electrode

Abstract

Provided is an electrode exhibiting less deterioration or a secondary battery exhibiting less deterioration. The electrode has a first region and a second region, wherein the first region has silicon-bearing particles, the second region has silicon-bearing particles and a graphene compound, and the second region contacts the first region so as to cover at least a portion of the first region. In addition, the electrode has a plurality of silicon-bearing particles and a graphene compound, wherein each of the plurality of silicon-bearing particles has a functional group containing oxygen and carbon, a functional group containing oxygen, or a fluorine atom on at least a portion the surface, the graphene compound has at least one of hydrogen-terminated carbon and fluorine-terminated carbon on the plane of the graphene compound, and the graphene compound is in close contact with the plurality of silicon-bearing particles. The silicon-bearing particles preferably have amorphous silicon or polycrystalline silicon.

Description

[Technical Field]

[0001] One aspect of the present invention relates to an electrode and a method for manufacturing the same; or to an active material having an electrode and a method for manufacturing the same; or to a secondary battery and a method for manufacturing the same; or to a mobile device including a vehicle having a secondary battery, as well as a portable information terminal, electronic device, 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, with their 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.

[0006] In addition to its stability, it is important that a secondary battery has a high capacity. Silicon-based materials have a high capacity and are used as active materials for secondary batteries. Silicon materials can be characterized by chemical shift values obtained from NMR spectra (Patent Document 1).

[0007] For improving the cycle characteristics and increasing the capacity of lithium-ion secondary batteries, the improvement of the negative electrode with a coating has been studied (Patent Document 2).

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] Secondary batteries used in moving bodies such as electric vehicles and hybrid vehicles need to have an increased capacity in order to extend the driving distance.

[0010] In addition, in portable terminals and the like, the power consumption is increasing with the increase in functionality. Also, secondary batteries used in portable terminals and the like are required to be miniaturized and lightweight. Therefore, there is also a demand for increasing the capacity of secondary batteries used in portable terminals.

[0011] The electrodes of a secondary battery are composed of materials such as active material, conductive agent, and binder. The higher the proportion of materials that contribute to charge and discharge capacity, such as active material, the higher the capacity of the secondary battery can be. By having a conductive agent in the electrodes, the conductivity of the electrodes is increased, and excellent output characteristics can be obtained. Also, during the charging and discharging of a secondary battery, the active material repeatedly expands and contracts, which can cause the active material to detach from the electrodes, the conductive path to be blocked, etc. In such cases, the presence of a conductive agent and binder in the electrodes can suppress the detachment of the active material and the blocking of the conductive path. On the other hand, by using a conductive agent and binder, the proportion of active material decreases, which may reduce the capacity of the secondary battery.

[0012] One aspect of the present invention aims to provide an electrode having excellent properties. Alternatively, one aspect of the present invention aims to provide an active material having excellent properties. Alternatively, one aspect of the present invention aims to provide a novel electrode.

[0013] Alternatively, one aspect of the present invention aims to provide a mechanically robust negative electrode. Alternatively, one aspect of the present invention aims to provide a mechanically robust positive electrode. Alternatively, one aspect of the present invention aims to provide a negative electrode with high capacity. Alternatively, one aspect of the present invention aims to provide a positive electrode with high capacity. Alternatively, one aspect of the present invention aims to provide a negative electrode with minimal degradation. Alternatively, one aspect of the present invention aims to provide a positive electrode with minimal degradation.

[0014] Alternatively, one aspect of the present invention aims to provide a secondary battery that undergoes less degradation. Alternatively, one aspect of the present invention aims to provide a secondary battery that is highly safe. Alternatively, one aspect of the present invention aims to provide a secondary battery with high energy density. Alternatively, 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, drawings, and claims. [Means for solving the problem]

[0016] An electrode according to one aspect of the present invention comprises particles and a sheet-like material, wherein the particles have functional groups containing oxygen and carbon, and regions terminated by functional groups containing oxygen or fluorine atoms.

[0017] Furthermore, it is more preferable that the particles of an electrode according to one embodiment of the present invention have a functional group containing oxygen and carbon, a functional group containing oxygen and hydrogen, a functional group containing oxygen and lithium, a functional group containing fluorine, a hydrogen atom, or a region terminated by a fluorine atom. Examples of functional groups containing oxygen and hydrogen include hydroxyl groups, carboxyl groups, or functional groups containing hydroxyl groups.

[0018] 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. The sheet surface includes, for example, a surface facing the particles and a surface on its reverse side. The sheet surface is not limited to a flat surface but includes curved surfaces, and the area of ​​the sheet surface refers to the surface area including both the flat and curved surfaces. In the regions terminated by hydrogen atoms, it is preferable that the hydrogen atoms terminating these regions are located, for example, on the surface in contact with the particles. By providing multiple hydrogen-terminated regions widely across the sheet surface, the area on which the sheet-like material adheres to the particles can be increased. The adherence area refers to the area where the sheet surface and the particle surface are in contact. Furthermore, the sheet-like material described above may have hydrogen bonding regions, and these hydrogen bonding regions may be localized and distributed. This distribution allows the oxygen or fluorine atoms of the terminating functional groups of the particles to tightly bind to the hydrogen bonding regions through intermolecular forces and other interactions.

[0019] Furthermore, an electrode according to one aspect of the present invention has a material having a particle and sheet-like shape, and the electrode has a first region in which a plurality of the particles are aggregated, and a second region having the material having the particle and sheet-like shape.

[0020] Furthermore, it is preferable that the particles of the electrode according to one embodiment of the present invention have a region terminated by one or more of the following: a functional group containing oxygen and carbon, a functional group containing oxygen and hydrogen, a functional group containing oxygen and lithium, or a hydrogen atom.

[0021] 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.

[0022] The particles in the electrode according to one aspect of the present invention preferably contain silicon. The silicon is preferably amorphous silicon. Furthermore, the silicon is preferably polycrystalline silicon.

[0023] It is preferable that the material having a sheet-like shape contains a graphene compound. For example, it is preferable to use graphene as the graphene compound in which carbon atoms within the sheet surface are terminated by atoms other than carbon or functional groups.

[0024] 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.

[0025] 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, the atoms constituting the pores refer to, for example, atoms at the periphery of the opening, atoms at the end of the opening, etc.

[0026] A graphene compound according to one embodiment of the present invention has a pore composed of a multi-membered ring consisting of 9 or more carbon atoms, 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 in the multi-membered ring terminated by fluorine is less than 40% of the number of carbon atoms terminated by hydrogen atoms.

[0027] Pores in graphene compounds can be identified using high-resolution images obtained with TEM (transmission electron microscope) or STEM (scanning transmission electron microscope). When using TEM to observe pores in graphene compounds, applying FFT (Fast Fourier Transform) filtering to the TEM image reduces noise, making it easier to identify the grid.

[0028] 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.

[0029] 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.

[0030] One aspect of the present invention is an electrode having a first region and a second region, wherein the first region has first particles having silicon, and the second region has second particles having silicon and a graphene compound, and the second region is in contact with at least a portion of the first region.

[0031] Furthermore, one aspect of the present invention is an electrode having a first region and a second region, wherein the first region has first particles having silicon, and the second region has second particles having silicon and a graphene compound, and the second region is in contact with the first region so as to cover at least a portion of it.

[0032] In the electrode described in any one of the above, it is preferable that the graphene compound is in contact with the second particle in a manner that it adheres to it.

[0033] In the electrode described in any one of the above, it is preferable that the first particle and the second particle have a region on their surface terminated by one or more functional groups containing oxygen and carbon, functional groups containing oxygen and hydrogen, functional groups containing oxygen and lithium, or hydrogen atoms.

[0034] In the electrode described in any one of the above, it is preferable that the first particle and the second particle have oxygen, carbon, and lithium in at least a portion of their surface layer.

[0035] In the electrode described in any one of the above, it is preferable that the first particle and the second particle have amorphous silicon.

[0036] In the electrode described in any one of the above, it is preferable that the first particle and the second particle have polycrystalline silicon.

[0037] Furthermore, one aspect of the present invention comprises silicon-containing particles and a graphene compound, wherein the silicon-containing particles have functional groups containing oxygen and carbon, functional groups containing oxygen, or bonds with fluorine atoms on at least a portion of their surface, the graphene compound has hydrogen or functional groups containing hydrogen, and the graphene compound is an electrode that adheres tightly to the silicon-containing particles.

[0038] Furthermore, one aspect of the present invention comprises a plurality of silicon particles and a graphene compound, wherein at least a portion of the surface of each silicon particle has a functional group containing oxygen and carbon, a functional group containing oxygen, or a bond with a fluorine atom, the graphene compound has hydrogen or a functional group containing hydrogen, and the graphene compound is an electrode that closely adheres to the plurality of silicon particles.

[0039] In the electrode described in any one of the above, it is preferable that the silicon-containing particles have a carbonate group, a bicarbonate group, a hydroxyl group, an epoxy group, or a carboxyl group.

[0040] In the electrode described in any one of the above, it is preferable that the silicon particles have a region on their surface terminated by one or more of the following: a functional group containing oxygen and carbon, a functional group containing oxygen and hydrogen, a functional group containing oxygen and lithium, or a hydrogen atom.

[0041] In the electrode described in any one of the above, it is preferable that the silicon-containing particles have oxygen, carbon, and lithium in at least a portion of their surface layer.

[0042] In the electrode described in any one of the above, it is preferable that the silicon-containing particles are amorphous silicon.

[0043] In the electrode described in any one of the above, it is preferable that the silicon-containing particles are polycrystalline silicon.

[0044] In the electrode described in any one of the above, it is preferable that the graphene compound has pores.

[0045] In the electrode described in any one of the above, the graphene compound preferably has a plurality of carbon atoms and one or more hydrogen atoms, each of the one or more hydrogen atoms terminates at one of the plurality of carbon atoms, and a pore is formed by the plurality of carbon atoms and one or more hydrogen atoms.

[0046] Furthermore, one aspect of the present invention is a secondary battery having an electrode and an electrolyte as described in any one of the above.

[0047] Furthermore, one aspect of the present invention is a mobile device having a secondary battery as described in any one of the above.

[0048] Furthermore, one aspect of the present invention is an electronic device having a secondary battery as described in any one of the above.

[0049] Furthermore, one aspect of the present invention is a method for producing a negative electrode active material, comprising: a first step of mixing silicon-containing particles, lithium fluoride, a halogen-containing material, and a material containing oxygen and carbon to produce a first mixture; and a second step of heating the first mixture, wherein the heating in the second step is carried out at a temperature of 350°C to 900°C for a period of 1 hour to 60 hours, and the heating in the second step is carried out under a nitrogen atmosphere or a rare gas atmosphere.

[0050] Furthermore, one aspect of the present invention is a method for producing a negative electrode active material layer, comprising: a first step of mixing a negative electrode active material, a graphene compound, and a solvent prepared using the negative electrode active material production method described above to produce a first mixture; a second step of mixing the first mixture, a polyimide precursor, and a solvent to produce a second mixture; a third step of coating the second mixture onto a metal foil to produce a first coating film; a fourth step of drying the first coating film to produce a second coating film; and a fifth step of heating the second coating film, wherein the heating in the fifth step is carried out in a reducing atmosphere, and the heating in the fifth step reduces the graphene compound and imidizes the polyimide precursor.

[0051] 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 lithium carbonate to produce a first mixture; a second step of heating the first mixture to obtain silicon-containing particles; a third step of mixing the silicon-containing particles and a solvent to produce a second mixture; a fourth step of mixing the second mixture and a graphene compound to produce a third mixture; a fifth step of mixing the third mixture, a polyimide precursor and a solvent to produce a fourth mixture; a sixth step of coating the fourth mixture onto a metal foil; a seventh step of drying the fourth mixture; and an eighth step of heating the fourth mixture to produce an electrode, wherein the heating in the eighth step is carried out in a reducing atmosphere.

[0052] In the method for manufacturing electrodes for lithium-ion secondary batteries described in any one of the above, it is preferable that the silicon-containing particles have oxygen, carbon, and lithium in at least a portion of their surface layer.

[0053] In the method for manufacturing electrodes for lithium-ion secondary batteries described in any one of the above, it is preferable that the silicon-containing particles are amorphous silicon.

[0054] In the method for manufacturing electrodes for lithium-ion secondary batteries described in any one of the above, it is preferable that the silicon-containing particles are polycrystalline silicon. [Effects of the Invention]

[0055] According to one aspect of the present invention, an electrode with excellent properties can be provided. Furthermore, according to one aspect of the present invention, a novel electrode can be provided.

[0056] 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 mechanically robust positive electrode can be provided. Furthermore, according to one aspect of the present invention, a negative electrode with high capacity can be provided. Furthermore, according to one aspect of the present invention, a positive electrode with high capacity can be provided. Furthermore, according to one aspect of the present invention, a negative electrode with less degradation can be provided. Furthermore, according to one aspect of the present invention, a positive electrode with less degradation can be provided.

[0057] 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.

[0058] 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]

[0059] Figures 1A to 1C show examples of cross-sections of electrodes. Figures 2A to 2C illustrate an example illustrating the degree to which the graphene compound adheres to the particles. Figures 3A and 3B show examples of cross-sections of electrodes, and Figures 3C and 3D show examples of the first and second regions. Figures 4A to 4D show examples of cross-sections of the negative electrode active material. Figures 5A and 5B are diagrams relating to quantum molecular dynamics calculations. Figure 6 is a diagram relating to quantum molecular dynamics calculations. Figures 7A and 7B show an example of a model containing silicon. Figure 8 shows an example of a model containing silicon and a model containing graphene compounds. Figures 9A and 9B show examples of models with silicon and graphene compounds. Figures 10A and 10B show examples of models with silicon and graphene compounds. Figures 11A and 11B show examples of graphene compound models. Figures 12A and 12B show examples of models with silicon and graphene compounds. Figures 13A and 13B show examples of models with silicon and graphene compounds. Figures 14A and 14B show examples of models with silicon and graphene compounds. Figure 15 is a diagram relating to dissipative particle dynamics calculations. Figures 16A and 16B show examples of models of silicon-containing particles and graphene compounds. Figures 17A and 17B show examples of models of silicon-containing particles and graphene compounds. Figures 18A and 18B are graphs relating to the dissipation particle dynamics calculations. Figure 19 shows an example of a method for producing a negative electrode active material according to one embodiment of the present invention. Figure 20 shows an example of a method for producing a negative electrode active material according to one embodiment of the present invention. Figure 21 shows an example of a method for manufacturing an electrode according to one aspect of the present invention. Figure 22 illustrates the charging depth and crystal structure of a positive electrode active material according to one embodiment of the present invention. Figure 23 shows the XRD pattern calculated from the crystal structure. Figure 24 illustrates the charging depth and crystal structure of the positive electrode active material in the comparative example. Figure 25 shows the XRD pattern calculated from the crystal structure. Figures 26A and 26B show the method for preparing the materials. Figure 27 is an example of a cross-sectional view illustrating one aspect of the present invention. Figure 28 shows an example of a cross-section of a secondary battery. Figure 29A is an exploded perspective view of a coin-type rechargeable battery, Figure 29B is a perspective view of a coin-type rechargeable battery, and Figure 29C is a cross-sectional perspective view thereof. Figures 30A and 30B show examples of cylindrical secondary batteries, Figure 30C shows examples of multiple cylindrical secondary batteries, and Figure 30D shows examples of energy storage systems having multiple cylindrical secondary batteries. Figures 31A and 31B illustrate examples of secondary batteries, while Figure 31C shows the inside of a secondary battery. Figures 32A, 32B, and 32C illustrate examples of secondary batteries. Figures 33A and 33B show the external appearance of a secondary battery. Figures 34A, 34B, and 34C illustrate the method for manufacturing a secondary battery. Figure 35A is a perspective view showing the battery pack, Figure 35B is a block diagram of the battery pack, and Figure 35C is a block diagram of a vehicle with a motor. Figures 36A to 36D illustrate an example of a transport vehicle. Figure 36E illustrates an example of an artificial satellite. Figures 37A and 37B illustrate the energy storage device. Figures 38A to 38D illustrate an example of an electronic device. Figure 39A shows a surface SEM image, and Figure 39B shows a cross-sectional SEM image. Figures 40A and 40B are SEM images of the surface and cross-section of the electrode in Example 3. Figures 41A and 41B are enlarged SEM images of Figure 40B. Figures 42A and 42B show the cycle characteristics. [Modes for carrying out the invention]

[0060] 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.

[0061] Furthermore, in drawings, size, layer thickness, or area may be exaggerated for clarity. Therefore, the scale is not necessarily limited.

[0062] 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.

[0063] (Embodiment 1) This embodiment describes an electrode, active material, conductive agent, etc., according to one aspect of the present invention.

[0064] <Example of an electrode 1> 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. Figures 1B and 1C are enlarged views of the area enclosed by the dashed line in Figure 1A. The active material layer 572 comprises an electrolyte 581, particles 582, and a sheet-like material.

[0065] The particles 582 preferably function as an active material. A material that functions as an active material can be used as the particles 582. Alternatively, it is preferable that the particles 582 have, for example, a material that functions as an active material. Furthermore, the sheet-like material of the electrode 570 preferably functions as a conductive agent. In one embodiment of the present invention, since the conductive agent can adhere to the active material by hydrogen bonding, an electrode with high conductivity can be realized. Various materials can be used as the particles 582.

[0066] Figures 1B and 1C show examples in which graphene compound 583 is used as a sheet-like material.

[0067] When particles 582 are used that are particles according to one embodiment of the present invention, having functional groups containing oxygen and carbon or fluorine in their surface layer, or having a region terminated by functional groups containing oxygen and carbon or fluorine atoms on their surface, the affinity between particles 582 and graphene compound 583 is improved, as shown in Figure 1C, and the graphene compound 583 can adhere closely to the particles 582. Because the graphene compound 583 can adhere closely to the particles 582, a highly conductive electrode can be realized. The state of adhering closely can also be described as making contact in close proximity rather than at a point. It can also be described as making contact along the particle surface, or as making surface contact with multiple particles. Materials that can be used as particles 582 will be described later.

