Electrodes, secondary batteries, moving bodies, electronic devices

Abstract

Provided is a negative electrode that is not susceptible to deterioration. Also provided is a novel negative electrode. The present invention also provides a power storage device that is not susceptible to deterioration. The present invention also provides a novel power storage device. This electrode has silicon, graphite, and a graphene compound. Silicon particles having a grain diameter of 1 µm or less adhere to graphite particles having a grain diameter at least 10 times that of the silicon particles, and the graphene compound contacts the graphite particles so as to cover the silicon particles.

Description

[Technical Field]

[0001] This invention relates to electrodes and methods for manufacturing them; or to active materials contained in electrodes and methods for manufacturing them; or to secondary batteries and methods for manufacturing them; or to mobile devices including vehicles having secondary batteries, as well as portable information terminals, electronic devices, etc.

[0002] One aspect of the present invention relates to a product, a method, or a method of manufacture; or to a process, a machine, a manufacture, or a composition of matter. Another 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 of manufacturing the same.

[0003] In this specification, "electronic equipment" refers to all devices that have an energy storage device, and all electro-optical devices with an energy storage device, information terminal devices with an energy storage device, etc., are considered electronic equipment.

[0004] In this specification, the term "energy storage device" refers to all elements and devices that have an energy storage function. For example, this includes energy storage devices such as lithium-ion secondary batteries (also called secondary batteries), lithium-ion capacitors, and electric double-layer capacitors. [Background technology]

[0005] In recent years, there has been a great deal of development on various energy storage devices, including lithium-ion secondary batteries, lithium-ion capacitors, and air batteries. In particular, lithium-ion secondary batteries, which offer high output and high energy density, are seeing rapidly expanding demand in conjunction with the development of the semiconductor industry. They are used in mobile information terminals such as mobile phones, smartphones, and notebook computers, as well as portable music players, digital cameras, medical equipment, and next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), and plug-in hybrid vehicles (PHV). As a rechargeable energy source, they have become indispensable to today's information society. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2002-216751 [Patent Document 2] Special Publication No. 2019-522886 [Overview of the Initiative] [Problems that the invention aims to solve]

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

[0008] Furthermore, power consumption in mobile devices is increasing due to their multi-functionality. Additionally, there is a demand for smaller and lighter rechargeable batteries used in mobile devices. Therefore, there is a need for higher capacity rechargeable batteries for mobile devices.

[0009] In addition to stability, high capacity is crucial for secondary batteries. Alloy materials such as silicon-based materials have high capacity and are promising as active materials for secondary batteries. However, alloy materials with high charge / discharge capacity suffer from problems such as pulverization and shedding of the active material due to volume changes associated with charging and discharging, resulting in insufficient cycle characteristics.

[0010] To address the aforementioned problems with alloy materials, composite materials of alloy materials with graphite or carbonaceous materials have been investigated. Patent Document 1 describes a composite material in which a coating layer made of carbon is formed on the surface of a porous particle nucleus formed by the bonding of silicon-containing particles and carbon-containing particles. Patent Document 2 describes composite particles containing silicon (Si), lithium fluoride (LiF), and carbon material. However, none of the above documents have adequately solved the problem of pulverization and detachment of the active material due to the expansion of alloy materials during charging and discharging.

[0011] The electrodes of a secondary battery are composed of materials such as an active material, a conductive agent, and a binder, for example. The higher the proportion of the materials that contribute to the charge-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, in the charge-discharge of a 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 cases, 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 robust negative electrode. Or, one aspect of the present invention aims to provide a mechanically robust 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 degradation. Or, one aspect of the present invention aims to provide a positive electrode with less degradation.

[0014] Or, one aspect of the present invention aims to provide a secondary battery with less degradation. 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] Furthermore, the description of these problems does not preclude the existence of other problems. Moreover, one aspect of the present invention does not need to solve all of these problems. It is possible to extract other problems from the description in the specification, drawings, and claims. [Means for solving the problem]

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

[0017] Furthermore, an electrode according to one aspect of the present invention comprises a material having a particle and sheet-like shape, wherein the particle comprises a first particle and a second particle, the first particle and the sheet-like material being larger in size than the second particle, and the sheet-like material having a region that contacts the first particle in a manner that covers, wraps around, or clings to the second particle located on the surface of the first particle.

[0018] A sheet-like material preferably has a first region, which is 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 that atom. Alternatively, the first region is, for example, a region having multiple atoms capable of bonding with hydrogen.

[0019] A hydrogen atom in the first region and an oxygen atom in a functional group terminating the surface of the first or second particle can form a hydrogen bond.

[0020] The sheet-like material can bend towards the particles due to intermolecular forces, and can adhere to the particles through hydrogen bonding. Preferably, the sheet-like material has multiple regions terminated by hydrogen atoms on its sheet surface.

[0021] Alternatively, the first region may be terminated by an oxygen-containing functional group. Examples of oxygen-containing functional groups include hydroxyl groups, epoxy groups, carboxyl groups, etc. The hydrogen atoms of hydroxyl groups and carboxyl groups, etc., can form hydrogen bonds with the oxygen atoms of the functional group terminating the particle. Furthermore, the oxygen atoms of hydroxyl groups, epoxy groups, and carboxyl groups can form hydrogen bonds with the hydrogen atoms of the functional group terminating the particle.

[0022] Furthermore, if the sheet-like material has a second region terminated by fluorine atoms, the fluorine atoms in the second region and the hydrogen atoms in the functional group terminating the particle can form a hydrogen bond. This makes the sheet-like material even more likely to cling to the particle.

[0023] Furthermore, the first region may have pores formed on the sheet surface, where the pores are composed, for example, of a plurality of atoms bonded in a ring and atoms terminating the plurality of atoms. The plurality of atoms may also be terminated by functional groups.

[0024] The particles in one embodiment of the present invention preferably function as an active material. The particles in one embodiment of the present invention may be made of a material that functions as an active material. Alternatively, the particles in one embodiment of the present invention preferably have a material that functions as an active material. Furthermore, the sheet-like material in one embodiment of the present invention preferably functions as a conductive agent. In one embodiment of the present invention, the conductive agent can adhere to the active material through hydrogen bonding, thereby achieving an electrode with high conductivity.

[0025] Furthermore, it is preferable that the first particles 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 that undergoes small volume changes with charging and discharging, and are preferably 10 times or more the size of the second particles. Furthermore, it is preferable that the sheet-shaped material in the electrode according to one aspect of the present invention functions as, for example, a conductive agent. In one aspect of the present invention, the sheet-shaped material can come into contact with the first particles in a way that covers, wraps around, or clings to the second particles located on the surface of the first particles, thereby enabling the realization of an electrode with high conductivity.

[0026] Furthermore, a sheet-like material can adhere to the active material, thereby preventing the peeling of the active material at the electrode. A sheet-like material can also adhere to multiple active materials. When using a material with a large volume change during charging and discharging, such as silicon, repeated charging and discharging can gradually weaken the adhesion between the active material and the conductive agent, or between multiple active materials, potentially leading to the peeling of the active material at the electrode. In one embodiment of the present invention, when silicon is used as the second particle, the second particle, located on the surface of the first particle which has a small volume change during charging and discharging, can come into contact with the first particle by covering, enveloping, or clinging to it. Therefore, peeling of the active material at the electrode is suppressed even during repeated charging and discharging, resulting in a stable and highly reliable electrode. Silicon has a very high theoretical capacity of 4000 mAh / g or more, which can increase the energy density of secondary batteries. In one aspect of the present invention, by using an active material with small volume changes associated with charging and discharging as the first particle, and a silicon-containing material as the second particle, a highly reliable secondary battery with high energy density and stable characteristics even after repeated charging and discharging can be realized.

[0027] A second particle according to one aspect of the present invention has silicon atoms terminated by hydroxyl groups. Alternatively, a particle according to one aspect of the present invention has silicon, with at least a portion of its surface terminated by hydroxyl groups. Alternatively, a particle according to one aspect of the present invention is a silicon compound with at least a portion of its surface terminated by hydroxyl groups. Alternatively, a particle according to one aspect of the present invention is silicon with at least a portion of its surface terminated by hydroxyl groups.

[0028] Alternatively, it is preferable that the first particles in one aspect of the present invention have a first material and the second particles have a second material.

[0029] Furthermore, in the above configuration, the first material is preferably one or more selected from graphite, easily graphitizable carbon, poorly graphitizable carbon, carbon nanotubes, carbon black, and graphene.

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

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

[0032] Graphene has a structure in which its edges are terminated by hydrogen. Furthermore, a graphene sheet has a two-dimensional structure formed of six-membered carbon rings, and when defects or pores are formed in this two-dimensional structure, carbon atoms near the defects or carbon atoms constituting the pores may be terminated by various functional groups or atoms such as hydrogen atoms or fluorine atoms.

[0033] In one embodiment 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., thereby allowing the graphene to adhere to the particles of the electrode. Preferably, the amount of defects or pores formed in the graphene is such that the overall conductivity of the graphene is not significantly impaired. Here, "constituting a pore" refers, for example, to atoms at the periphery of the opening, atoms at the end of the opening, etc.

[0034] A graphene compound according to one embodiment of the present invention has a pore composed of a multi-membered ring consisting of 7 or more carbon-based rings, preferably 18 or more, and more preferably 22 or more. In addition, one of the carbon atoms in the multi-membered ring is terminated by a hydrogen atom. In another embodiment of the present invention, one of the carbon atoms in the multi-membered ring is terminated by a hydrogen atom, and the other is terminated by a fluorine atom. In another embodiment of the present invention, the number of carbon atoms terminated by fluorine in the multi-membered ring is less than 40% of the number of carbon atoms terminated by hydrogen atoms.

[0035] A graphene compound according to one aspect of the present invention has pores, each pore composed of a plurality of cyclically bonded carbon atoms and a plurality of atoms or functional groups terminating the carbon atoms. One or more of the cyclically bonded carbon atoms may be substituted with a Group 13 element such as boron, a Group 15 element such as nitrogen, and a Group 16 element such as oxygen.

[0036] In one embodiment of the present invention, it is preferable that carbon atoms other than those at the edges of the graphene compound are terminated by hydrogen atoms, fluorine atoms, functional groups having hydrogen atoms or fluorine atoms, functional groups having oxygen, etc. Furthermore, in one embodiment of the present invention, it is preferable that carbon atoms near the center of the graphene surface are terminated by hydrogen atoms, fluorine atoms, functional groups having hydrogen atoms or fluorine atoms, functional groups having oxygen, etc.

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

[0038] In the electrode described in 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 described in any one of the above, it is preferable that the graphene compound is in contact with the second active material such that it adheres to the first active material.

[0040] In the electrode described in 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 described in 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 described in any one of the above, it is preferable that the silicon is amorphous silicon.

[0043] In the electrode described in any one of the above, the graphene compound has a pore and comprises a plurality of carbon atoms and one or more hydrogen atoms, and each of the one or more hydrogen atoms terminates at one of the plurality of carbon atoms, and it is preferable that the pore is formed by the plurality of carbon atoms and one or more hydrogen atoms.

[0044] Alternatively, one aspect of the present invention is a secondary battery having an electrode and an electrolyte as described in any one of the above.

[0045] Alternatively, one aspect of the present invention is a mobile body having a secondary battery as described in any one of the above.

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

[0047] Furthermore, one aspect of the present invention is a method for producing an electrode for a lithium-ion secondary battery, comprising: 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 onto 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 under reduced pressure, and the graphene compound is reduced and the polyimide precursor is imidized by the heating.

[0048] Furthermore, in the above configuration, the graphene compound preferably contains graphene oxide, and the graphite is preferably 10 times or more in size than the silicon. [Effects of the Invention]

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

[0050] Furthermore, according to one aspect of the present invention, a mechanically robust negative electrode can be provided. Furthermore, according to one aspect of the present invention, a robust positive electrode can be provided. Furthermore, according to one aspect of the present invention, a negative electrode with minimal degradation can be provided. Furthermore, according to one aspect of the present invention, a positive electrode with minimal degradation can be provided. Furthermore, according to one aspect of the present invention, a negative electrode with minimal degradation can be provided. Furthermore, according to one aspect of the present invention, a positive electrode with minimal degradation can be provided.

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

[0052] Furthermore, the description of these effects does not preclude the existence of other effects. Moreover, one aspect of the present invention does not necessarily have to possess all of these effects. Other effects will naturally become apparent from the description in the specification, drawings, and claims, and it is possible to extract other effects from the description in the specification, drawings, and claims. [Brief explanation of the drawing]

[0053] Figures 1A and 1B show examples of cross-sections of electrodes. Figure 1C shows a perspective view of a particle. Figures 2A and 2B show the changes in particle shape during charging and discharging. Figures 3A and 3B show examples of graphene compound models. Figure 4 shows an example of a method for manufacturing an electrode according to one aspect of the present invention. Figure 5 illustrates the crystal structure of the positive electrode active material. Figure 6 illustrates the crystal structure of the positive electrode active material. Figure 7 shows an example of a cross-section of a secondary battery. Figure 8A is an exploded perspective view of a coin-type rechargeable battery, Figure 8B is a perspective view of a coin-type rechargeable battery, and Figure 8C is a cross-sectional perspective view thereof. Figures 9A and 9B show examples of cylindrical secondary batteries, Figure 9C shows examples of multiple cylindrical secondary batteries, and Figure 9D shows examples of energy storage systems having multiple cylindrical secondary batteries. Figures 10A and 10B illustrate examples of secondary batteries, while Figure 10C shows the inside of a secondary battery. Figures 11A, 11B, and 11C illustrate examples of secondary batteries. Figures 12A and 12B show the external appearance of a secondary battery. Figures 13A, 13B, and 13C illustrate the method for manufacturing a secondary battery. Figure 14A is a perspective view showing the battery pack, Figure 14B is a block diagram of the battery pack, and Figure 14C is a block diagram of a vehicle with a motor. Figures 15A to 15D illustrate an example of a transport vehicle. Figures 16A and 16B illustrate the energy storage device. Figures 17A to 17D illustrate an example of an electronic device. Figures 18A and 18B are SEM images. Figures 19A and 19B are SEM images. Figures 20A and 20B are SEM images. Figures 21A and 21B are SEM images. Figures 22A and 22B show the cycle characteristics. Figure 23 shows the relationship between electrode composition ratio and cycle characteristics. [Modes for carrying out the invention]

[0054] Embodiments of the present invention will be described in detail below with reference to the drawings. However, it will be readily apparent to those skilled in the art that the present invention is not limited to the following description, and its form and details can be modified in various ways. Furthermore, the present invention is not to be interpreted as being limited to the embodiments described below.

