and the carbon bonded to the removed 6-membered ring is terminated by hydrogen.

[0097] The structure shown in FIG. 3B has a 22-membered ring, and among the 8 carbons constituting the 22-membered ring, 6 carbons are terminated by hydrogen and 2 carbons are terminated by fluorine. Also, in graphene, it can be said that it has a structure in which two connected 6-membered rings are removed and the carbons that were bonded to the removed 6-membered rings are terminated with hydrogen or fluorine.

[0098] Silicon terminated with a hydroxy group is considered to have a large interaction with a graphene compound having pores because a hydrogen bond is formed between the hydrogen of the hydroxy group on the silicon surface and the hydrogen atom of the graphene compound or the fluorine atom of the graphene compound.

[0099] Since the graphene compound 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, a hydrogen bond is also formed between the hydrogen atom of the hydroxy group and the fluorine atom of the graphene compound, and it is considered that the interaction between the particles having silicon and the graphene compound becomes stronger and more stable.

[0100] When graphene has pores, for example, it may be possible to observe a spectrum based on features caused by the pores by mapping measurement of Raman spectroscopy. Also, it may be possible to observe the bonds, functional groups, etc. constituting the pores by ToF-SIMS. Also, it may be possible to analyze the vicinity of the pores, the periphery of the pores, etc. by TEM observation.

[0101] <An example of a negative electrode active material> When the electrode 570 is a negative electrode, as the second particle 582, a particle having a negative electrode active material can be used. As the negative electrode active material, it is preferable to use a material capable of reacting with the carrier ions of the secondary battery, a material capable of inserting and desorbing carrier ions, a material capable of alloying reaction with a metal serving as a carrier ion, a material capable of dissolving and depositing a metal serving as a carrier ion, etc.

[0102] An example of the negative electrode active material will be described below.

[0103] As the negative electrode active material, silicon can be used. It is preferable that the electrode 570 uses particles having silicon as the second particles 582.

[0104] In addition, as the negative electrode active material included in the second particles 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-based compounds using such elements include Mg2Si, Mg2Ge, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, SbSn, and the like.

[0105] Alternatively, materials with reduced resistance can be used by adding phosphorus, arsenic, boron, aluminum, gallium, etc. as impurity elements to silicon. A silicon material pre-doped with lithium may also be used. Examples of pre-doping methods include mixing silicon with lithium fluoride, lithium carbonate, etc. and annealing, mechanical alloying of lithium metal and silicon, etc. Also, after forming as an electrode, it can be combined with an electrode such as lithium metal and doped with lithium by a charge-discharge reaction, and then a secondary battery can be fabricated by combining the doped electrode with an electrode serving as a counter electrode (for example, a positive electrode for a pre-doped negative electrode).

[0106] For example, nanosilicon particles can be used as the second particles 582. The average diameter of the nanosilicon 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, and even more preferably 10 nm or more and 100 nm or less.

[0107] The nano silicon particles may have a spherical shape, a flattened spherical shape, or a cuboid shape with rounded corners. The size of the nano silicon particles is preferably 5 nm or more and less than 1 μm, more preferably 10 nm or more and 300 nm or less, and still more preferably 10 nm or more and 100 nm or less, for example, 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. When it is below the measurement lower limit of laser diffraction particle size distribution measurement, the major axis of the particle cross-section may be measured by analysis such as SEM or TEM.

[0108] 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.

[0109] As a material having silicon, for example, SiO x (x is preferably less than 2, more preferably 0.5 or more and 1.6 or less) can be used.

[0110] 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. Also, the silicon oxide may be amorphous. It may be a particle in which a graphene compound is attached to the secondary particles of silicon.

[0111] Also, the compound having silicon can have, for example, Li2SiO3 and Li4SiO4. Li2SiO3 and Li4SiO4 may each have crystallinity or may be amorphous.

[0112] The analysis of the compound containing silicon can be carried out using NMR, XRD, Raman spectroscopy, SEM, TEM, EDX, etc.

[0113] The first particle 581 included in the electrode 570 preferably has graphite.

[0114] The first particle 581 preferably functions as a negative electrode active material, and more preferably is a material with a small volume change associated with charge and discharge.

[0115] Regarding the volume change of the first particle 581 associated with charging or discharging, when the minimum volume in charging or discharging is set to 1, the maximum volume in charging or discharging is preferably 2 or less, more preferably 1.5 or less, and even more preferably 1.1 or less.

[0116] It is desirable that the particle size of the first particle 581 is larger than the particle size of the second particle 582.

[0117] For example, in laser diffraction particle size distribution measurement, the D50 of the first particle 581 is preferably 1.5 times or more and less than 1000 times the D50 of the second particle 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 diameter 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.

[0118] Also, as the first particle 581, for example, carbon-based materials such as graphite, easily graphitizable carbon, hardly graphitizable carbon, carbon nanotubes, carbon black, and graphene compounds, which have a small volume change associated with charge and discharge, can be used.

[0119] Also, as the first particle 581, for example, oxides having one or more elements selected from titanium, niobium, tungsten, and molybdenum can be used.

[0120] As the first particle 581, a plurality of combinations of the metals, materials, compounds, etc. shown above can be used.

[0121] As the first particle 581, for example, oxides such as SnO, SnO2, titanium dioxide (TiO2), lithium titanate (Li4Ti5O 12 )、lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), molybdenum oxide (MoO2), etc. can be used.

[0122] In addition, a material in which a conversion reaction occurs can also be used as the first particle 581. For example, transition metal oxides that do not undergo an alloying reaction with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), iron oxide (FeO), etc., may be used for the first particle 581. Materials in which a conversion reaction occurs further include oxides such as Fe2O3, CuO, Cu2O, RuO2, Cr2O3, CoS 0.89 , sulfides such as NiS, CuS, nitrides such as Zn3N2, Cu3N, Ge3N4, phosphides such as NiP2, FeP2, CoP3, and fluorides such as FeF3, BiF3. Note that since the potential of the above fluorides is high, they may be used as the positive electrode material.

[0123] <Method for manufacturing an electrode> FIG. 4 is a flowchart showing an example of a method for manufacturing an electrode according to an aspect of the present invention.

[0124] First, in step S61, as the second particle 582, particles containing silicon are prepared. As the particles containing silicon, for example, the particles described as the second particle 582 above can be used.

[0125] 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.

[0126] 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.

[0127] Next, in step S72, as the first particles 581, particles having graphite are prepared. As the particles having graphite, for example, the particles described as the first particles 581 above can be used.

[0128] 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.

[0129] Next, in step S80, a graphene compound is prepared.

[0130] Next, in step S81, mixture E-2 and the graphene compound 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.

[0131] 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 in which the particles having silicon and the graphene compound are well mixed can be formed.

[0132] Next, in step S84, the kneaded mixture is mixed. For the mixing, for example, a kneader or the like can be used. The mixture after mixing is recovered in step S85.

[0133] It is preferable to repeat the steps of step S83 to step 85 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.

[0134] After repeating steps S83 to S85 n times, mixture E-3 is obtained (step S86).

[0135] 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.

[0136] 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.

[0137] Next, the mixture whose viscosity was adjusted in step S89 is mixed in step S90 and 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.

[0138] Next, a current collector is prepared in step S93.

[0139] 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, or a combination thereof can be used. Also, a continuous coater or the like may be used for coating.

[0140] 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.

[0141] For example, the first heating can be performed by heat-treating 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, heat-treating 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.

[0142] Alternatively, heat treatment may be performed using a drying furnace or the like. When using a drying furnace, 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.

[0143] Or the temperature may be increased stepwise. For example, after performing 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.

[0144] 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. Also, 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. Also, it is preferable that a reduction reaction of the graphene compound 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.

[0145] 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.

[0146] For example, the second heating may be performed 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 more and 10 hours or less.

[0147] In step S97, an electrode having an active material layer provided on the current collector is obtained.

[0148] 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.

[0149] 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.

[0150] After volatilizing the solvent 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.

[0151] <An example of the positive electrode active material> Examples of the positive electrode active material include lithium-containing composite oxides having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure.

[0152] As the positive electrode active material of one aspect of the present invention, it is preferable to use a positive electrode active material having a layered crystal structure.

[0153] Examples of the layered crystal structure include a layered rock salt-type crystal structure. Examples of the lithium-containing composite oxide having a layered rock salt-type crystal structure include LiM x O y (where x > 0 and y > 0, more specifically, for example, y = 2 and 0.8 < x < 1.2). Here, M is a metal element, preferably one or more selected from cobalt, manganese, nickel, and iron. Alternatively, M is, for example, two or more selected from cobalt, manganese, nickel, iron, aluminum, titanium, zirconium, lanthanum, copper, and zinc.

[0154] LiM x O y Examples of the lithium-containing composite oxide represented by LiMO₂ include LiCoO₂, LiNiO₂, LiMnO₂, etc. Also, examples of the NiCo-based represented by LiNi x Co 1-x O₂ (0 < x < 1), and examples of the lithium-containing composite oxide represented by LiMO₂ include the NiMn-based represented by LiNi x O y LiNi x Mn 1-x O₂ (0 < x < 1), etc.

[0155] Also, examples of the lithium-containing composite oxide represented by LiMO₂ include LiNi x Co y Mn zExamples include NiCoMn-based (also referred to as NCM) represented by O2 (x > 0, y > 0, 0.8 < x + y + z < 1.2). Specifically, for example, it is preferable to satisfy 0.1x < y < 8x and 0.1x < z < 8x. As an example, x, y, and z preferably satisfy x:y:z = 1:1:1 or values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 5:2:3 or values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 8:1:1 or values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 6:2:2 or values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 1:4:1 or values in the vicinity thereof.

[0156] Examples of the lithium-containing composite oxide having a layered rock salt-type crystal structure include Li2MnO3, Li2MnO3-LiMeO2 (Me is Co, Ni, Mn), etc.

[0157] In the positive electrode active material having a layered crystal structure typified by the above lithium-containing composite oxide, a secondary battery with a high lithium content per volume and a high capacity per volume may be realized. In such a positive electrode active material, the amount of lithium desorbed per volume during charging is also large, and in order to perform stable charge and discharge, stabilization of the crystal structure after desorption is required. Also, the crystal structure may collapse during charge and discharge, which may inhibit high-speed charging or high-speed discharging.