[0068] Furthermore, Figure 1C shows a schematic diagram of an active material layer having a graphene compound 583 as a sheet-like material, with particles 582 being particles according to one embodiment of the present invention, which have functional groups containing oxygen and carbon or fluorine in their surface layer, or regions terminated by functional groups containing oxygen and carbon or fluorine atoms on their surface. By using the active material according to one embodiment of the present invention as particles 582, the affinity with the graphene compound 583 is improved, and as shown in Figure 1C, the graphene compound 583 can come into close contact with the active material, closely adhering to it.

[0069] An example illustrating the state of close, clinging contact will be explained using Figure 2. Figure 2A shows a schematic diagram of a case where a cross section, indicated by a dashed line, is cut out of two adjacent particles 582 and a graphene compound 583 in contact with these two particles 582, including the surface of the first particle 582a in contact with the graphene compound 583, the surface of the second particle 582b in contact with the graphene compound 583, and the approximate central part of each particle 582. Figure 2B shows a schematic diagram of the cross section indicated by the dashed line in Figure 2A. In the schematic cross-sectional view shown in Figure 2B, the first distance 592 is defined as the distance between the first point of contact between the first particle 582 and the first tangent line 591, and the second point of contact between the second particle 582 and the first tangent line 591, and the distance between the first portion of the cross-sectional curve of the graphene compound 583 that is in contact with the first and second points of contact. The second distance 593 is defined as the distance between the first portion of the cross-sectional curve of the graphene compound 583 that is in contact with the first and second points of contact. Here, comparing the first distance 592 and the second distance 593, if the second distance 593 is longer than the first distance 592, and the first portion of the cross-sectional curve of the graphene compound 583 is located closer to the active material particle than the first tangent line 591, then the particles are in a state of clinging to each other. Furthermore, when the second distance 593 is 105% or more when the first distance 592 is set to 100%, the two objects are in close contact, clinging to each other. When the first distance 592 is set to 100%, the second distance 593 is preferably greater than 101%, more preferably 105% or more, and even more preferably 110% or more. Figure 2C shows examples when the second distance 593 is 100%, 101%, 105%, 110%, and 120% when the first distance 592 is set to 100%.

[0070] When the graphene compound adheres closely to the active material, the contact area between the graphene compound and the active material increases, improving the conductivity of electrons moving through the graphene compound. Furthermore, when the volume of the active material changes significantly due to charging and discharging, the close contact of the graphene compound with the active material effectively prevents the active material from falling off. These effects become even more pronounced when the contact is dense. Here, the graphene compound has vacancies large enough to allow Li ions to pass through, and it is desirable that the number of vacancies be large enough not to hinder the electronic conductivity of the graphene compound.

[0071] The active material layer 572 preferably contains a carbon-based material such as a graphene compound, carbon black, graphite, carbon fiber, or fullerene, and is particularly preferably a graphene compound. 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. Figures 1B and 1C show an example in which the active material layer 572 contains a graphene compound 583.

[0072] As carbon fibers, for example, mesophase pitch carbon fibers and isotropic pitch carbon fibers can be used. Alternatively, carbon nanofibers and carbon nanotubes can also be used. Carbon nanotubes can be fabricated, for example, by vapor deposition.

[0073] The active material layer may also contain metal powders or fibers such as copper, nickel, aluminum, silver, or gold, or conductive ceramic materials as conductive agents.

[0074] The content of the conductive agent relative to the total amount of the active material layer is preferably 1 wt% to 10 wt%, and more preferably 1 wt% to 5 wt%.

[0075] Unlike granular conductive agents such as carbon black, which make point contact with the active material, graphene compounds enable surface contact with low contact resistance. Therefore, a smaller amount of graphene compound can improve the electrical conductivity between the granular active material and the graphene compound compared to conventional conductive agents. Consequently, the ratio of the active material in the active material layer can be increased. This, in turn, can increase the discharge capacity of the secondary battery.

[0076] Furthermore, since the graphene compound according to one embodiment of the present invention has excellent lithium permeability, it can increase the charge and discharge rate of secondary batteries.

[0077] 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 without significantly changing the total weight of a vehicle equipped with the same weight of secondary batteries.

[0078] Furthermore, as the capacity of a vehicle's secondary battery increases, more power is required for charging, and it is desirable to complete the charging process in a short time. In addition, regenerative charging, which temporarily generates electricity when the vehicle brakes are applied and then charges the battery, is performed under high-rate charging conditions, so good rate characteristics are required for vehicle secondary batteries.

[0079] In the active material layer 572 shown in Figures 1B and 1C, multiple graphene compounds 583 are arranged in a three-dimensional network, with particles 582 between the multiple graphene compounds 583.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] As a binder, fluorine-containing polymer materials such as fluoropolymers, 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.

[0086] 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.

[0087] 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, as well as starch. It is even preferable to use these water-soluble polymers in combination with the aforementioned rubber material.

[0088] You may use a combination of several of the binders mentioned above.

[0089] Furthermore, the graphene compound 583 is flexible and pliable, and can cling to the particles 582 like natto (fermented soybeans). For example, the particles 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, multiple active materials, multiple carbon-based materials, etc., present in 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 materials such as 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 leakage of electrolyte from the current collector can be suppressed. In addition, in the above-mentioned structure with arranged polygons, 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.

[0090] The particle 582 can have various shapes, such as rounded shapes or angular shapes. Furthermore, in the cross-section of the electrode, the 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-section of the particle 582 has a rounded shape, but the cross-section of the particle 582 may also have angular shapes. Alternatively, part of the particle may be rounded and part of it may have angular shapes.

[0091] <Example of electrodes 2> Figure 3A is a schematic cross-sectional view showing an electrode according to one embodiment of the present invention. The electrode 570 shown in Figure 3A 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.

[0092] Figure 3B is an enlarged view of the area enclosed by the dashed line in Figure 3A. Figure 3B shows one embodiment of a structure in which a sheet-like material adheres to and surrounds particles.

[0093] As shown in Figure 3B, the active material layer 572 comprises particles 582, a graphene compound 583 as a sheet-like material, and an electrolyte 584. Materials that can be used as particles 582 will be described later. Figures 3C and 3D show a first region 585 where particles 582 are aggregated, and a second region 586 having particles 582 and a sheet-like material. The particles 582 preferably function as an active material. Any material that functions as an active material can be used as the particles 582. Furthermore, the graphene compound 583 in the active material layer 572 preferably functions as a conductive agent, for example. In one embodiment of the present invention, the conductive agent can adhere to the active material by hydrogen bonding, thereby realizing an electrode with high conductivity. Various materials can be used as particles 582. When particles 582 are used that are particles according to one aspect of the present invention, such as particles having an oxygen-containing functional group in their surface layer, particles having a region terminated by an oxygen-containing functional group in their surface layer, or particles having a region containing oxygen and carbon in their surface layer, the affinity between particles 582 and graphene compound 583 is improved, as shown in Figure 3B, and the graphene compound 583 can come into contact with particles 582 in a way that covers, encases, or clings to them, as shown in Figure 3B. Because the graphene compound 583 can cling to particles 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. It can also be described as making contact along the particle surface. It can also be described as making surface contact with multiple particles. When particles 582 are used that have functional groups containing oxygen in their surface layer, particles that have regions terminated by functional groups containing oxygen in their surface layer, or particles that have regions containing oxygen and carbon in their surface layer, the affinity between particles 582 and each other is improved, as shown in Figure 3B, and regions where multiple particles 582 are aggregated can be formed.The active material layer 572 may have a first region 585 where particles 582 are aggregated, and a second region 586 having particles 582 and a graphene compound 583. As shown in Figures 3C and 3D, it may have composite particles having the first region 585 and the second region 586. In the composite particles, it is preferable that the second region 586 is in contact with at least a part of the first region 585, and more preferably that the second region 586 is in contact so as to cover at least a part of the first region 585. Furthermore, it is preferable that two or more adjacent composite particles have their respective second regions 586 in contact with each other, and more preferably that their respective second regions 586 have a bonded portion. The active material layer 572 may also have a first region 585 that does not form composite particles, and a second region 586 that does not form composite particles.

[0094] The active material layer 572 may contain carbon-based materials such as carbon black, graphite, carbon fiber, and fullerene, in addition to the graphene compound. 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.

[0095] The materials that can be used as carbon fibers can be found in the description above.

[0096] The content of the conductive agent 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%.

[0097] 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. Other materials that can be used as a binder are as described above.

[0098] Furthermore, the graphene compound 583 is flexible and pliable, and can cling to the particles 582 like natto (fermented soybeans). For example, the particles 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, multiple active materials, multiple carbon-based materials, etc., present in 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 materials such as 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 leakage of electrolyte from the current collector can be suppressed. In addition, in the above-mentioned structure with arranged polygons, 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.

[0099] The particle 582 can have various shapes, such as rounded shapes or angular shapes. Furthermore, in the cross-section of the electrode, the particle 582 can have various cross-sectional shapes, such as circles, ellipses, curved shapes, polygons, etc. For example, Figure 3B shows an example where the cross-section of the particle 582 has a rounded shape, but the cross-section of the particle 582 may also have angular shapes. Alternatively, part of the particle may be rounded and part of it may have angular shapes.

[0100] <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 defined as a material having carbon, having a plate-like or sheet-like shape, and possessing a two-dimensional structure formed by a six-membered carbon ring. This two-dimensional structure formed by the six-membered carbon ring may also be called a carbon sheet. Graphene compounds may also have functional groups containing oxygen. Furthermore, graphene compounds preferably have a bent shape. Furthermore, graphene compounds may be rolled up to resemble carbon nanofibers.

[0101] 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.

[0102] 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 stacked. 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 amounts. 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 amounts.

[0103] In some cases, pores can be created in graphene compounds by reducing graphene oxide.

[0104] Alternatively, a material in which the ends of graphene are terminated with fluorine may be used.

[0105] 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.

[0106] 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.

[0107] Here, it is preferable to use graphene oxide as the graphene compound, mix it with the active material to form a layer that will become the active material layer, and then reduce it. In other words, it is preferable that the completed active material layer has reduced graphene oxide. By using graphene oxide, which has extremely high dispersibility in polar solvents, for the formation of the graphene compound, the graphene compound can be dispersed approximately uniformly within the internal region of the active material layer. By volatilizing and removing the solvent from the dispersion medium containing the uniformly dispersed graphene oxide and reducing the graphene oxide, the graphene compounds remaining in the active material layer partially overlap and are dispersed to the extent that they are in surface contact with each other, thereby forming three-dimensional conductive paths. The reduction of graphene oxide may be carried out, for example, by heat treatment or by using a reducing agent.

[0108] Furthermore, by using a spray-drying device beforehand, a graphene compound, which is a conductive agent, can be formed as a coating to cover the entire surface of the active material, and then the active material particles can be electrically connected with the graphene compound to form conductive paths.

[0109] Furthermore, the active material layer may be made by mixing the graphene compound with the material used to form the graphene compound. For example, particles used as a catalyst when forming the graphene compound may be mixed together with the graphene compound. Examples of catalysts used when forming the graphene compound include silicon dioxide (SiO2, SiO2). x Examples of particles include those having (x<2), aluminum oxide, iron, nickel, ruthenium, iridium, platinum, copper, germanium, etc. Preferably, the D50 of the particles is 1 μm or less, and more preferably 100 nm or less.

[0110] 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.

[0111] 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 by 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 pores 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.

[0112] <Examples of negative electrode active materials> When electrode 570 is the negative electrode, particles having a negative electrode active material can be used as 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.

[0113] An example of a negative electrode active material is described below.

[0114] Silicon can be used as the negative electrode active material. For electrode 570, it is preferable to use silicon-containing particles as particles 582. The silicon-containing particles are preferably amorphous silicon. Furthermore, the silicon-containing particles are preferably polycrystalline silicon. The silicon-containing particles are preferably amorphous silicon and polycrystalline silicon.

[0115] Furthermore, it is more preferable that the particles 582 of the electrode 570 have a region terminated by one or more of the following: a functional group containing oxygen and carbon, a functional group containing oxygen and hydrogen, a functional group containing oxygen and lithium, or a hydrogen atom.

[0116] Alternatively, it is more preferable that the particles 582 of the electrode 570 have regions containing oxygen, carbon, and lithium in at least a portion of the surface layer of the particles 582. For example, if the surface layer of the particles 582 has regions containing oxygen, carbon, and lithium, multiple particles 582 tend to aggregate with each other, and the sheet-like graphene compound 583 tends to adhere to the particles 582.

[0117] In addition, as the negative electrode active material of the particles 582, a metal or a compound having one or more elements selected from tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium can be used. Examples of alloy-based compounds using such elements include Mg2Si, Mg2Ge, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, SbSn, and the like.

[0118] In addition, nitrogen, phosphorus, arsenic, boron, aluminum, gallium, etc. can be used as additive elements for silicon, and a material with reduced resistance may be used. The concentration of the additive element is 10 18 atoms / cm 3 or more and 10 22 atoms / cm 3 or less. The concentration of nitrogen, phosphorus, or boron is preferably 10 18 atoms / cm 3 or more and 10 22 atoms / cm 3 or less. The concentration of the additive element can be analyzed by analytical methods such as secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS). The additive element can be introduced into silicon using an ion implantation method or a thermal diffusion method. Nitrogen, phosphorus, or boron is preferably introduced into silicon using a thermal diffusion method. For example, at least boron can be diffused into silicon by using a thermal diffusion method using boron nitride (BN). The thermal diffusion method can use a temperature of 600 °C or higher and 1200 °C or lower.

[0119] For example, nanosilicon can be used as the particles 582. The average diameter of the nanosilicon is, for example, preferably 5 nm or more and less than 1 μm, more preferably 10 nm or more and 300 nm or less, and even more preferably 10 nm or more and 100 nm or less.

[0120] The nanosilicon may have a spherical shape, a flattened spherical shape, or a rectangular parallelepiped shape with rounded corners. The size of the nanosilicon 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.

[0121] Here, D50 is the particle diameter, or median, at which the cumulative amount accounts for 50% of the cumulative amount curve of the particle size distribution measurement results. Particle size measurement is not limited to laser diffraction particle size distribution measurement; if the size is below the lower limit of the laser diffraction particle size distribution measurement, the major axis of the particle cross-section may be measured by analysis such as SEM (scanning electron microscope) or TEM (transmission electron microscope).

[0122] Nanosilicon may be crystalline. Furthermore, nanosilicon may have both crystalline regions and amorphous regions.

[0123] 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.

[0124] 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.

[0125] Furthermore, silicon-containing materials can include, for example, Li2SiO3 and Li4SiO4. Li2SiO3 and Li4SiO4 may be crystalline or amorphous, respectively.

[0126] The analysis of silicon-containing materials can be performed using methods such as NMR (Nuclear Magnetic Resonance), XRD (X-ray Diffraction), Raman spectroscopy, SEM, TEM, and EDX (Energy dispersive X-ray spectroscopy).

[0127] In addition to silicon-based materials, the electrode 570 can utilize carbon-based materials such as graphite, easily graphitizable carbon, poorly graphitizable carbon, carbon nanotubes, carbon black, and graphene compounds.

[0128] Furthermore, in addition to materials containing silicon, the electrode 570 can also be an oxide containing one or more elements selected from titanium, niobium, tungsten, and molybdenum.

[0129] Furthermore, in addition to silicon-containing materials, electrode 570 can also be made of materials such as SnO, SnO2, titanium dioxide (TiO2), and 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.

[0130] Furthermore, electrode 570 may also use materials that undergo a conversion reaction in addition to silicon-containing materials. 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 for particle 582. 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.

[0131] Furthermore, in addition to silicon-containing materials, the electrode 570 can be used in combination with multiple metals, materials, compounds, etc., as described above.

[0132] Alternatively, lithium-predoped silicon material may be used. Methods of predoping include mixing silicon with lithium fluoride, lithium carbonate, etc., and heating, or using a mechanical alloy of lithium metal and silicon. Alternatively, after forming electrodes, lithium may be doped by a charge-discharge reaction in combination with an electrode made of lithium metal, etc., and then a secondary battery may be fabricated by combining the doped electrodes with a counter electrode (for example, a positive electrode to a predoped negative electrode).

[0133] Furthermore, the active material in one embodiment of the present invention preferably has fluorine in its surface layer, and more preferably has lithium, carbon, and oxygen. It is also more preferable that the surface of the active material has regions terminated by fluorine atoms or carbonate groups.

[0134] In secondary batteries, irreversible reactions, such as those between electrodes and electrolytes, can reduce charge-discharge efficiency. This decrease in efficiency is particularly noticeable during the initial charge-discharge cycle.

[0135] In one embodiment of the present invention, when a negative electrode active material having halogens in its surface layer is used, it is possible to suppress the decrease in charge-discharge efficiency. It is believed that the presence of halogens in the surface layer of the negative electrode active material in one embodiment of the present invention suppresses the reaction with the electrolyte on the surface of the active material. Furthermore, in one embodiment of the present invention, at least a portion of the surface of the negative electrode active material may be covered by a region containing halogens. This region may be, for example, in the form of a film. It is also preferable that the surface of the active material has regions terminated by halogen atoms or carbonate groups.

[0136] The surface layer is preferably a region within 50 nm from the surface, more preferably within 35 nm, and even more preferably within 20 nm. The region deeper than the surface layer is called the interior.

[0137] In one embodiment of the present invention, the negative electrode active material has a halogen on its surface, which enables excellent performance even at high charge-discharge rates in a secondary battery. Therefore, the charge-discharge rate can be increased. When the negative electrode active material has graphite internally and a halogen on its surface, halogen or halogen compounds may be inserted between the layers of graphite. The insertion of halogen or halogen compounds between the layers widens the interlayer distance on or near the surface of the graphite, making it easier for carrier ions to be inserted into and removed from the interlayer, which may enable excellent performance at high charge-discharge rates in a secondary battery. The interlayer distance of graphite can be analyzed using XRD, transmission electron microscopy, EDX analysis, etc.