[0055] Furthermore, in drawings, size, layer thickness, or area may be exaggerated for clarity. Therefore, the scale is not necessarily limited.

[0056] Furthermore, the ordinal numbers used in this specification, such as "first," "second," etc., are for convenience only and do not indicate the order of processes or stacking. Therefore, for example, "first" can be replaced with "second" or "third," etc., as appropriate in the explanation. Also, the ordinal numbers described in this specification may not be the same as the ordinal numbers used to specify an aspect of the present invention.

[0057] (Embodiment 1) This embodiment describes an electrode, active material, conductive agent, etc., according to one aspect of the present invention.

[0058] <Example of an electrode> Figure 1A is a schematic cross-sectional view showing an electrode according to one embodiment of the present invention. The electrode 570 shown in Figure 1A can be applied to the positive and / or negative electrodes 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] Figure 1B is an enlarged view of the area enclosed by the dashed line in Figure 1A. As shown in Figure 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. Figure 1C is a schematic diagram showing how the graphene compound 583 contacts the first particle 581 in a way that covers, wraps around, or clings to the second particle 582 located on the surface of the first particle 581. Materials that function as active materials can be used as the first particle 581 and the second particle 582. Alternatively, it is preferable that at least the second particle 582 has a material that functions as an active material. Furthermore, it is preferable that the graphene compound 583 in the electrode 570 functions as a conductive agent. In one embodiment 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, thereby realizing an electrode with high conductivity.

[0060] Various materials can be used as the first particle 581 and the second particle 582. When particles according to one aspect of the present invention are used as the first particle 581 and the second particle 582, the affinity between the first particle 581 and the second particle 582 and the graphene compound 583 is improved, as shown in Figures 1B and 1C, and the graphene compound 583 can come into contact with the first particle 581 in a way that covers, encases, or clings to the second particle 582 located on the surface of the first particle 581. As particles according to one aspect of the present invention, for example, particles having an oxygen-containing functional group or fluorine in the surface layer, or particles having a region terminated by an oxygen-containing functional group or fluorine atom on the surface can be used. Because the graphene compound 583 can cling to the first particle 581 and the second particle 582, highly conductive electrodes can be realized. The state of clinging to the particles can also be described as making close contact rather than point contact. This can also be rephrased as "contacting along the surface of the particles." Furthermore, it can be rephrased as "in surface contact with multiple particles." The materials that can be used as the first particle 581 and the second particle 582 will be described later.

[0061] The case in which an active material with a large volume change during charging and discharging is used as the second particle 582 will be explained using Figure 2. The material comprises a first particle 581, a second particle 582, and a graphene compound 583 as a sheet-like material. Figure 2A shows how the graphene compound 583 comes into contact with the first particle 581, covering, wrapping around, or clinging to the second particle 582 located on the surface of the first particle 581. The second particle 582 is located between the first particle 581 and the graphene compound 583, and it can also be said that the graphene compound 583 is in contact with both the first particle 581 and the second particle 582. Figure 2B shows the case in which the volume of the second particle 582 shown in Figure 2A increases due to charging or discharging. Because the graphene compound 583 is in contact with the first particle 581 in a way that covers, encases, or clings to the second particle 582 located on the surface of the first particle 581, electrical contact between the second particle 582 and the first particle 581 can be maintained even when the volume of the second particle 582 increases due to charging or discharging. Furthermore, peeling of the active material of the electrode can be suppressed.

[0062] When the graphene compound 583 adheres to the active material, such as the first particle 581 and the second particle 582, the contact area between the graphene compound 583 and the active material increases, improving the conductivity of electrons moving through the graphene compound 583. Furthermore, when the volume of the active material changes significantly due to charging and discharging, the adhesion of the graphene compound 583 to the active material effectively prevents the active material from falling off. These effects become even more pronounced when the adhesion is dense. Here, the graphene compound 583 has pores large enough to allow Li ions to pass through, and it is desirable that the number of pores be large enough not to hinder the electronic conductivity of the graphene compound 583.

[0063] In this example, graphene compound 583 is used as the sheet-like material, but the sheet-like material is not limited to graphene compound 583; other sheet-like materials with high electronic conductivity may also be used.

[0064] The active material layer 572 may contain carbon-based materials such as carbon black, graphite, carbon fiber, or fullerene, in addition to the graphene compound 583. For example, acetylene black (AB) can be used as the carbon black. For example, natural graphite or artificial graphite such as mesocarbon microbeads can be used as the graphite. These carbon-based materials have high conductivity and can function as conductive agents in the active material layer. These carbon-based materials may also function as the active material.

[0065] As carbon fibers, for example, mesophase pitch carbon fibers and isotropic pitch carbon fibers can be used. Alternatively, carbon nanofibers or carbon nanotubes can be used. Carbon nanotubes can be fabricated, for example, by vapor deposition.

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

[0067] The content of the conductive additive relative to the total amount of solids in the active material layer is preferably 0.5 wt% to 10 wt%, and more preferably 0.5 wt% to 5 wt%.

[0068] Unlike granular conductive materials such as carbon black, which make point contact with the active material, graphene compound 583 enables surface contact with low contact resistance. Therefore, it is possible to improve the electrical conductivity between granular active material and graphene compound 583 with a smaller amount than conventional conductive materials. Consequently, the ratio of active material in the active material layer can be increased. This allows for an increase in the discharge capacity of the secondary battery.

[0069] Furthermore, since graphene compound 583 according to one embodiment of the present invention has excellent lithium permeability, it can increase the charge and discharge rate of secondary batteries.

[0070] Particulate carbon-containing compounds such as carbon black and graphite, and fibrous carbon-containing compounds such as carbon nanotubes, readily enter minute spaces. These minute spaces refer, for example, to regions between multiple active materials. By combining carbon-containing compounds that readily enter minute spaces with sheet-like carbon-containing compounds such as graphene, which can impart conductivity across multiple particles, the electrode density can be increased, and excellent conductive paths can be formed. Furthermore, by having an electrolyte according to one aspect of the present invention in a secondary battery, the stability of the secondary battery's operation can be improved. In other words, a secondary battery according to one aspect of the present invention can combine high energy density and stability, making it effective as a secondary battery for vehicles. Increasing the number of secondary batteries increases the weight of the vehicle, which in turn increases the energy required to move it, thus shortening the driving range. By using high-density secondary batteries, the driving range can be extended even if the weight of the secondary batteries installed in the vehicle remains the same, that is, even if the total weight of the vehicle remains the same.

[0071] Furthermore, as the capacity of a vehicle's secondary battery increases, more power is required for charging, making it desirable to complete the charging process in a short time. In addition, regenerative charging, which involves temporarily generating electricity when the vehicle brakes are applied and then charging the battery, is performed under high-rate charging conditions, so good rate characteristics are required for vehicle secondary batteries.

[0072] By using an electrolyte according to one aspect of the present invention, a secondary battery for automotive use having a wide operating temperature range can be obtained.

[0073] Furthermore, the secondary battery according to one embodiment of the present invention can be miniaturized due to its high energy density, and rapid charging is possible due to its high conductivity. Therefore, the configuration of the secondary battery according to one embodiment of the present invention is also effective in portable information terminals.

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

[0075] It is preferable to use materials such as polystyrene, methyl polyacrylate, polymethyl methacrylate (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, and nitrocellulose as binders.

[0076] Polyimides possess excellent thermal, mechanical, and chemical stability. Furthermore, when polyimides are used as a binder, dehydration and cyclization (imidization) reactions are performed. These reactions can be carried out, for example, by heat treatment. In one embodiment of the present invention, when graphene having an oxygen-containing functional group is used as the graphene compound and polyimides as the binder, the reduction of the graphene compound can also be performed by the heat treatment, simplifying the process. Due to its excellent heat resistance, the heat treatment can be performed at a heating temperature of, for example, 200°C or higher. By performing the heat treatment at a heating temperature of 200°C or higher, the reduction reaction of the graphene compound can be sufficiently carried out, further improving the conductivity of the electrode.

[0077] Fluorine-containing polymer materials, specifically polyvinylidene fluoride (PVDF), can be used. PVDF is a resin with a melting point in the range of 134°C to 169°C, and is a material with excellent thermal stability.

[0078] Furthermore, it is preferable to use rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, or ethylene-propylene-diene copolymer as a binder. Fluororubber can also be used as a binder.

[0079] Furthermore, it is preferable to use a water-soluble polymer as the binder. Examples of water-soluble polymers include polysaccharides. Examples of polysaccharides include cellulose derivatives such as carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, diacetylcellulose, and regenerated cellulose, or starch. It is even more preferable to use these water-soluble polymers in combination with the aforementioned rubber material.

[0080] You may use a combination of several of the binders mentioned above.

[0081] Furthermore, the graphene compound 583 is flexible and pliable, and can cling to the second particle 582 like natto (fermented soybeans). For example, the second particle 582 can be likened to soybeans, and the graphene compound 583 to a sticky component, such as polyglutamic acid. By arranging the graphene compound 583 between the electrolyte, the second particle 582 and other active materials, and multiple carbon-based materials of the active material layer 572, not only is a good conductive path formed within the active material layer 572, but these materials can also be bound or fixed using the graphene compound 583. For example, by forming a three-dimensional network structure, a structure with arranged polygons, such as a honeycomb structure with hexagons arranged in a matrix, using multiple graphene compounds 583, and arranging the electrolyte, multiple active materials, and multiple carbon-based materials in the network, the graphene compound 583 can form a three-dimensional conductive path, and the detachment of the electrolyte from the current collector can be suppressed. Furthermore, in the structure in which the above polygons are arranged, polygons with different numbers of sides may be mixed together. Therefore, the graphene compound 583 may function as both a conductive agent and a binder in the active material layer 572.

[0082] The first particle 581 and the second particle 582 can have various shapes, such as rounded shapes or angular shapes. Furthermore, in the cross-section of the electrode, the first particle 581 and the second particle 582 can have various cross-sectional shapes, such as circles, ellipses, curved shapes, polygons, etc. For example, Figures 1B and 1C show an example where the cross-sections of the first particle 581 and the second particle 582 have rounded shapes, but the cross-sections of the first particle 581 and the second particle 582 may also have angular shapes. Alternatively, they may be partially rounded and partially angular.

[0083] <Graphene compound> In this specification, graphene compounds include graphene, multilayer graphene, multigraphene, graphene oxide, multilayer graphene oxide, multigraphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multigraphene oxide, graphene quantum dots, etc. A graphene compound is a material having carbon, having a plate-like or sheet-like shape, and having a two-dimensional structure formed by a six-membered carbon ring. The two-dimensional structure formed by the six-membered carbon ring may also be called a carbon sheet. Graphene compounds may have functional groups containing oxygen. Furthermore, graphene compounds preferably have a bent shape. Furthermore, graphene compounds may be rolled up to resemble carbon nanofibers.

[0084] In this specification, graphene oxide refers to, for example, a material having carbon and oxygen, having a sheet-like structure, and having functional groups, particularly epoxy groups, carboxyl groups, or hydroxyl groups.

[0085] In this specification, reduced graphene oxide refers to, for example, a material having carbon and oxygen, having a sheet-like shape, and possessing a two-dimensional structure formed by a six-membered carbon ring. It may also be called a carbon sheet. Reduced graphene oxide can function as a single sheet, but multiple sheets may be laminated together. It is preferable that reduced graphene oxide has a portion where the carbon concentration is greater than 80 atomic%, and the oxygen concentration is between 2 atomic% and 15 atomic%. With such carbon and oxygen concentrations, it can function as a highly conductive material even in small quantities. It is also preferable that reduced graphene oxide has a G / D intensity ratio of 1 or more in the Raman spectrum. Reduced graphene oxide with such an intensity ratio can function as a highly conductive material even in small quantities.

[0086] In some cases, pores can be created in the reduced graphene oxide by reducing it.

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

[0088] In the longitudinal section of the active material layer, sheet-like graphene compounds are dispersed approximately uniformly within the internal region of the active material layer. Multiple graphene compounds are formed to partially cover multiple granular active materials or to adhere to the surfaces of multiple granular active materials, and thus are in surface contact with one another.

[0089] Here, multiple graphene compounds can bond together to form a mesh-like graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net). When the active material is coated with the graphene net, the graphene net can also function as a binder that binds the active materials together. Therefore, the amount of binder can be reduced or eliminated, thereby improving the ratio of active material to electrode volume and electrode weight. In other words, the charge and 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 an active material layer, and then reduce the graphene oxide. In other words, it is preferable that the completed active material layer has reduced graphene oxide. When forming the active material layer containing the graphene compound, by using graphene oxide, which has extremely high dispersibility in a polar solvent, the graphene compound can be dispersed approximately uniformly within the internal region of the active material layer.