[0158] Also, it is preferable to mix a lithium-containing material having a spinel-type crystal structure containing manganese such as LiMn2O4 as the positive electrode active material with lithium nickelate (LiNiO2 or LiNi 1-x M x O2 (0 < x < 1) (M = Co, Al, etc.)). By adopting such a configuration, the characteristics of the secondary battery can be improved.

[0159] Also, as the positive electrode active material, the composition formula Li a Mn b Mc O d It is possible to use a lithium manganese composite oxide that can be represented by. Here, the element M is preferably a metal element selected from those other than lithium and manganese, or silicon or phosphorus, and more preferably nickel. When measuring the entire lithium manganese composite oxide particles, it is preferable to satisfy 0 < a / (b + c) < 2, c > 0, and 0.26 ≦ (b + c) / d < 0.5 during discharge. The composition of metals, silicon, phosphorus, etc. in the entire lithium manganese composite oxide particles can be measured using, for example, ICP-MS (Inductively Coupled Plasma Mass Spectrometer). Also, the oxygen composition of the entire lithium manganese composite oxide particles can be measured using, for example, EDX (Energy Dispersive X-ray Analysis Method). Further, it can be determined by using valence evaluation of melting gas analysis and XAFS (X-ray Absorption Fine Structure) analysis in combination with ICPMS analysis. The lithium manganese composite oxide refers to an oxide containing at least lithium and manganese, and may contain at least one element selected from the group consisting of chromium, cobalt, aluminum, nickel, iron, magnesium, molybdenum, zinc, indium, gallium, copper, titanium, niobium, silicon, and phosphorus.

[0160] [Structure of the positive electrode active material] Materials having a layered rock salt type crystal structure such as lithium cobalt oxide (LiCoO2) 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 LiMO2. The metal M contains the metal Me1. The metal Me1 is one or more metals containing cobalt. Also, in addition to the metal Me1, the metal M can further contain the metal X. The metal X is one or more metals selected from magnesium, calcium, zirconium, lanthanum, barium, copper, potassium, sodium, and zinc.

[0161] 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.

[0162] In a compound having nickel, distortion may easily occur due to the Jahn-Teller effect. Therefore, when charging is performed at a high voltage in LiNiO2, there is a concern that the crystal structure may collapse due to the distortion. It is suggested that the influence of the Jahn-Teller effect is small in LiCoO2, and the resistance to charging at a high voltage may be more excellent and preferable.

[0163] The positive electrode active material will be described with reference to FIGS. 5 and 6.

[0164] The positive electrode active material produced in one aspect of the present invention can reduce the shift of the CoO2 layer in repeated charging and discharging at a high voltage. Furthermore, the volume change can be reduced. Therefore, the compound can achieve excellent cycle characteristics. In addition, the compound can have a stable crystal structure in a charged state at a high voltage. Therefore, when the compound holds a charged state at a high voltage, a short circuit may hardly occur. In such a case, the safety is further improved, which is preferable.

[0165] In this compound, the change in the crystal structure and the difference in volume per the same number of transition metal atoms in a fully discharged state and a state charged at a high voltage are small.

[0166] The positive electrode active material is preferably represented by a layered rock salt type structure, and the region is represented by the space group R-3m. The positive electrode active material is a region having lithium, metal Me1, oxygen, and metal X. An example of the crystal structure of the positive electrode active material before and after charge and discharge is shown in FIG. 5. In addition, the surface layer portion of the positive electrode active material may have crystals having titanium, magnesium, and oxygen and represented by a structure different from the layered rock salt type structure, in addition to or instead of the region represented by the layered rock salt type structure described in FIG. 5 and the like. For example, it may have crystals having titanium, magnesium, and oxygen and represented by a spinel structure.

[0167] The crystal structure of the 0% state of charge (discharged state) in Fig. 5 is the same R-3m (O3) as in Fig. 6. On the other hand, the cathode active material shown in Fig. 5 has crystals with a structure different from the H1-3 type crystal structure when fully charged to a state of charge (e.g., 0.8). This structure is in the space group R-3m and is not a spinel-type crystal structure, but ions such as cobalt and magnesium occupy the oxygen six-coordination positions, and the arrangement of the cations has symmetry similar to that of the spinel type. Also, the periodicity of the CoO2 layer in this structure is the same as that of the O3 type. Therefore, in this specification, etc., this structure is referred to as the O3'-type crystal structure or a pseudo-spinel-type crystal structure. Thus, the O3'-type crystal structure and the pseudo-spinel-type crystal structure may be used interchangeably. In the figure of the pseudo-spinel-type crystal structure shown in Fig. 5, the display of lithium is omitted for the purpose of explaining the symmetry of cobalt atoms and oxygen atoms, but in reality, for example, 20 atomic% or less of lithium exists relative to cobalt between the CoO2 layers. Also, in both the case of the O3-type crystal structure and the pseudo-spinel-type crystal structure, it is preferable that magnesium exists thinly between the CoO2 layers, that is, at the lithium sites. Also, halogens such as fluorine may exist randomly and thinly at the oxygen sites.

[0168] Note that in the pseudo-spinel-type crystal structure, light elements such as lithium may occupy the oxygen four-coordination positions, and in this case as well, the arrangement of the ions has symmetry similar to that of the spinel type.

[0169] Also, the pseudo-spinel-type crystal structure can be said to be a crystal structure similar to the CdCl2 type, although it has Li randomly between the layers. This crystal structure similar to the CdCl2 type is close to the crystal structure when lithium nickelate is charged to a state of charge of 0.94 (Li 0.06 NiO2), but it is known that pure lithium cobaltate or a layered rock salt-type cathode active material containing a large amount of cobalt usually does not take this crystal structure.

[0170] In layered rock salt-type crystals and rock salt-type crystals, the anions adopt a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that in pseudo-spinel-type crystals as well, the anions adopt a cubic close-packed structure. When these are in contact, there is a crystal plane where the orientations of the cubic close-packed structures composed of anions are aligned. However, since the space groups of layered rock salt-type crystals and pseudo-spinel-type crystals are R-3m, which is different from the space groups of rock salt-type crystals, Fm-3m (the space group of a general rock salt-type crystal) and Fd-3m (the space group of a rock salt-type crystal with the simplest symmetry), the Miller indices of the crystal planes satisfying the above conditions are different between layered rock salt-type crystals and pseudo-spinel-type crystals and rock salt-type crystals. In this specification, in the case of layered rock salt-type crystals, pseudo-spinel-type crystals, and rock salt-type crystals, when the orientations of the cubic close-packed structures composed of anions are aligned, it may be said that the crystal orientations are approximately the same.

[0171] In the cathode active material shown in FIG. 5, the change in crystal structure when charging at a high voltage and many lithium ions are detached is suppressed more than in the comparative examples described later. For example, as shown by the broken line in FIG. 5, in these crystal structures, there is almost no shift in the CoO2 layer.

[0172] More specifically, the cathode active material shown in FIG. 5 has high structural stability even when the charging voltage is high. For example, in the comparative examples, there is a region of charging voltage where the crystal structure of R-3m (O3) can be maintained even at a charging voltage that results in an H1-3 type crystal structure, for example, at a voltage of about 4.6 V based on the potential of lithium metal, and there is also a region where a pseudo-spinel type crystal structure can be adopted even in a region where the charging voltage is further increased, for example, at a voltage of about 4.65 V to 4.7 V based on the potential of lithium metal. Only when the charging voltage is further increased, an H1-3 type crystal may be observed. In addition, when using graphite as the anode active material in a secondary battery, for example, there is a region of charging voltage where the crystal structure of R-3m (O3) can be maintained even when the voltage of the secondary battery is 4.3 V or more and 4.5 V or less, and there is also a region where a pseudo-spinel type crystal structure can be adopted even in a region where the charging voltage is further 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.

[0173] Therefore, in the positive electrode active material shown in FIG. 5, the crystal structure is difficult to collapse even when high-voltage charging and discharging are repeated.

[0174] The pseudo-spinel type crystal structure can be shown by the coordinates of cobalt and oxygen in the unit cell within the range of Co(0,0,0.5), O(0,0,x), and 0.20 ≤ x ≤ 0.25.

[0175] Magnesium randomly and thinly present in the CoO2 layer space, that is, the lithium site, has the effect of suppressing the displacement of the CoO2 layer when charged at a high voltage. Therefore, when magnesium is present in the CoO2 layer space, it is likely to form a pseudo-spinel type crystal structure.

[0176] However, if the heat treatment temperature is too high, cation mixing occurs and 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. Furthermore, if the heat treatment temperature is too high, there are also concerns about adverse effects such as cobalt being reduced to divalent and lithium being evaporated or sublimated.

[0177] 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 portion of the particles. Adding the 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 portion of the particles at a temperature at which cation mixing is less likely to occur. Furthermore, if a fluorine compound is present, it can be expected that the corrosion resistance against hydrofluoric acid generated by the decomposition of the electrolyte will be improved.

[0178] Incidentally, 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 positive electrode active material produced according to one embodiment of the present invention is preferably 0.001 times or more and 0.1 times or less the number of cobalt atoms, more preferably greater than 0.01 and less than 0.04, and even more preferably about 0.02. The magnesium concentration shown here may be, for example, a value obtained by performing elemental analysis of the entire particles of the 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 producing the positive electrode active material.

[0179] The number of nickel atoms in the positive electrode active material is preferably 7.5% or less of the number of cobalt atoms, more preferably 0.05% or more and 4% or less, and even more preferably 0.1% or more and 2% or less. The nickel concentration shown here may be, for example, a value obtained by performing elemental analysis of the entire particles of the 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 producing the positive electrode active material.

[0180] <Particle size> If the particle size of the positive electrode active material is too large, there are problems such as difficulty in lithium diffusion and 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 diameter (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.

[0181] <Analysis method> Whether a certain cathode active material exhibits a pseudo-spinel type (also called O3’ structure) crystal structure when charged at a high voltage can be determined by analyzing the cathode charged at a high voltage using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. In particular, XRD is preferable in that it can analyze the symmetry of transition metals such as cobalt in the cathode 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 cathode obtained by disassembling the secondary battery as it is.