[0138] In one embodiment of the present invention, the negative electrode active material has halogen, lithium, and oxygen on its surface, enabling excellent performance even at high charge-discharge rates in a secondary battery. Therefore, the charge-discharge speed can be increased. When the negative electrode active material has silicon internally and halogen on its surface, a compound having silicon, halogen, lithium, and oxygen on its surface can be formed. By having a compound having silicon, halogen, lithium, and oxygen on its surface, the diffusivity of carrier ions is improved, potentially enabling excellent performance at high charge-discharge rates in a secondary battery.

[0139] Furthermore, if the negative electrode active material in one embodiment of the present invention has a halogen on its surface, the solvent solvated by carrier ions in the electrolyte may be more easily desorbed from the surface of the negative electrode active material. This easier desorption of the solvated solvent may enable the secondary battery to achieve excellent performance at high charge-discharge rates.

[0140] In one embodiment of the present invention, the negative electrode active material preferably contains fluorine as the halogen.

[0141] Compounds containing lithium, silicon, and oxygen may also contain fluorine. Examples of compounds containing lithium, silicon, oxygen, and fluorine include those with the general formula Li x Si (1-x) O (2-y) F y It may also be a composite oxide represented by .

[0142] In one aspect of the present invention, the negative electrode active material has a region on its surface terminated by functional groups containing oxygen and carbon or by fluorine atoms, thereby improving the affinity between the negative electrode active material and the graphene compound, allowing the graphene compound to adhere closely to the negative electrode active material. Because the conductive agent can adhere closely to the active material, an electrode with high conductivity can be realized. The state of adhering closely can also be described as being in close contact. Furthermore, it can also be described as being in contact along the particle surface or being in surface contact with multiple particles.

[0143] Fluorine has high electronegativity, and the presence of fluorine on the surface of the negative electrode active material may have the effect of facilitating the removal of the solvated solvent from the surface of the negative electrode active material.

[0144] Furthermore, although particle 582 may undergo volume changes during charging and discharging, by arranging a fluorine-containing electrolyte between multiple particles 582 within the electrode, the particles become more fluid even when volume changes occur during charging and discharging, suppressing cracking and dramatically improving cycle characteristics. It is important that fluorine-containing organic compounds are present between the multiple active materials that make up the electrode.

[0145] Figures 4A, 4B, 4C, and 4D show examples of cross-sections of the negative electrode active material 400. The negative electrode active material 400 can be used as particles 582.

[0146] In the negative electrode active material 400, the cross-section can be exposed by processing, allowing for observation and analysis of the cross-section.

[0147] The negative electrode active material 400 shown in Figure 4A has region 401 and region 402. Region 402 is located outside region 401. It is also preferable that region 402 is in contact with the surface of region 401.

[0148] Preferably, at least a portion of region 402 includes the surface of the negative electrode active material 400.

[0149] Region 401 is, for example, a region that includes the interior of the negative electrode active material 400.

[0150] Region 401 contains the first material 801. Region 402 is a region formed using material 802 containing halogens and material 803 containing oxygen and carbon. Region 402 contains, for example, halogens, oxygen, carbon, metal A1, and metal A2. Examples of halogens are fluorine, chlorine, etc. Note that region 402 may not contain some of the elements among halogens, oxygen, carbon, metal A1, and metal A2. Alternatively, the concentration of some of the elements among halogens, oxygen, carbon, metal A1, and metal A2 in region 402 may be low and undetectable by analysis.

[0151] For example, one or more metals selected from lithium, magnesium, aluminum, sodium, potassium, calcium, barium, lanthanum, cerium, chromium, manganese, iron, cobalt, nickel, zinc, zirconium, titanium, vanadium, and niobium can be used as metal A1. For example, one or more metals selected from lithium, magnesium, aluminum, sodium, potassium, calcium, barium, lanthanum, cerium, chromium, manganese, iron, cobalt, and nickel can be used as metal A2.

[0152] Region 402 is sometimes referred to as the surface layer of the negative electrode active material 400, etc.

[0153] The negative electrode active material 400 can take various forms, such as a single particle, an aggregate of multiple particles, or a thin film.

[0154] Region 401 may consist of particles of the first material 801. Alternatively, region 401 may be an aggregate of multiple particles of the first material 801. Alternatively, region 401 may be a thin film of the first material 801.

[0155] Region 402 may be part of a particle. For example, region 402 may be the surface layer of a particle. Alternatively, region 402 may be part of a thin film. For example, region 402 may be the upper layer of a thin film.

[0156] Region 402 may be a coating layer formed on the surface of the particles.

[0157] Furthermore, region 402 may be a region having a bond between an element constituting the first material 801 and a halogen. For example, the surface of the first material 801 may be modified with a halogen or a halogen-containing functional group in region 402, or at the interface between region 401 and region 402. Therefore, in a negative electrode active material according to one aspect of the present invention, a bond between an element constituting the first material 801 and a halogen may be observed. For example, if the first material 801 is graphite and the halogen is fluorine, a CF bond may be observed. Also, as an example, if the first material 801 contains silicon and the halogen is fluorine, a Si-F bond may be observed.

[0158] As an example of a first material 801 having silicon and a halogen being fluorine, a compound having lithium, silicon, oxygen, and fluorine is, for example, a compound with the general formula Li x Si (1-x) O (2-y) F y It may also be a composite oxide represented by .

[0159] When the first material 801 has silicon and lithium carbonate is used as material 803 which has oxygen and carbon, region 402 may contain carbonate groups.

[0160] For example, when silicon is used as the first material 801, region 401 is silicon particles and region 402 is a coating layer over the silicon particles. Alternatively, for example, when silicon is used as the first material 801, region 401 is a region including the interior of the silicon particles and region 402 is the surface layer of the silicon particles.

[0161] Region 402 may, for example, have a bond between a halogen and carbon. It may also have a bond between a halogen and metal A1. Furthermore, region 402 may, for example, have a carbonate group.

[0162] In the example shown in Figure 4B, region 401 has an area that is not covered by region 402. Also, in the example shown in Figure 4C, region 402 that covers the recessed area on the surface of region 401 is thicker.

[0163] In the negative electrode active material 400 shown in Figure 4D, region 401 has region 401a and region 401b. Region 401a is a region that includes the interior of region 401, and region 401b is located outside region 401a. It is also preferable that region 401b is in contact with region 402.

[0164] Region 401b is the surface layer of region 401.

[0165] Region 401b contains one or more elements present in region 402, such as halogens, oxygen, carbon, metal A1, and metal A2. Furthermore, in region 401b, the elements present in region 402, such as halogens, oxygen, carbon, metal A1, and metal A2, may have a concentration gradient in which the concentration gradually decreases from the surface or near the surface towards the interior.

[0166] The halogen concentration in region 401b is higher than the halogen concentration in region 401a. Furthermore, it is preferable that the halogen concentration in region 401b is lower than the halogen concentration in region 402.

[0167] The oxygen concentration in region 401b may be higher than that in region 401a. Conversely, the oxygen concentration in region 401b may be lower than that in region 402.

[0168] Although not shown in the diagram, the surface layer of the negative electrode active material 400 may contain either one or both of the following: a halogen-containing material 802 and a material 803 containing oxygen and carbon.

[0169] When measuring a negative electrode active material according to one aspect of the present invention by energy-dispersive X-ray spectroscopy (EDX) using a scanning electron microscope (SEM), it is preferable that halogens are detected. Furthermore, it is preferable that the halogen concentration has a range of, for example, 0.6 atomic% to 20 atomic%, and more preferably 4 atomic% to 20 atomic%, with the total concentration of halogen and oxygen being 100 atomic%.

[0170] Region 402 has, for example, a thickness of 50 nm or less, more preferably 1 nm to 35 nm, and even more preferably 5 nm to 20 nm.

[0171] Region 401b has, for example, a thickness of 50 nm or less, more preferably 1 nm to 35 nm, and even more preferably 5 nm to 20 nm.

[0172] When fluorine is used as the halogen and lithium as metal A1 and metal A2, region 402 may have a region covered by the region containing lithium fluoride and a region covered by the region containing lithium carbonate. Furthermore, since region 402 does not hinder the insertion and removal of lithium, an excellent secondary battery can be realized without reducing the output characteristics of the secondary battery.

[0173] <Calculation 1> <Reactions during annealing of silicon, LiF, and Li2CO3> Next, we will explain the verification results using quantum molecular dynamics calculations regarding the surface of silicon-containing particles.

[0174] <Quantum molecular dynamics> The reactions between lithium fluoride and lithium carbonate and the surface of silicon-containing particles were investigated using quantum molecular dynamics. Here, the calculations were performed assuming the surface of the silicon-containing particles was SiO2.

[0175] Atomic relaxation calculations were performed using the first-principles electronic state calculation package VASP. The specific calculation conditions for quantum molecular dynamics are shown in Table 1.

[0176] [Table 1]

[0177] First, a mixed phase of LiF and Li2CO3 was formed. Specifically, a structure was prepared in which LiF and Li2CO3 were in contact, and the structure was relaxed for 1 ps at a temperature of 1200 K to form a mixed phase of LiF and Li2CO3.

[0178] Furthermore, structural relaxation was performed for 1 ps at a temperature of 1200K to form an SiO2 phase.

[0179] Next, the structure shown in Figure 5A was prepared as the initial state. In the structure shown in Figure 5A, the SiO2 phase, which had undergone prior structural relaxation, and the mixed phase of LiF and Li2CO3 were arranged in contact with each other. In addition, to prevent reactions from the region outside the periodic boundary, helium atoms were arranged and fixed near the periodic boundary. The number of atoms in the structure shown in Figure 5A is 64 lithium atoms, 16 carbon atoms, 40 silicon atoms, 128 oxygen atoms, 32 fluorine atoms, and 24 helium atoms.

[0180] Figure 5B shows the structure after structural relaxation at 1200 K and 1.23 ps compared to the initial state shown in Figure 5A. Diffusion of lithium atoms and fluorine atoms from the LiF and Li2CO3 mixed phase into the SiO2 phase was observed. Bonding of silicon atoms with fluorine atoms was also observed. Figure 6 shows a partial structure of Figure 5B.

[0181] Quantum molecular dynamics calculations suggested that the reaction between lithium fluoride and lithium carbonate and the surface of silicon-containing particles forms compounds containing lithium, silicon, oxygen, and fluorine.

[0182] <Calculation 2> <Silicon-containing particles and graphene compounds> The interaction between silicon-containing particles and graphene compounds was optimized and evaluated using density functional theory (DFT). Gaussian 09 was used for the optimization calculations. The main calculation conditions are shown in Table 2.

[0183] [Table 2]

[0184] Two models were used for silicon-containing particles: hydrogen-terminated silicon (model S_H) and hydroxyl-terminated silicon (model S_OH). For model S_H, the structure shown in Figure 7A, consisting of 35 silicon atoms and 35 hydrogen atoms, was used. For model S_OH, the structure shown in Figure 7B, consisting of 35 silicon atoms, 35 oxygen atoms, and 35 hydrogen atoms, was used.

[0185] A graphene structure consisting of 170 carbon atoms and 36 hydrogen atoms was used as the graphene (Model G-1). All 36 hydrogen atoms terminate at the ends of the graphene.

[0186] Five different graphene compounds were used: graphene with one carbon atom bonded to an epoxy group (Model G-2), graphene with two carbon atoms bonded to a hydroxyl group (Model G-3), graphene with two hydrogen-terminated carbon atoms (Model G-4), and graphene with two fluorine-terminated carbon atoms (Model G-5). In each model, the carbon atoms terminated to functional groups or atoms are located near the center of the graphene plane.

[0187] Figure 8 shows an example of the interaction between silicon-containing particles and a graphene compound after optimization. The optimization shows that the silicon-containing particles move closer to the graphene compound. Furthermore, the graphene compound appears to bend. This bending is thought to be due to London dispersion forces. Note that Figure 8 shows the interaction when hydroxyl-terminated silicon (model S_OH) and graphene (model G-1) approach each other.

[0188] To investigate the interaction between silicon-containing particles and graphene compounds, the stabilization energy was calculated for each combination. The results are shown in Table 3. The energy when the silicon-containing particles and graphene compounds are placed at infinity was used as a baseline, and the absolute value of the difference from the baseline was defined as the stabilization energy. In Table 3, and Table 4 described later, a higher stabilization energy value indicates greater stability.

[0189] [Table 3]

[0190] As shown in Table 3, the stabilization energy was higher for hydroxyl-terminated silicon (model S_OH) compared to hydrogen-terminated silicon (model S_H). Furthermore, graphene compounds (models G-2 to G-5) with carbon atoms bonded to functional groups, hydrogen atoms, or fluorine atoms in a two-dimensional structure formed from a six-membered carbon ring had higher stabilization energy compared to graphene (model G-1).

[0191] Figure 9A shows what happens when silicon terminated with a hydroxyl group (model S_OH) is brought close to graphene (model G-2) which has a carbon atom bonded to an epoxy group. This suggests that hydrogen bonds are formed between the oxygen on the epoxy group and the hydroxyl group on the silicon surface.

[0192] Figure 9B shows what happens when silicon terminated with a hydroxyl group (model S_OH) and graphene with a carbon atom bonded to a hydroxyl group (model G-3) are brought close together. This suggests that hydrogen bonds are formed between the hydroxyl groups of both materials.

[0193] Figure 10A shows what happens when silicon terminated with a hydroxyl group (model S_OH) is brought close to graphene (model G-4) which has carbon terminated with a hydrogen atom. This suggests that hydrogen bonds are formed between the hydrogen atoms of graphene and the hydroxyl groups on the silicon surface.

[0194] Figure 10B shows what happens when silicon terminated with a hydroxyl group (model S_OH) is brought close to graphene (model G-5) which has carbon terminated with a fluorine atom. This suggests that hydrogen bonds are formed between the fluorine atom on the graphene and the hydroxyl group on the silicon surface.

[0195] It is believed that the stabilization energy is increased by the formation of hydrogen bonds between the silicon surface and the graphene compound, as the silicon surface is terminated with hydroxyl groups.

[0196] Next, we examined a model in which graphene has pores.

[0197] Figures 11A and 11B show an example of the structure of a graphene compound with pores.

[0198] The structure shown in Figure 11A (hereinafter referred to as Model G-22H8) has a 22-membered ring, and eight of the carbon atoms constituting the 22-membered ring are each terminated with hydrogen. Model G-22H8 has a structure in graphene 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.

[0199] The structure shown in Figure 11B (hereinafter referred to as Model G-22H6F2) has a 22-membered ring, and of the eight carbon atoms constituting the 22-membered ring, six are terminated with hydrogen and two are terminated with fluorine. Model G-22H6F2 has a structure in graphene 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.

[0200] The stabilization energy was calculated for combinations of silicon-containing particles and porous graphene compounds. The results are shown in Table 4.

[0201] [Table 4]

[0202] As shown in Table 4, hydroxyl-terminated silicon (model S_OH) has a higher stabilization energy than hydrogen-terminated silicon (model S_H), suggesting greater interaction with porous graphene compounds.

[0203] Figure 12A shows what happens when a hydroxyl-terminated silicon (model S_OH) is brought close to model G-22H8. Figure 12B is a magnified view including the region where the hydroxyl-terminated silicon (model S_OH) and model G-22H8 are close together. As shown by the dashed line in Figure 12B, it is suggested that hydrogen bonds are formed between the hydrogen atoms of graphene and the hydroxyl groups on the silicon surface.

[0204] Figure 13A shows what happens when a hydroxyl-terminated silicon (model S_OH) and model G-22H6F2 are brought close together. Figure 13B is an enlarged view including the region where the hydroxyl-terminated silicon (model S_OH) and model G-22H6F2 are close together. As shown by the dashed line in Figure 13B, it is suggested that hydrogen bonds are formed between the hydrogen atoms of graphene and the oxygen atoms of the hydroxyl groups on the silicon surface. It is also suggested that hydrogen bonds are formed between the fluorine atoms of graphene and the hydrogen atoms of the hydroxyl groups on the silicon surface.

[0205] The presence of fluorine in addition to hydrogen in the graphene compound suggests that, in addition to the hydrogen bond between the oxygen atom of the hydroxyl group and the hydrogen atom of the graphene compound, a hydrogen bond is also formed between the hydrogen atom of the hydroxyl group and the fluorine atom of the graphene compound. This strengthens the interaction between the silicon-containing particles and the graphene compound, and further increases the stabilization energy.

[0206] On the other hand, as shown in Table 4, the stabilization energy with graphene compounds having two types of pores was lower for hydrogen-terminated silicon (model S_H) than for hydroxyl-terminated silicon (model S_OH).

[0207] It is believed that the silicon surface is terminated by hydroxyl groups, and the graphene compound has pores terminated by hydrogen and fluorine, which leads to the formation of hydrogen bonds and a higher stabilization energy.

[0208] Next, we calculated the interaction between the silicon-containing particles and the graphene compound when the particles are silicon oxide. A structure consisting of 20 silicon atoms, 28 hydrogen atoms, and 54 oxygen atoms was used as the silicon oxide model (hereinafter referred to as Model S_Ox). The terminal dangling bonds were terminated with hydroxyl groups.

[0209] Table 5 shows the results of calculating the stabilization energy. Figure 14A shows the optimized state of silicon oxide and graphene with hydroxyl-terminated carbon (model G-3), and Figure 14B shows the optimized state of silicon oxide and graphene with fluorine-terminated carbon (model G-5).

[0210] [Table 5]

[0211] The study suggested that even in silicon oxide terminated by hydroxyl groups, the presence of functional groups and pores in the graphene compound strengthens the bond.

[0212] 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.