[0091] In an active material layer prepared by coating a dispersion of graphene oxide, in which graphene oxide is dispersed in a solvent in a generally uniform manner, onto a current collector, volatilizing and removing the solvent, and then reducing the graphene oxide, the graphene compounds in the active material layer partially overlap. In this way, the reduced graphene oxide is dispersed to the extent that it is in surface contact with each other, thereby forming a three-dimensional conductive path. The reduction of graphene oxide may be carried out, for example, by heat treatment or by using a reducing agent.

[0092] Furthermore, by pre-covering the surface of the active material with a graphene compound, a conductive coating can be formed on the surface of the active material, and then conductive paths can be formed by electrically connecting the active material parts with the graphene compound.

[0093] In one embodiment of the present invention, the graphene compound preferably has pores in a portion of the carbon sheet. In one embodiment of the present invention, by providing pores in a portion of the carbon sheet through which carrier ions such as lithium ions can pass, the insertion and removal of carrier ions becomes easier on the surface of the active material covered with the graphene compound, thereby improving the rate characteristics of the secondary battery. The pores provided in a portion of the carbon sheet may be called voids, defects, or cavities.

[0094] A graphene compound according to one aspect of the present invention preferably has pores formed by a plurality of carbon atoms and one or more fluorine atoms. Furthermore, it is preferable that the plurality of carbon atoms are bonded in a ring, and that one or more of the ring-bonded plurality of carbon atoms are terminated with fluorine. Fluorine has high electronegativity and readily carries a negative charge. When a positively charged lithium ion approaches, an interaction occurs, the energy stabilizes, and the barrier energy for lithium ions to pass through the pore can be lowered. Therefore, because the pores of the graphene compound contain fluorine, lithium ions can easily pass through even small pores, and a graphene compound with excellent conductivity can be realized. Furthermore, one or more of the ring-bonded plurality of carbon atoms may be terminated with hydrogen.

[0095] Figures 3A and 3B show an example of the structure of a graphene compound with pores.

[0096] The structure shown in Figure 3A has a 22-membered ring, and eight of the carbon atoms constituting the 22-membered ring are each terminated by hydrogen atoms. Alternatively, it can be said that in graphene, two linked 6-membered rings have been removed, and the carbon atoms that were bonded to the removed 6-membered rings have been terminated by hydrogen atoms.

[0097] The structure shown in Figure 3B has a 22-membered ring, in which 6 of the 8 carbon atoms constituting the 22-membered ring are terminated with hydrogen, and 2 carbon atoms are terminated with fluorine. Alternatively, it can be said that graphene has a structure in which two linked 6-membered rings are removed, and the carbon atoms that were bonded to the removed 6-membered rings are terminated with hydrogen or fluorine.

[0098] Because hydroxyl-terminated silicon forms hydrogen bonds between the hydrogen atoms of the hydroxyl groups on the silicon surface and the hydrogen atoms or fluorine atoms of the graphene compound, it is thought that hydroxyl-terminated silicon has a strong interaction with porous graphene compounds.

[0099] Because the graphene compound contains fluorine in addition to hydrogen, hydrogen bonds are formed not only between the oxygen atom of the hydroxyl group and the hydrogen atom of the graphene compound, but also between the hydrogen atom of the hydroxyl group and the fluorine atom of the graphene compound. This is thought to make the interaction between the silicon-containing particles and the graphene compound stronger and more stable.

[0100] If graphene contains pores, it may be possible to observe spectra based on features caused by the pores through, for example, Raman spectroscopy mapping. Furthermore, it may be possible to observe the bonds and functional groups constituting the pores using ToF-SIMS. Additionally, TEM observation may allow for analysis of the vicinity and surrounding areas of the pores.

[0101] <An example of a negative electrode active material> When electrode 570 is the negative electrode, particles having a negative electrode active material can be used as the second particle 582. It is preferable to use a material that can react with carrier ions of a secondary battery, a material that can insert and remove carrier ions, a material that can alloy with a metal that becomes a carrier ion, a material that can dissolve and precipitate a metal that becomes a carrier ion, etc., as the negative electrode active material.

[0102] An example of a negative electrode active material is described below.

[0103] Silicon can be used as the negative electrode active material. For electrode 570, it is preferable to use silicon-containing particles as the second particle 582.

[0104] Furthermore, as the negative electrode active material of the second particle 582, a metal or compound having one or more elements selected from tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium can be used. Examples of alloy compounds using such elements include Mg2Si, Mg2Ge, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, and SbSn.

[0105] Alternatively, materials with reduced resistance may be used, which are silicon to which impurity elements such as phosphorus, arsenic, boron, aluminum, and gallium have been added. Alternatively, lithium-predoped silicon materials may be used. Methods of pre-doping include annealing silicon with lithium fluoride, lithium carbonate, etc., and mechanical alloying of lithium metal and silicon. Furthermore, after forming electrodes, lithium may be doped by a charge-discharge reaction in combination with electrodes such as lithium metal, and then a secondary battery may be fabricated by combining the doped electrodes with a counter electrode (for example, a positive electrode to a pre-doped negative electrode).

[0106] For example, nanosilicon particles can be used as the second particle 582. The average diameter of the nanosilicon particles is 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 nanosilicon particles may have a spherical shape, a flattened spherical shape, or a rectangular parallelepiped shape with rounded corners. The size of the nanosilicon particles is 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, as measured by the D50 of laser diffraction particle size distribution measurement. Here, D50 is the particle diameter, i.e., the median, at which the cumulative amount accounts for 50% of the cumulative particle amount curve of the particle size distribution measurement result. The measurement of particle size is not limited to laser diffraction particle size distribution measurement; if it is below the lower limit of measurement for 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] It is preferable that the nanosilicon particles have amorphous silicon. It is also preferable that the nanosilicon particles have polycrystalline silicon. It is preferable that the nanosilicon particles have both amorphous silicon and polycrystalline silicon. Furthermore, the nanosilicon particles may have both crystalline regions and amorphous regions.

[0109] For example, a material containing silicon is SiO x A material represented by (where x is preferably less than 2, and more preferably between 0.5 and 1.6) can be used.

[0110] As a material containing silicon, for example, a form having multiple crystal grains within a single particle can be used. For example, a form having one or more silicon crystal grains within a single particle can be used. Furthermore, the single particle may have silicon oxide surrounding the silicon crystal grain. Furthermore, the silicon oxide may be amorphous. It may also be a particle in which a graphene compound is attached to a secondary silicon particle.

[0111] Furthermore, silicon-containing compounds can include, for example, Li2SiO3 and Li4SiO4. Li2SiO3 and Li4SiO4 may be crystalline or amorphous, respectively.

[0112] The analysis of silicon-containing compounds can be performed using NMR, XRD, Raman spectroscopy, SEM, TEM, EDX, etc.

[0113] The first particle 581 of 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 that undergoes small volume changes during charging and discharging.

[0115] As for the volume change of the first particle 581 during charging or discharging, when the minimum volume during charging or discharging is set to 1, the maximum volume during 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 be 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 but less than 1000 times the D50 of the second particle 582, more preferably 2 times or more but 500 times or less, and even more preferably 10 times or more but 100 times or less. Here, D50 is the particle diameter, i.e., the median, when the cumulative amount accounts for 50% in the cumulative particle amount curve of the particle size distribution measurement result. Note that the measurement of 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] Furthermore, as the first particle 581, carbon-based materials such as graphite, easily graphitizable carbon, poorly graphitizable carbon, carbon nanotubes, carbon black, and graphene compounds, which exhibit small volume changes during charging and discharging, can be used.

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

[0120] Multiple metals, materials, compounds, etc., as described above can be used as the first particle 581.

[0121] For example, the first particle 581 could be SnO, SnO2, titanium dioxide (TiO2), lithium titanium oxide (Li4Ti5O2). 12 ), lithium-graphite intercalation compound (Li x Oxides such as C6, niobium pentoxide (Nb2O5), tungsten oxide (WO2), and molybdenum oxide (MoO2) can be used.

[0122] Furthermore, a material that undergoes a conversion reaction can also be used as the first particle 581. For example, transition metal oxides that do not undergo alloying reactions with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may be used as the first particle 581. Other materials that undergo a conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, Cr2O3, and CoS 0.89 This phenomenon also occurs with sulfides such as NiS and CuS, nitrides such as Zn3N2, Cu3N, and Ge3N4, phosphides such as NiP2, FeP2, and CoP3, and fluorides such as FeF3 and BiF3. Furthermore, because the potential of these fluorides is high, they may be used as positive electrode materials.

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

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

[0125] In step S62, prepare the solvent. As the solvent, one or more of the following can be used: water, methanol, ethanol, acetone, tetrahydrofuran (THF), dimethylformamide (DMF), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

[0126] Next, in step S63, the silicon-containing particles prepared in step S61 and the solvent prepared in step S62 are mixed, the mixture is collected in step S64, and mixture E-1 is obtained in step S65. A kneader or the like can be used for mixing. For example, a rotary-orbit mixer can be used as a kneader.

[0127] Next, in step S72, a particle containing graphite is prepared as the first particle 581. For example, the particle described above as the first particle 581 can be used as the particle containing graphite.

[0128] Next, in step S73, mixture E-1 is mixed with the graphite-containing particles prepared in step S72, the mixture is recovered in step S74, and mixture E-2 is obtained in step S75. A kneader or the like can be used for mixing. For example, a rotary-orbit mixer can be used as a kneader.

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

[0130] Next, in step S81, mixture E-2 is mixed with the graphene compound prepared in step S80, and the mixture is recovered in step S82. The recovered mixture is preferably highly viscous. The high viscosity of the mixture allows for solid kneading (kneading at high viscosity) in the next step S83.

[0131] Next, in step S83, the mixture is kneaded. This kneading can be done using, for example, a spatula. By kneading, the silicon-containing particles and the graphene compound are well mixed, forming a mixture with excellent dispersibility of the graphene compound.

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

[0133] It is preferable to repeat steps S83 to 85 n times with the mixture recovered in step S85. n is, for example, a natural number between 2 and 10. Also, in step S83, if the mixture is dry, it is preferable to add solvent. On the other hand, if too much solvent is added, the viscosity will decrease and the effect of solid kneading will be reduced.

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

[0135] Next, in step S87, the binder is prepared. The materials described above can be used as the binder, and polyimide is particularly preferred. In step S87, a precursor of the material to be used as the binder may be prepared. For example, a precursor of polyimide may be prepared.

[0136] Next, in step S88, mixture E-3 is mixed with the binder prepared in step S87. Then, 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, it may be possible to adjust, for example, the thickness, density, etc. of the electrode obtained in step S97.

[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, in step S93, the current collector is prepared.

[0139] Next, in step S94, the mixture E-4 is applied to the current collector prepared in step S93. For application, a slot die method, gravure coating, blade coating, or a combination thereof can be used. A continuous coating machine may also be used for application.

[0140] Next, in step S95, a first heating is performed. The solvent evaporates during the first heating. The first heating is preferably performed in a temperature range of 40°C to 200°C, preferably 50°C to 150°C. The first heating is sometimes referred to as drying.

[0141] The first heating process can be carried out, for example, by heating on a hot plate in an air atmosphere at a temperature of 30°C to 70°C for 10 minutes or more, followed by heating in a reduced pressure environment at a temperature of room temperature to 100°C for 1 hour to 10 hours.

[0142] Alternatively, heat treatment may be performed using a drying oven or the like. If a drying oven is used, for example, heat treatment should be performed at a temperature of 30°C to 120°C for 30 seconds to 2 hours.

[0143] Alternatively, the temperature may be increased in stages. For example, after heating at 60°C or below for 10 minutes or less, the temperature may be further heated at 65°C or above for 1 minute or more.

[0144] Next, in step S96, a second heating is performed. When polyimide is used as the binder, it is preferable that a cycloaddition reaction of polyimide occurs during the second heating. Alternatively, a dehydration reaction of polyimide may occur during the second heating. Furthermore, a cyclization reaction of polyimide may occur during the first heating. It is also preferable that a reduction reaction of the graphene compound occurs during the second heating. The second heating is sometimes referred to as imidation heat treatment, reduction heat treatment, or thermal reduction treatment.

[0145] The second heating should be carried out in a temperature range of 150°C to 500°C, preferably 200°C to 450°C.

[0146] The second heating process can be carried out, for example, by heating at a temperature of 200°C to 450°C for 1 to 10 hours under a reduced pressure of 10 Pa or less, or under an inert atmosphere such as nitrogen or argon.

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

[0148] The thickness of the active material layer formed in this manner is preferably, for example, 5 μm to 300 μm, and more preferably 10 μm to 150 μm. The amount of active material supported in the active material layer is preferably, for example, 2 mg / cm³. 2 More than 50mg / cm 2 The following is acceptable.

[0149] The active material layer may be formed on both sides of the current collector, or on only one side. Alternatively, it may partially have regions where the active material layer is formed on both sides.

[0150] After the solvent has evaporated from the active material layer, the material may be pressed using a compression method such as a roll press or a flat plate press. Heat may also be applied during the pressing process.

[0151] <An example of a 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] Preferably, a positive electrode active material having a layered crystal structure is used as the positive electrode active material of one aspect of the present invention.

[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 LiCoO2, LiNiO2, LiMnO2, etc. Further, 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 LiM x O y include the NiMn-based represented by LiNi x Mn 1-x O2 (0 <x <1), etc.

[0155] Further, 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 represented by the above lithium-containing composite oxide, it may be possible to realize a secondary battery having a large lithium content per volume and a high capacity per volume. 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, in some cases, high-speed charging or high-speed discharging may be inhibited due to the collapse of the crystal structure during charge and discharge.