[0182] As described above, the cathode active material is characterized by having little change in crystal structure between the charged state at a high voltage and the discharged state. A material in which a crystal structure with a large change from the discharged state occupies 50 wt% or more in the charged state at a high voltage is not preferable because it cannot withstand the charge and discharge at a high voltage. It should be noted that the desired crystal structure may not be obtained only by adding impurity elements. For example, even though they have in common the point of lithium cobaltate having magnesium and fluorine, there are cases where the pseudo-spinel type crystal structure becomes 60 wt% or more and cases where the H1-3 type crystal structure occupies 50 wt% or more in the charged state at a high voltage. Also, at a predetermined voltage, the pseudo-spinel type crystal structure may become almost 100 wt%, and when the predetermined voltage is further increased, the H1-3 type crystal structure may occur. Therefore, it is preferable that the crystal structure of the cathode active material is analyzed by XRD or the like. By using it in combination with measurements such as XRD, more detailed analysis can be performed.

[0183] However, the cathode active material in the charged state or discharged state at a high voltage may change its crystal structure when exposed to the atmosphere. For example, it may change from a pseudo-spinel type crystal structure to an H1-3 type crystal structure. Therefore, it is preferable to handle all samples in an inert atmosphere such as an atmosphere containing argon.

[0184] The positive electrode active material shown in Fig. 6 is lithium cobaltate (LiCoO₂) without the addition of metal X. The lithium cobaltate shown in Fig. 6 has a crystal structure that changes depending on the depth of charge.

[0185] As shown in Fig. 6, lithium cobaltate at a charge depth of 0 (discharged state) has a region with a crystal structure of space group R-3m and three CoO₂ layers in the unit cell. Therefore, this crystal structure is sometimes called the O3-type crystal structure. Note that the CoO₂ layer refers to a structure in which octahedral structures with six oxygen atoms coordinated to cobalt are continuously arranged in a plane in a state of sharing edges.

[0186] Also, when the charge depth is 1, it has a crystal structure of space group P-3m1 and one CoO₂ layer in the unit cell. Therefore, this crystal structure is sometimes called the O1-type crystal structure.

[0187] Moreover, lithium cobaltate when the charge depth is about 0.8 has a crystal structure of space group R-3m. This structure can also be said to be a structure in which the CoO₂ structure such as P-3m1 (O1) and the LiCoO₂ structure such as R-3m (O3) are alternately laminated. Therefore, this crystal structure is sometimes called the H1-3 type crystal structure. In reality, the H1-3 type crystal structure has twice the number of cobalt atoms per unit cell compared to other structures. However, in this specification including Fig. 6, for the sake of easy comparison with other structures, it will be shown in a figure with the c-axis of the H1-3 type crystal structure halved to that of the unit cell.

[0188] As an example, the coordinates of cobalt and oxygen in the unit cell of the H1-3 type crystal structure can be expressed as Co(0, 0, 0.42150 ± 0.00016), O1(0, 0, 0.27671 ± 0.00045), and O2(0, 0, 0.11535 ± 0.00045). O1 and O2 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 pseudo-spinel 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 in the case of the pseudo-spinel structure and the H1-3 type structure, the symmetry between cobalt and oxygen is different, and the change of the pseudo-spinel structure from the O3 structure is smaller than that of the H1-3 type structure. Which unit cell should be used to represent the crystal structure of the positive electrode active material can be determined, for example, by Rietveld analysis of XRD. In this case, a unit cell with a smaller GOF (goodness of fit) value may be adopted.

[0189] 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 the depth of charge becomes 0.8 or more, and discharging are repeated, lithium cobaltate repeats a change in crystal structure (i.e., non-equilibrium phase change) between the H1-3 type crystal structure and the R-3m(O3) structure in the discharged state.

[0190] However, the shift of the CoO2 layer is large between these two crystal structures. As shown by the dotted line and arrow in FIG. 6, in the H1-3 type crystal structure, the CoO2 layer is largely shifted from R-3m(O3). Such dynamic structural changes can have an adverse effect on the stability of the crystal structure.

[0191] 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 3.0% or more.

[0192] In addition, the structure in which CoO2 layers such as P-3m1(O1) with an H1-3 type crystal structure are continuous is likely to be unstable.

[0193] Therefore, when high-voltage charging and discharging are repeated, the crystal structure of lithium cobaltate collapses. The collapse of the crystal structure causes deterioration of the cycle characteristics. This is thought to be because when the crystal structure collapses, the sites where lithium can exist stably decrease, and it becomes difficult for lithium to be inserted and removed.

[0194] <Electrolyte> When a liquid electrolyte layer is used in a secondary battery, for example, as the electrolyte layer, one of 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., or any combination and ratio of two or more of these can be used.

[0195] In addition, by using one or more ionic liquids (room-temperature molten salts) that are flame-retardant and have low volatility as the solvent of the electrolyte, 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 includes 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.

[0196] 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 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.

[0197] When lithium ions are used as the carrier ions, for example, the electrolyte contains a lithium salt. Examples of the lithium salt include LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl 10 、Li2B 12 Cl 12 、LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, etc. can be used.

[0198] 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.

[0199] As the fluorinated cyclic carbonate, ethylene carbonate fluoride such as 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 clusters of several to several tens.

[0200] By using a fluorinated cyclic carbonate as an electrolyte, the energy required for desolvation when lithium ions solvated in the electrolyte 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 where the coordinating solvent molecules are replaced. When lithium ions can be 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 decomposition products of the electrolyte during charge and discharge of the secondary battery may adhere to the surface of the active material, causing deterioration of the secondary battery. However, when the electrolyte contains fluorine, the electrolyte is less viscous, and it becomes difficult for the decomposition products of the electrolyte to adhere to the surface of the active material. Therefore, deterioration of the secondary battery can be suppressed.

[0201] Multiple solvated lithium ions may form clusters in the electrolyte and move within the negative electrode, between the positive and negative electrodes, within the positive electrode, etc.

[0202] An example of a fluorinated cyclic carbonate is shown below.

[0203] Monofluoroethylene carbonate (FEC) is represented by the following formula (1).

[0204]

Chemical formula

[0205] Tetrafluoroethylene carbonate (F4EC) is represented by the following formula (2).

[0206]

Chemical formula

[0207] Difluoroethylene carbonate (DFEC) is represented by the following formula (3).

[0208]

Chem.

[0209] In this specification, the electrolyte is a general term including solid electrolytes, liquid electrolytes, or semi-solid gel electrolytes, etc.

[0210] 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, deterioration that can occur at the interface between the active material and the electrolyte, typically alteration of the electrolyte or increase in the viscosity of the electrolyte, can be prevented. Further, a binder or a graphene compound, etc. may be configured to cling to or be retained with respect to the electrolyte containing fluorine. By adopting such a configuration, it becomes possible to maintain a state in which the viscosity of the electrolyte is reduced, in other words, a state in which the electrolyte is smooth, and the reliability of the secondary battery can be improved. DFEC having two fluorines and F4EC having four bonds are lower in viscosity, smoother, and have a weaker coordination bond with lithium compared to FEC having one fluorine bond. Therefore, it is possible to reduce the adhesion of high-viscosity decomposition products to the active material particles. When high-viscosity decomposition products adhere to or cling to the active material particles, it becomes difficult for lithium ions to move at the interface of the active material particles. By the solvation of the electrolyte containing fluorine, the generation of decomposition products formed on the surface of the active material (positive electrode active material or negative electrode active material) is alleviated. Further, by using an electrolyte containing fluorine, the generation and growth of dendrites can be prevented by preventing the adhesion of decomposition products.

[0211] Further, using an electrolyte containing fluorine as a main component is also one of the features, 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.

[0212] In this specification, the main component of the electrolyte refers to that which is 5% by volume or more of the entire electrolyte of the secondary battery. Also, the 5% by volume or more of the entire electrolyte of the secondary battery here refers to the proportion 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 what proportions each of the multiple types of electrolytes were, but it is possible to determine whether a certain type of organic compound is 5% by volume or more of the entire electrolyte.

[0213] By using an electrolyte having fluorine, a secondary battery operable in a wide temperature range, specifically, -40°C or higher and 150°C or lower, preferably -40°C or higher and 85°C or lower, can be realized.

[0214] Also, 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 with respect to the entire electrolyte.

[0215] Also, in addition to the above, the electrolyte may have one or more aprotic organic solvents such as γ-butyrolactone, acetonitrile, dimethoxyethane, and tetrahydrofuran.

[0216] Also, 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.

[0217] As the polymer material, for example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, etc., and copolymers containing them can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. Further, the formed polymer may have a porous shape.

[0218] 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 manufactured.

[0219] In this specification and the like, also in the case of a secondary battery using a liquid electrolyte and in the case of a semi-solid battery, the layer disposed between the positive electrode and the negative electrode shall be referred to as the 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.

[0220] In addition, 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, and the negative electrode. Here, the semi-solid 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. If 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.

[0221] 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 and the negative electrode. Polymer electrolyte secondary batteries include dry (or true) polymer electrolyte batteries and polymer gel electrolyte batteries. Also, the polymer electrolyte secondary battery may be referred to as a semi-solid battery.

[0222] When a semi-solid battery is fabricated using the negative electrode of one embodiment of the present invention, the semi-solid battery becomes a secondary battery with a large charge-discharge capacity. Further, it is possible to obtain a semi-solid battery with a high charge-discharge voltage. Alternatively, it is possible to realize a semi-solid battery with high safety or reliability.

[0223] Here, an example of fabricating a semi-solid battery will be described with reference to FIG. 7.

[0224] FIG. 7 is a schematic cross-sectional view of a secondary battery according to one embodiment of the present invention. The secondary battery according to one embodiment of the present invention has a negative electrode 570a and a positive electrode 570b. 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, and 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. The secondary battery also has an electrolyte 576 between the negative electrode 570a and the positive electrode 570b.

[0225] The electrolyte 576 contains a lithium ion conductive polymer and a lithium salt.

[0226] As used herein, the lithium ion conductive polymer is a polymer having conductivity for 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 provided with an ether group, an ester group, a nitrile group, a carbonyl group, a siloxane, or the like.