[0213] <Calculation 3> <Interaction between graphene compounds and silicon-containing particles> This paper presents calculation results regarding the interaction between silicon containing oxygen, carbon, and lithium regions and graphene compound 583. The morphological changes due to the interaction between graphene compound 583 and particle 582 were calculated using dissipative particle dynamics (DPD). HOOMD-blue (version 2.9.0) was used for the calculations. Particle 582 is assumed to be a silicon-containing particle. Table 6 shows the Lennard-Jones potential parameters used in the calculations for the particles constituting graphene compound 583 and the silicon-containing particle 582. Compared to calculation condition C-1, calculation condition C-2 was set to increase the attractive forces between the particles constituting graphene compound 583 and the silicon-containing particle 582, as well as the attractive forces between two silicon-containing particles 582. Calculation condition C-1 assumes silicon that has not undergone lithium carbonate treatment, while calculation condition C-2 assumes silicon that has undergone lithium carbonate treatment (silicon containing regions with oxygen, carbon, and lithium). Silicon treated with lithium carbonate will be discussed later.

[0214] [Table 6]

[0215] Figure 15 shows the initial configuration of the calculation models for the graphene compound and silicon-containing particles under calculation conditions C-1 and C-2. In Figure 15, the graphene compound is represented as a single sheet of 400 particles bonded together, and five graphene compounds are placed in the model. Also in Figure 15, 245 silicon-containing particles are placed in the model as independent particles. Note that the graphene compound and silicon-containing particles shown in Figures 15 to 17 are coarse-grained, and the graphene compound is assumed to have a carbon hexagonal network surface.

[0216] Figures 16A and 16B show the arrangement after a certain period of time has elapsed using the dissipative particle dynamics method under calculation condition C-1. Figure 16A illustrates both graphene compound and silicon-containing particles, while Figure 16B illustrates only silicon-containing particles.

[0217] Figures 17A and 17B show the arrangement after a certain period of time has elapsed using the dissipative particle dynamics method under calculation condition C-2. Figure 17A illustrates both graphene compound and silicon-containing particles, while Figure 17B illustrates only silicon-containing particles.

[0218] Comparing Figures 16B and 17B, it can be seen that under calculation condition C-2, which assumes silicon treated with lithium carbonate, there is a high degree of aggregation of silicon particles.

[0219] Figures 18A and 18B show the calculation results of the radial distribution function under calculation conditions C-1 and C-2. The radial distribution function shows the distance from a given particle and the probability distribution of the presence of other particles. Figure 18A shows the radial distribution function between silicon-containing particles, and Figure 18B shows the radial distribution function between silicon-containing particles and graphene compounds. As shown in Figure 18A, it can be seen that under calculation condition C-2, there are more other silicon-containing particles near the silicon-containing particles compared to calculation condition C-1. Also, as shown in Figure 18B, it can be seen that under both calculation conditions C-1 and C-2, the probability of graphene compounds being present around silicon-containing particles is high. Therefore, under calculation condition C-2, which assumes lithium carbonate-treated silicon, it is possible for both aggregation of silicon-containing particles and adhesion of graphene compounds to silicon-containing particles to occur simultaneously.

[0220] <Method for preparing negative electrode active material 1> A negative electrode active material according to one aspect of the present invention can be produced, for example, by mixing a first material 801 that can contribute to the reaction of a secondary battery with a second material and then performing a heat treatment. In addition, a third material that undergoes a eutectic reaction with the second material may be mixed as a third material in addition to the second material. This makes it possible to produce a negative electrode active material that has been found in the electrode shown in Example 1 of the electrode.

[0221] A method for producing a negative electrode active material according to one aspect of the present invention will be explained with reference to Figure 19. Figure 19 shows an example in which a halogen-containing material 802 is used as the second material, and a material 803 containing oxygen and carbon is used as the third material.

[0222] The eutectic point resulting from the eutectic reaction is preferably lower than at least one of the melting points of the halogen-containing material 802 and the oxygen and carbon-containing material 803. The decrease in melting point due to the eutectic reaction makes it easier for the halogen-containing material 802 and the oxygen and carbon-containing material 803 to cover the surface of the first material 801 during heat treatment, potentially improving coverage.

[0223] Furthermore, by using materials containing a metal whose ions function as carrier ions in the reaction of a secondary battery, as the halogen-containing material 802 and the oxygen and carbon-containing material 803, if the negative electrode active material contains the metal, it may be possible to contribute to charging and discharging as a carrier ion.

[0224] As the material 803 having oxygen and carbon, for example, a material 803 having oxygen and carbon can be used. As the material having oxygen and carbon, for example, a carbonate can be used. Alternatively, as the material having oxygen and carbon, for example, an organic compound can be used. It may also be used as an organic compound.

[0225] Alternatively, a hydroxide may be used as the material 803 having oxygen and carbon.

[0226] Carbonates, hydroxides, etc., are preferred because many of them are inexpensive and highly safe materials. Furthermore, carbonates, hydroxides, etc., may form eutectic points with materials containing halogens, which is also preferable.

[0227] Furthermore, the negative electrode active material described below may have the effect of increasing conductivity at the electrode. In addition, if it has the effect of increasing conductivity, the amount of reaction between the negative electrode active material and carrier ions described below may be small.

[0228] Furthermore, the method for producing the negative electrode active material described below may be applied to the method for producing the conductive agent. For example, as a fluorine modification of graphene as a conductive agent, in the flow chart of Figure 19 described below, the first material 801 is graphene, and steps S31 to S53 are performed to obtain fluorine-modified graphene as a conductive material.

[0229] Let's look at a more specific example of material 802 containing halogens and material 803 containing oxygen and carbon. When lithium fluoride is used as material 802 containing halogens, when it is mixed with the first material 801 and heated, the lithium fluoride may not coat the surface of the first material, and may instead aggregate on its own. In such cases, using a material 803 containing oxygen and carbon that undergoes a eutectic reaction with lithium fluoride may improve the coating properties on the surface of the first material.

[0230] As an example of material 803 having oxygen and carbon that undergoes a eutectic reaction with lithium fluoride, lithium carbonate will be described.

[0231] Regarding the relationship between the ratio of LiF and Li2CO3 and the temperature, the melting point of LiF is approximately 850°C, but the melting point can be lowered by mixing it with Li2CO3. Therefore, for example, at the same heating temperature, using a mixture of LiF and Li2CO3 makes it easier to dissolve compared to using LiF alone, and can improve the coating properties on the surface of the first material. In addition, the heating temperature can be lowered.

[0232] In particular, the melting point is lowest (approximately 615°C) when the molar amount of LiF relative to the total molar amounts of LiF and Li2CO3 [LiF / (Li2CO3+LiF)] is approximately 0.48. That is, if the molar ratio of LiF to Li2CO3 is LiF:Li2CO3=a1:(1-a1), the melting point can be lowest by setting a1 to a value around 0.48.

[0233] Furthermore, by setting a1 to a value greater than 0.48, the surface of the first material can be coated with a material having a higher fluorine content. Therefore, a1 is preferably greater than 0.2, and more preferably 0.3 or higher. However, if the fluorine content is too high, the coating performance may deteriorate due to an increase in the melting point. For example, a1 is preferably less than 0.9, and more preferably 0.8 or lower.

[0234] An example of a method for producing a negative electrode active material according to one embodiment of the present invention will be explained using the flow chart shown in Figure 19.

[0235] In step S21, the first material 801 is prepared.

[0236] It is preferable to use a material as the first material 801 that can react with carrier ions of a secondary battery, a material that can insert and remove carrier ions, a material that can react with a metal that will become a carrier ion, a material that can dissolve and precipitate a metal that will become a carrier ion, etc.

[0237] For example, alkali metal ions such as lithium ions, sodium ions, and potassium ions, or alkaline earth metal ions such as calcium ions, strontium ions, barium ions, beryllium ions, and magnesium ions can be used as carrier ions in secondary batteries.

[0238] Further, as the first material 801, for example, a metal, material or compound having one or more elements selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium can be used.

[0239] As silicon, nanosilicon can be used. The average diameter of the nanosilicon is, for example, preferably 5 nm or more and less than 1 μm, more preferably 10 nm or more and 300 nm or less, still more preferably 10 nm or more and 100 nm or less.

[0240] The nanosilicon may have a spherical form, a flattened spherical form, or a rectangular parallelepiped form with rounded corners. The size of the nanosilicon is, for example, as the D50 of laser diffraction particle size distribution measurement, preferably 5 nm or more and less than 1 μm, more preferably 10 nm or more and 300 nm or less, still more preferably 10 nm or more and 1 hundred nm or less.

[0241] The nanosilicon may have crystallinity. Further, the nanosilicon may have a crystalline region and an amorphous region.

[0242] Further, nitrogen, phosphorus, arsenic, boron, aluminum, gallium, etc. may be added to silicon as an additive element to reduce the resistance.

[0243] As a material containing silicon, for example, a material represented by SiO x (x is preferably less than 2, more preferably 0.5 or more and 1.6 or less) can be used.

[0244] As a material containing silicon, for example, a form having a plurality of crystal grains in one particle can be used. For example, a form having one or more silicon crystal grains in one particle can be used. Further, the one particle may have silicon oxide around the silicon crystal grains. Further, the silicon oxide may have an amorphous region.

[0245] Also, for example, Li2SiO3 and Li4SiO4 can be used as the particles containing silicon. Li2SiO3 and Li4SiO4 may each be crystalline or amorphous.

[0246] Analysis of the particles containing silicon can be performed using NMR, XRD, Raman spectroscopy, etc.

[0247] Also, for example, carbon materials such as graphite, graphitizable carbon, non-graphitizable carbon, carbon nanotubes, carbon black, and graphene can be used as the first material 801.

[0248] Also, for example, an oxide having one or more elements selected from titanium, niobium, tungsten, and molybdenum can be used as the first material 801.

[0249] A plurality of the metals, materials, compounds, etc. shown above can be combined and used as the first material 801.

[0250] When heating the first material 801, a reaction with oxygen in the atmosphere may occur during the heating, and an oxide film may be formed on the surface.

[0251] Here, silicon is prepared as the first material 801. As the silicon, single crystal silicon, polycrystalline silicon, amorphous silicon, etc. can be used. Also, it may have a crystalline region and an amorphous region. Nitrogen, phosphorus, arsenic, boron, aluminum, gallium, etc. may be added as additive elements to the silicon to reduce the resistance.

[0252] As the silicon, silicon nanoparticles can be used. The average diameter of the silicon nanoparticles is, for example, preferably 5 nm or more and less than 1 μm, more preferably 10 nm or more and 300 nm or less, still more preferably 10 nm or more and 100 nm or less.

[0253] Silicon particles preferably have oxygen in their surface layer. Due to the effect of adsorbed water, the surface of the silicon particles may be terminated with O or OH.

[0254] In step S22, a second material, a halogen-containing material 802, is prepared. As the halogen-containing material, a halogen compound having metal A1 can be used. As metal A1, one or more selected from lithium, magnesium, aluminum, sodium, potassium, calcium, barium, lanthanum, cerium, chromium, manganese, iron, cobalt, nickel, zinc, zirconium, titanium, vanadium, and niobium can be used. As the halogen compound, for example, a fluoride or chloride can be used. Here, lithium fluoride is prepared as an example.

[0255] In step S23, a third material, material 803 having oxygen and carbon, is prepared. As the material having oxygen and carbon, for example, a carbonate having metal A2 can be used. As metal A2, for example, one or more selected from lithium, magnesium, aluminum, sodium, potassium, calcium, barium, lanthanum, cerium, chromium, manganese, iron, cobalt, and nickel can be used. Here, lithium carbonate is prepared as an example.

[0256] Next, in step S31, the first material 801, the halogen-containing material 802, and the oxygen and carbon-containing material 803 are mixed, the mixture is recovered in step S32, and the mixture 804 is obtained in step S33.

[0257] The halogen-containing material 802 and the oxygen and carbon-containing material 803 are preferably mixed in the ratio (halogen-containing material 802):(oxygen and carbon-containing material 803)=a1:(1-a1) [unit is moles], where a1 is preferably greater than 0.2 and less than 0.9, and more preferably between 0.3 and 0.8.

[0258] Furthermore, it is preferable to mix the first material 801 and the halogen-containing material 802 in a ratio of (first material 801):(halogen-containing material 802)=1:b1 [unit is moles], where b1 is preferably 0.001 or more and 0.2 or less.

[0259] Next, in step S51, the mixture 804 is heated.

[0260] Heating under a reducing atmosphere is preferable because it suppresses oxidation of the surface of the first material 801 and the reaction between the first material 801 and oxygen. For example, the reducing atmosphere can be a nitrogen atmosphere or a noble gas atmosphere. Alternatively, a mixture of two or more gases from nitrogen and noble gases may be used. Heating may also be carried out under reduced pressure.

[0261] When the melting point of the halogen-containing material 802 is expressed as M2[K], the heating temperature is preferably higher than (M2-550)[K] and lower than (M2+50)[K], and more preferably between (M2-400)[K] and (M2)[K].

[0262] Furthermore, solid-phase diffusion is more likely to occur in compounds at temperatures above the Tammann temperature. For example, the Tammann temperature is 0.757 times the melting point for oxides. Therefore, it is preferable that the heating temperature is 0.757 times or higher than the melting point or eutectic point, or a temperature near those points.

[0263] Furthermore, as a typical example of a halogen-containing material, lithium fluoride shows a rapid increase in evaporation rate above its melting point. Therefore, for example, it is preferable that the heating temperature be below the melting point of the halogen-containing material.

[0264] The eutectic points of material 802 containing halogens and material 803 containing oxygen and carbon are M 23 When expressed as [K], the heating temperature is, for example, (M 23 It is preferable that it is higher than (M2+50)[K] and lower than (M 23It is preferably not less than (M × 0.75)[K] and not more than (M2 + 20)[K], and 23 it is preferably not less than (M × 0.75)[K] and not more than (M2 + 20)[K], and M 23 is preferably higher than M[K] and lower than (M2 + 10)[K], and (M 23 is more preferably not less than (M × 0.8)[K] and not more than M2[K], and (M 23 ) is more preferably not less than [K] and not more than M2[K].

[0265] When lithium fluoride is used as the material 802 having halogen and lithium carbonate is used as the material 803 having oxygen and carbon, the heating temperature is preferably, for example, greater than 350°C and less than 900°C, more preferably 390°C or higher and 850°C or lower, still more preferably 520°C or higher and 910°C or lower, still more preferably 570°C or higher and 860°C or lower, and still more preferably 610°C or higher and 860°C or lower.

[0266] The heating time is preferably, for example, not less than 1 hour and not more than 60 hours, and more preferably not less than 3 hours and not more than 20 hours.

[0267] When silicon particles are used as the first material 801, lithium fluoride is used as the material 802 having halogen, and lithium carbonate is used as the material 803 having oxygen and carbon during heating, the reaction of the following chemical reaction formula (1) may occur on the surface portion of the silicon particles. Note that silicon particles usually have a natural oxide film formed on the surface under normal atmospheric conditions, and it is known that the surface termination becomes O or OH due to the influence of adsorbed water on the surface. In the chemical reaction formula (1), it is expressed as SiOx(OH)y

[0268]

Number

[0269] By heating, one or more elements such as halogen, oxygen, carbon, metal A1, and metal A2 may diffuse into the surface layer of the first material 801. The presence of these elements in the first material may facilitate the insertion and removal of carrier ions. It may also facilitate the desolvation of carrier ions. Alternatively, it may suppress the collapse of the crystal structure of the first material 801 caused by repeated insertion and removal of carrier ions.

[0270] It is particularly preferable that the halogen contains fluorine.

[0271] When silicon is used for the first material 801 and lithium fluoride for the halogen-containing material 802, heating may form a compound containing lithium, silicon, and oxygen on the surface of the first material 801. Depending on the heating conditions, the entire first material 801 may become a compound containing lithium, silicon, and oxygen. Examples of compounds containing lithium, silicon, and oxygen include Li2SiO3 and Li4SiO4. Li2SiO3 and Li4SiO4 may be crystalline or amorphous. The compound containing lithium, silicon, and oxygen may further contain fluorine. Furthermore, the surface may have functional groups containing oxygen and carbon, functional groups containing oxygen atoms, or regions terminated by fluorine atoms.

[0272] Compounds containing lithium, silicon, and oxygen may also contain fluorine. Examples of compounds containing lithium, silicon, oxygen, and fluorine include those with the general formula Li x Si (1-x) O (2-y) F y It may also be a composite oxide represented by .

[0273] Next, in step S52, the heated mixture is recovered, and in step S53, particles 805 are obtained. The particles 805 can be used as particles 582 in the negative electrode active material layer.

[0274] By following the steps described above, a negative electrode active material according to one embodiment of the present invention can be obtained.

[0275] When particle 805 contains a compound with lithium, silicon, and oxygen in its surface layer, insertion and desolvation of carrier ions may become easier in particle 805. Furthermore, desolvation of carrier ions may become easier. Alternatively, the collapse of the crystal structure of particle 805 due to repeated insertion and desolvation of carrier ions may be suppressed.

[0276] If the surface of particle 805 has functional groups containing oxygen and carbon, functional groups having oxygen atoms, or regions terminated by fluorine atoms, and hydrogen bonding regions are formed by hydrogen atoms contained in the functional groups of the graphene compound, then the graphene compound can adhere tightly to particle 805 through the action of intermolecular forces or the like.

[0277] <Method for preparing negative electrode active material 2> A negative electrode active material according to one aspect of the present invention can be produced, for example, by mixing a first material 801 that can contribute to the reaction of a secondary battery with a material 803 having oxygen and carbon, and then performing a heat treatment. This makes it possible to produce the negative electrode active material shown in Example 2 of the electrode.

[0278] Furthermore, by using a material 803 containing oxygen and carbon that has a metal whose ions function as carrier ions in the reaction of a secondary battery, if the negative electrode active material contains the metal, it may be possible to contribute to charging and discharging as a carrier ion.

[0279] Furthermore, as the material 803 having oxygen and carbon, for example, a carbonate can be used. Alternatively, as the material having oxygen and carbon, for example, an organic compound can be used.