[0158] Also, in a lithium-containing material having a spinel-type crystal structure containing manganese such as LiMn2O4 as a positive electrode active material, it is preferable to mix 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 A lithium manganese composite oxide can be used, which can be represented as follows: Here, element M is preferably a metallic element selected from lithium and manganese, or silicon or phosphorus, and more preferably nickel. When measuring the entire particle of lithium manganese composite oxide, <a / (b+c)<2、かつc>it is preferable that the discharge is 0 0 and 0.26 ≤ (b+c) / d < 0.5. The composition of metals, silicon, phosphorus, etc., of the entire particle of lithium manganese composite oxide can be measured, for example, using ICP-MS (inductively coupled plasma mass spectrometer). The oxygen composition of the entire particle of lithium manganese composite oxide can be measured, for example, using EDX (energy dispersive X-ray spectrometry). It can also be determined by using valence evaluation of molten gas analysis and XAFS (X-ray absorption fine structure) analysis in combination with ICPMS analysis. Lithium manganese composite oxide refers to an oxide containing at least lithium and manganese, and may also 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 with a layered rock salt crystal structure, such as lithium cobalt oxide (LiCoO2), are known to have high discharge capacity and are excellent as positive electrode active materials for secondary batteries. Examples of materials with a layered rock salt crystal structure include composite oxides represented by LiMO2. Metal M contains metal Me1. Metal Me1 is one or more metals containing cobalt. In addition to metal Me1, metal M may also contain metal X. 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 differs in strength depending on the number of electrons in the d orbitals of the transition metal.

[0162] ​ In nickel-containing compounds, distortion can easily occur due to the Jahn-Teller effect. Therefore, when LiNiO2 is charged at high voltage, there is a concern that the crystal structure may collapse due to distortion. In LiCoO2, the effect of the Jahn-Teller effect is suggested to be smaller, and it may have better resistance to high-voltage charging, making it preferable.

[0163] The positive electrode active material will be explained using Figures 5 and 6.

[0164] A positive electrode active material produced according to one aspect of the present invention can reduce the displacement of the CoO2 layer during repeated high-voltage charging and discharging. Furthermore, it can reduce volume changes. Therefore, the compound can achieve excellent cycle characteristics. In addition, the compound can adopt a stable crystal structure in a high-voltage charged state. Therefore, when the compound is maintained in a high-voltage charged state, short circuits may be less likely to occur. In such cases, safety is further improved, which is preferable.

[0165] In this compound, the difference in crystal structure and volume per unit number of transition metal atoms between a fully discharged state and a high-voltage charged state is small.

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

[0167] The crystal structure at charge depth 0 (discharge state) in Figure 5 is R-3m(O3), the same as in Figure 6. On the other hand, the positive electrode active material shown in Figure 5 has a crystal structure different from the H1-3 type crystal structure when fully charged at a charge depth (e.g., 0.8). This structure has a space group R-3m and is not a spinel type crystal structure, but ions such as cobalt and magnesium occupy the oxygen 6-coordinate positions, and the arrangement of cations has a symmetry similar to that of the spinel type. Furthermore, the periodicity of the CoO2 layer in this structure is the same as that of the O3 type. Therefore, in this specification, this structure is referred to as the O3' type crystal structure or the pseudo-spinel type crystal structure. Accordingly, the O3' type crystal structure and the pseudo-spinel type crystal structure may be used interchangeably. Note that in the diagram of the pseudo-spinel type crystal structure shown in Figure 5, the representation of lithium is omitted in order to explain the symmetry of the cobalt atoms and the symmetry of the oxygen atoms, but in reality, lithium exists between the CoO2 layers, for example, at a concentration of less than 20 atoms relative to the cobalt. Furthermore, in both the O3-type crystal structure and the pseudo-spinel-type crystal structure, it is preferable that magnesium be present in a dilute manner between the CoO2 layers, i.e., at the lithium sites. In addition, halogens such as fluorine may be present randomly and dilutely at the oxygen sites.

[0168] Furthermore, in pseudo-spinel crystal structures, light elements such as lithium may occupy the oxygen 4-coordinate position, and in this case as well, the ion arrangement exhibits a symmetry similar to that of the spinel type.

[0169] Furthermore, the pseudo-spinel crystal structure, although it has Li randomly between layers, can be said to be a crystal structure similar to the CdCl2 type crystal structure. This crystal structure similar to the CdCl2 type is observed when lithium nickelate is charged to a depth of charge of 0.94 (Li 0.06 Although its crystal structure is similar to that of NiO2, it is known that pure lithium cobaltate or layered rock salt-type cathode active materials containing a large amount of cobalt do not usually adopt this crystal structure.

[0170] The anions in layered rock salt crystals and rock salt crystals adopt a cubic close-packed structure (face-centered cubic lattice structure). It is also presumed that the anions in pseudo-spinel crystals adopt a cubic close-packed structure. When these are in contact, there exists a crystal plane in which the orientation of the cubic close-packed structure composed of anions is aligned. However, the space group of layered rock salt crystals and pseudo-spinel crystals is R-3m, which is different from the space group of rock salt crystals Fm-3m (the space group of a typical rock salt crystal) and Fd-3m (the space group of a rock salt crystal with the simplest symmetry). Therefore, the Miller indices of the crystal planes that satisfy the above conditions are different for layered rock salt crystals and pseudo-spinel crystals and for rock salt crystals. In this specification, when the orientation of the cubic close-packed structure composed of anions is aligned in layered rock salt crystals, pseudo-spinel crystals, and rock salt crystals, it is sometimes said that the crystal orientation is approximately the same.

[0171] In the positive electrode active material shown in Figure 5, the change in crystal structure when charged at high voltage and a large amount of lithium is released is suppressed compared to the comparative example described later. For example, as shown by the dashed line in Figure 5, there is almost no displacement of the CoO2 layer in these crystal structures.

[0172] More specifically, the positive electrode active material shown in Figure 5 exhibits high structural stability even at high charging voltages. For example, in the comparative example, there is a charging voltage range in which the R-3m(O3) crystal structure can be maintained even at a charging voltage of approximately 4.6V relative to the potential of lithium metal, which results in an H1-3 type crystal structure. Furthermore, there is a range in which a pseudo-spinel type crystal structure can be adopted even at higher charging voltages, such as 4.65V to 4.7V relative to the potential of lithium metal. Only when the charging voltage is increased even further can an H1-3 type crystal be observed. In addition, when graphite is used as the negative electrode active material in a secondary battery, for example, there is a charging voltage range in which the R-3m(O3) crystal structure can be maintained even when the secondary battery voltage is between 4.3V and 4.5V. Furthermore, there is a range in which a pseudo-spinel type crystal structure can be adopted even at higher charging voltages, such as 4.35V to 4.55V relative to the potential of lithium metal.

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

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

[0175] Magnesium, randomly and dilutely present between CoO2 layers, i.e., at lithium sites, has the effect of suppressing the displacement of the CoO2 layers when charged at high voltage. Therefore, the presence of magnesium between CoO2 layers tends to result in a pseudo-spinel type crystal structure.

[0176] However, if the heat treatment temperature is too high, cation mixing will occur, increasing the likelihood of magnesium entering the cobalt site. The magnesium present in the cobalt site does not help maintain the R-3m structure under high-voltage charging conditions. Furthermore, if the heat treatment temperature is too high, there are concerns about adverse effects such as the reduction of cobalt to its divalent state and the evaporation or sublimation of lithium.

[0177] Therefore, it is preferable to add a halogen compound such as a fluorine compound to lithium cobalt oxide before the heat treatment to distribute magnesium throughout the surface layer of the particles. Adding a halogen compound causes a melting point depression of lithium cobalt oxide. By lowering the melting point, it becomes easier to distribute magnesium throughout the surface layer 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 to hydrofluoric acid produced by the decomposition of the electrolyte will be improved.

[0178] Furthermore, if the magnesium concentration is increased beyond the desired value, the effect on stabilizing the crystal structure may decrease. This is thought to be because magnesium will enter 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 aspect of the present invention is preferably 0.001 times or more and 0.1 times the number of cobalt atoms, more preferably greater than 0.01 and less than 0.04, and even more preferably around 0.02. The magnesium concentration shown here may be, for example, a value obtained by elemental analysis of the entire particle of the positive electrode active material using ICP-MS, or it may be based on the value of the raw material composition during 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, preferably 0.05% to 4%, and more preferably 0.1% to 2%. The nickel concentration shown here may be the value obtained by elemental analysis of the entire particle of the positive electrode active material using ICP-MS, for example, or it may be based on the value of the raw material composition during the manufacturing process of the positive electrode active material.

[0180] <Particle size> If the particle size of the positive electrode active material is too large, problems arise such as difficulty in lithium diffusion and excessive roughness of the surface of the active material layer when coated onto the current collector. On the other hand, if it is too small, problems arise such as difficulty in supporting the active material layer when coating onto the current collector and excessive reaction with the electrolyte. Therefore, the average particle size (D50: also called 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 positive electrode active material exhibits a pseudo-spinel type (also called an O3' structure) crystal structure when charged at high voltage can be determined by analyzing the high-voltage charged positive electrode using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. XRD is particularly preferable because it can analyze the symmetry of transition metals such as cobalt in the positive electrode active material with high resolution, compare the crystallinity and crystal orientation, analyze the periodic distortion of the lattice and crystallite size, and obtain sufficient accuracy even when measuring a positive electrode obtained by disassembling a secondary battery.

[0182] As mentioned above, positive electrode active materials have the characteristic of showing little change in crystal structure between the high-voltage charged state and the discharged state. Materials in which the crystal structure that changes significantly from the discharged state accounts for 50 wt% or more when charged at high voltage are undesirable because they cannot withstand high-voltage charging and discharging. It is important to note that simply adding impurity elements may not result in the desired crystal structure. For example, even if both materials are lithium cobalt oxide containing magnesium and fluorine, when charged at high voltage, there are cases where the pseudo-spinel type crystal structure accounts for 60 wt% or more, and cases where the H1-3 type crystal structure accounts for 50 wt% or more. Furthermore, at a given voltage, the pseudo-spinel type crystal structure may account for almost 100 wt%, and if the given voltage is further increased, the H1-3 type crystal structure may be generated. Therefore, it is preferable to analyze the crystal structure of positive electrode active materials by XRD or the like. By using XRD or the like in combination with other measurements, more detailed analysis can be performed.

[0183] However, positive electrode active materials in a high-voltage charged or discharged state may undergo changes in their crystal structure when exposed to air. For example, they 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 argon-containing atmosphere.

[0184] The positive electrode active material shown in Figure 6 is lithium cobalt oxide (LiCoO2) without the addition of metal X. The crystal structure of lithium cobalt oxide shown in Figure 6 changes depending on the depth of charge.

[0185] As shown in Figure 6, lithium cobalt oxide at charge depth 0 (discharge state) has a region with a crystal structure of space group R-3m, and there are three CoO2 layers in the unit cell. For this reason, this crystal structure is sometimes called an O3 type crystal structure. The CoO2 layer refers to a structure in which octahedral structures, in which oxygen atoms are coordinated to cobalt in a 6-coordinate manner, are continuous in a plane with shared edges.

[0186] Furthermore, at a charge depth of 1, it has a crystal structure of space group P-3m1, with one CoO2 layer present in the unit cell. For this reason, this crystal structure is sometimes called an O1 type crystal structure.

[0187] Furthermore, lithium cobalt oxide at a charge depth of approximately 0.8 has a crystal structure with space group R-3m. This structure can be described as a structure in which CoO2 structures such as P-3m1(O1) and LiCoO2 structures such as R-3m(O3) are alternately stacked. For this reason, 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 Figure 6, the c-axis of the H1-3 type crystal structure is shown as half the unit cell for easier comparison with other structures.

[0188] As an example, the H1-3 type crystal structure can be represented by the coordinates of cobalt and oxygen in a unit cell as follows: 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 oxygen atoms. On the other hand, as will be described later, the pseudo-spinel type crystal structure of one embodiment of the present invention is preferably represented by a unit cell using one cobalt and one oxygen atom. This indicates that the symmetry between cobalt and oxygen differs between the pseudo-spinel structure and the H1-3 type structure, and that the pseudo-spinel structure shows less variation from the O3 structure compared to the H1-3 type structure. The appropriate unit cell to represent the crystal structure of the positive electrode active material can be determined, for example, by Rietveld analysis using XRD. In this case, the unit cell that yields the smallest GOF (goodness of fit) value should be selected.

[0189] When high-voltage charging occurs, such as when the charging voltage is 4.6V or higher relative to the oxidation-reduction potential of lithium metal, or when deep charging occurs, such as when the charging depth is 0.8 or higher, and when this charging and discharging cycle is repeated, lithium cobalt oxide undergoes repeated changes in its crystal structure (i.e., non-equilibrium phase changes) between the H1-3 type crystal structure and the R-3m(O3) structure in the discharged state.

[0190] However, these two crystal structures exhibit a significant displacement of the CoO2 layer. As shown by the dotted line and arrows in Figure 6, in the H1-3 type crystal structure, the CoO2 layer is significantly shifted from R-3m(O3). Such dynamic structural changes can negatively affect the stability of the crystal structure.

[0191] Furthermore, the volume difference is also significant. When comparing the same number of cobalt atoms, the volume difference between the H1-3 type crystal structure and the O3 type crystal structure in the discharged state is more than 3.0%.

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

[0193] Therefore, repeated high-voltage charging and discharging causes the crystal structure of lithium cobalt oxide to break down. This breakdown of the crystal structure leads to a deterioration of the cycle characteristics. This is thought to be because the breakdown of the crystal structure reduces the number of sites where lithium can exist stably, and also makes it more difficult for lithium to be inserted and removed.

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

[0195] Furthermore, by using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as the solvent for the electrolyte, it is possible to prevent the secondary battery from rupturing or igniting even if the internal temperature rises due to a short circuit or overcharging in the internal region of the secondary battery. Ionic liquids consist of cations and anions, and include organic cations and anions. Examples of organic cations include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, as well as aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions include monovalent amide anions, monovalent methide anions, fluorosulfonic acid anions, perfluoroalkyl sulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, or perfluoroalkyl phosphate anions.