[0227] Examples of the lithium ion conductive polymer include polyethylene oxide (PEO), derivatives having polyethylene oxide as the main chain, polypropylene oxide, polyacrylate ester, polymethacrylate ester, polysiloxane, polyphosphazene, and the like.

[0228] The lithium ion conductive polymer may be branched, crosslinked, or a copolymer. The molecular weight is preferably, for example, 10,000 or more, and more preferably 100,000 or more.

[0229] In a lithium ion conductive polymer, lithium ions move while changing polar groups that interact through the segmental motion (also called segment motion) of the polymer chain. For example, in the case of PEO, lithium ions move while changing oxygen atoms that interact 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 melts 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.

[0230] According to the ionic radii of Shannon et al. (Acta A 32 (1976) 751.), the radius of monovalent lithium ions is 0.590 Å in the case of 4 coordination, 0.76 Å in the case of 6 coordination, and 0.92 Å in the case of 8 coordination. Also, the radius of divalent oxygen ions is 1.35 Å in the case of 2 coordination, 1.36 Å in the case of 3 coordination, 1.38 Å in the case of 4 coordination, 1.40 Å in the case of 6 coordination, and 1.42 Å in the case of 8 coordination. The distance between polar groups of adjacent lithium ion conductive polymer chains is preferably not less than the distance at which lithium ions and anions of polar groups can stably exist while maintaining the ionic radii as described above. And it is preferably a distance at which sufficient interaction occurs between lithium ions and polar groups. However, as described above, due to the occurrence of segmental motion, it is not always necessary to maintain a constant distance. It is sufficient that the distance is appropriate when lithium ions pass through.

[0231] As the lithium salt, for example, a compound having at least one of phosphorus, fluorine, nitrogen, sulfur, oxygen, chlorine, arsenic, boron, aluminum, bromine, iodine together with lithium can be used. For example, LiPF6, LiN(FSO2)2 (lithium bis(fluorosulfonyl)imide, LiFSI), LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl 10 、Li2B 12 Cl 12One or more of lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, lithium bis(oxalate) borate (LiBOB) can be used in any combination and ratio.

[0232] In particular, when using LiFSI, the low-temperature characteristics are good, which is preferable. Also, LiFSI and LiTFSA are less likely to react with water compared to LiPF6 etc. Therefore, it becomes easier to control the dew point when fabricating electrodes and electrolyte layers using LiFSI. For example, it can be handled not only in an inert atmosphere such as argon with as little moisture excluded as possible and a dry room with controlled dew point, but also in a normal atmospheric atmosphere. Therefore, the productivity is improved, which is preferable. Also, when using highly dissociable and plasticizing-effect Li salts such as LiFSI and LiTFSA, it is particularly preferable when using lithium conduction utilizing the segmental motion of the ether chain because it can be used in a wide temperature range.

[0233] Also, in this specification etc., the binder refers to a polymer compound that is mixed only for binding active materials, conductive materials, 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, fluorine rubber, polystyrene, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, ethylene propylene diene polymer and other materials.

[0234] 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-discharge reaction. Therefore, the less the binder, the more materials such as the active material and the electrolyte that contribute to the charge-discharge can be increased. Therefore, a secondary battery with improved discharge capacity, cycle characteristics, etc. can be obtained.

[0235] By having no or very little organic solvent, a secondary battery that is less likely to catch fire or ignite can be obtained, which is preferable as the safety is improved. Also, if the electrolyte layer 576 is an electrolyte layer having no or very little organic solvent, sufficient strength can be achieved without a separator and it is possible to electrically insulate the positive electrode and the negative electrode. Since a separator is not required, a highly productive secondary battery can be obtained. If the electrolyte 576 is an electrolyte layer having an inorganic filler, the strength can be further increased and a more safe secondary battery can be obtained.

[0236] In order to make the electrolyte 576 an electrolyte layer having no or 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.

[0237] 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.

[0238] In addition, in each of the above configurations, a solid electrolyte material may be further included in the negative electrode to improve flame retardancy. It is preferable to use an oxide-based solid electrolyte as the solid electrolyte material.

[0239] Examples of the oxide-based solid electrolyte include lithium composite oxides such as LiPON, Li2O, Li2CO3, Li2MoO4, Li3PO4, Li3VO4, Li4SiO4, LLT (La 2 / 3-x Li 3x TiO3), LLZ (Li7La3Zr2O 12 ) and lithium oxide materials.

[0240] LLZ is a garnet-type oxide containing Li, La, and Zr, and may also be a compound containing Al, Ga, or Ta.

[0241] Alternatively, a polymer-based solid electrolyte such as PEO (polyethylene oxide) formed by a coating method or the like may be used. Since such a polymer-based solid electrolyte can also function as a binder, when using a polymer-based solid electrolyte, the components of the electrode can be reduced and the manufacturing cost can be reduced.

[0242] This embodiment can be used in appropriate combination with other embodiments.

[0243] (Embodiment 2) In this embodiment, an example of a secondary battery according to an aspect of the present invention will be described.

[0244] <Configuration Example of Secondary Battery> Hereinafter, a secondary battery in which a positive electrode, a negative electrode, and an electrolytic solution are wrapped in an exterior body will be taken as an example for explanation.

[0245] [Negative Electrode] As the negative electrode, the negative electrode shown in the previous embodiment can be used.

[0246] [Current Collector] As the positive current collector and the negative current collector, metals such as stainless steel, gold, platinum, zinc, iron, copper, aluminum, titanium, and alloys thereof, which have high conductivity and do not alloy with carrier ions such as lithium, can be used. Further, an aluminum alloy added with elements for improving heat resistance such as silicon, titanium, neodymium, scandium, molybdenum, etc. can be used. Further, 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 shape, net shape, punching metal shape, expanded metal shape, etc. The current collector preferably has a thickness of 10 μm or more and 30 μm or less.

[0247] Note that it is preferable to use a material for the negative current collector that does not alloy with carrier ions such as lithium.

[0248] A titanium compound may be provided by laminating on the above-described metal element as the current collector. As the titanium compound, for example, titanium nitride, titanium oxide, titanium nitride in which a part of nitrogen is substituted with oxygen, titanium oxide in which a part of oxygen is substituted with nitrogen, and titanium oxynitride (TiO x N y , 0 < x < 2, 0 < y < 1), one selected therefrom, or two or more 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 and the metal in the active material layer formed on the current collector can be 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 in 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.

[0249] [Positive Electrode] The positive electrode has a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer has a positive electrode active material and may have a conductive material and a binder. As the positive electrode active material, the positive electrode active material shown in the previous embodiment can be used.

[0250] As the conductive material and the binder that the positive electrode active material layer can have, the same materials as those that the negative electrode active material layer can have can be used.

[0251] [Separator] A separator is disposed between the positive electrode and the negative electrode. As the separator, for example, 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. It is preferable that the separator is processed into a bag shape and disposed so as to wrap either the positive electrode or the negative electrode.

[0252] 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.

[0253] 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.

[0254] 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.

[0255] 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, and a fluorine-based material may be coated on the surface that contacts the negative electrode.

[0256] When using a separator with a multilayer structure, even if the overall thickness of the separator is thin, the safety of the secondary battery can be maintained, so the capacity per unit volume of the secondary battery can be increased.

[0257] 〔Outer package〕 As the exterior body of the secondary battery, for example, a metal material such as aluminum and a resin material can be used. Also, a film-shaped exterior body can be used. As the film, for example, on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc., a metal thin film with excellent flexibility such as aluminum, stainless steel, copper, nickel, etc. is provided, and further on the metal thin film, an insulating synthetic resin film such as a polyamide-based resin or a polyester-based resin is provided as the outer surface of the exterior body. 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 can realize an excellent secondary battery. Examples of the fluororesin film include PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxyalkane: copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether), FEP (perfluoroethylene propene copolymer: copolymer of tetrafluoroethylene and hexafluoropropylene), ETFE (ethylene tetrafluoroethylene copolymer: copolymer of tetrafluoroethylene and ethylene), etc.

[0258] This embodiment can be used in appropriate combination with other embodiments.

[0259] (Embodiment 3) In this embodiment, examples of the shapes of a plurality of types of secondary batteries having a positive electrode or a negative electrode produced by the production method described in the previous embodiment will be described.

[0260] [Coin-type secondary battery] An example of a coin-type secondary battery will be described. Fig. 8A is an exploded perspective view of a coin-type (single-layer flat type) secondary battery, Fig. 8B is an external view, and Fig. 8C is a cross-sectional view thereof. The coin-type secondary battery is mainly used for small electronic devices.

[0261] In FIG. 8A, for the sake of clarity, it is a schematic diagram so that the overlap (vertical relationship and positional relationship) of the members can be understood. Therefore, FIGS. 8A and 8B are not considered to be completely corresponding diagrams that match exactly.

[0262] In FIG. 8A, the positive electrode 304, the separator 310, the negative electrode 307, the spacer 322, and the washer 312 are stacked. These are sealed with the negative electrode can 302 and the positive electrode can 301. In FIG. 8A, 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.

[0263] A laminated structure in which a positive electrode active material layer 306 is formed on the positive electrode current collector 305 is used as the positive electrode 304.

[0264] To prevent short - circuit between the positive electrode and the negative electrode, the separator 310 and the 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.

[0265] FIG. 8B is a perspective view of the completed coin - type secondary battery.

[0266] The coin - type secondary battery 300 has 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, which are insulated and sealed with a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact therewith. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact therewith. 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.

[0267] 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 on only one side.

[0268] 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 or alloys of these with other metals (such as stainless steel, etc.) can be used. Also, in order to prevent corrosion by the electrolyte, 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.

[0269] Immerse these negative electrode 307, positive electrode 304, and separator 310 in the electrolyte. As shown in FIG. 8C, with the positive electrode can 301 facing downwards, stack the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 in this order, and press-bond the positive electrode can 301 and the negative electrode can 302 via the gasket 303 to manufacture the coin-shaped secondary battery 300.

[0270] By making it a secondary battery, a coin-shaped secondary battery 300 with high capacity, high charge-discharge capacity, and excellent cycle characteristics can be obtained.