[0280] An example of a method for producing a negative electrode active material according to one embodiment of the present invention will be explained using the flow chart shown in Figure 20.

[0281] In step S21, the first material 801 is prepared.

[0282] The aforementioned material can be used as the first material 801.

[0283] Here, silicon is prepared as the first material 801. Single-crystal silicon, polycrystalline silicon, amorphous silicon, etc., can be used as the silicon. It may also have both crystalline and amorphous regions. Nitrogen, phosphorus, arsenic, boron, aluminum, gallium, etc., may be added to the silicon as additive elements to reduce its resistance.

[0284] Nanosilicon can be used as the silicon. The average diameter of the nanosilicon 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.

[0285] Silicon preferably has oxygen in its surface layer. Due to the effect of adsorbed water, the surface of silicon may be terminated with O or OH.

[0286] In step S22, a material 803 having oxygen and carbon is prepared. As the material 803 having oxygen and carbon, for example, a carbonate having metal A1 can be used. As metal A1, for example, one or more selected from lithium, magnesium, aluminum, sodium, potassium, calcium, barium, lanthanum, cerium, chromium, manganese, iron, cobalt, and nickel can be used.

[0287] Here, lithium carbonate is prepared as material 803, which contains oxygen and carbon.

[0288] Next, in step S31, the first material 801 and the material 803 having oxygen and carbon are mixed, the mixture is recovered in step S32, and the mixture 856 is obtained in step S33. During recovery, crushing and sieving may be carried out as necessary.

[0289] Furthermore, it is preferable to mix the first material 801 and the material 803 having oxygen and carbon in a ratio of (first material 801):(material 803 having oxygen and carbon)=1:a1 [unit is moles], where a1 is preferably 0.001 or more and 0.2 or less.

[0290] Next, in step S51, the mixture 856 is heated.

[0291] Heating under a reducing atmosphere is preferable because it suppresses oxidation of the surface of the first material 801 and the reaction between the first material 801 and oxygen. For example, the reducing atmosphere can be a nitrogen atmosphere or a noble gas atmosphere. Alternatively, a mixture of two or more gases from nitrogen and noble gases may be used. Heating may also be carried out under reduced pressure.

[0292] Furthermore, solid-phase diffusion is more likely to occur in compounds at temperatures above the Tammann temperature. For example, the Tammann temperature is 0.757 times the melting point for oxides. Therefore, it is preferable that the heating temperature is 0.757 times or higher than the melting point or eutectic point, or a temperature near those points.

[0293] When lithium carbonate is used as the oxygen and carbon-containing material 803, the heating temperature is preferably, for example, greater than 350°C and less than 900°C, more preferably between 390°C and 850°C, even more preferably between 520°C and 910°C, even more preferably between 570°C and 860°C, and even more preferably between 610°C and 860°C.

[0294] The heating time is preferably between 1 hour and 60 hours, and more preferably between 3 hours and 20 hours.

[0295] Next, in step S52, the heated mixture is recovered, and in step S53, particles are obtained. The particles 807 can be called the negative electrode active material. Also, when silicon is used as the first material 801 and lithium carbonate is used as the material 803 having oxygen and carbon, the particles 807 can be called lithium carbonate treated silicon. The particles 807 can be used as particles 582 in the negative electrode active material layer.

[0296] Heating may cause one or more of the elements A1, oxygen, and carbon to diffuse into the surface layer of particle 582. The presence of these elements in particle 582 may facilitate the insertion and removal of carrier ions. It may also facilitate the desolvation of carrier ions. Alternatively, it may suppress the deformation of particle 582 caused by repeated insertion and removal of carrier ions. Alternatively, multiple particles may become more prone to agglomeration, and sheet-like materials may adhere more easily to the particles.

[0297] By following the steps described above, a negative electrode active material according to one embodiment of the present invention can be obtained.

[0298] If particle 582 has a compound containing one or more lithium, silicon, oxygen, and carbon in its surface layer, insertion and detachment of carrier ions may become easier in particle 582. Also, desolvation of carrier ions may become easier. Alternatively, the deformation of particle 582 caused by repeated insertion and detachment of carrier ions may be suppressed. Alternatively, multiple particles 582 may become more prone to agglomeration, and the sheet-like graphene compound 583 may become more prone to clinging to particle 582.

[0299] If the surface of particle 582 has functional groups containing oxygen and carbon, functional groups having oxygen atoms, or regions terminated by fluorine atoms, and hydrogen bonding regions are formed by hydrogen atoms contained in the functional groups of graphene compound 583, then graphene compound 583 can adhere tightly to particle 582 through the action of intermolecular forces or the like.

[0300] <Method for fabricating electrodes> Figure 21 is a flowchart showing an example of a method for manufacturing an electrode according to one aspect of the present invention.

[0301] First, in step S71, silicon-containing particles are prepared. As silicon-containing particles, the particles described as particle 582 above can be used, for example, particle 805 shown in the negative electrode active material preparation method 1 and / or particle 807 shown in the negative electrode active material preparation method 2 can be used.

[0302] In step S72, 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).

[0303] Next, in step S73, the silicon-containing particles prepared in step S71 and the solvent prepared in step S72 are mixed, the mixture is recovered in step S74, and mixture E-1 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.

[0304] Next, in step S80, the graphene compound is prepared.

[0305] Next, in step S81, mixture E-1 is mixed with the graphene compound prepared in step S80, and in step S82, the mixture is recovered. It is preferable that the recovered mixture has high viscosity. The high viscosity of the mixture allows for solid kneading (kneading at high viscosity) in the next step S83.

[0306] 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.

[0307] 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.

[0308] It is preferable to repeat steps S83 to S85 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.

[0309] After repeating steps S83 to S85 n times, mixture E-2 is obtained (step S86).

[0310] 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.

[0311] Next, in step S88, mixture E-2 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 S72 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.

[0312] Next, the mixture whose viscosity was adjusted in step S89 is mixed in step S90 and recovered in step S91 to obtain mixture E-3 (step S92). The mixture E-3 obtained in step S92 is called, for example, a slurry.

[0313] Next, in step S93, the current collector is prepared.

[0314] Next, in step S94, the mixture E-3 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.

[0315] 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 50°C to 200°C, preferably 60°C to 150°C.

[0316] For example, the material can be heated on a hot plate in an air atmosphere at a temperature between 30°C and 70°C for at least 10 minutes, and then heated again in a reduced-pressure environment at a temperature between room temperature and 100°C for at least 1 to 10 hours.

[0317] 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.

[0318] 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.

[0319] 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. Or, a dehydration reaction of polyimide may occur during the first 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.

[0320] The second heating should be carried out in a temperature range of 150°C to 500°C, preferably 200°C to 450°C.

[0321] For example, the heat treatment can be performed at a temperature between 200°C and 450°C for a period of 1 to 10 hours under reduced pressure of 10 Pa or less, or under an inert atmosphere such as nitrogen or argon.

[0322] In step S97, an electrode is obtained in which an active material layer is provided on the current collector.

[0323] 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.

[0324] The active material layer may be formed on both sides of the current collector, or on only one side. Alternatively, it may have regions where the active material layer is formed on both sides in part.

[0325] After volatilizing the solvent from the active material layer, pressing may be performed by a compression method such as a roll press method or a flat press method. When pressing, heat may be applied.

[0326] <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.

[0327] It is preferable to use a positive electrode active material having a layered crystal structure as the positive electrode active material of one aspect of the present invention.

[0328] 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) can be used. Here, the metal M may have one or more metals selected from cobalt, nickel, manganese, aluminum, iron, vanadium, chromium, and niobium (herein represented as metal M).

[0329] In addition to the metals listed above, the metal M can further contain a metal X. The metal X is a metal other than cobalt, and as the metal X, for example, one or more metals such as magnesium, calcium, zirconium, lanthanum, barium, copper, potassium, sodium, and zinc can be used. Particularly, it is preferable to use magnesium as the metal X.

[0330] In addition to the metals listed above, the metal M can further contain a metal Z. The metal Z is a metal other than cobalt, and as the metal Z, for example, one or more metals selected from nickel, aluminum, manganese, titanium, vanadium, and chromium can be used. Particularly, it is preferable to add one or more of nickel and aluminum as the metal Z.

[0331] LiMx O y Examples of the lithium-containing composite oxide represented by include LiCoO2, LiNiO2, LiMnO2, etc. Further, NiCo-based represented by LiNi x Co 1-x O2 (0 < x < 1), and NiMn-based represented by LiM x O y Examples of the lithium-containing composite oxide represented by include LiNi x Mn 1-x O2 (0 < x < 1), etc.

[0332] Further, examples of the lithium-containing composite oxide represented by LiMO2 include NiCoMn-based (also referred to as NCM) represented by LiNi x Co y Mn z 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.

[0333] Further, 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.

[0334] In a cathode 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 high lithium content per volume and a high capacity per volume. In such a cathode 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. In addition, the crystal structure may collapse during charge and discharge, which may inhibit high-speed charging or high-speed discharging.

[0335] Further, it is preferable to mix a lithium-containing material having a spinel-type crystal structure containing manganese such as LiMn2O4 as a cathode active material with lithium nickelate (LiNiO2 or LiNi 1-x M x O2 (0 < x < 1) (M = Co, Al, etc.)). By adopting such a configuration, the characteristics of the secondary battery can be improved.

[0336] Further, as the cathode active material, a composition formula Li a Mn b M c O dA 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.

[0337] [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.

[0338] 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.

[0339] ​In nickel-containing compounds, distortion can easily occur due to the Jahn-Teller effect. Therefore, when LiNiO2 is charged and discharged at high voltages, 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 and discharging, making it preferable.

[0340] The positive electrode active material will be explained using Figures 22 to 25. Figures 22 to 25 describe the case where cobalt is used as the metal M in the positive electrode active material.

[0341] <Conventional positive electrode active material> The positive electrode active material shown in Figure 24 is lithium cobalt oxide (LiCoO2) without halogen and magnesium added, prepared using the method described later. As shown in Figure 24, the crystal structure of lithium cobalt oxide changes depending on the depth of charge.

[0342] As shown in Figure 24, 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.

[0343] 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.

[0344] 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 24, the c-axis of the H1-3 type crystal structure is shown as half the unit cell for easier comparison with other structures.

[0345] 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 O3' type crystal structure in one aspect 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 O3' type crystal structure and the H1-3 type structure, and that the O3' type crystal 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.

[0346] 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.

[0347] However, these two crystal structures exhibit a large displacement of the CoO2 layer. As shown by the dotted line and arrows in Figure 24, 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.

[0348] 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%.

[0349] In addition, the H1-3 type crystal structure, which consists of continuous CoO2 layers such as P-3m1(O1), is likely to be unstable.

[0350] 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.

[0351] <Cathode active material> A positive electrode active material 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, a positive electrode active material according to one aspect of the present invention can achieve excellent cycle characteristics. In addition, a positive electrode active material according to one aspect of the present invention can adopt a stable crystal structure in a high-voltage charged state. Therefore, a positive electrode active material according to one aspect of the present invention may be less prone to short circuits when a high-voltage charged state is maintained. In such cases, safety is further improved, which is preferable.

[0352] In one embodiment of the present invention, the positive electrode active material exhibits small changes in crystal structure and a small difference in volume per unit of the same number of transition metal atoms between a fully discharged state and a high-voltage charged state.

[0353] Figure 22 shows the crystal structure of the positive electrode active material before and after charging and discharging. The positive electrode active material is a composite oxide containing lithium, cobalt as metal M, and oxygen. In addition to the above, it is preferable to have magnesium, aluminum, nickel, titanium, and zirconium as additives. It is also preferable to have halogens such as fluorine, chlorine, and bromine as additives.

[0354] The crystal structure at charge depth 0 (discharge state) in Figure 22 is R-3m(O3), the same as in Figure 24. On the other hand, the positive electrode active material, at a fully charged charge depth, has a crystal structure different from the H1-3 type crystal structure. 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 pseudo-spinel type crystal structure. Accordingly, the O3' type crystal structure may be rephrased as the pseudo-spinel type crystal structure. Note that in the crystal structure diagram of the O3' type crystal structure shown in Figure 22, 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 of, for example, less than 20 atomic percent relative to cobalt is present between the CoO2 layers. Furthermore, in both the O3-type and O3'-type crystal structures, it is preferable that magnesium be present in a dilute manner between the CoO2 layers, i.e., at the lithium sites. It is also preferable that halogens such as fluorine be present randomly and dilutely at the oxygen sites.

[0355] Furthermore, in the O3' type crystal structure, 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.

[0356] Furthermore, the O3' type crystal structure can be described as a crystal structure similar to the CdCl2 type crystal structure, although it has Li randomly placed between layers. This crystal structure similar to the CdCl2 type is observed when lithium nickelate is charged to a depth of charge of 0.94 (Li 0.06Although 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.

[0357] In one embodiment of the present invention, the change in crystal structure when charged at high voltage and a large amount of lithium is released is suppressed compared to conventional positive electrode active materials. For example, as shown by the dotted line in Figure 22, there is almost no displacement of the CoO2 layer in these crystal structures.

[0358] More specifically, the positive electrode active material according to one embodiment of the present invention exhibits high structural stability even at high charging voltages. For example, in conventional positive electrode active materials, there is a charging voltage range in which the R-3m(O3) crystal structure can be maintained even at a charging voltage that results in an H1-3 type crystal structure, for example, a voltage of about 4.6V relative to the potential of lithium metal. Furthermore, there is a range in which an O3' type crystal structure can be adopted even at a higher charging voltage, for example, a voltage of about 4.65V to 4.7V relative to the potential of lithium metal. Only when the charging voltage is increased even further may an H1-3 type crystal be observed. In addition, in secondary batteries, for example, when graphite is used as the negative electrode active material, there is a charging voltage range in which the R-3m(O3) crystal structure can be maintained even when the voltage of the secondary battery is 4.3V to 4.5V. Furthermore, there is a range in which an O3' type crystal structure can be adopted even at a higher charging voltage, for example, a voltage of 4.35V to 4.55V relative to the potential of lithium metal.

[0359] Therefore, in the positive electrode active material according to one aspect of the present invention, the crystal structure is less likely to collapse even when repeatedly charged and discharged at high voltage.

[0360] Furthermore, in the positive electrode active material, the difference in volume per unit cell between the O3-type crystal structure at a charging depth of 0 and the O3'-type crystal structure at a charging depth of 0.8 is 2.5% or less, more specifically 2.2% or less.

[0361] Furthermore, the O3' type crystal structure can be represented by showing the coordinates of cobalt and oxygen in the unit cell as follows: Co(0,0,0.5), O(0,0,x), within the range of 0.20≦x≦0.25.

[0362] Additives such as magnesium, which are randomly and dilutely present between CoO2 layers, i.e., at lithium sites, have the effect of suppressing the displacement of the CoO2 layers. Therefore, when magnesium is present between CoO2 layers, an O3' type crystal structure is more likely to be formed. For this reason, it is preferable that magnesium be present in at least a part of the surface layer of the particles of the positive electrode active material according to one embodiment of the present invention, preferably in more than half of the surface layer of the particles, and more preferably in the entire surface layer of the particles. Furthermore, in order to distribute magnesium throughout the entire surface layer of the particles, it is preferable to perform a heat treatment in the manufacturing process of the positive electrode active material according to one embodiment of the present invention.

[0363] However, if the heat treatment temperature is too high, cation mixing will occur, increasing the likelihood that additives, such as magnesium, will enter the cobalt site. 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 divalent status and the evaporation or sublimation of lithium.

[0364] 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 decrease in the melting point 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.

[0365] 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 according to one embodiment of the present invention is preferably 0.001 times or more and 0.1 times or less the number of metal M atoms, more preferably greater than 0.01 times and less than 0.04 times, and even more preferably about 0.02 times. 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 manufacturing process of the positive electrode active material.

[0366] Lithium cobalt oxide may be mixed with one or more metals other than cobalt (hereinafter referred to as metal Z), such as nickel, aluminum, manganese, titanium, vanadium, and chromium, and it is particularly preferable to add nickel and one or more aluminum. Manganese, titanium, vanadium, and chromium may be stable in a tetravalent state and may contribute significantly to structural stability. By adding metal Z, the crystal structure of the positive electrode active material in one embodiment of the present invention may become more stable, for example, in a high-voltage charged state. Here, in the positive electrode active material in one embodiment of the present invention, it is preferable that metal Z is added at a concentration that does not significantly change the crystallinity of lithium cobalt oxide. For example, it is preferable that the amount is such that the aforementioned Jahn-Teller effect does not occur.

[0367] As shown in the legend in Figure 22, transition metals such as nickel and manganese, and aluminum are preferably present at the cobalt site, but some may be present at the lithium site. Magnesium is also preferably present at the lithium site. Oxygen may be partially substituted with fluorine.

[0368] In one embodiment of the present invention, the capacity of the positive electrode active material may decrease as the magnesium concentration increases. One possible reason for this is that the amount of lithium contributing to charging and discharging may decrease due to the presence of magnesium at the lithium sites. In addition, excess magnesium may generate magnesium compounds that do not contribute to charging and discharging. In one embodiment of the present invention, the capacity per unit weight and per unit volume can be increased by including nickel as metal Z in addition to magnesium. In another embodiment of the present invention, the capacity per unit weight and per unit volume can be increased by including aluminum as metal Z in addition to magnesium. In yet another embodiment of the present invention, the capacity per unit weight and per unit volume can be increased by including nickel and aluminum in addition to magnesium.

[0369] The concentrations of elements such as magnesium and metal Z in the positive electrode active material according to one embodiment of the present invention are expressed below in terms of the number of atoms.

[0370] The number of nickel atoms in the positive electrode active material according to one embodiment of the present invention is preferably 10% or less of the number of cobalt atoms, more preferably 7.5% or less, even more preferably 0.05% to 4%, and particularly preferably 0.1% to 2%. The nickel concentration shown herein 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 manufacturing process of the positive electrode active material.