[0196] A secondary battery according to one aspect of the present invention has, for example, one or more 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 carrier ions, the electrolyte, for example, contains a lithium salt. Examples of lithium salts include LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, and 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 a fluorine-containing electrolyte, for example, an electrolyte having one or more types of fluorinated cyclic carbonates and lithium ions can be used. Fluorinated cyclic carbonates can improve flammability and enhance the safety of lithium-ion secondary batteries.

[0199] As fluorinated cyclic carbonates, fluorinated ethylene carbonates such as monofluoroethylene carbonate (fluoroethylene carbonate, FEC, F1EC), difluoroethylene carbonate (DFEC, F2EC), trifluoroethylene carbonate (F3EC), and tetrafluoroethylene carbonate (F4EC) can be used. Note that DFEC has isomers such as cis-4,5 and trans-4,5. As an electrolyte, it is important to solvate lithium ions using one or more types of fluorinated cyclic carbonates and transport them within the electrolyte contained in the electrodes during charging and discharging in order to operate at low temperatures. By contributing to the transport of lithium ions during charging and discharging, rather than using fluorinated cyclic carbonates as small additives, low-temperature operation becomes possible. In secondary batteries, lithium ions move in clusters of several to several dozen ions.

[0200] By using fluorinated cyclic carbonates as the electrolyte, the desolvation energy required for lithium ions solvated within the electrolyte to enter the active material particles is reduced. Reducing this desolvation energy makes it easier for lithium ions to insert into or detach from the active material particles, even at low temperatures. While lithium ions may move while remaining solvated, a hopping phenomenon can occur where the coordinating solvent molecules are replaced. Easier desolvation of lithium ions can facilitate hopping, thus improving lithium ion movement. There is a concern that the decomposition products of the electrolyte during charging and discharging of secondary batteries can adhere to the surface of the active material, leading to battery degradation. However, when the electrolyte contains fluorine, the electrolyte is fluid, making it difficult for the decomposition products to adhere to the surface of the active material. Therefore, battery degradation can be suppressed.

[0201] 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] [ka]

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

[0206] [ka]

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

[0208] [ka]

[0209] In this specification, the term "electrolyte" is a general term that includes solid electrolytes, liquid electrolytes, or semi-solid gel-like electrolytes.

[0210] Degradation is prone to occur at interfaces within secondary batteries, such as the interface between the active material and the electrolyte. In one embodiment of the present invention, the presence of a fluorine-containing electrolyte prevents degradation that may occur at the interface between the active material and the electrolyte, typically resulting in alteration of the electrolyte or increased viscosity of the electrolyte. Alternatively, a binder or graphene compound may be attached to or retained around the fluorine-containing electrolyte. This configuration makes it possible to maintain a state where the viscosity of the electrolyte is reduced, in other words, a free-flowing state of the electrolyte, thereby improving the reliability of the secondary battery. DFEC with two fluorine atoms and F4EC with four fluorine atoms have lower viscosity and are freer than FEC with one fluorine atom, resulting in weaker coordination bonds with lithium. Therefore, the adhesion of highly viscous decomposition products to the active material particles can be reduced. When highly viscous decomposition products adhere to or cling to the active material particles, lithium ions become less able to move at the interface of the active material particles. Solvation by the fluorine-containing electrolyte mitigates the formation of decomposition products that adhere to the surface of the active material (positive electrode active material or negative electrode active material). Furthermore, by using an electrolyte containing fluorine, the formation and growth of dendrites can be prevented by preventing the adhesion of decomposition products.

[0211] Another characteristic is the use of an electrolyte containing fluorine as the main component, with the fluorine-containing electrolyte being 5% or more by volume, 10% or more by volume, preferably 30% to 100% by volume.

[0212] In this specification, the main component of the electrolyte refers to a component that accounts for 5% or more by volume of the total electrolyte of the secondary battery. Furthermore, "5% or more by volume of the total electrolyte of the secondary battery" here refers to the proportion of the total electrolyte measured during the manufacturing of the secondary battery. In addition, when a secondary battery is disassembled after its manufacture, it is difficult to quantify the proportion of each of the multiple types of electrolytes, but it is possible to determine whether a particular organic compound accounts for 5% or more by volume of the total electrolyte.

[0213] By using an electrolyte containing fluorine, a secondary battery capable of operating over a wide temperature range, specifically from -40°C to 150°C, preferably from -40°C to 85°C, can be realized.

[0214] Furthermore, additives such as vinylene carbonate, propanesultone (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 should be, for example, 0.1% or more and less than 5% by volume relative to the total electrolyte.

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

[0216] Furthermore, the presence of a polymer material that gels the electrolyte enhances safety against leakage and other issues. Typical examples of polymer materials that gel include silicone gels, acrylic gels, acrylonitrile gels, polyethylene oxide gels, polypropylene oxide gels, and fluorine-based polymer gels.

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

[0218] Furthermore, the above configuration is an example of a secondary battery using a liquid electrolyte, but is not particularly limited. For example, semi-solid-state batteries and all-solid-state batteries can also be fabricated.

[0219] In this specification, whether it is a secondary battery using a liquid electrolyte or a semi-solid battery, the layer placed between the positive and negative electrodes will be referred to as the electrolyte layer. The electrolyte layer of a semi-solid battery is a layer formed by film deposition and can be distinguished from the liquid electrolyte layer.

[0220] Furthermore, in this specification, a semi-solid battery refers to a battery having a semi-solid material in at least one of its components: the electrolyte layer, the positive electrode, and the negative electrode. Here, "semi-solid" does not mean that the solid material makes up 50% of the battery. "Semi-solid" means possessing solid properties, such as small volume change, while also having some liquid-like properties, such as flexibility. As long as these properties are met, the battery may consist of a single material or multiple materials. For example, a liquid material may be impregnated into a porous solid material.

[0221] Furthermore, in this specification, a polymer electrolyte secondary battery refers to a secondary battery having a polymer in the electrolyte layer between the positive and negative electrodes. Polymer electrolyte secondary batteries include dry (or intrinsic) polymer electrolyte batteries and polymer gel electrolyte batteries. Polymer electrolyte secondary batteries may also be called semi-solid batteries.

[0222] When a semi-solid battery is manufactured using the negative electrode according to one embodiment of the present invention, the semi-solid battery becomes a secondary battery with a large charge / discharge capacity. Furthermore, it can be a semi-solid battery with a high charge / discharge voltage. Alternatively, it can be a semi-solid battery that is safe or highly reliable.

[0223] Here, using Figure 7, we show an example of how to fabricate a semi-solid battery.

[0224] Figure 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] Electrolyte 576 comprises a lithium-ion conductive polymer and a lithium salt.

[0226] In this specification, a lithium-ion conductive polymer is a polymer that has the conductivity of a cation such as lithium. More specifically, it is a polymer compound having a polar group to which a cation can coordinate. Preferably, the polar group is an ether group, ester group, nitrile group, carbonyl group, siloxane, etc.

[0227] Examples of lithium-ion conductive polymers that can be used include polyethylene oxide (PEO), derivatives having polyethylene oxide as the main chain, polypropylene oxide, polyacrylic acid esters, polymethacrylate esters, polysiloxanes, and polyphosphazenes.

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

[0229] In lithium-ion conductive polymers, lithium ions move while changing the polar groups they interact with through partial motion (also called segmental motion) of the polymer chains. For example, in PEO, lithium ions move while changing the oxygen groups they interact with through segmental motion of the ether chains. When the temperature is close to or higher than the melting or softening point of the lithium-ion conductive polymer, the crystalline region dissolves and the amorphous region increases, and the motion of the ether chains becomes more active, resulting in higher ionic conductivity. Therefore, when using PEO as a lithium-ion conductive polymer, it is preferable to perform charging and discharging at 60°C or higher.

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

[0231] Furthermore, as lithium salts, compounds can be used that contain lithium along with at least one of the following: phosphorus, fluorine, nitrogen, sulfur, oxygen, chlorine, arsenic, boron, aluminum, bromine, and iodine. 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 12Lithium 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), etc., can be used individually or in any combination and ratio of two or more of these.

[0232] In particular, using LiFSI is preferable because it exhibits good low-temperature characteristics. Furthermore, LiFSI and LiTFSA are less reactive with water compared to LiPF6, etc. Therefore, it is easier to control the dew point when fabricating electrodes and electrolyte layers using LiFSI. For example, they can be handled not only in an inert atmosphere such as argon with moisture removed as much as possible, and in a dry room with controlled dew point, but also in a normal atmospheric atmosphere. This improves productivity, which is preferable. Moreover, using Li salts with high dissociability and plasticizing effects, such as LiFSI and LiTFSA, is particularly preferable when using lithium conduction utilizing the segmental motion of the ether chain, because it can be used over a wide temperature range.

[0233] In this specification, "binder" refers to a polymer compound mixed solely for the purpose of binding active materials, conductive materials, etc., onto a current collector. Examples include rubber materials such as polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, butadiene rubber, and ethylene-propylene-diene copolymer, as well as materials such as fluororubber, polystyrene, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, and ethylene-propylene-diene polymer.

[0234] Since lithium-ion conductive polymers are high-molecular-weight compounds, thoroughly mixing them and using them in the active material layer allows for the bonding of the active material and conductive material onto the current collector. Therefore, electrodes can be fabricated without the use of a binder. A binder is a material that does not contribute to the charge-discharge reaction. Consequently, the less binder used, the more materials that contribute to charge-discharge, such as the active material and electrolyte, can be increased. This allows for the creation of secondary batteries with improved discharge capacity or cycle characteristics.

[0235] The absence or very low amount of organic solvents makes it possible to create a secondary battery that is less prone to ignition and combustion, thus improving safety, which is desirable. Furthermore, if the electrolyte layer 576 is an electrolyte layer that has no organic solvents or very little organic solvents, it has sufficient strength even without a separator and can electrically insulate the positive and negative electrodes. Since a separator is not used, a secondary battery with high productivity can be created. If the electrolyte layer 576 contains inorganic fillers, the strength will be further increased, resulting in a secondary battery with even higher safety.

[0236] It is preferable that the electrolyte 576 is thoroughly dried in order to create an electrolyte layer that is free of or contains very little organic solvent. In this specification, a electrolyte layer is considered thoroughly dried if the weight change of the electrolyte layer after drying under reduced pressure at 90°C for 1 hour is within 5%.

[0237] Nuclear magnetic resonance (NMR), for example, can be used to identify materials such as lithium-ion conductive polymers, lithium salts, binders, and additives contained in secondary batteries. Analysis results from other methods such as 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), and liquid chromatography-mass spectrometry (LC / MS) may also be used as a basis for determination. It is preferable to suspend the active material layer in a solvent to separate the active material from other materials before subjecting it to analysis such as NMR.

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

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

[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, polymer-based solid electrolytes such as PEO (polyethylene oxide) formed by coating methods may be used. Since such polymer-based solid electrolytes can also function as binders, using them can reduce the number of electrode components and lower manufacturing costs.

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

[0243] (Embodiment 2) This embodiment describes an example of a secondary battery according to one aspect of the present invention.

[0244] <Example of a secondary battery configuration> The following explanation uses a secondary battery, in which the positive electrode, negative electrode, and electrolyte are enclosed in an outer casing, as an example.

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

[0246] [Current collector] As the positive electrode current collector and the negative electrode 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 such as silicon, titanium, neodymium, scandium, molybdenum, etc. to improve heat resistance 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-like, net-like, punching metal-like, expanded metal-like, etc. The current collector preferably has a thickness of 10 μm or more and 30 μm or less.

[0247] In addition, it is preferable to use a material for the negative electrode 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 by oxygen, titanium oxide in which a part of oxygen is substituted by nitrogen, and titanium oxynitride (TiO x N y , where 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 comprises a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer contains a positive electrode active material and may also contain 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] The conductive material and binder that can be present in the positive electrode active material layer can be the same materials as those that can be present in the negative electrode active material layer.

[0251] [Separator] A separator is placed between the positive and negative electrodes. The separator can be made from materials such as cellulose fibers including paper, nonwoven fabrics, glass fibers, ceramics, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, or polyurethane. It is preferable that the separator be processed into a bag shape and positioned to enclose either the positive or negative electrode.

[0252] The separator is a porous material having pores approximately 20 nm in diameter, preferably 6.5 nm or larger in diameter, and more preferably at least 2 nm in diameter. In the case of the semi-solid secondary battery described above, the separator can 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 material, a fluorine material, a polyamide material, or a mixture thereof. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aramid (meta-aramid, para-aramid).

[0254] Coating with ceramic materials improves oxidation resistance, suppressing separator degradation during high-voltage charging and discharging, and thus improving the reliability of secondary batteries. Coating with fluorine-based materials improves adhesion between the separator and electrodes, thereby improving output characteristics. Coating with polyamide materials, particularly aramid, improves heat resistance, thus enhancing the safety of secondary batteries.

[0255] For example, a polypropylene film may be coated on both sides with a mixture of aluminum oxide and aramid. Alternatively, the side of the polypropylene film in contact with the positive electrode may be coated with a mixture of aluminum oxide and aramid, and the side in contact with the negative electrode may be coated with a fluorine-based material.

[0256] By using a multi-layered separator, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, thus increasing the capacity per unit volume of the secondary battery.