[0271] [Cylindrical secondary battery] An example of a cylindrical secondary battery will be described with reference to FIG. 9A. As shown in FIG. 9A, the cylindrical secondary battery 616 has a positive electrode cap (battery lid) 601 on its upper surface and a battery can (outer can) 602 on its side surface and bottom surface. The battery can (outer can) 602 is formed of a metal material and has excellent water permeation barrier properties and gas barrier properties. The positive electrode cap 601 and the battery can (outer can) 602 are insulated by a gasket (insulating packing) 610.

[0272] FIG. 9B is a diagram schematically showing a cross-section of a cylindrical secondary battery. The cylindrical secondary battery shown in FIG. 9B has a positive electrode cap (battery lid) 601 on its upper surface and a battery can (outer can) 602 on its side surface and bottom surface. The positive electrode cap and the battery can (outer can) 602 are insulated by a gasket (insulating packing) 610.

[0273] 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 center pin. 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 electrolyte, or alloys thereof, as well as alloys of these with other metals (for example, stainless steel, etc.) can be used. Further, in order to prevent corrosion by the electrolyte, 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, the inside of the battery can 602 in which the battery element is provided is filled with an electrolyte (not shown). As the electrolyte, the same one as that used in a coin-type secondary battery can be used.

[0274] 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.

[0275] By using the negative electrode obtained in Embodiment 1, a cylindrical secondary battery 616 with high capacity, high charge and discharge capacity, and excellent cycle characteristics can be obtained.

[0276] 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. Further, the PTC element 611 is a thermal sensing resistor 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 (BaTiO3)-based semiconductor ceramics or the like can be used.

[0277] FIG. 9C 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 charge / discharge control circuit that performs charge / discharge and the like, as well as a protection circuit that prevents overcharge and / or overdischarge, can be applied.

[0278] FIG. 9D shows an example of the 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, may be connected in series, or may be connected in parallel and then further connected in series. By configuring the power storage system 615 having a plurality of secondary batteries 616, a large amount of power can be extracted.

[0279] A plurality of secondary batteries 616 may be connected in parallel and then further connected in series.

[0280] 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 likely to be affected by the outside air temperature.

[0281] Also, in FIG. 9D, 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.

[0282] [Other Structural Examples of Secondary Batteries] Structural examples of secondary batteries will be described with reference to FIGS. 10 and 11.

[0283] The secondary battery 913 shown in FIG. 10A 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 an electrolyte 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. 10A, for the sake of convenience, the housing 930 is shown separated, 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 (such as aluminum) or a resin material can be used.

[0284] Note that, as shown in FIG. 10B, the housing 930 shown in FIG. 10A may be formed of a plurality of materials. For example, the secondary battery 913 shown in FIG. 10B 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.

[0285] 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.

[0286] Furthermore, the structure of the wound body 950 is shown in FIG. 10C. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 overlap and are laminated with the separator 933 interposed therebetween, and the laminated sheet is wound. Note that a plurality of laminations of the negative electrode 931, the positive electrode 932, and the separator 933 may be further stacked.

[0287] Moreover, a secondary battery 913 having a wound body 950a as shown in FIG. 11 may be used. The wound body 950a shown in FIG. 11A has 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.

[0288] By using an electrolyte having fluorine for the negative electrode 931, a secondary battery 913 having a high charge-discharge capacity and excellent cycle characteristics can be obtained.

[0289] 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 the negative electrode active material layer 931a and the positive electrode active material layer 932a. Also, it is preferable in terms 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. Further, the wound body 950a having such a shape is preferable in terms of safety and productivity.

[0290] As shown in FIGS. 11A and 11B, the negative electrode 931 is electrically connected to a terminal 951. The terminal 951 is electrically connected to a terminal 911a. Also, the positive electrode 932 is electrically connected to a terminal 952. The terminal 952 is electrically connected to a terminal 911b.

[0291] As shown in FIG. 11C, the winding body 950a and the electrolyte are covered by the housing 930 to form 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 inside of the housing 930 reaches a predetermined pressure to prevent battery rupture.

[0292] As shown in FIG. 11B, the secondary battery 913 may have a plurality of winding bodies 950a. By using a plurality of winding bodies 950a, a secondary battery 913 with a larger charge and discharge capacity can be obtained. For other elements of the secondary battery 913 shown in FIGS. 11A and 11B, reference can be made to the description of the secondary battery 913 shown in FIGS. 10A to 10C.

[0293] <Laminated secondary battery> Next, an example of the appearance of a laminated secondary battery is shown in FIGS. 12A and 12B. FIGS. 12A and 12B 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.

[0294] FIG. 13A shows the appearance 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. The positive electrode 503 also has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as the 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. The negative electrode 506 also has a region where the negative electrode current collector 504 is partially exposed, that is, the 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. 13A.

[0295] <Method for manufacturing a laminated secondary battery> Here, an example of the method for manufacturing the laminated secondary battery whose appearance is shown in FIG. 12A will be described with reference to FIGS. 13B and 13C.

[0296] First, stack the negative electrode 506, the separator 507, and the positive electrode 503. Figure 13B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example is shown where five sets of negative electrodes and four sets of positive electrodes are used. This can also be called a laminate composed of a negative electrode, a separator, and a positive electrode. Next, join the tab regions of the positive electrode 503 together and join the positive electrode lead electrode 510 to the tab region of the outermost positive electrode. For the joining, for example, ultrasonic welding or the like can be used. Similarly, join the tab regions of the negative electrode 506 together and join the negative electrode lead electrode 511 to the tab region of the outermost negative electrode.

[0297] Next, arrange the negative electrode 506, the separator 507, and the positive electrode 503 on the exterior body 509.

[0298] Next, as shown in Figure 13C, bend the exterior body 509 at the portion indicated by the dashed line. Then, join the outer peripheral portion of the exterior body 509. For the joining, for example, thermocompression bonding or the like can be used. At this time, provide a region (hereinafter referred to as an inlet) that is not joined to a part (or one side) of the exterior body 509 so that the electrolyte 508 can be put in later. It is preferable to use a film for the exterior body 509 that has excellent water vapor barrier properties and gas barrier properties. Also, the exterior body 509 has a laminated structure, and by using a metal foil (for example, aluminum foil) as one of its intermediate layers, high water vapor barrier properties and gas barrier properties can be realized.

[0299] Next, introduce the electrolyte 508 (not shown) into the interior of the exterior body 509 through the inlet provided in the exterior body 509. The introduction of the electrolyte 508 is preferably carried out under a reduced pressure atmosphere or an inert atmosphere. And finally, join the inlet. In this way, the laminated secondary battery 500 can be manufactured.

[0300] By using, for the negative electrode 506, the electrode that closely adheres to the negative electrode structure obtained in Embodiment 1, that is, the material obtained by mixing and heating particles having graphene compounds and silicon, a material having a halogen, and a material having oxygen and carbon, a secondary battery 500 with high capacity, high charge and discharge capacity, and excellent cycle characteristics can be obtained.

[0301] This embodiment can be used in appropriate combination with other embodiments.

[0302] (Embodiment 4) This embodiment is an example different from that of FIG. 9D which is a cylindrical secondary battery. An example of applying it to an electric vehicle (EV) is shown using FIG. 14C.

[0303] In an 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 for starting 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 does not need to have a large capacity, and the capacity of the second battery 1311 is smaller compared to the first batteries 1301a and 1301b.

[0304] The internal structure of the first battery 1301a may be the wound type shown in FIG. 10A, or may be the stacked type shown in FIGS. 12A and 12B.

[0305] In this embodiment, an example in which the first batteries 1301a and 1301b are connected in parallel is shown, 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 taken out. The plurality of secondary batteries may be connected in parallel, may be connected in series, or may be connected in parallel and then further connected in series. The plurality of secondary batteries are also called a battery pack.

[0306] 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 high voltage without using tools, and is provided in the first battery 1301a.

[0307] In addition, the power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to in-vehicle components of the 42V system (such as the electric power steering 1307, the heater 1308, the defroster 1309, etc.) via the DCDC circuit 1306. Even when the rear wheels have the rear motor 1317, the first battery 1301a is used to rotate the rear motor 1317.

[0308] In addition, the second battery 1311 supplies power to in-vehicle components of the 14V system (such as the audio 1313, the power window 1314, the lamps 1315, etc.) via the DCDC circuit 1310.

[0309] In addition, the first battery 1301a will be described with reference to FIG. 14A.

[0310] FIG. 14A 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, one electrode is fixed by a fixing part 1413 made of an insulator, and the other electrode is fixed by a fixing part 1414 made of an insulator. In the present embodiment, an example of fixing by the fixing parts 1413 and 1414 is shown, but it may also be configured to be housed in a battery housing box (also called a casing). Since it is assumed that the vehicle is subjected to vibration or shaking from the outside (such as the road surface), it is preferable to fix a plurality of secondary batteries with the fixing parts 1413 and 1414 and the battery housing box. Also, one electrode is electrically connected to the control circuit unit 1320 by a wiring 1421. The other electrode is also electrically connected to the control circuit unit 1320 by a wiring 1422.

[0311] In addition, the control circuit unit 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).

[0312] The control circuit unit 1320 detects the terminal voltage of the secondary battery and manages 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.

[0313] Also, an example of the block diagram of the battery pack 1415 shown in FIG. 14A is shown in FIG. 14B.

[0314] The control circuit unit 1320 includes a switch unit 1324 including at least a switch for preventing overcharging and a switch for preventing overdischarging, 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 the upper limit of the input current from the outside and the upper limit of the output current to the outside are set. The range within 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 overdischarging and / or 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).

[0315] 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, the switch section 1324 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), GaOx (gallium oxide; x is a real number greater than 0), or the like. Further, since a memory element using an OS transistor can be freely arranged by being stacked on a circuit using an Si transistor or the like, integration can be easily performed. Further, since the OS transistor can be manufactured using the same manufacturing apparatus as the Si transistor, it can be manufactured at low cost. That is, the control circuit section 1320 using the OS transistor can be stacked and integrated on the switch section 1324 to form one chip. Since the occupied volume of the control circuit section 1320 can be reduced, miniaturization is possible.