[0371] If a high-voltage charge is maintained for an extended period, the constituent elements of the positive electrode active material may dissolve into the electrolyte, potentially disrupting its crystalline structure. However, by including nickel in the above proportions, it may be possible to suppress the dissolution of constituent elements from the positive electrode active material.

[0372] The number of aluminum atoms in the positive electrode active material according to one embodiment of the present invention is preferably 0.05% to 4% of the number of cobalt atoms, and more preferably 0.1% to 2%. The aluminum 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 manufacturing process of the positive electrode active material.

[0373] When the electrolyte contains LiPF6, hydrolysis may generate hydrogen fluoride. Hydrogen fluoride may also be generated by the reaction between PVDF, used as a component of the positive electrode, and alkali. Reducing the hydrogen fluoride concentration in the charging solution may suppress corrosion of the current collector and / or peeling of the coating. Furthermore, it may suppress the decrease in adhesion due to gelation and / or insolubilization of PVDF.

[0374] When the positive electrode active material according to one embodiment of the present invention contains magnesium, it exhibits extremely high stability in a high-voltage charged state. Furthermore, when the positive electrode active material according to one embodiment of the present invention contains phosphorus, the number of phosphorus atoms is preferably 1% to 20% of the number of cobalt atoms, more preferably 2% to 10%, and even more preferably 3% to 8%. In addition, the number of magnesium atoms is preferably 0.1% to 10% of the number of cobalt atoms, more preferably 0.5% to 5%, and even more preferably 0.7% to 4%. The concentrations of phosphorus and magnesium shown here may be values ​​obtained by elemental analysis of the entire particle of the positive electrode active material using, for example, ICP-MS, or they may be based on the values ​​of the raw material composition during the manufacturing process of the positive electrode active material.

[0375] If the positive electrode active material has cracks, the presence of phosphorus, or more specifically, a compound containing phosphorus and oxygen, within the cracks may suppress the progression of the cracks.

[0376] ≪Surface layer≫ It is preferable that magnesium is distributed throughout the entire surface layer of the particles of the positive electrode active material according to one embodiment of the present invention, but in addition, it is preferable that the magnesium concentration in the surface layer a is higher than the average of the entire particle. For example, it is preferable that the magnesium concentration in the surface layer measured by XPS or the like is higher than the average magnesium concentration of the entire particle measured by ICP-MS or the like.

[0377] Furthermore, in one embodiment of the present invention, when the positive electrode active material contains one or more metals other than cobalt, such as nickel, aluminum, manganese, iron, and chromium, it is preferable that the concentration of the metal near the particle surface is higher than the average concentration of the entire particle. For example, it is preferable that the concentration of elements other than cobalt in the surface layer, as measured by XPS or the like, is higher than the average concentration of those elements in the entire particle, as measured by ICP-MS or the like.

[0378] The particle surface is essentially entirely composed of crystal defects, and during charging, lithium leaches out from the surface, making it a region where the lithium concentration tends to be lower than in the interior. Therefore, it is a region prone to instability and structural collapse. A higher magnesium concentration in the surface layer can more effectively suppress changes in the crystal structure. Furthermore, a higher magnesium concentration in the surface layer can also be expected to improve corrosion resistance to hydrofluoric acid produced by the decomposition of the electrolyte.

[0379] Furthermore, it is preferable that the concentration of halogens such as fluorine in the surface layer of the positive electrode active material in one embodiment of the present invention is higher than the average concentration of the entire particle. The presence of halogens in the surface layer, which is the region in contact with the electrolyte, can effectively improve corrosion resistance to hydrofluoric acid.

[0380] Thus, it is preferable that the surface layer of the positive electrode active material according to one aspect of the present invention has a different composition from the interior, with higher concentrations of additives, such as magnesium and fluorine. Furthermore, it is preferable that the surface layer has a crystalline structure that is stable at room temperature. For this reason, the surface layer may have a different crystalline structure from the interior. For example, at least a portion of the surface layer a of the positive electrode active material according to one aspect of the present invention may have a rock salt-type crystalline structure. Also, when the surface layer and the interior have different crystalline structures, it is preferable that the orientation of the crystals in the surface layer and the interior are roughly the same.

[0381] Layered rock salt crystals and the anions in rock salt crystals adopt a cubic close-packed structure (face-centered cubic lattice structure). It is also presumed that the anions in O3' type crystals adopt a cubic close-packed structure. In this specification, if the anions are arranged in a structure where three layers are stacked with a slight offset from each other, such as ABCABC, it will be referred to as cubic close-packed. Therefore, the anions do not have to be strictly cubic. At the same time, since real crystals always have defects, the analytical results do not necessarily conform to theory. For example, in FFT (Fast Fourier Transform) such as electron diffraction or TEM images, spots may appear at positions slightly different from the theoretical positions. For example, if the orientation from the theoretical position is 5 degrees or less, or 2.5 degrees or less, it can be said that it adopts a cubic close-packed structure.

[0382] When layered rock salt crystals are in contact with other rock salt crystals, there exists a crystal plane in which the orientation of the cubic close-packed structure composed of anions is aligned.

[0383] Alternatively, it can be explained as follows: In the cubic crystal structure, anions in the (111) plane have a triangular arrangement. The layered rock salt type has a space group R-3m and a rhombohedral structure, but to facilitate understanding of the structure, it is generally represented by a composite hexagonal lattice, and the (000l) plane of the layered rock salt type has a hexagonal lattice. The triangular lattice of the cubic (111) has a similar atomic arrangement to the hexagonal lattice of the (000l) plane of the layered rock salt type. The consistency between the two lattices can be described as the orientation of the cubic close-packed structure being aligned.

[0384] However, the space group of layered rock salt crystals and O3'-type crystals is R-3m, which differs from the space groups Fm-3m (the space group of typical rock salt crystals) and Fd-3m (the space group of rock salt crystals with the simplest symmetry). Therefore, the Miller indices of crystal planes satisfying the above conditions differ between layered rock salt crystals, O3'-type crystals, and rock salt crystals. In this specification, it is sometimes said that the crystal orientations are approximately the same when the orientations of the cubic close-packed structure composed of anions are aligned in layered rock salt crystals, O3'-type crystals, and rock salt crystals.

[0385] 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. When the crystal orientations are general agreement, it can be observed in TEM images, etc., that the difference in direction of the rows in which cations and anions are arranged alternately in a linear fashion 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.

[0386] However, if the surface layer consists only of MgO, or only of a solid solution of MgO and CoO(II), lithium insertion and removal becomes difficult. Therefore, the surface layer must contain at least cobalt, and in the discharge state, it must also contain lithium and have pathways for lithium insertion and removal. Furthermore, a higher concentration of cobalt than magnesium is preferable.

[0387] ≪Particle size≫ In one embodiment of the present invention, 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 the particle size 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.

[0388] <Analysis method> Whether a particular positive electrode active material exhibits an O3'-type crystal structure when charged at a high voltage and is a positive electrode active material according to one embodiment of the present invention can be determined by analyzing the positive electrode charged at a high voltage 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.

[0389] As described above, a positive electrode active material according to one aspect of the present invention is characterized by minimal 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 both high-voltage charging and discharging. It is important to note that simply adding additives may not result in the desired crystal structure. For example, even if both materials are lithium cobalt oxide containing magnesium and fluorine, there are cases where the O3' type crystal structure accounts for 60 wt% or more when charged at high voltage, and cases where the H1-3 type crystal structure accounts for 50 wt% or more. Furthermore, at a predetermined charging voltage, the O3' type crystal structure may account for almost 100 wt%, and if the predetermined voltage is further increased, the H1-3 type crystal structure may be generated. Therefore, to determine whether or not a material is a positive electrode active material according to one aspect of the present invention, analysis of the crystal structure, including XRD, is necessary.

[0390] 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 an O3' 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 atmosphere.

[0391] ≪Charging method≫ High-voltage charging to determine whether a certain composite oxide is a positive electrode active material according to one aspect of the present invention can be performed, for example, by fabricating a coin cell (CR2032 type, 20 mm in diameter and 3.2 mm in height) with lithium as the counter electrode and then charging it.

[0392] More specifically, the positive electrode can be made by coating an aluminum foil positive electrode current collector with a slurry of a mixture of positive electrode active material, conductive agent, and binder.

[0393] Lithium metal can be used for the counter electrode. However, if a material other than lithium metal is used for the counter electrode, the potential of the secondary battery and the potential of the positive electrode will differ. Unless otherwise specified, the voltage and potential in this specification refer to the potential of the positive electrode.

[0394] The electrolyte in the electrolyte solution may be 1 mol / L lithium hexafluoride phosphate (LiPF6), and the electrolyte solution may be a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC=3:7, and vinylene carbonate (VC) at 2 wt%.

[0395] Polypropylene with a thickness of 25 μm can be used for the separator.

[0396] The positive electrode and negative electrode cans can be made of stainless steel (SUS).

[0397] The coin cell prepared under the above conditions is charged with a constant current of 4.6V and 0.5C, and then charged with a constant voltage until the current value becomes 0.01C. Here, 1C is defined as 137mA / g. The temperature is set to 25℃. After charging in this manner, the coin cell is disassembled in a glove box under an argon atmosphere, and the positive electrode is removed to obtain a positive electrode active material charged at high voltage. When performing various analyses thereafter, it is preferable to seal it under an argon atmosphere to suppress reactions with external components. For example, XRD can be performed by sealing it in a sealed container under an argon atmosphere.

[0398] ≪XRD≫ Figures 23 and 25 show the ideal powder XRD patterns calculated using CuKα1 rays from the O3' type crystal structure and the H1-3 type crystal structure models. For comparison, ideal XRD patterns calculated from the crystal structures of LiCoO2(O3) with a charging depth of 0 and CoO2(O1) with a charging depth of 1 are also shown. The patterns for LiCoO2(O3) and CoO2(O1) were created using the Reflex Powder Diffraction module in Materials Studio (BIOVIA) from crystal structure information obtained from ICSD (Inorganic Crystal Structure Database). The 2θ range was set to 15° to 75°, the step size was 0.01, the wavelength λ1 was 1.540562 × 10⁻¹⁰ m, λ2 was not set, and the monochromator was set to single. The pattern for the H1-3 type crystal structure was created similarly from the crystal structure information for the H1-3 type crystal structure mentioned above. The crystal structure pattern of the O3' type crystal structure was estimated from the XRD pattern of the positive electrode active material of one embodiment of the present invention, fitted using TOPAS ver.3 (crystal structure analysis software manufactured by Bruker), and an XRD pattern was created in the same manner as for the others.

[0399] As shown in Figure 23, in the O3' type crystal structure, diffraction peaks appear at 2θ = 19.30 ± 0.20° (19.10° to 19.50°) and 2θ = 45.55 ± 0.10° (45.45° to 45.65°). More specifically, sharp diffraction peaks appear at 2θ = 19.30 ± 0.10° (19.20° to 19.40°) and 2θ = 45.55 ± 0.05° (45.50° to 45.60°). However, as shown in Figure 25, these peaks do not appear in the H1-3 type crystal structure and CoO2 (P-3m1, O1). Therefore, the appearance of peaks at 2θ = 19.30 ± 0.20° and 2θ = 45.55 ± 0.10° when charged at high voltage can be said to be a characteristic of the positive electrode active material in one embodiment of the present invention.

[0400] This can also be described as the position where the XRD diffraction peaks appear being close between the crystal structure at a charging depth of 0 and the crystal structure after high-voltage charging. More specifically, it can be said that for two or more, more preferably three or more, of the main diffraction peaks of the two, the difference in the position where the peaks appear is 2θ = 0.7 or less, and more preferably 2θ = 0.5 or less.

[0401] In addition, the positive electrode active material of one embodiment of the present invention has an O3' type crystal structure when charged with a high voltage, but not all particles have to have an O3' type crystal structure. Other crystal structures may be included, or some may be amorphous. However, when Rietveld analysis is performed on the XRD pattern, it is preferable that the O3' type crystal structure is 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more. If the O3' type crystal structure is 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more, a positive electrode active material with sufficiently excellent cycle characteristics can be obtained.

[0402] Furthermore, even after more than 100 charge-discharge cycles from the start of measurement, it is preferable that the O3' type crystal structure is 35 wt% or more, more preferably 40 wt% or more, and even more preferably 43 wt% or more when Rietveld analysis is performed.

[0403] Furthermore, the crystallite size of the O3'-type crystal structure possessed by the particles of the positive electrode active material decreases to only about 1 / 10th of that of LiCoO2(O3) in the discharged state. Therefore, even under the same XRD measurement conditions as the positive electrode before charging and discharging, a clear peak of the O3'-type crystal structure can be confirmed after high-voltage charging. On the other hand, in simple LiCoO2, even if some parts can adopt a structure similar to the O3'-type crystal structure, the crystallite size becomes smaller, and the peak becomes broad and small. The crystallite size can be determined from the full width at half maximum of the XRD peak.

[0404] In one embodiment of the present invention, the positive electrode active material preferably has a small effect of the Jahn-Teller effect, as described above. The positive electrode active material in one embodiment of the present invention preferably has a layered rock salt type crystal structure and mainly contains cobalt as a transition metal. In addition, in one embodiment of the present invention, the positive electrode active material may contain metal Z as described above, in addition to cobalt, as long as the effect of the Jahn-Teller effect is small.

[0405] <Method for preparing positive electrode active material> Next, an example of a method for producing LiMO2, one embodiment of a material applicable as a positive electrode active material, will be described using Figures 26A and 26B. The metal M can be any of the metals listed above. In addition to metal M, the metals X and / or Z listed above may also be included. It is particularly preferable to use magnesium as metal X. It is also preferable to use nickel and aluminum as metal Z. Figure 26A illustrates a cobalt-containing material where metal X is Mg. Figure 26B illustrates a cobalt-containing material where metal X is Mg and metal Z is nickel and aluminum. Note that the positive electrode active material according to one embodiment of the present invention has a crystalline structure of a lithium composite oxide represented as LiMO2, but its composition is not limited to Li:M:O=1:1:2.

[0406] First, in step S11, a composite oxide having lithium, a transition metal, and oxygen is used as the composite oxide 851. Here, it is preferable to use one or more metals M that include cobalt as a transition metal.

[0407] A composite oxide containing lithium, a transition metal, and oxygen can be synthesized by heating a lithium source and a transition metal source in an oxygen atmosphere. As the transition metal source, it is preferable to use a metal that can form a layered rock salt type composite oxide belonging to space group R-3m together with lithium. For example, at least one of manganese, cobalt, and nickel can be used. In addition to these transition metals, aluminum may also be used. That is, a cobalt source alone may be used as the transition metal source, a nickel source alone may be used, two sources (cobalt and manganese), two sources (cobalt and nickel), or three sources (cobalt, manganese, and nickel). Furthermore, an aluminum source may also be used in addition to these metal sources. The heating temperature at this time is preferably higher than that of step S17, which will be described later. For example, it can be done at 1000°C. This heating process is sometimes called calcination.

[0408] When using a pre-synthesized composite oxide containing lithium, a transition metal, and oxygen, it is preferable to use one with low impurities. In this specification, the main components of the composite oxide containing lithium, a transition metal, and oxygen, cobalt-containing material, and positive electrode active material are lithium, cobalt, nickel, manganese, aluminum, and oxygen, and elements other than the above main components are considered impurities. For example, when analyzed by glow discharge mass spectrometry, the combined impurity concentration is preferably 10,000 ppmw (parts per million weight) or less, and more preferably 5,000 ppmw or less. In particular, the combined impurity concentration of transition metals such as titanium and arsenic is preferably 3,000 ppmw or less, and more preferably 1,500 ppmw or less.

[0409] For example, lithium cobalt oxide particles manufactured by Nippon Chemical Industrial Co., Ltd. (product name: Cellseed C-10N) can be used as pre-synthesized lithium cobalt oxide. This lithium cobalt oxide has an average particle size (D50) of approximately 12 μm, and impurity analysis by glow discharge mass spectrometry (GD-MS) shows that the magnesium and fluorine concentrations are 50 ppmw or less, the calcium, aluminum, and silicon concentrations are 100 ppmw or less, the nickel concentration is 150 ppmw or less, the sulfur concentration is 500 ppmw or less, the arsenic concentration is 1100 ppmw or less, and the concentrations of other elements other than lithium, cobalt, and oxygen are 150 ppmw or less.

[0410] The composite oxide 851 in step S11 preferably has a layered rock salt-type crystalline structure with few defects and strains. Therefore, it is preferable that the composite oxide has few impurities. If a composite oxide containing lithium, a transition metal, and oxygen contains many impurities, it is highly likely to have a crystalline structure with many defects or strains.

[0411] In step S12, fluoride 852 is prepared. Suitable fluorides include lithium fluoride (LiF), magnesium fluoride (MgF2), aluminum fluoride (AlF3), titanium fluoride (TiF4), cobalt fluoride (CoF2, CoF3), nickel fluoride (NiF2), zirconium fluoride (ZrF4), vanadium fluoride (VF5), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF2), calcium fluoride (CaF2), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF2), cerium fluoride (CeF2), lanthanum fluoride (LaF3), sodium aluminum hexafluoride (Na3AlF6), etc. Any fluoride 852 that functions as a fluorine source is acceptable. Therefore, instead of fluoride 852, or as part thereof, for example, fluorine (F2), carbon fluoride, sulfur fluoride, oxygen fluoride (OF2, O2F2, O3F2, O4F2, O2F), etc. may be used and mixed into the atmosphere.

[0412] If fluoride 852 is a compound containing metal X, it can also be used in conjunction with compound 853 (a compound containing metal X), which will be described later.

[0413] In this embodiment, lithium fluoride (LiF) is used as fluoride 852. LiF is preferred because it has cations common to LiCoO2. Furthermore, LiF is preferred because it has a relatively low melting point of 848°C and is easily melted in the annealing process described later.

[0414] Furthermore, when using LiF as fluoride 852, it is preferable to prepare compound 853 (a compound containing metal X) in addition to fluoride 852 as step S13. Compound 853 is a compound containing metal X.