[0257] [Exterior] The outer casing of a secondary battery can be made of metal materials such as aluminum or resin materials. A film-like outer casing can also be used. As a film, for example, a three-layer film can be used, in which a highly flexible metal thin film such as aluminum, stainless steel, copper, or nickel is provided on a film made of materials such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide resin or polyester resin is provided on the metal thin film as the outer surface of the outer casing. Furthermore, it is preferable to use a fluororesin film as the film. Fluororesin films have high stability against acids, alkalis, organic solvents, etc., and suppress side reactions, corrosion, etc. associated with the reactions of the secondary battery, thereby realizing a superior secondary battery. Examples of fluororesin films include PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxyalkane: copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether), FEP (perfluoroethylenepropene copolymer: copolymer of tetrafluoroethylene and hexafluoropropylene), and ETFE (ethylenetetrafluoroethylene copolymer: copolymer of tetrafluoroethylene and ethylene).

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

[0259] (Embodiment 3) This embodiment describes examples of multiple shapes of secondary batteries having a positive or negative electrode, manufactured by the manufacturing method described in the previous embodiment.

[0260] [Coin-type rechargeable battery] An example of a coin-type rechargeable battery is described below. Figure 8A is an exploded perspective view of a coin-type (single-layer flat type) rechargeable battery, Figure 8B is an external view, and Figure 8C is a cross-sectional view thereof. Coin-type rechargeable batteries are mainly used in small electronic devices.

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

[0262] In FIG. 8A, the positive electrode 304, separator 310, negative electrode 307, spacer 322, and washer 312 are stacked. These are sealed with the negative electrode can 302 and the positive electrode can 301. Note that in FIG. 8A, the gasket for sealing is not shown. The spacer 322 and 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 washer 312 are made of stainless steel or 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 so as to be in contact with it. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided so as to be in contact with it. Also, the negative electrode 307 is not limited to a laminated structure, and a lithium metal foil or an alloy foil of lithium and aluminum may be used.

[0267] Note that for the positive electrode 304 and the negative electrode 307 used in the coin - type secondary battery 300, the active material layer may be formed on only one side.

[0268] The positive electrode can 301 and the negative electrode can 302 can be made of metals such as nickel, aluminum, or titanium, which are corrosion-resistant to the electrolyte, or alloys thereof, or alloys of these with other metals (e.g., stainless steel). Furthermore, it is preferable to coat them with nickel and aluminum, etc., to prevent corrosion by the electrolyte. 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.

[0269] The negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte, and as shown in Figure 8C, the positive electrode 304, separator 310, negative electrode 307, and negative electrode 302 are stacked in this order with the positive electrode 301 at the bottom, and the positive electrode 301 and negative electrode 302 are pressed together via a gasket 303 to manufacture a coin-type secondary battery 300.

[0270] By using a rechargeable battery, a coin-type rechargeable battery 300 can be created that has high capacity, high charge / discharge capacity, and excellent cycle characteristics.

[0271] [Cylindrical rechargeable battery] An example of a cylindrical secondary battery will be explained with reference to Figure 9A. As shown in Figure 9A, the cylindrical secondary battery 616 has a positive electrode cap (battery cover) 601 on the top surface and a battery casing (outer casing) 602 on the sides and bottom. The battery casing (outer casing) 602 is made of a metal material and has excellent water permeability barrier properties and gas barrier properties. The positive electrode cap 601 and the battery casing (outer casing) 602 are insulated by a gasket (insulating packing) 610.

[0272] Figure 9B is a schematic diagram showing a cross-section of a cylindrical secondary battery. The cylindrical secondary battery shown in Figure 9B has a positive electrode cap (battery cover) 601 on the top surface and a battery casing (outer casing) 602 on the sides and bottom. The positive electrode cap and the battery casing (outer casing) 602 are insulated from each other 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 in between. Although not shown, the battery element is wound around a center pin. The battery can 602 is closed at one end and open at the other. The battery can 602 can be made of metals such as nickel, aluminum, or titanium, or alloys thereof, or alloys of these with other metals (e.g., stainless steel), which are corrosion resistant to the electrolyte. Furthermore, it is preferable to coat the battery can 602 with nickel and aluminum, etc., to prevent corrosion by the electrolyte. Inside the battery can 602, the battery element in which the positive electrode, negative electrode, and separator are wound is sandwiched between a pair of opposing insulating plates 608 and 609. In addition, an electrolyte (not shown) is injected into the inside of the battery can 602 in which the battery element is provided. The electrolyte can be the same as that used in coin-type secondary batteries.

[0274] Since the positive and negative electrodes used in cylindrical storage batteries 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 / discharge capacity, and excellent cycle characteristics can be obtained.

[0276] A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode 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 metal materials 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. The PTC element 611 is a thermal resistance element whose resistance increases when the temperature rises, and it prevents abnormal heat generation by limiting the amount of current through the increase in resistance. Barium titanate (BaTiO3) based semiconductor ceramics can be used for the PTC element.

[0277] Figure 9C shows an example of an energy storage system 615. The energy storage system 615 has multiple secondary batteries 616. The positive electrode of each secondary battery is in contact with a conductor 624 separated by an insulator 625 and is electrically connected. The conductor 624 is electrically connected to a control circuit 620 via wiring 623. The negative electrode of each secondary battery is also electrically connected to the control circuit 620 via wiring 626. The control circuit 620 can be a charge / discharge control circuit that performs charging and discharging, as well as a protection circuit that prevents overcharging and / or over-discharging.

[0278] Figure 9D shows an example of an energy storage system 615. The energy storage system 615 has multiple secondary batteries 616, which are sandwiched between conductive plates 628 and 614. The multiple secondary batteries 616 are electrically connected to conductive plates 628 and 614 by wiring 627. The multiple secondary batteries 616 may be connected in parallel, in series, or connected in parallel and then in series. By configuring an energy storage system 615 with multiple secondary batteries 616, a large amount of power can be extracted.

[0279] After a plurality of secondary batteries 616 are connected in parallel, they may be 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 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 using 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 separately, but actually, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. As the housing 930, a metal material (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] For the housing 930a, an insulating material such as organic resin can be used. In particular, by using a material such as 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 housing 930a is small, the antenna may be placed inside housing 930a. For housing 930b, for example, a metal material can be used.

[0286] Furthermore, the structure of the wound body 950 is shown in Figure 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 are stacked on top of each other with the separator 933 in between, and the stacked sheets are wound up. Note that multiple stacks of the negative electrode 931, positive electrode 932, and separator 933 may be stacked.

[0287] Alternatively, the secondary battery 913 may have a wound body 950a as shown in Figure 11. The wound body 950a shown in Figure 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 a fluorine-containing electrolyte in the negative electrode 931, a secondary battery 913 with high charge / discharge capacity and excellent cycle characteristics can be obtained.

[0289] The separator 933 has a wider width than the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap with the negative electrode active material layer 931a and the positive electrode active material layer 932a. Furthermore, it is preferable from a safety standpoint that the negative electrode active material layer 931a is wider than the positive electrode active material layer 932a. A wound body 950a of this shape is also preferable due to its good safety and productivity.

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

[0291] As shown in Figure 11C, the coiled body 950a and electrolyte are covered by the housing 930, forming a 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 in order to prevent the battery from rupturing.

[0292] As shown in Figure 11B, the secondary battery 913 may have multiple windings 950a. By using multiple windings 950a, a secondary battery 913 with a larger charge and discharge capacity can be made. Other elements of the secondary battery 913 shown in Figures 11A and 11B can be referenced from the description of the secondary battery 913 shown in Figures 10A to 10C.

[0293] <Laminated rechargeable battery> Next, an example of a laminate-type secondary battery is shown in Figures 12A and 12B, which show an example of its external appearance. Figures 12A and 12B show a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0294] Figure 13A shows the external views 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, i.e., the tab region. The area and shape of the tab regions of the positive and negative electrodes are not limited to the example shown in Figure 13A.

[0295] <Method for manufacturing laminated rechargeable batteries> Here, an example of a method for manufacturing a laminate-type secondary battery, whose external view is shown in Figure 12A, will be explained using Figures 13B and 13C.

[0296] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. Figure 13B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example using 5 sets of negative electrodes and 4 sets of positive electrodes is shown. This can also be called a laminate consisting of negative electrodes, separators, and positive electrodes. Next, the tab regions of the positive electrode 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For joining, ultrasonic welding, for example, can be used. Similarly, the tab regions of the negative electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0297] Next, the negative electrode 506, separator 507, and positive electrode 503 are placed on the outer casing 509.

[0298] Next, as shown in Figure 13C, the outer casing 509 is folded along the dashed line. Then, the outer periphery of the outer casing 509 is joined. For joining, for example, heat sealing may be used. At this time, a region that is not joined (hereinafter referred to as an inlet) is provided on a part (or one side) of the outer casing 509 so that the electrolyte 508 can be inserted later. It is preferable to use a film for the outer casing 509 that has excellent water permeability barrier properties and gas barrier properties. Furthermore, the outer casing 509 can be made into a laminated structure, and high water permeability barrier properties and gas barrier properties can be achieved by making one of the intermediate layers a metal foil (for example, aluminum foil).

[0299] Next, the electrolyte 508 (not shown) is introduced into the inside of the outer casing 509 through an inlet provided in the outer casing 509. It is preferable to introduce the electrolyte 508 under reduced pressure or an inert atmosphere. Finally, the inlet is sealed. In this way, a laminate-type secondary battery 500 can be manufactured.

[0300] By using the negative electrode structure obtained in Embodiment 1, i.e., an electrode in which a graphene compound is densely attached to a material obtained by mixing and heating silicon-containing particles, a halogen-containing material, and a material containing oxygen and carbon, as the negative electrode 506, a secondary battery 500 with high capacity, high charge / 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 a different example from Figure 9D, which is a cylindrical secondary battery. Figure 14C shows an example of its application to an electric vehicle (EV).

[0303] Electric vehicles are equipped with a first battery 1301a and 1301b as the main secondary battery for propulsion, and a second battery 1311 that supplies power to the inverter 1312 that starts the motor 1304. The second battery 1311 is also called the cranking battery (or starter battery). The second battery 1311 only needs to be able to output power, and does not require a large capacity, so its capacity is smaller than that of the first batteries 1301a and 1301b.

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

[0305] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more may be connected in parallel. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack with multiple secondary batteries, a large amount of power can be extracted. Multiple secondary batteries may be connected in parallel, in series, or connected in parallel and then in series. Multiple secondary batteries are also called a battery pack.

[0306] Furthermore, the vehicle-mounted secondary battery has a service plug or circuit breaker that can cut off high voltage without using tools in order to interrupt power from multiple secondary batteries, and this is provided in the first battery 1301a.

[0307] Furthermore, the power from the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V onboard components (electric power steering 1307, heater 1308, defogger 1309, etc.) via the DC-DC circuit 1306. If a rear motor 1317 is located on the rear wheels, the first battery 1301a is used to rotate the rear motor 1317.

[0308] Furthermore, the second battery 1311 supplies power to 14V automotive components (audio 1313, power windows 1314, lights 1315, etc.) via the DC-DC circuit 1310.

[0309] Furthermore, the first battery 1301a will be explained using Figure 14A.

[0310] Figure 14A shows an example where nine rectangular secondary batteries 1300 are arranged in a single battery pack 1415. In this example, nine rectangular secondary batteries 1300 are connected in series, with one electrode fixed by an insulating fixing part 1413 and the other electrode fixed by an insulating fixing part 1414. While this embodiment shows an example of fixing with fixing parts 1413 and 1414, the batteries may also be housed in a battery housing box (also called a casing). Since vehicles are expected to be subjected to vibrations or shaking from external sources (such as the road surface), it is preferable to fix multiple secondary batteries using fixing parts 1413 and 1414 and a battery housing box. Furthermore, one electrode is electrically connected to the control circuit unit 1320 by wiring 1421, and the other electrode is electrically connected to the control circuit unit 1320 by wiring 1422.

[0311] Furthermore, the control circuit unit 1320 may also use a memory circuit that includes a transistor made of an oxide semiconductor. A charging control circuit or battery control system having a memory circuit that includes a transistor made of an oxide semiconductor may be referred to as a 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 charging and discharging state of the secondary battery. For example, to prevent overcharging, both the output transistor and the cutoff switch of the charging circuit can be turned off almost simultaneously.

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

[0314] The control circuit unit 1320 includes at least a switch to prevent overcharging, a switch unit 1324 including a switch to prevent over-discharging, a control circuit 1322 that controls the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 has upper and lower voltage limits set for the secondary battery used, as well as upper limits for external input current and external output current. Within the range between the lower voltage limit and the upper voltage limit of the secondary battery, it is within the recommended voltage range for use, and if it falls outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit unit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent over-discharge and / or overcharge. For example, if the control circuit 1322 detects a voltage that is likely to cause overcharging, it cuts off the current by turning off the switch in the switch unit 1324. Furthermore, a PTC element may be provided in the charge / discharge path to provide a function to cut off the current in response to the rise in temperature. Furthermore, the control circuit unit 1320 has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0315] The switch section 1324 can be constructed by combining n-channel and p-channel transistors. The switch section 1324 is not limited to switches using Si transistors made of single-crystal silicon, but may also be formed using power transistors made of, for example, 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), etc. Furthermore, since memory elements using OS transistors can be freely arranged by stacking them on circuits using Si transistors, integration can be easily achieved. Also, since OS transistors can be manufactured using the same manufacturing equipment as Si transistors, they can be manufactured at low cost. That is, by stacking a control circuit section 1320 using OS transistors on the switch section 1324 and integrating them, it is possible to create a single chip. This allows for miniaturization as the occupied volume of the control circuit section 1320 can be reduced.

[0316] The first batteries 1301a and 1301b primarily supply power to 42V (high-voltage) in-vehicle equipment, while the second battery 1311 supplies power to 14V (low-voltage) in-vehicle equipment. Lead-acid batteries are often used for the second battery 1311 due to their cost advantages.

[0317] This embodiment shows an example in which lithium-ion secondary batteries are used for both the first battery 1301a and the second battery 1311. The second battery 1311 may be a lead-acid battery, an all-solid-state battery, or an electric double-layer capacitor.