[0316] The first batteries 1301a and 1301b mainly supply power to in-vehicle devices of a 42V system (high voltage system), and the second battery 1311 supplies power to in-vehicle devices of a 14V system (low voltage system). The second battery 1311 is often adopted because a lead storage battery is advantageous in terms of cost.

[0317] In the present embodiment, an example in which a lithium-ion secondary battery is used for both the first battery 1301a and the second battery 1311 is shown. The second battery 1311 may use a lead storage battery, an all-solid-state battery, or an electric double layer capacitor.

[0318] 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 battery controller 1302 through the control circuit unit 1321. 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 are capable of rapid charging.

[0319] 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.

[0320] In addition, although not shown, when connected to an external charger, the charger's outlet 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 through the control circuit unit 1320 to prevent overcharging. Also, in some cases, the connection cable 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. 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 and a GPU.

[0321] Next, an example of mounting a secondary battery, which is one aspect of the present invention, on a vehicle, typically a transportation vehicle, will be described.

[0322] In addition, when the secondary battery shown in any one of FIGS. 9D and 14A is mounted on a vehicle, next-generation clean energy vehicles such as a hybrid vehicle (HV), an electric vehicle (EV), or a plug-in hybrid vehicle (PHV) can be realized. Further, the secondary battery can also be mounted on transportation vehicles such as agricultural machinery, a motorized bicycle including an electric assist bicycle, a motorcycle, an electric wheelchair, an electric cart, a small or large ship, a submarine, an aircraft such as a fixed-wing aircraft or a rotary-wing aircraft, a rocket, a satellite, a space probe, a planetary probe, or a spaceship. The secondary battery of one aspect of the present invention can be a high-capacity secondary battery. Therefore, the secondary battery of one aspect of the present invention is suitable for miniaturization and weight reduction and can be preferably used for transportation vehicles.

[0323] In FIGS. 15A to 15D, a transportation vehicle using one aspect of the present invention is illustrated. The automobile 2001 shown in FIG. 15A 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, the secondary battery is installed at one location or at a plurality of locations. The automobile 2001 shown in FIG. 15A 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 is preferable to have a charge control device that is electrically connected to the secondary battery module.

[0324] In addition, the motor vehicle 2001 can be charged by receiving power supply from an external charging facility through a plug-in method or a non-contact power supply method or the like to the secondary battery of the motor vehicle 2001. When charging, the charging method, the specifications of the connector, etc. may be appropriately carried out 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 the plug-in technology, the power storage device mounted on the motor vehicle 2001 can be charged by an external power supply. Charging can be performed by converting AC power into DC power through a conversion device such as an AC-DC converter.

[0325] Also, although not shown, a power receiving device can be mounted on the vehicle, and power can be supplied non-contact from a power transmission device on the ground for charging. In the case of this non-contact power supply method, by incorporating the power transmission device into the road or the 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 may 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 field resonance method can be used.

[0326] FIG. 15B 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 voltage of 3.5V or more and 4.7V or less as cell units, and a maximum voltage of 170V with 48 cells connected in series. Since it has the same functions as FIG. 15A except for the number of secondary batteries constituting the secondary battery module of the battery pack 2201, the description is omitted.

[0327] FIG. 15C 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 by connecting more than a hundred secondary batteries, for example, with a voltage of 3.5V or more and 4.7V or less, in series. Therefore, a secondary battery with small characteristic variations is required. By using a secondary battery having a structure with an electrolyte containing fluorine in the negative electrode, a secondary battery having stable battery characteristics can be manufactured, and mass production at low cost is possible from the viewpoint of yield. Also, since it has the same functions as FIG. 15A except for the number of secondary batteries constituting the secondary battery module of the battery pack 2202, etc., the description is omitted.

[0328] FIG. 15D shows an aircraft 2004 having an engine that burns fuel as an example. Since the aircraft 2004 shown in FIG. 15D has wheels for takeoff and landing, it can be said to be a kind of transport vehicle, and has a battery pack 2203 including a secondary battery module configured by connecting a plurality of secondary batteries and a charge control device.

[0329] The secondary battery module of the aircraft 2004 has a maximum voltage of 32V by connecting 8 secondary batteries of 4V in series, for example. Since it has the same functions as FIG. 15A except for the number of secondary batteries constituting the secondary battery module of the battery pack 2203, etc., the description is omitted.

[0330] This embodiment can be used in appropriate combination with other embodiments.

[0331] (Embodiment 5) In this embodiment, an example of mounting a secondary battery, which is an aspect of the present invention, on a building will be described with reference to FIGS. 16A and 16B.

[0332] The house shown in Fig. 16A has a power storage device 2612 with a secondary battery, which is one aspect of the present invention, and a solar panel 2610. The power storage device 2612 is electrically connected to the solar panel 2610 via wiring 2611 and the like. Also, the power storage device 2612 and a ground-mounted charging device 2604 may be electrically connected. The power obtained by the solar panel 2610 can be used to charge the power storage device 2612. Further, the 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.

[0333] 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 is interrupted 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, electronic devices can be used.

[0334] Fig. 16B shows an example of a power storage device 700 according to one aspect of the present invention. As shown in Fig. 16B, a power storage device 791 according to one aspect of the present invention is installed in the underfloor space 796 of the building 799.

[0335] A control device 790 is installed in the power storage device 791, and the control device 790 is electrically connected to a distribution board 703, a power storage controller 705 (also referred to as a control device), a display 706, and a router 709 via wiring.

[0336] Power is sent from the commercial power source 701 to the distribution board 703 via the lead-in wire attachment part 710. Also, 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 a general load 707 and a power storage system load 708 via an outlet (not shown).

[0337] The general load 707 is, for example, an electrical device such as a television and a personal computer, and the power storage system load 708 is, for example, an electrical device such as a microwave oven, a refrigerator, and an air conditioner.

[0338] 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 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 amount predicted by the prediction unit 712.

[0339] 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. Also, it can be confirmed in electrical devices such as a television and a personal computer via the router 709. Further, 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 amount for each time period (or each hour) predicted by the prediction unit 712 can be confirmed by the display 706, the electrical device, and the portable electronic terminal.

[0340] This embodiment can be used in appropriate combination with other embodiments.

[0341] (Embodiment 6) 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 electronic devices 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 playback device, and a large game machine such as a pachinko machine. Examples of portable information terminals include a notebook personal computer, a tablet terminal, an e-book, and a mobile phone.

[0342] FIG. 17A 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 having a structure in which an electrolyte containing fluorine is included in a negative electrode, a high capacity can be achieved, and a configuration capable of coping with space saving associated with miniaturization of the housing can be realized.

[0343] The mobile phone 2100 can execute various applications such as mobile phone calls, e-mail, text viewing and creation, music playback, Internet communication, and computer games.

[0344] 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 a manner mode, and executing and canceling a power saving mode. For example, the functions of the operation buttons 2103 can be freely set by an operating system incorporated in the mobile phone 2100.

[0345] Also, the mobile phone 2100 can execute communication-standardized short-range wireless communication. For example, it can communicate with a wireless headset to make hands-free calls.

[0346] In addition, the mobile phone 2100 is 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.

[0347] 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, and body temperature sensors, touch sensors, pressure sensors, and acceleration sensors.

[0348] Figure 17B shows a drone 2300 having a plurality of rotors 2302. The drone 2300 may also be called an unmanned aerial vehicle. The drone 2300 has a secondary battery 2301, a camera 2303, and an antenna (not shown), which are aspects of the present invention. The drone 2300 can be remotely operated via the antenna. A secondary battery using a structure having an electrolyte containing fluorine in the negative 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 mounted on the drone 2300.

[0349] Figure 17C shows an example of a robot. The robot 6400 shown in Figure 17C 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.

[0350] The microphone 6402 has a function of detecting the user's voice and ambient sound, 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.

[0351] 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 enabled.

[0352] 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.

[0353] 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. A secondary battery using a structure having an electrolyte containing fluorine in the negative 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.

[0354] FIG. 17D shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 arranged on the upper surface of the housing 6301, a plurality of cameras 6303 arranged on the side surface, a brush 6304, operation buttons 6305, a secondary battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move autonomously, detect dust 6310, and suck the dust from the suction port provided on the lower surface.

[0355] For example, the cleaning robot 6300 can analyze the images 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 area. A secondary battery using a structure having an electrolyte containing fluorine in the negative 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.

[0356] This embodiment can be implemented in appropriate combination with other embodiments.

[0357] (Appendix regarding the description in this specification, etc.) In this specification, etc., crystal planes and directions are indicated by Miller indices. In crystallography, the notations of crystal planes and directions are represented by numbers with an overbar, but in this specification, etc., due to the constraints of the application notation, instead of attaching an overbar to the number, a - (minus sign) may be attached before the number for expression. Also, individual orientations indicating directions within the 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 {}.

[0358] In this specification, etc., segregation refers to a phenomenon in a solid composed of a plurality of elements (for example, A, B, C) in which a certain element (for example, B) is spatially non-uniformly distributed.

[0359] In this specification, etc., the surface layer part of particles such as active materials is preferably, for example, a region within 50 nm from the surface, more preferably within 35 nm, and even more preferably within 20 nm. The surface formed by cracks and fissures may also be referred to as the surface. Also, a region deeper than the surface layer part is referred to as the interior.

[0360] In this specification and the like, the layered rock salt-type crystal structure of the composite oxide containing lithium and a transition metal refers to a crystal structure having a rock salt-type ion arrangement in which cations and anions are alternately arranged, and in which the transition metal and lithium are regularly arranged to form a two-dimensional plane, enabling two-dimensional diffusion of lithium. Note that there may be defects such as cation or anion deficiencies. 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.

[0361] Also, 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 cation or anion deficiencies.

[0362] Also, in this specification and the like, the pseudo-spinel-type crystal structure of the composite oxide containing lithium and a transition metal is a space group R-3m, which is not a spinel-type crystal structure, but in which ions such as cobalt and magnesium occupy oxygen six-coordination positions, and the cation arrangement has symmetry similar to that of the spinel type.