[0415] Furthermore, in step S13, compound 853 is prepared. As compound 853, a fluoride, oxide, hydroxide, etc. of metal X can be used, and the use of a fluoride is particularly preferred.

[0416] When magnesium is used as metal X, MgF2 or similar compounds can be used as compound 853. Magnesium can be distributed at high concentrations near the surface of cobalt-containing materials.

[0417] In addition to fluoride 852 and compound 853, metal Z may be used as a material other than cobalt and metal X. As a material containing metal Z, for example, nickel source, manganese source, aluminum source, iron source, vanadium source, chromium source, niobium source, titanium source, etc., can be mixed. For example, it is preferable to pulverize the hydroxides, fluorides, oxides, etc. of each metal and mix them. Pulverization can be carried out, for example, by a wet process.

[0418] Furthermore, the order of steps S11, S12, and S13 may be freely combined.

[0419] Next, in step S14, the materials prepared in steps S11, S12, and S13 are mixed and pulverized. Mixing can be done dry or wet, but wet mixing is preferred because it allows for finer pulverization. If wet mixing is used, a solvent is prepared. Suitable solvents include ketones such as acetone, alcohols such as ethanol and isopropanol, ethers, dioxane, acetonitrile, N-methyl-2-pyrrolidone (NMP), etc. It is more preferable to use an aprotic solvent that does not react easily with lithium. In this embodiment, acetone is used.

[0420] For mixing, for example, a ball mill or a bead mill can be used. When using a ball mill, it is preferable to use zirconia balls as the media. It is preferable to carry out this mixing and grinding process thoroughly to finely pulverize the mixture 854.

[0421] Next, in step S15, the materials mixed and ground above are recovered, and in step S16, a mixture 854 is obtained.

[0422] The mixture 854 preferably has a D50 of 600 nm to 20 μm, and more preferably 1 μm to 10 μm.

[0423] It is more preferable that the annealing temperature is above the melting temperature of mixture 854. Furthermore, it is preferable that the annealing temperature is below the decomposition temperature of LiCoO2 (1130°C).

[0424] By using LiF as fluoride 852 and annealing S16 with a lid, a cathode active material 861 with good cycle characteristics can be produced. Furthermore, if LiF and MgF2 are used as fluoride 852, since the eutectic point of LiF and MgF2 is around 742°C, it is thought that if the annealing temperature of S16 is set to 742°C or higher, the reaction with LiCoO2 will be promoted and LiMO2 will be produced.

[0425] Furthermore, endothermic peaks are observed around 820°C by differential scanning calorimetry (DSC measurement) for LiF, MgF2, and LiCoO2. Therefore, an annealing temperature of 742°C or higher is preferred, and 820°C or higher is more preferred.

[0426] Therefore, the annealing temperature is preferably 742°C to 1130°C, more preferably 742°C to 1000°C. Furthermore, it is preferably 820°C to 1130°C, and more preferably 820°C to 1000°C.

[0427] Furthermore, in this embodiment, LiF, which is a fluoride, is considered to function as a flux. Therefore, since the volume inside the heating furnace is larger than the volume of the container and LiF is lighter than oxygen, it is expected that LiF will volatilize, and as the amount of LiF in mixture 854 decreases, the formation of LiMO2 will be suppressed. Therefore, it is necessary to heat the mixture while suppressing the volatilization of LiF.

[0428] Therefore, heating mixture 854 in an atmosphere containing LiF, that is, heating mixture 854 under conditions of high LiF partial pressure in the heating furnace, suppresses the volatilization of LiF in mixture 854. By covering the mixture with a fluoride (LiF or MgF) that forms a eutectic mixture and annealing, the annealing temperature can be lowered to below the decomposition temperature of LiCoO2 (1130°C), specifically to between 742°C and 1000°C, allowing for efficient formation of LiMO2. As a result, a cobalt-containing material with good properties can be produced, and the annealing time can also be shortened.

[0429] An example of the annealing method in S17 is shown in Figure 27.

[0430] The heating furnace 120 shown in Figure 27 has a heating furnace space 102, a heating plate 104, a heater section 106, and an insulating material 108. It is more preferable to place a lid 118 on the container 116 during annealing. With this configuration, the space 119 formed by the container 116 and the lid 118 can be made into a fluoride-containing atmosphere. During annealing, by maintaining the state by covering the space 119 so that the concentration of gasified fluoride in the space 119 remains constant or does not decrease, fluorine and magnesium can be incorporated near the particle surface. Since the volume of space 119 is smaller than the heating furnace space 102, a small amount of fluoride will volatilize, creating a fluoride-containing atmosphere. In other words, the reaction system can be made into a fluoride-containing atmosphere without significantly reducing the amount of fluoride contained in the mixture 854. Therefore, LiMO2 can be efficiently produced. Furthermore, by using the lid 118, the mixture 854 can be annealed in a fluoride-containing atmosphere simply and inexpensively.

[0431] Here, it is preferable that the valency of Co (cobalt) in LiMO2 produced according to one aspect of the present invention is approximately 3. Cobalt can be 2 or 3. Therefore, in order to suppress the reduction of cobalt, it is preferable that the atmosphere of the heating furnace space 102 contains oxygen, more preferably that the ratio of oxygen to nitrogen in the atmosphere of the heating furnace space 102 is greater than or equal to that of the atmosphere of air, and even more preferably that the oxygen concentration in the atmosphere of the heating furnace space 102 is greater than or equal to that of the atmosphere of air. Thus, it is necessary to introduce an oxygen-containing atmosphere into the heating furnace space. However, since cobalt atoms with magnesium atoms nearby may be more stable in the 2 valency state, not all cobalt atoms need to be 3.

[0432] Therefore, in one aspect of the present invention, before heating, the steps of creating an oxygen-containing atmosphere in the heating furnace space 102 and placing a container 116 containing the mixture 854 in the heating furnace space 102 are performed. By following this sequence, the mixture 854 can be annealed (heated) in an atmosphere containing oxygen and fluoride. Furthermore, it is preferable to seal the heating furnace space 102 during annealing to prevent gas from being carried to the outside. For example, it is preferable to perform annealing without gas flow.

[0433] There are no particular restrictions on the method for creating an oxygen-containing atmosphere in the heating furnace space 102, but examples include exhausting the heating furnace space 102 and then introducing an oxygen-containing gas such as oxygen gas or dry air, or introducing an oxygen-containing gas such as oxygen gas or dry air for a certain period of time. In particular, it is preferable to introduce oxygen gas (oxygen replacement) after exhausting the heating furnace space 102. The atmosphere inside the heating furnace space 102 may also be considered an oxygen-containing atmosphere.

[0434] When a lid 118 is placed on the container 116 and heated in an oxygen-containing atmosphere, an appropriate amount of oxygen enters the container 116 through the gap in the lid 118, and an appropriate amount of fluoride can be retained inside the container 116.

[0435] Furthermore, fluorides and other substances adhering to the inner walls of the container 116 and lid 118 may be re-flyed upon heating and adhere to the mixture 854.

[0436] The heating in step S17 is preferably carried out at an appropriate temperature and time. The appropriate temperature and time vary depending on conditions such as the particle size and composition of the composite oxide 851 in step S11. If the particles are small, a lower temperature or shorter time may be preferable than when the particles are large. The process includes removing the lid after heating in S17.

[0437] For example, if the average particle size (D50) of the particles in step S11 is about 12 μm, the annealing time is preferably 3 hours or more, and more preferably 10 hours or more.

[0438] On the other hand, if the average particle size (D50) of the particles in step S11 is about 5 μm, the annealing time is preferably, for example, 1 hour or more and 10 hours or less, and more preferably about 2 hours.

[0439] The cooling time after annealing is preferably, for example, 10 hours or more and 50 hours or less.

[0440] Next, in step S18, the annealed material is recovered, and in step S19, the positive electrode active material 861 is obtained.

[0441] Furthermore, Figure 26B illustrates the fabrication flow of a cobalt-containing material in which metal X is Mg and metal Z is nickel and aluminum. Steps S21 to S29 in Figure 26B can be the same as steps S11 to S19 shown in Figure 26A. In other words, the positive electrode active material 861 shown in Figure 26A can be used as the mixture 856 in step S29 of Figure 26B.

[0442] Next, prepare compound 857 (a compound containing metal Z) from step S23.

[0443] As a nickel source for compound 857, it is preferable to use a nickel-containing compound. Examples of nickel-containing compounds include nickel oxide, nickel hydroxide, nickel carbonate, and the like.

[0444] As the aluminum source for compound 857, it is preferable to use a compound containing aluminum. Examples of aluminum-containing compounds include aluminum hydroxide, aluminum oxide, aluminum sulfate, aluminum chloride, or aluminum nitrate, or their hydrates. Alternatively, aluminum alkoxides or organoaluminum complexes may be used as aluminum-containing compounds. Furthermore, aluminum organic acids, including aluminum acetate, or their hydrates may also be used as aluminum-containing compounds.

[0445] For compound 857 in step S23, for example, nickel hydroxide and aluminum hydroxide can be prepared by wet grinding. The wet grinding conditions can be the method described in step S14 above.

[0446] Next, in step S31, the mixture 856 and compound 857 are mixed and ground.

[0447] Next, in step S32, the mixed and crushed materials are recovered, and in step S33, mixture 860 is obtained. Then, in step S51, the mixture is heated, the heated material is recovered (S52), and in step S53, positive electrode active material 861 is obtained. The heating temperature in step S51 is lower than the heating temperature in S26.

[0448] Although the positive electrode active material 861 obtained by the flow shown in Figure 26A and the positive electrode active material 861 obtained by the flow shown in Figure 26B use the same designation, they may not be considered the same material depending on the materials used, heating conditions, etc.

[0449] Furthermore, by using the positive electrode active material 861 obtained in S19 instead of the composite oxide 851 in step S21, a metal or its oxide can be attached to the outside of the positive electrode active material 861 obtained in S19. For example, zirconium oxide can be attached to the positive electrode active material 861 containing cobalt and magnesium. In addition, a core-shell structure may be formed by combining the above methods.

[0450] <Electrolytes> 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.

[0451] 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 within 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.

[0452] A secondary battery according to one aspect of the present invention has, for example, alkali metal ions such as sodium ions and potassium ions, or alkaline earth metal ions such as calcium ions, strontium ions, barium ions, beryllium ions, and magnesium ions as carrier ions.

[0453] 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.

[0454] 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.

[0455] 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.

[0456] 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.

[0457] 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.

[0458] An example of a fluorinated cyclic carbonate is shown below.

[0459] Monofluoroethylene carbonate (FEC) is represented by the following formula (1).

[0460] [ka]

[0461] Tetrafluoroethylene carbonate (F4EC) is represented by the following formula (2).

[0462] [ka]

[0463] Difluoroethylene carbonate (DFEC) is represented by the following formula (3).

[0464] [ka]

[0465] In this specification, electrolytes are a general term that includes solid, liquid, or semi-solid materials.

[0466] 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, typically alteration of the electrolyte or increased viscosity of the electrolyte, that can occur at the interface between the active material and the electrolyte. Alternatively, a binder or graphene compound may be attached to or retained on 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. Fluorine-containing electrolytes mitigate the formation of decomposition products that adhere to the surface of the active material (positive electrode active material or negative electrode active material) through solvation. Furthermore, by using an electrolyte containing fluorine, the formation and growth of dendrites can be prevented by preventing the adhesion of decomposition products.

[0467] 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.

[0468] 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.

[0469] 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.

[0470] 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.

[0471] In addition to the above, the electrolyte may also contain one or more aprotic organic solvents such as γ-butyrolactone, acetonitrile, dimethoxyethane, and tetrahydrofuran.

[0472] 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.

[0473] 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.

[0474] 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.

[0475] 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.

[0476] 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 volume ratio of solid material is 50%. A 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, it may be a single material or a combination of materials. For example, it may be a liquid material impregnated into a porous solid material.

[0477] 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.

[0478] 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.

[0479] Here, using Figure 28, we show an example of how to fabricate a semi-solid battery.

[0480] Figure 28 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.

[0481] Electrolyte 576 comprises a lithium-ion conductive polymer and a lithium salt.

[0482] 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.

[0483] 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 polyphosphozenes.

[0484] 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.

[0485] 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 decreases 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.

[0486] 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.

[0487] 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.

[0488] 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.

[0489] In this specification, "binder" refers to a polymer compound mixed solely for the purpose of binding active materials, conductive agents, 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; fluororubber, polystyrene, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, and ethylene-propylene-diene polymer.

[0490] Since lithium-ion conductive polymers are high-molecular-weight compounds, thoroughly mixing them and using them in the active material layer allows for the binding of the active material and conductive agent 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.

[0491] 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 576 is an electrolyte layer that has no organic solvents or very little organic solvents, it has sufficient strength to electrically insulate the positive and negative electrodes even without a separator. Since a separator is not required, a secondary battery with high productivity can be created. If the electrolyte 576 is an electrolyte layer containing inorganic fillers, the strength will be further increased, resulting in a secondary battery with even higher safety.

[0492] 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%.

[0493] 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.

[0494] 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.

[0495] 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 ).

[0496] LLZ is a garnet-type oxide containing Li, La, and Zr, and may also be a compound containing Al, Ga, or Ta.

[0497] 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.

[0498] This embodiment can be used in appropriate combination with other embodiments.

[0499] (Embodiment 2) This embodiment describes an example of a secondary battery according to one aspect of the present invention.

[0500] <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.

[0501] [Negative electrode] As the negative electrode, the negative electrode shown in the previous embodiment can be used.

[0502] [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, etc., materials with high conductivity and that 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. Also, it may be formed of a metal element that reacts with silicon to form a silicide. Examples of the metal element that reacts with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, etc. The current collector can appropriately use shapes such as sheet-like, net-like, punching metal-like, expanded metal-like, etc. The current collector preferably has a thickness of 10 μm or more and 30 μm or less.

[0503] Note that for the negative electrode current collector, it is preferable to use a material that does not alloy with carrier ions such as lithium.

[0504] A titanium compound may be provided by laminating on the above-mentioned metal elements 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 a 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 may be a 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.

[0505] [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 agent and a binder. As the positive electrode active material, the positive electrode active material shown in the previous embodiment can be used.

[0506] The conductive agent and binder that can be present in the positive electrode active material layer can be the same materials as those used for the conductive agent and binder that can be present in the negative electrode active material layer.

[0507] [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.

[0508] The separator is a porous material having pores approximately 20 nm in size, preferably 6.5 nm or larger, and more preferably pores with a diameter of at least 2 nm. In the case of the semi-solid secondary battery described above, the separator can be omitted.

[0509] 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).

[0510] 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.

[0511] 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.

[0512] 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.

[0513] [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).

[0514] This embodiment can be used in appropriate combination with other embodiments.

[0515] (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.

[0516] [Coin-type rechargeable battery] An example of a coin-type rechargeable battery is described below. Figure 29A is an exploded perspective view of a coin-type (single-layer flat type) rechargeable battery, Figure 29B is an external view, and Figure 29C is a cross-sectional view thereof. Coin-type rechargeable batteries are mainly used in small electronic devices.

[0517] Figure 29A is a schematic diagram to show the overlapping (vertical and positional) of the components for clarity. Therefore, Figures 29A and 29B are not perfectly identical corresponding diagrams.

[0518] In Figure 29A, 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 the gasket for sealing is not shown in Figure 29A. The spacer 322 and washer 312 are used to protect the inside or to fix their position within the can when the positive electrode can 301 and the negative electrode can 302 are crimped together. The spacer 322 and washer 312 are made of stainless steel or insulating material.

[0519] The positive electrode 304 is a laminated structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305.

[0520] To prevent a short circuit between the positive and negative electrodes, a separator 310 and a ring-shaped insulator 313 are arranged to cover the sides and top surfaces of the positive electrode 304, respectively. The separator 310 has a larger planar area than the positive electrode 304.

[0521] Figure 29B is a perspective view of the completed coin-type rechargeable battery.

[0522] The coin-type secondary battery 300 has a positive electrode casing 301, which also serves as the positive electrode terminal, and a negative electrode casing 302, which also serves as the negative electrode terminal, insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with it. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with it. Furthermore, the negative electrode 307 is not limited to a laminated structure, and lithium metal foil or a lithium-aluminum alloy foil may be used.

[0523] Furthermore, for the positive electrode 304 and negative electrode 307 used in the coin-type secondary battery 300, the active material layer only needs to be formed on one side.

[0524] 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.

[0525] These negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte, and as shown in Figure 29C, 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.

[0526] By using a rechargeable battery, a coin-type rechargeable battery 300 can be made with high capacity, high charge / discharge capacity, and excellent cycle characteristics. Furthermore, if a rechargeable battery is used between the negative electrode 307 and the positive electrode 304, the separator 310 can be omitted.

[0527] [Cylindrical rechargeable battery] An example of a cylindrical secondary battery will be described with reference to Figure 30A. As shown in Figure 30A, 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.

[0528] Figure 30B is a schematic diagram showing a cross-section of a cylindrical secondary battery. The cylindrical secondary battery shown in Figure 30B 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.

[0529] 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.

[0530] 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.

[0531] 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.

[0532] 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.

[0533] Figure 30C 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.

[0534] Figure 30D 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.

[0535] Multiple secondary batteries 616 may be connected in parallel and then further connected in series.

[0536] A temperature control device may be provided between the multiple secondary batteries 616. When a secondary battery 616 overheats, it can be cooled by the temperature control device, and when a secondary battery 616 becomes too cold, it can be heated by the temperature control device. This makes the performance of the energy storage system 615 less susceptible to the influence of ambient temperature.

[0537] Furthermore, in Figure 30D, the energy storage system 615 is electrically connected to the control circuit 620 via wiring 621 and wiring 622. Wiring 621 is electrically connected to the positive terminals of the multiple secondary batteries 616 via conductive plate 628, and wiring 622 is electrically connected to the negative terminals of the multiple secondary batteries 616 via conductive plate 614.