[0318] Furthermore, the regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305 and charged the second battery 1311 via the control circuit unit 1321 from the motor controller 1303 and battery controller 1302. Alternatively, it is charged the first battery 1301a via the control circuit unit 1320 from the battery controller 1302. Alternatively, it is charged 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 and charging current 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 being used and enable rapid charging.

[0320] Although not shown in the diagram, when an external charger is connected, the charger's outlet or connection cable is electrically connected to the battery controller 1302. Power supplied from the external charger charges the first batteries 1301a and 1301b via the battery controller 1302. In some cases, the charger may have a control circuit and may not use the functions of the battery controller 1302, but it is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320 to prevent overcharging. In some cases, the connection cable or the charger's connection cable may also have a control circuit. The control circuit unit 1320 is sometimes called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) installed in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU also includes a microcomputer. The ECU also uses a CPU and a GPU.

[0321] Next, we will describe an example in which a secondary battery, which is one aspect of the present invention, is implemented in a vehicle, typically a transport vehicle.

[0322] Furthermore, by mounting the secondary battery shown in either Figure 9D or Figure 14A onto a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV) can be realized. Secondary batteries can also be mounted on agricultural machinery, motorized bicycles including electric-assist bicycles, motorcycles, electric wheelchairs, electric carts, small or large vessels, submarines, aircraft such as fixed-wing or rotary-wing aircraft, rockets, satellites, space probes, planetary probes, or spacecraft. A secondary battery according to one embodiment of the present invention can be a high-capacity secondary battery. Therefore, a secondary battery according to one embodiment of the present invention is suitable for miniaturization and weight reduction, and can be suitably used in transport vehicles.

[0323] Figures 15A to 15D illustrate a transport vehicle using one embodiment of the present invention. The automobile 2001 shown in Figure 15A is an electric vehicle that uses an electric motor as a power source for driving. Alternatively, it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as power sources for driving. When a secondary battery is installed in the vehicle, the secondary battery is installed in one or more locations. The automobile 2001 shown in Figure 15A has a battery pack 2200, and the battery pack has a secondary battery module in which multiple secondary batteries are connected. Furthermore, it is preferable to have a charging control device that is electrically connected to the secondary battery module.

[0324] Furthermore, the automobile 2001 can be charged by receiving power from an external charging facility via a plug-in or contactless power supply method to the secondary battery it possesses. For charging, the charging method and connector specifications may be carried out appropriately using a prescribed method such as CHAdeMO® or Combo. The secondary battery may be a charging station installed in a commercial facility, or it may be a household power supply. For example, the energy storage device mounted on the automobile 2001 can be charged by an external power supply using plug-in technology. Charging can be performed by converting AC power to DC power via a conversion device such as an AC / DC converter.

[0325] Although not shown in the diagram, the vehicle can also be charged by mounting a power receiving device on the vehicle and receiving power wirelessly from a ground-based power transmission device. In this wireless power supply method, charging can be performed not only when the vehicle is stopped but also while it is in motion by incorporating the power transmission device into the road or exterior wall. Furthermore, this wireless power supply method can be used to transmit and receive power between two vehicles. In addition, solar panels can be installed on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped and when it is in motion. For such wireless power supply, electromagnetic induction or magnetic resonance methods can be used.

[0326] Figure 15B shows a large transport vehicle 2002 equipped with an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 has a maximum voltage of 170V, achieved by connecting 48 cells in series, each consisting of four secondary batteries with a voltage of 3.5V to 4.7V. The secondary battery module of the battery pack 2201 has the same functions as Figure 15A, except for differences in the number of secondary batteries that make up the module, so the explanation is omitted.

[0327] Figure 15C shows a large transport vehicle 2003 equipped with an electrically controlled motor as an example. The secondary battery module of the transport vehicle 2003 has a maximum voltage of 600V, achieved by connecting more than 100 secondary batteries in series, for example, with voltages between 3.5V and 4.7V. Therefore, secondary batteries with small variation in characteristics are required. By using secondary batteries with a structure that has a fluorine-containing electrolyte in the negative electrode, it is possible to manufacture secondary batteries with stable battery characteristics, enabling low-cost mass production from a yield perspective. Furthermore, since the battery pack 2202 has the same functions as Figure 15A except for differences in the number of secondary batteries constituting the secondary battery module, the explanation is omitted.

[0328] Figure 15D shows an example of an aircraft 2004 having a fuel-burning engine. The aircraft 2004 shown in Figure 15D can be considered a type of transport vehicle because it has wheels for takeoff and landing, and it has a battery pack 2203 which includes a secondary battery module formed by connecting multiple secondary batteries and a charging control device.

[0329] The secondary battery module of aircraft 2004 has a maximum voltage of 32V, for example, by connecting eight 4V secondary batteries in series. The secondary battery module of battery pack 2203 has the same functions as Figure 15A, except for the number of secondary batteries that make up the module, so the explanation is omitted.

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

[0331] (Embodiment 5) In this embodiment, an example of implementing a secondary battery, which is one aspect of the present invention, in a building will be explained using Figures 16A and 16B.

[0332] The house shown in Figure 16A has a power storage device 2612 having a secondary battery, which is one embodiment 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, etc. The power storage device 2612 may also be electrically connected to a ground-mounted charging device 2604. The electricity obtained from the solar panel 2610 can be used to charge the power storage device 2612. The electricity 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 used effectively. Alternatively, the power storage device 2612 may be installed on the floor.

[0333] The electricity stored in the energy storage device 2612 can also supply power to other electronic devices in the house. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, electronic devices can be used by using the energy storage device 2612 according to one aspect of the present invention as an uninterruptible power supply.

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

[0335] The energy storage device 791 is equipped with a control device 790, which is electrically connected by wiring to the distribution board 703, the energy storage controller 705 (also called the control device), the display unit 706, and the router 709.

[0336] Power is supplied from the commercial power supply 701 to the distribution panel 703 via the service drop connection section 710. Power is also supplied to the distribution panel 703 from the energy storage device 791 and the commercial power supply 701, and the distribution panel 703 supplies the supplied power to the general load 707 and the energy storage system load 708 via outlets (not shown).

[0337] General loads 707 are electrical equipment such as televisions and personal computers, while energy storage loads 708 are electrical equipment such as microwave ovens, refrigerators, and air conditioners.

[0338] The energy storage controller 705 includes a measurement unit 711, a prediction unit 712, and a planning unit 713. The measurement unit 711 has the function of measuring the amount of electricity consumed by the general load 707 and the energy storage system load 708 during a day (for example, from 0:00 to 24:00). The measurement unit 711 may also have the function of measuring the amount of electricity consumed by the energy storage device 791 and the amount of electricity supplied from the commercial power supply 701. The prediction unit 712 has the function of predicting the amount of electricity demanded by the general load 707 and the energy storage system load 708 during the next day, based on the amount of electricity consumed by the general load 707 and the energy storage system load 708 during the day. The planning unit 713 has the function of planning the charging and discharging of the energy storage device 791 based on the amount of electricity demand predicted by the prediction unit 712.

[0339] The amount of electricity consumed by the general load 707 and the energy storage system load 708, as measured by the measurement unit 711, can be checked on the display unit 706. It can also be checked on electrical equipment such as televisions and personal computers via the router 709. Furthermore, it can be checked on mobile electronic devices such as smartphones and tablets via the router 709. Additionally, the amount of electricity demand for each time period (or hourly) predicted by the prediction unit 712 can be checked on the display unit 706, electrical equipment, and mobile electronic devices.

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

[0341] (Embodiment 6) This embodiment describes an example of mounting a secondary battery, which is one aspect of the present invention, in an electronic device. Examples of electronic devices on which a secondary battery is mounted include television equipment (also called televisions or television receivers), monitors for computers, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game consoles, personal information terminals, sound playback devices, and large game machines such as pachinko machines. Personal information terminals include notebook personal computers, tablet terminals, e-books, and mobile phones.

[0342] Figure 17A shows an example of a mobile phone. The mobile phone 2100 includes a display unit 2102 built into the housing 2101, as well as operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. The mobile phone 2100 also has a secondary battery 2107. By incorporating a secondary battery 2107 with a structure that has a fluorine-containing electrolyte in the negative electrode, a high capacity can be achieved, and a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0343] The mobile phone 2100 can run various applications such as making phone calls, sending emails, reading and creating documents, playing music, communicating on the internet, and playing computer games.

[0344] The operation button 2103 can be assigned various functions, including time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, and power saving mode activation / deactivation. For example, the function of the operation button 2103 can be freely configured by the operating system built into the mobile phone 2100.

[0345] Furthermore, the 2100 mobile phone is capable of performing standardized short-range wireless communication. For example, it can communicate with a wireless headset to enable hands-free calling.

[0346] Furthermore, the mobile phone 2100 is equipped with an external connection port 2104, which allows for direct data exchange with other information terminals via a connector. It can also be charged via the external connection port 2104. Note that charging may also be performed wirelessly without using the external connection port 2104.

[0347] The mobile phone 2100 preferably has sensors. For example, it is preferable that the mobile phone be equipped with human body sensors such as a fingerprint sensor, pulse sensor, and body temperature sensor, as well as touch sensors, pressure sensors, and acceleration sensors.

[0348] Figure 17B shows an unmanned aerial vehicle 2300 having multiple rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 has a secondary battery 2301, a camera 2303, and an antenna (not shown), which are embodiments of the present invention. The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. A secondary battery using a structure in which a fluorine-containing electrolyte is contained in the negative electrode has a high energy density and high safety, so it can be used safely for long periods of time over a long period of time and is suitable as a secondary battery to be mounted on an unmanned aerial vehicle 2300.

[0349] Figure 17C shows an example of a robot. The robot 6400 shown in Figure 17C is equipped with 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 and an obstacle sensor 6407, a movement mechanism 6408, a computing device, and the like.

[0350] Microphone 6402 has the function of detecting the user's voice and ambient sounds. Speaker 6404 has the function of emitting sound. Robot 6400 can communicate with the user using microphone 6402 and speaker 6404.

[0351] The display unit 6405 has the function of displaying various types of 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. The display unit 6405 may also be a detachable information terminal, and by installing it in a fixed position on the robot 6400, charging and data transfer can be made possible.

[0352] The upper camera 6403 and lower camera 6406 have the function of imaging the area around the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize its surrounding environment and move safely using the upper camera 6403, lower camera 6406 and obstacle sensor 6407.

[0353] The robot 6400 is equipped with a secondary battery 6409 according to one aspect of the present invention and a semiconductor device or electronic components in its internal region. A secondary battery using a structure in which a fluorine-containing electrolyte is contained in the negative electrode has a high energy density and high safety, so it can be used safely for a long period of time, making it suitable as a secondary battery 6409 to be mounted on the robot 6400.

[0354] Figure 17D shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 located on the top surface of the housing 6301, multiple cameras 6303 located on the sides, a brush 6304, operation buttons 6305, a secondary battery 6306, and various sensors. Although not shown, the cleaning robot 6300 is equipped with wheels, a suction port, etc. The cleaning robot 6300 is self-propelled, can detect dirt 6310, and can suck up the dirt from a suction port located on the bottom surface.

[0355] For example, the cleaning robot 6300 can analyze images captured by the camera 6303 to determine the presence or absence of obstacles such as walls, furniture, or steps. Furthermore, if the image analysis detects an object that might become entangled in the brush 6304, such as wiring, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 is equipped with a secondary battery 6306 according to one aspect of the present invention and a semiconductor device or electronic component within its internal region. A secondary battery using a structure with a fluorine-containing electrolyte in the negative electrode has high energy density and high safety, allowing for safe use over long periods, making it suitable as a secondary battery 6306 for the cleaning robot 6300.

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

[0357] (Notes regarding the descriptions in this specification, etc.) Furthermore, in this specification, crystal planes and directions are indicated by Miller indices. In crystallography, crystal planes and directions are indicated by a superscript bar above the number, but in this specification, due to limitations in patent application notation, a minus sign (-) may be placed before the number instead of a bar above it. In addition, individual orientations indicating directions within a crystal are indicated by [ ], collective orientations indicating all equivalent directions are indicated by < >, individual planes indicating crystal planes are indicated by ( ), and collective planes having equivalent symmetry are indicated by {}.

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

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

[0360] In this specification, the layered rock salt crystal structure of a composite oxide containing lithium and a transition metal refers to a crystal structure having a rock salt-type ionic arrangement in which cations and anions are arranged alternately, and in which the transition metal and lithium are regularly arranged to form a two-dimensional plane, thereby enabling two-dimensional diffusion of lithium. Defects such as vacancies in cations or anions may be present. Furthermore, strictly speaking, a layered rock salt crystal structure may have a distorted lattice structure of the rock salt crystal.

[0361] In this specification, a rock salt-type crystal structure refers to a structure in which cations and anions are arranged alternately. However, deficiencies in cations or anions are acceptable.

[0362] Furthermore, in this specification, the pseudo-spinel crystal structure of a composite oxide containing lithium and a transition metal refers to a crystal structure that has a space group R-3m and is not a spinel crystal structure, but in which ions such as cobalt and magnesium occupy the oxygen 6-coordinate positions and the arrangement of cations has a symmetry similar to that of a spinel.

[0363] The general agreement of crystal orientation between two regions can be determined from TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle scattering 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 a basis 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 orientation of the cubic close-packed structure is aligned in layered rock salt crystals and rock salt crystals, it can be observed that the angle between the repetition of bright and dark lines between crystals is 5 degrees or less, more preferably 2.5 degrees or less. Note that light elements such as oxygen and fluorine may not be clearly visible in TEM images, etc., but in such cases, the agreement of orientation can be determined from the arrangement of metallic elements.