[0363] 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, etc. X-ray diffraction (XRD), electron diffraction, neutron diffraction, etc. can also be used as materials for determination. In TEM images, etc., the arrangement of cations and anions can be observed as a repetition of bright and dark lines. When the orientations of the cubic close-packed structures in the layered rock salt-type crystal and the rock salt-type crystal are aligned, it can be observed that the angle formed by the repetition of the bright and dark lines between the crystals is 5 degrees or less, more preferably 2.5 degrees or less. Note that in TEM images, etc., light elements such as oxygen and fluorine may not be clearly observable, but in such cases, the alignment can be determined from the arrangement of the metal elements.

[0364] 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 LiCoO2 is 274 mAh / g, the theoretical capacity of LiNiO2 is 274 mAh / g, and the theoretical capacity of LiMn2O4 is 148 mAh / g.

[0365] In this specification and the like, the state of charge when all the insertable and removable lithium has been inserted is defined as 0, and the state of charge when all the insertable and removable lithium in the positive electrode active material has been removed is defined as 1.

[0366] In this specification and the like, charging refers to moving lithium ions from the positive electrode to the negative electrode in the battery and moving electrons from the positive electrode to the negative electrode in the external circuit. For the positive electrode active material, removing lithium ions is referred to as charging. In some cases, a positive electrode active material with a state of charge of 0.7 or more and 0.9 or less is called a positively charged active material charged at a high voltage.

[0367] Similarly, discharging refers to moving lithium ions from the negative electrode to the positive electrode in the battery and moving electrons from the negative electrode to the positive electrode in the external circuit. For the positive electrode active material, inserting lithium ions is referred to as discharging. Also, a positive electrode active material with a state of charge of 0.06 or less, or a positive electrode active material that has discharged 90% or more of its charge capacity from a state charged at a high voltage, is referred to as a fully discharged positive electrode active material.

[0368] In this specification and the like, non-equilibrium phase change refers to a phenomenon that causes a non-linear change in a physical quantity. For example, non-equilibrium phase changes occur before and after the peak in the dQ / dV curve obtained by differentiating the capacitance (Q) with respect to the voltage (V) (dQ / dV), and it is considered that the crystal structure has changed significantly.

[0369] A secondary battery has, for example, a positive electrode and a negative electrode. As a material constituting the positive electrode, there is a positive electrode active material. The positive electrode active material is, for example, a substance that undergoes a reaction contributing to the charge-discharge capacity. Note that the positive electrode active material may contain, in part, a substance that does not contribute to the charge-discharge capacity. As a material constituting the negative electrode, there is a negative electrode active material. The negative electrode active material is, for example, a substance that undergoes a reaction contributing to the charge-discharge capacity. Note that the negative electrode active material may contain, in part, a substance that does not contribute to the charge-discharge capacity.

[0370] In this specification and the like, the positive electrode active material of one aspect of the present invention may be expressed as a positive electrode material, or a positive electrode material for a secondary battery, etc. Also, in this specification and the like, the positive electrode active material of one aspect of the present invention preferably has a compound. Also, in this specification and the like, the positive electrode active material of one aspect of the present invention preferably has a composition. Also, in this specification and the like, the positive electrode active material of one aspect of the present invention preferably has a composite.

[0371] In this specification and the like, the negative electrode active material of one aspect of the present invention may be expressed as a negative electrode material, or a negative electrode material for a secondary battery, etc. Also, in this specification and the like, the negative electrode active material of one aspect of the present invention preferably has a compound. Also, in this specification and the like, the negative electrode active material of one aspect of the present invention preferably has a composition. Also, in this specification and the like, the negative electrode active material of one aspect of the present invention preferably has a composite.

[0372] The discharge rate is the relative ratio of the current during discharge to the battery capacity, and is expressed in units of C. In a battery with a rated capacity of X (Ah), a current equivalent to 1C is X (A). When discharging with a current of 2X (A), it is said to be discharging at 2C, and when discharging with a current of X / 5 (A), it is said to be discharging at 0.2C. Also, the charge rate is the same. When charging with a current of 2X (A), it is said to be charging at 2C, and when charging with a current of X / 5 (A), it is said to be charging at 0.2C.

[0373] Constant current charging refers to a method of charging with a constant charging rate, for example. Constant voltage charging refers to a method of charging with a constant voltage once the charging reaches the upper limit voltage, for example. Constant current discharging refers to a method of discharging with a constant discharging rate, for example.

Example

[0374] In this example, the negative electrode of one aspect of the present invention was fabricated and the fabricated negative electrode was evaluated.

[0375] <Fabrication of Negative Electrode> The negative electrode was fabricated according to the flow shown in FIG. 4. As the particles having silicon, Aldrich-made nanosilicon particles were used. As the particles having graphite, spheroidized graphite particles CGB-15 manufactured by Nippon Graphite Industry Co., Ltd. were used. Graphene oxide was used as the graphene compound. A polyimide precursor manufactured by Toray Industries, Inc. was used as the polyimide.

[0376] As the negative electrodes, electrode GS1, electrode GS2, electrode GS3, and electrode GS4 were fabricated. Electrodes GS1 to GS4 were fabricated in the same manner except for the electrode compounding ratios described in Table 1. Note that the electrode compounding ratios shown in Table 1 are the weight ratios of the materials prepared in steps S61, S72, S80, and S87 of FIG. 4 in the fabrication of electrodes GS1 to GS4. Details will be described below.

[0377]

Table 1

[0378] The nanosilicon particles and the solvent were prepared and mixed (steps S61, S62, S63 in FIG. 4). 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. 4).

[0379] Next, spherical graphite particles were prepared and mixed with mixture E-1 (Steps S72 and S73 in FIG. 4). The mixing was carried out at 2000 rpm for 3 minutes using a rotary mixer, and then the mixture was recovered to obtain mixture E-2 (Steps S74 and S75 in FIG. 4).

[0380] 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 rotary mixer, and then the mixture was recovered (Steps S80, S81, and S82 in FIG. 4). Next, the recovered mixture was kneaded, and NMP was appropriately added, and the mixture was mixed at 2000 rpm for 3 minutes using a rotary mixer, and then the mixture was recovered (Steps S83, S84, and S85 in FIG. 4). Steps S83 to S85 were repeated 5 times to obtain mixture E-3 (Step S86 in FIG. 4).

[0381] Next, mixture E-3 and the polyimide precursor were mixed (Step S88 in FIG. 4). The mixing was carried out at 2000 rpm for 3 minutes using a rotary mixer. Then, NMP was prepared and added to the mixture to adjust the viscosity (Step S89 in FIG. 4), and further mixing was carried out (2000 rpm for 3 minutes twice using a rotary mixer), and then the mixture was recovered to obtain mixture E-4 as a slurry (Steps S90, S91, and S92 in FIG. 4).

[0382] Next, a current collector was prepared, and mixture E-4 was coated (Steps S93 and S94 in FIG. 4). As the current collector, a copper foil with an undercoat was prepared, and mixture E-3 was coated on the copper foil using a doctor blade with a gap thickness of 100 μm to obtain mixture E-4. The thickness of the copper in the prepared copper foil was 18 μm, and as the undercoat, a current collector with a carbon-containing coating layer was used. AB was used as a raw material for the carbon-containing coating layer.

[0383] Next, the copper foil coated with the mixture E-4 was subjected to the first heating at 50°C for 1 hour (step S95 in FIG. 4). Thereafter, the second heating was performed at 400°C for 5 hours under reduced pressure (step S96 in FIG. 4), and an electrode was obtained. By heating, graphene oxide is reduced and the amount of oxygen decreases.

[0384] <sem> SEM observation of the surface of the fabricated electrode was carried out. The SEM observation was performed at the timing after the first heating. SU8030 manufactured by Hitachi High-Technologies was used for the SEM. The acceleration voltage was set to 5 kV.

[0385] Figures 18A and 18B are observation images of the surface of electrode GS1, respectively. Figures 19A and 19B are observation images of the surface of electrode GS2, respectively. Figures 20A and 20B are observation images of the surface of electrode GS3, respectively. Figures 21A and 21B are observation images of the surface of electrode GS4, respectively. In the SEM images, the nanosilicon particles show relatively bright contrast.

[0386] Figure 18B is an enlarged image of the surface of graphite particles with a particle size of approximately 10 μm or more and 20 μm or less in electrode GS1. Nanosilicon particles with a size of approximately 50 nm or more and 250 nm or less exist on the surface of the graphite particles, and regions covered with graphene oxide and regions not covered with graphene oxide were observed.

[0387] Figure 19B is an enlarged image of the surface of graphite particles with a particle size of approximately 10 μm or more and 20 μm or less in electrode GS2. Nanosilicon particles with a size of approximately 50 nm or more and 250 nm or less exist on the surface of the graphite particles, and regions covered with graphene oxide and regions not covered with graphene oxide were observed. In GS2, there is a tendency for more regions to be covered with graphene oxide than in GS1.

[0388] Figure 20B is an enlarged image of the surface of graphite particles with a particle size of approximately 10 μm or more and 20 μm or less in electrode GS3. Nanosilicon particles with a size of approximately 50 nm or more and 250 nm or less exist on the surface of the graphite particles, and regions covered with graphene oxide and regions not covered with graphene oxide were observed. In GS3, there is a tendency for more regions to be covered with graphene oxide than in GS2.

[0389] FIG. 21B is an enlarged image of the surface of graphite particles having a particle size of approximately 10 μm or more and 20 μm or less, which are included in the electrode GS4. Nano-silicon particles having a size of approximately 50 nm or more and 250 nm or less are present on the surface of the graphite particles, and regions covered with graphene oxide and regions not covered with graphene oxide were observed. In GS4, there is a tendency for there to be more regions covered with graphene oxide than in GS3, and most of the nano-silicon is covered with a plurality of graphene oxides.

[0390] <Fabrication of Coin Cells> Next, CR2032 type (diameter 20 mm, height 3.2 mm) coin cells were fabricated using the fabricated electrodes GS1 to GS4.

[0391] Lithium metal was used as the counter electrode. As the electrolyte, a mixture of lithium hexafluorophosphate (LiPF6) with ethylene carbonate (EC) and diethyl carbonate (DEC) mixed at a volume ratio of EC:DEC = 3:7, mixed at a concentration of 1 mol / L, was used.

[0392] A separator made of polypropylene with a thickness of 25 μm was used.

[0393] For the positive electrode can and the negative electrode can, those made of stainless steel (SUS) were used.