[0364] Furthermore, in this specification, the theoretical capacity of the positive electrode active material refers to the amount of electricity when all of the insertable and detachable lithium present in the positive electrode active material has been detached. 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] Furthermore, in this specification, the charging depth when all insertable and detachable lithium is inserted is defined as 0, and the charging depth when all insertable and detachable lithium in the positive electrode active material has been detached is defined as 1.

[0366] In this specification, charging refers to the movement of lithium ions from the positive electrode to the negative electrode within the battery, and the movement of electrons from the positive electrode to the negative electrode in the external circuit. For positive electrode active material, the release of lithium ions is referred to as charging. Furthermore, positive electrode active material with a charging depth of 0.7 to 0.9 may be referred to as positive electrode active material charged with high voltage.

[0367] Similarly, discharge refers to the movement of lithium ions from the negative electrode to the positive electrode within the battery, and the movement of electrons from the negative electrode to the positive electrode in the external circuit. For positive electrode active materials, the insertion of lithium ions is called discharge. Furthermore, a positive electrode active material with a charge depth of 0.06 or less, or a positive electrode active material that has been discharged to 90% or more of its charge capacity from a state where it was charged at a high voltage, is considered a sufficiently discharged positive electrode active material.

[0368] Furthermore, in this specification, a non-equilibrium phase change refers to a phenomenon that causes a nonlinear change in a physical quantity. For example, a non-equilibrium phase change is thought to occur around the peak in the dQ / dV curve obtained by differentiating capacitance (Q) with respect to voltage (V) (dQ / dV), indicating a significant change in the crystal structure.

[0369] A secondary battery has, for example, a positive electrode and a negative electrode. The positive electrode is composed of a positive electrode active material. The positive electrode active material is, for example, a substance that performs a reaction that contributes to the charge and discharge capacity. However, the positive electrode active material may also contain a substance that does not contribute to the charge and discharge capacity. The negative electrode is composed of a negative electrode active material. The negative electrode active material is, for example, a substance that performs a reaction that contributes to the charge and discharge capacity. However, the negative electrode active material may also contain a substance that does not contribute to the charge and discharge capacity.

[0370] In this specification, the positive electrode active material of one aspect of the present invention may be expressed as a positive electrode material, a positive electrode material for secondary batteries, etc. In this specification, it is preferable that the positive electrode active material of one aspect of the present invention has a compound. In this specification, it is preferable that the positive electrode active material of one aspect of the present invention has a composition. In this specification, it is preferable that the positive electrode active material of one aspect of the present invention has a composite.

[0371] In this specification, the negative electrode active material according to one aspect of the present invention may be expressed as a negative electrode material, a negative electrode material for secondary batteries, etc. In this specification, it is preferable that the negative electrode active material according to one aspect of the present invention has a compound. In this specification, it is preferable that the negative electrode active material according to one aspect of the present invention has a composition. In this specification, it is preferable that the negative electrode active material according to one aspect of the present invention has a composite.

[0372] The discharge rate is the relative ratio of the discharge current to the battery capacity, and is expressed in units of C. For a battery with a rated capacity of X (Ah), the current equivalent to 1C is X (A). If the battery is discharged with a current of 2X (A), it is said to have been discharged at 2C, and if it is discharged with a current of X / 5 (A), it is said to have been discharged at 0.2C. Similarly, the charge rate is also expressed in the same way: if the battery is charged with a current of 2X (A), it is said to have been charged at 2C, and if it is charged with a current of X / 5 (A), it is said to have been charged at 0.2C.

[0373] Constant current charging refers to a method of charging while maintaining a constant charging rate. Constant voltage charging refers to a method of charging while maintaining a constant voltage once the upper voltage limit is reached. Constant current discharging refers to a method of discharging while maintaining a constant discharge rate. [Examples]

[0374] In this embodiment, a negative electrode according to one aspect of the present invention was fabricated, and the fabricated negative electrode was evaluated.

[0375] <Fabrication of the negative electrode> The negative electrode was fabricated according to the flow shown in Figure 4. Nanosilicon particles from ALDRICH were used as silicon-containing particles. Spheroidal graphite particles CGB-15 from Nippon Graphite Industries Co., Ltd. were used as graphite-containing particles. Graphene oxide was used as the graphene compound. A polyimide precursor from Toray Industries, Inc. was used as the polyimide.

[0376] Electrodes GS1, GS2, GS3, and GS4 were fabricated as negative electrodes. Electrodes GS1 through GS4 were fabricated using the same method, except for the electrode composition ratios shown in Table 1. The electrode composition ratios shown in Table 1 represent the weight ratios of the materials prepared in steps S61, S72, S80, and S87 of Figure 4 during the fabrication of electrodes GS1 through GS4. Further details are explained below.

[0377] [Table 1]

[0378] Nanosilicon particles and a solvent were prepared and mixed (steps S61, S62, S63 in Figure 4). NMP was used as the solvent. The mixture was mixed at 2000 rpm for 3 minutes using a rotary-orbit mixer (Awatori Rentaro, manufactured by THINKY Co., Ltd.), collected, and obtained mixture E-1 (steps S64, S65 in Figure 4).

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

[0380] Next, mixture E-2 and the graphene compound were repeatedly mixed while adding solvent. Graphene oxide was prepared as the graphene compound, and the mixture was mixed at 2000 rpm for 3 minutes using a rotary-orbit mixer, and then collected (steps S80, S81, S82 in Figure 4). Next, the collected mixture was kneaded, NMP was added as needed, and the mixture was mixed at 2000 rpm for 3 minutes using a rotary-orbit mixer, and then collected (steps S83, S84, S85 in Figure 4). Steps S83 to S85 were repeated 5 times to obtain mixture E-3 (step S86 in Figure 4).

[0381] Next, mixture E-3 and the polyimide precursor were mixed (step S88 in Figure 4). Mixing was carried out using a rotary-orbit mixer at 2000 rpm for 3 minutes. Then, NMP was prepared and added to the mixture to adjust the viscosity (step S89 in Figure 4), and further mixing was performed (twice at 2000 rpm for 3 minutes using the rotary-orbit mixer). The mixture was then collected and obtained as a slurry, which is mixture E-4 (steps S90, S91, S92 in Figure 4).

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

[0383] Next, the copper foil coated with mixture E-4 was subjected to a first heating at 50°C for 1 hour (step S95 in Figure 4). Subsequently, a second heating was performed under reduced pressure at 400°C for 5 hours (step S96 in Figure 4) to obtain the electrode. Heating reduces the graphene oxide, decreasing the amount of oxygen.

[0384] <sem> SEM observation was performed on the surface of the fabricated electrodes. The SEM observation was carried out after the first heating stage. A Hitachi High-Technologies SU8030 SEM was used. The acceleration voltage was set to 5kV.

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

[0386] Figure 18B is a magnified image of the surface of graphite particles with a particle size of approximately 10 μm to 20 μm on electrode GS1. Nanosilicon particles of approximately 50 nm to 250 nm are present on the surface of the graphite particles, and regions covered by graphene oxide and regions not covered by graphene oxide were observed.

[0387] Figure 19B is a magnified image of the surface of graphite particles with a particle size of approximately 10 μm to 20 μm on electrode GS2. Nanosilicon particles of approximately 50 nm to 250 nm are present on the surface of the graphite particles, and regions covered by graphene oxide and regions not covered by graphene oxide were observed. GS2 tends to have a larger area covered by graphene oxide than GS1.

[0388] Figure 20B is a magnified image of the surface of graphite particles with a particle size of approximately 10 μm to 20 μm on electrode GS3. Nanosilicon particles of approximately 50 nm to 250 nm are present on the surface of the graphite particles, and regions covered by graphene oxide and regions not covered by graphene oxide were observed. GS3 tends to have a larger area covered by graphene oxide than GS2.

[0389] Figure 21B is a magnified image of the surface of graphite particles with a particle size of approximately 10 μm to 20 μm on electrode GS4. Nanosilicon particles of approximately 50 nm to 250 nm are present on the surface of the graphite particles, and regions covered by graphene oxide and regions not covered by graphene oxide were observed. GS4 tends to have a larger area covered by graphene oxide than GS3, with most of the nanosilicon being covered by multiple layers of graphene oxide.

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

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

[0392] A 25 μm thick polypropylene separator was used for the separator.

[0393] The positive electrode and negative electrode cans were made of stainless steel (SUS).

[0394] <Charge / discharge characteristics> The charge and discharge characteristics were evaluated using the fabricated coin cell. In the fabricated coin cell, lithium is absorbed into the electrodes during discharge and released from the electrodes during charging.

[0395] The discharge conditions (lithium storage) consisted of 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) consisted of constant current charging (0.1C, upper limit voltage 1V). Discharge and charging were performed at 25°C. The change in capacity with respect to the number of charge-discharge cycles is shown in Figures 22A and 22B. The maximum charge capacity in the charge-discharge cycle test and the charge capacity retention rate after 40 cycles are shown in Table 2.

[0396] [Table 2]

[0397] Figure 23 shows the electrode composition ratios and characteristics of electrodes GS1 to GS4, plotting the GO / silicon ratio of electrodes GS1 to GS4 against the discharge capacity retention rate after 40 cycles. It can be seen that, when the amount of silicon is set to 1, the electrode composition ratio of graphene oxide to silicon is preferably 0.05 or higher, more preferably 0.10 or higher, and even more preferably 0.30 or higher. The electrode composition ratios shown in Table 2 represent the weight ratios of the materials prepared in steps S61, S72, and S80 of Figure 4 during the fabrication of electrodes GS1 to GS4. [Explanation of Symbols]

[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: Outer casing, 510: Positive electrode lead electrode, 511: Negative electrode lead electrode, 5 70: 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: Sheet-shaped material, 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: Energy 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: energy storage device, 701: commercial power supply, 703: distribution board, 705: energy storage controller, 706: display unit, 707: general load, 708: energy storage system load, 709: router, 710: service drop connection section, 711: measurement section, 712: prediction section, 713: planning section, 790: control device, 791: energy storage device, 796: underfloor space section, 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: Winding body, 950a: Winding body, 951: Terminal, 952: Terminal, 1300: Rectangular 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: Defogger, 1310: DC-DC circuit,1311: Battery, 1312: Inverter, 1313: Audio, 1314: Power windows, 1315: Lights, 1316: Tires, 1317: Rear motor, 1320: Control circuit unit, 1321: Control circuit unit, 1322: Control circuit, 1324: Switch unit, 1325: External terminals, 1326: External terminals, 1413: Fixing unit, 1414: Fixing unit, 1415: Battery pack, 1421: Wiring, 1422: Wiring, 2001: Automobile, 2002: Transport vehicle, 2003: Transport vehicle, 2004: Aircraft, 2100: Mobile phone, 2101: Housing, 2102: Display unit, 2103: Operation buttons, 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: Rechargeable battery, 2302: Rotor, 2303: Camera, 2603: Vehicle, 2604: Charging device, 2610: Solar panel, 2611: Wiring, 2612: Energy storage device, 6300: Cleaning robot, 6301: Housing, 6302: Display unit, 6303: Camera, 6304: Brush, 6305: Operation button, 6306: Rechargeable battery, 6310: Dust, 6400: Robot, 6401: Illuminance sensor, 6402: Microphone, 6403: Upper camera, 6404: Speaker, 6405: Display unit, 6406: Lower camera, 6407: Obstacle sensor, 6408: Movement mechanism, 6409: Rechargeable battery,< / sem>

Claims

1. It comprises a first active material, a second active material, and a graphene compound. The first active material has an average particle size of less than 1 μm and contains silicon. The second active material has a larger average particle size than the first active material and contains graphite. The first active material is located on the surface of the second active material, The graphene compound has a region in contact with the first active material and a region in contact with the second active material. The graphene compound has pores, The graphene compound has a plurality of carbon atoms constituting the pore, one or more hydrogen atoms, and one or more fluorine atoms. Each of the one or more hydrogen atoms and the one or more fluorine atoms terminates on one of the plurality of carbon atoms. The aforementioned hole is an electrode composed of a multi-membered ring with 18 or more members.

2. It comprises a first active material, a second active material, and a graphene compound. The first active material has an average particle size of less than 1 μm and contains silicon. The aforementioned silicon has at least a portion of its surface terminated with hydroxyl groups, The second active material has a larger average particle size than the first active material and contains graphite. The first active material is located on the surface of the second active material, The graphene compound has a region in contact with the first active material and a region in contact with the second active material. The graphene compound has pores, The graphene compound has a plurality of carbon atoms constituting the pore, one or more hydrogen atoms, and one or more fluorine atoms. Each of the one or more hydrogen atoms and the one or more fluorine atoms terminates on one of the plurality of carbon atoms. The aforementioned hole is an electrode composed of a multi-membered ring with 18 or more members.

3. In claim 1 or claim 2, The graphene compound is an electrode having a region that is in contact with the first active material and covers the first active material.

4. In claim 1 or claim 2, The first active material is an electrode having a region located between the second active material and the graphene compound.

5. In any one of claims 1 to 4, An electrode in which the average particle diameter of the second active material is 10 times or more the average particle diameter of the first active material.

6. In any one of claims 1 to 5, The silicon in question is an electrode having amorphous silicon.

7. In any one of claims 1 to 6, The aforementioned hole is an electrode composed of a multi-membered ring with 22 or more members.

8. In any one of claims 1 to 7, An electrode in which, among the multiple carbon atoms constituting the pore, the number of carbon atoms terminated by fluorine atoms is less than 40% of the number of carbon atoms terminated by hydrogen atoms.

9. In any one of claims 1 to 8, The graphene compound is an electrode comprising graphene oxide, multilayer graphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, or graphene quantum dots.

10. An electrode according to any one of claims 1 to 9, Electrolytes, A rechargeable battery.

11. A mobile body having a secondary battery as described in claim 10.

12. An electronic device having a secondary battery as described in claim 10.

Images