[0394] <Charge and Discharge Characteristics> The charge and discharge characteristics of the fabricated coin cells were evaluated. In the fabricated coin cells, lithium is occluded in the electrode during discharge and released from the electrode during charging.

[0395] The discharge conditions (lithium occlusion) were constant current discharge (0.1C, lower limit voltage 0.01V) followed by constant voltage discharge (lower limit current density 0.01C), and the charging conditions (lithium release) were constant current charging (0.1C, upper limit voltage 1V). Discharge and charging were performed at 25°C. The transition of the capacity with the number of charge and discharge cycles is shown in FIGS. 22A and 22B. Table 2 shows the maximum charge capacity in the charge and discharge cycle test and the charge capacity retention rate after 40 cycles.

[0396]

Table 2

[0397] Regarding the electrode mixing ratios and characteristics of electrodes GS1 to GS4, Fig. 23 shows a plot of the GO / silicon ratio of electrodes GS1 to GS4 and the discharge capacity retention rate after 40 cycles. It can be seen that in the production of the electrodes, when the amount of silicon is set to 1, the ratio of the amount of graphene oxide is preferably 0.05 or more, more preferably 0.10 or more, and even more preferably 0.30 or more. Note that the electrode mixing ratios shown in Table 2 are the weight ratios of the materials prepared in steps S61, S72, and S80 of Fig. 4 in the production of electrodes GS1 to GS4.

Description of Reference Numerals

[0398] 300: Secondary battery, 301: Positive electrode can, 302: Negative electrode can, 303: Gasket, 304: Positive electrode, 305: Positive electrode current collector, 306: Positive electrode active material layer, 307: Negative electrode, 308: Negative electrode current collector, 309: Negative electrode active material layer, 310: Separator, 312: Washer, 313: Ring-shaped insulator, 322: Spacer, 500: Secondary battery, 501: Positive electrode current collector, 502: Positive electrode active material layer, 503: Positive electrode, 504: Negative electrode current collector, 505: Negative electrode active material layer, 506: Negative electrode, 507: Separator, 508: Electrolyte, 509: Exterior body, 510: Positive electrode lead electrode, 511: Negative electrode lead electrode, 570: Electrode, 570a: Negative electrode, 570b: Positive electrode, 571: Current collector, 571a: Negative electrode current collector, 571b: Positive electrode current collector, 572: Active material layer, 572a: Negative electrode active material layer, 572b: Positive electrode active material layer, 576: Electrolyte, 581: First particle, 582: Second particle, 583: Material having a sheet-like shape, 584: Electrolyte, 601: Positive electrode cap, 602: Battery can, 603: Positive electrode terminal, 604: Positive electrode, 605: Separator, 606: Negative electrode, 607: Negative electrode terminal, 608: Insulating plate, 609: Insulating plate, 611: PTC element, 613: Safety valve mechanism, 614: Conductive plate, 615: Power storage system, 616: Secondary battery, 620: Control circuit, 621: Wiring, 622: Wiring, 623: Wiring, 624: Conductor, 625: Insulator, 626: Wiring, 627: Wiring, 628: Conductive plate, 700: Power storage device, 701: Commercial power supply, 703: Distribution board, 705: Power storage controller, 706: Display, 707: General load, 708: Power storage system load, 709: Router, 710: Lead wire attachment part, 711: Measurement part, 712: Prediction part, 713: Planning part, 790: Control device, 791: Power storage device, 796: Underfloor space part, 799: Building, 911a: Terminal, 911b: Terminal, 913: Secondary battery, 930: Housing, 930a: Housing, 930b: Housing, 931: Negative electrode, 931a: Negative electrode active material layer, 932: Positive electrode, 932a: Positive electrode active material layer, 933: Separator, 950: Wound body, 950a: Wound body, 951: Terminal, 952: Terminal, 1300: Square secondary battery, 1301a: Battery, 1301b: Battery, 1302: Battery controller, 1303: Motor controller, 1304: Motor, 1305: Gear, 1306: DC-DC circuit, 1307: Electric power steering, 1308: Heater, 1309: Defroster, 1310: DC-DC circuit,1311: Battery, 1312: Inverter, 1313: Audio, 1314: Power window, 1315: Lamps, 1316: Tires, 1317: Rear motor, 1320: Control circuit section, 1321: Control circuit section, 1322: Control circuit, 1324: Switch section, 1325: External terminal, 1326: External terminal, 1413: Fixing section, 1414: Fixing section, 1415: Battery pack, 1421: Wiring, 1422: Wiring, 2001: Automobile, 2002: Transport vehicle, 2003: Transport vehicle, 2004: Aircraft, 2100: Mobile phone, 2101: Housing, 2102: Display section, 2103: Operation button, 2104: External connection port, 2105: Speaker, 2106: Microphone, 2107: Secondary battery, 2200: Battery pack, 2201: Battery pack, 2202: Battery pack, 2203: Battery pack, 2300: Unmanned aerial vehicle, 2301: Secondary battery, 2302: Rotor, 2303: Camera, 2603: Vehicle, 2604: Charging device, 2610: Solar panel, 2611: Wiring, 2612: Power storage device, 6300: Vacuum cleaner robot, 6301: Housing, 6302: Display section, 6303: Camera, 6304: Brush, 6305: Operation button, 6306: Secondary battery, 6310: Dust, 6400: Robot, 6401: Illuminance sensor, 6402: Microphone, 6403: Upper camera, 6404: Speaker, 6405: Display section, 6406: Lower camera, 6407: Obstacle sensor, 6408: Moving mechanism, 6409: Secondary battery< / sem>

Claims

1. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The negative electrode includes a first negative electrode active material including silicon particles having a particle size of 1 μm or less, 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 contact with the first negative electrode active material and the second negative electrode active material; The silicon particles include silicon oxide. Lithium-ion secondary battery.

2. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, the negative electrode includes a first negative electrode active material including a silicon-containing compound having a particle size of 1 μm or less, a second negative electrode active material including graphite having a particle size larger than that of the silicon-containing compound, and graphene or a graphene compound; the silicon-containing compound is in contact with the graphite, and the graphene or graphene compound is in contact with the first negative electrode active material and the second negative electrode active material. Lithium-ion secondary battery.

3. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The negative electrode has a first negative electrode active material including SiOx (x is smaller than 2) having a particle size of 1 μm or less, 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 graphene compound is in contact with the first negative electrode active material and the second negative electrode active material. Lithium-ion secondary battery.

4. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The negative electrode includes a first negative electrode active material including silicon particles having a particle size of 1 μm or less, 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. Lithium-ion secondary battery.

5. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, the negative electrode has a first negative electrode active material including a silicon-containing compound having a particle size of 1 μm or less, 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, and the graphene or graphene compound is in contact with the first negative electrode active material and the second negative electrode active material. Lithium-ion secondary battery.

6. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The negative electrode has a first negative electrode active material including SiOx (x is smaller than 2) having a particle size of 1 μm or less, 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, and the graphene or graphene compound is in contact with the first negative electrode active material and the second negative electrode active material. Lithium-ion secondary battery.

7. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The negative electrode includes a first negative electrode active material including silicon particles having a particle size of 1 μm or less, a second negative electrode active material having a smaller volume change than 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. Lithium-ion secondary battery.

8. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The negative electrode has a first negative electrode active material including a silicon-containing compound having a particle size of 1 μm or less, a second negative electrode active material having a smaller volume change than 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, and the graphene or graphene compound is in contact with the first negative electrode active material and the second negative electrode active material. Lithium-ion secondary battery.

9. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The negative electrode includes a first negative electrode active material including silicon particles having a particle size of 1 μm or less, a second negative electrode active material including graphite having a particle size larger than that of the silicon particles, and a conductive assistant; the silicon particles are in contact with the second negative electrode active material, During charging, lithium released from the positive electrode is inserted 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 negative electrode has a first negative electrode active material including SiOx (x is smaller than 2) having a particle size of 1 μm or less, a second negative electrode active material including graphite having a particle size larger than that of the SiOx, and a conductive assistant; The SiOx is in contact with the second negative electrode active material, During charging, lithium released from the positive electrode is inserted into the SiOx of the negative electrode, resulting in a charge-discharge state. Lithium-ion secondary battery.

11. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The negative electrode includes a first negative electrode active material including silicon particles having a particle size of 1 μm or less, a second negative electrode active material including graphite having a particle size 10 times or more 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 contact with the first negative electrode active material and the second negative electrode active material; The silicon includes silicon oxide. Lithium-ion secondary battery.

12. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The negative electrode has a first negative electrode active material containing SiOx (x is smaller than 2) having a smaller particle size than graphite, a second negative electrode active material containing the graphite, and graphene or a graphene compound; The SiOx is in contact with the graphite, and the graphene or graphene compound is in contact with the first negative electrode active material and the second negative electrode active material. Lithium-ion secondary battery.

13. A lithium ion secondary battery having a positive electrode, a negative electrode, an electrolyte, and a separator, The negative electrode comprises a first negative electrode active material including SiOx (x is smaller than 2) having a particle size of 1 μm or less, a second negative electrode active material including graphite having a particle size 10 times or more larger than that of the SiOx, and graphene or a graphene compound; The SiOx is in contact with the graphite, and the graphene or graphene compound is in contact with the first negative electrode active material and the second negative electrode active material. Lithium-ion secondary battery.

14. In any one of claims 1, 4, 7, and 9, The silicon comprises polycrystalline silicon or amorphous silicon. Lithium-ion secondary battery.

15. In any one of claims 2, 5, and 8, The silicon-containing compound is Li ２ SiO ３ , or Li ４ SiO ４ having Lithium-ion secondary battery.

16. In any one of claims 1 to 15, The negative electrode further comprises a binder. Lithium-ion secondary battery.

17. In any one of claims 1 to 16, The second negative electrode active material has a particle size 10 times or more larger than that of the first negative electrode active material. Lithium-ion secondary battery.

18. In any one of claims 1 to 15, The size of the first negative electrode active material is 50 nm or more and 250 nm or less, The size of the second negative electrode active material is 10 μm or more and 20 μm or less. Lithium-ion secondary battery.

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

20. In any one of claims 1 to 19, 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.

21. In any one of claims 1 to 20, 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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