[0538] [Other structural examples of secondary batteries] Examples of secondary battery structures will be explained using Figures 31 and 32.

[0539] The secondary battery 913 shown in Figure 31A has a wound body 950 with terminals 951 and 952 inside a housing 930. The wound body 950 is immersed in an electrolyte inside the housing 930. Terminal 952 is in contact with the housing 930, while terminal 951 is not in contact with the housing 930, due to the use of an insulating material or the like. In Figure 31A, the housing 930 is shown separated for convenience, but in reality, the wound body 950 is covered by the housing 930, and terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (e.g., aluminum) or a resin material.

[0540] Furthermore, as shown in Figure 31B, the housing 930 shown in Figure 31A may be formed from multiple materials. For example, in the secondary battery 913 shown in Figure 31B, housing 930a and housing 930b are bonded together, and the winding body 950 is provided in the area surrounded by housing 930a and housing 930b.

[0541] 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.

[0542] Furthermore, the structure of the wound body 950 is shown in Figure 31C. 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.

[0543] Alternatively, the secondary battery 913 may have a wound body 950a as shown in Figure 32. The wound body 950a shown in Figure 32A 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.

[0544] 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.

[0545] 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.

[0546] As shown in Figures 32A and 32B, 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.

[0547] As shown in Figure 32C, 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.

[0548] As shown in Figure 32B, 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 32A and 32B can be referenced from the description of the secondary battery 913 shown in Figures 31A to 31C.

[0549] <Laminated rechargeable battery> Next, an example of a laminate-type secondary battery is shown in Figures 33A and 33B, which show an example of its external appearance. Figures 33A and 33B 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.

[0550] Figure 34A 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 34A.

[0551] <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 33A, will be explained using Figures 34B and 34C.

[0552] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. Figure 34B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example using five sets of negative electrodes 506 and four sets of positive electrodes 503 is shown. The stacked negative electrode 506, separator 507, and positive electrode 503 can also be called a laminate consisting of the negative electrode 506, separator 507, and positive electrode 503. 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.

[0553] Next, the negative electrode 506, separator 507, and positive electrode 503 are placed on the outer casing 509.

[0554] Next, as shown in Figure 34C, 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 can be added later. It is preferable to use a film that has both excellent water permeability barrier properties and gas barrier properties for the outer casing 509. 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).

[0555] Next, an electrolyte (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 under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is sealed. In this way, a laminate-type secondary battery 500 can be manufactured.

[0556] 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.

[0557] This embodiment can be used in appropriate combination with other embodiments.

[0558] (Embodiment 4) In this embodiment, we will show an example of application to an electric vehicle (EV) using Figure 35A, which is a different example from Figure 30D, which is a cylindrical secondary battery.

[0559] Figure 35C shows a block diagram of an example of an electric vehicle. The electric vehicle is 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 the capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0560] The internal structure of the first battery 1301a may be a wound type as shown in Figure 31A, or a stacked type as shown in Figures 33A and 33B.

[0561] 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.

[0562] 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.

[0563] 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.

[0564] 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.

[0565] Furthermore, the first battery 1301a will be explained using Figure 35A.

[0566] Figure 35A 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.

[0567] 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).

[0568] 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.

[0569] Furthermore, an example of a block diagram of the battery pack 1415 shown in Figure 35A is shown in Figure 35B.

[0570] 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 is set to an upper and lower voltage limit for the secondary battery being used, and limits the upper limit of external current and the upper limit of output current to the outside. Within the range between the lower voltage limit and the upper voltage limit of the secondary battery, it is within the voltage range for which use is recommended, and if it goes 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 (+IN) 1325 and an external terminal (-IN) 1326.

[0571] 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.

[0572] 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.

[0573] 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.

[0574] 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.

[0575] 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.

[0576] 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.

[0577] 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.

[0578] By mounting the secondary battery shown in either Figure 30D or Figure 35A 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. Furthermore, 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. One embodiment of the present invention allows for high-capacity secondary batteries. Therefore, one embodiment of the present invention is suitable for miniaturization and weight reduction, and can be suitably used in transport vehicles.

[0579] Figures 36A to 36E illustrate a transport vehicle using one embodiment of the present invention. The automobile 2001 shown in Figure 36A 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 36A 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.

[0580] 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.

[0581] 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.

[0582] Figure 36B 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 36A, except for differences in the number of secondary batteries that make up the module, so the explanation is omitted.

[0583] Figure 36C shows, as an example, a large transport vehicle 2003 equipped with an electrically controlled motor. 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 36A except for differences in the number of secondary batteries constituting the secondary battery module, the explanation is omitted.

[0584] Figure 36D shows an aircraft 2004 having a fuel-burning engine as an example. The aircraft 2004 shown in Figure 36D has wheels for takeoff and landing, and can therefore be considered part of a transport vehicle. It has a battery pack 2203 which includes a secondary battery module formed by connecting multiple secondary batteries and a charging control device.

[0585] 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 functionality as Figure 36A, except for differences in the number of secondary batteries that make up the module, so the explanation is omitted.

[0586] Figure 36E shows an example of a satellite using a battery management system according to one embodiment of the present invention. The satellite 2005 shown in Figure 36E has a secondary battery 2204. Since the satellite 2005 will be used in the extremely cold environment of outer space, it is desirable that the secondary battery 2204 be mounted inside the satellite 2005, covered by a heat-insulating material.

[0587] This embodiment can be used in appropriate combination with other embodiments.

[0588] (Embodiment 5) In this embodiment, an example of mounting a secondary battery, which is one aspect of the present invention, in a building will be explained using Figures 37A and 37B.

[0589] The house shown in Figure 37A 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.

[0590] The power stored in the energy storage device 2612 can also be supplied 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.

[0591] Figure 37B shows an example of an energy storage device 700 according to one aspect of the present invention. As shown in Figure 37B, an energy storage device 791 according to one aspect of the present invention is installed in the underfloor space 796 of the building 799.

[0592] 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.

[0593] 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).

[0594] 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.

[0595] 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.

[0596] 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.

[0597] This embodiment can be used in appropriate combination with other embodiments.

[0598] (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.

[0599] Figure 38A 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.

[0600] 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.

[0601] 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.

[0602] 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.

[0603] 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.

[0604] 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.

[0605] Figure 38B 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.

[0606] Figure 38C shows an example of a robot. The robot 6400 shown in Figure 38C 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.

[0607] 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.

[0608] 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.

[0609] 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.

[0610] 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.

[0611] Figure 38D 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.

[0612] 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.

[0613] This embodiment can be implemented in appropriate combination with other embodiments.

[0614] (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 {}.

[0615] 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).

[0616] 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.

[0617] 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.

[0618] 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.

[0619] 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.

[0620] 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.

[0621] 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.

[0622] 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.

[0623] 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.

[0624] 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.

[0625] 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.

[0626] 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.

[0627] 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.

[0628] 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]

[0629] In this embodiment, a negative electrode active material according to one aspect of the present invention was prepared, and the prepared negative electrode active material was evaluated.

[0630] <Fabrication of negative electrode active material> The negative electrode active material was prepared according to the flow shown in Figure 19. Silicon was used as the first material 801, and ALDRICH nanosilicon particles were used as the silicon. Lithium fluoride was used as the halogen-containing material 802. Lithium carbonate was used as the oxygen and carbon-containing material 803.

[0631] Samples AS1, AS2, and AS3 were prepared as negative electrode active materials.

[0632] [AS1] Silicon, lithium fluoride, and lithium carbonate were prepared as the materials for sample AS1 (see steps S21, S22, and S23 in Figure 19). The materials were blended in a ratio of silicon:lithium fluoride:lithium carbonate = 100:5:5 (weight%) and dry mixing was performed (see steps S31 to S33 in Figure 19).

[0633] [AS2] Silicon and lithium fluoride were prepared as the materials for sample AS2. They were mixed in a ratio of silicon:lithium fluoride = 100:10 (weight%) and dry mixing was performed.

[0634] [AS3] Silicon and lithium carbonate were prepared as the materials for sample AS3. They were mixed in a ratio of silicon:lithium carbonate = 100:10 (weight%) and dry mixing was performed.

[0635] The mixtures of materials for each sample were calcined at 850°C for 10 hours in a nitrogen atmosphere to obtain each sample (see steps S51 to S53 in Figure 19).

[0636] <sem-edx> Next, samples AS1, AS2, and AS3 were analyzed using SEM-EDX. EDX measurements were performed using a Hitachi High-Technologies Corporation SEM, model SU8030, equipped with a Horiba, Ltd. EX-350X-MaX80 EDX unit. The acceleration voltage for EDX analysis was 10kV. Tables 6, 7, and 8 show the results of the EDX analysis. Units are expressed as atomic concentration. The sum of the atomic concentrations of carbon, nitrogen, oxygen, fluorine, and silicon was defined as a 100-atom concentration. Three EDX analyses were performed on each sample.

[0637] [Table 7]

[0638] [Table 8]

[0639] [Table 9] [Examples]

[0640] <Electrode fabrication> Next, electrodes were fabricated using sample AS1 according to the flow chart shown in Figure 21.

[0641] Silicon-containing particles (sample AS1) and a solvent were prepared in a ratio of silicon-containing particles:solvent = 1:1 (by weight) and mixed (steps S71, S72, S73 in Figure 21). NMP was used as the solvent. The mixture was mixed using a rotary-orbit mixer (Awatori Rentaro, manufactured by THINKY Inc.) at 2000 rpm for 3 minutes, then collected to obtain mixture E-1 (steps S74, S75 in Figure 21).

[0642] Next, mixture E-1 and the graphene compound were repeatedly mixed while adding solvent. The weight of the graphene compound was 0.0625 times (5 / 80 times) the weight of the silicon-containing particles prepared in step S71. Graphene oxide was used as the graphene compound. The mixture was mixed using a rotary-orbit mixer at 2000 rpm for 3 minutes and then collected (steps S81 and S82 in Figure 21). Next, the collected mixture was kneaded, NMP was added as needed, and the mixture was mixed using a rotary-orbit mixer at 2000 rpm for 3 minutes and then collected (steps S83, S84, and S85 in Figure 21). Steps S83 to S85 were repeated 5 times to obtain mixture E-2 (step S86 in Figure 21).

[0643] Next, mixture E-2 and the polyimide precursor were mixed (step S88 in Figure 21). The weight of the prepared polyimide was 0.1875 times (15 / 80 times) the weight of the silicon-containing particles prepared in step S71. Mixing was carried out using a rotary-orbit mixer at 2000 rpm for 3 minutes. Then, an amount of NMP equal to 1.5 times the weight of the silicon-containing particles prepared in step S71 was prepared and added to the mixture to adjust the viscosity (step S89 in Figure 21), and further mixing was carried out (twice at 2000 rpm for 3 minutes using a rotary-orbit mixer), and the mixture was collected to obtain mixture E-3 as a slurry (steps S90, S91, S92 in Figure 21).

[0644] Next, the current collector was prepared and coated with mixture E-3 (steps S93 and S94 in Figure 21). As the current collector, copper foil with an undercoat was prepared, and mixture E-3 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.

[0645] Next, the copper foil coated with mixture E-3 was subjected to a first heating at 50°C for 1 hour (step S95 in Figure 21). Subsequently, a second heating was performed under reduced pressure at 400°C for 5 hours (step S96 in Figure 21) to obtain the electrode. Heating reduces the graphene oxide, decreasing the amount of oxygen.

[0646] <sem> SEM observation was performed on the surface and cross-section of the fabricated electrodes. In Example 2, a Hitachi High-Technologies S-4800 SEM was used. The acceleration voltage was set to 5kV. The electrodes to be observed in cross-section were processed using the ion milling method before observation to expose the cross-section.

[0647] Figures 39A and 39B show observational images of the surface and cross-section of an electrode fabricated using sample AS1, respectively. In sample AS1, which was heat-treated with LiF and Li2CO3, it was observed that the graphene compound was densely attached to the silicon particles. When the degree of attachment was measured in the cross-sectional SEM image of sample AS1, as shown in Figure 2 of Embodiment 1, the value exceeded 120%, indicating that the graphene compound was densely attached to the silicon particles. [Examples]

[0648] In this embodiment, a negative electrode active material according to one aspect of the present invention was prepared, and the prepared negative electrode active material was evaluated.

[0649] <Fabrication of the negative electrode> Next, electrodes were prepared using sample AS3 following the flow chart shown in Figure 21.

[0650] Silicon-containing particles (sample AS3, also called lithium carbonate-treated silicon) and a solvent were prepared in a silicon-containing particles:solvent = 1:1 (by weight ratio) and mixed (steps S71, S72, S73 in Figure 21). NMP was used as the solvent. The mixture was mixed using a rotary-orbit mixer (Awatori Rentaro, manufactured by THINKY Inc.) at 2000 rpm for 3 minutes, then collected to obtain mixture E-1 (steps S74, S75 in Figure 21).

[0651] Next, mixture E-1 and the graphene compound were repeatedly mixed while adding solvent. The weight of the graphene compound was 0.0625 times (5 / 80 times) the weight of the silicon-containing particles prepared in step S71. Graphene oxide was used as the graphene compound. The mixture was mixed using a rotary-orbit mixer at 2000 rpm for 3 minutes and then collected (steps S81 and S82 in Figure 21). Next, the collected mixture was kneaded, NMP was added as needed, and the mixture was mixed using a rotary-orbit mixer at 2000 rpm for 3 minutes and then collected (steps S83, S84, and S85 in Figure 21). Steps S83 to S85 were repeated 5 times to obtain mixture E-2 (step S86 in Figure 21).

[0652] Next, mixture E-2 and a polyimide precursor were mixed (step S88 in Figure 21). A polyimide precursor manufactured by Toray Industries, Inc. was used as the polyimide. The weight of the prepared polyimide was 0.1875 times (15 / 80 times) the weight of the silicon-containing particles prepared in step S71. Mixing was performed using a rotary-orbit mixer at 2000 rpm for 3 minutes. Then, an amount of NMP equal to 1.5 times the weight of the silicon-containing particles prepared in step S71 was prepared and added to the mixture to adjust the viscosity (step S89 in Figure 21), and further mixing was performed (twice at 2000 rpm for 3 minutes using a rotary-orbit mixer), and the mixture was collected to obtain mixture E-3 as a slurry (steps S90, S91, S92 in Figure 21).

[0653] Next, the current collector was prepared and coated with mixture E-3 (steps S93 and S94 in Figure 21). As the current collector, copper foil with an undercoat was prepared, and mixture E-3 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.

[0654] Next, the copper foil coated with mixture E-3 was subjected to a first heating at 50°C for 1 hour (step S95 in Figure 21). Subsequently, a second heating was performed under reduced pressure at 400°C for 5 hours (step S96 in Figure 21) to obtain the electrode. Upon heating, the graphene oxide in the electrode was reduced to RGO (Reduced Graphene Oxide), and the oxygen content decreased.

[0655] <sem> Surface and cross-sectional SEM observations were performed on the electrodes fabricated in this embodiment. A Hitachi High-Technologies S4800 SEM was used. The acceleration voltage was set to 5kV. Before cross-sectional observation, the electrodes were processed using ion milling to expose the cross-section.

[0656] Figures 40A and 40B are SEM images of the surface and cross-section of the electrode in this embodiment, respectively. In Figures 40A and 40B, regions where nanosilicon is aggregated and regions containing nanosilicon and RGO were observed. Furthermore, it was observed that composite particles were formed in which the regions containing nanosilicon and RGO covered and were in contact with the regions where nanosilicon is aggregated.

[0657] Figures 41A and 41B are magnified SEM images of a portion of the cross-sectional observation area shown in Figure 40B. Figure 41A shows an observation image of a region where nanosilicon is aggregated, and Figure 41B shows an observation image of a region containing nanosilicon and RGO. In the region containing nanosilicon and RGO shown in Figure 41B, it was observed that the RGO was clinging to the nanosilicon.

[0658] <Coin cell fabrication> Next, a CR2032 type coin cell (20 mm in diameter, 3.2 mm in height) was fabricated using the electrodes prepared in this example.

[0659] 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.

[0660] A 25 μm thick polypropylene separator was used for the separator.

[0661] The positive electrode and negative electrode cans were made of stainless steel (SUS).

[0662] <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.

[0663] 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 42A and 42B. The maximum charge capacity in the charge-discharge cycle test and the charge capacity retention rate after 50 cycles are shown in Table 9. As shown in Figures 42A, 42B and Table 9, good charge-discharge cycle characteristics were confirmed.

[0664] [Table 10] [Explanation of symbols]

[0665] 570: Electrode, 570a: Negative electrode, 570b: Positive electrode, 571: Current collector, 571a: Negative electrode current collector, 571b: Positive electrode current collector, 572: Active material layer, 572a: Negative electrode active material layer, 572b: Positive electrode active material layer, 576: Electrolyte, 581: Electrolyte, 582: Particle, 582a: First particle, 582b: Second particle, 583: Graphene compound, 584: Electrolyte, 585: First region, 586: Second region, 591: First tangent, 592: First distance, 593: Second distance, 801: First material, 802: Material containing halogen, 803: Material containing oxygen and carbon, 804: Mixture, 805: Particle, 806: Mixture, 807: Particle< / sem> < / sem>

Claims

1. It comprises multiple silicon particles and a graphene compound, Each of the silicon-containing particles has at least a portion of its surface having a functional group containing oxygen and carbon, and a functional group containing oxygen, The silicon-containing particle has a region having a bond between the silicon and fluorine, The graphene compound has a functional group containing hydrogen or hydrogen, The graphene compound has pores composed of multi-membered rings of 9 or more members, which are made of carbon. One of the carbon atoms constituting the pore is terminated by a fluorine atom. The graphene compound is an electrode having a region that contacts the surface of at least two silicon-containing particles among the plurality of silicon-containing particles.

2. In claim 1, Each of the silicon-containing particles is an electrode having a carbonate group, a bicarbonate group, a hydroxyl group, an epoxy group, or a carboxyl group.

3. In one of claims 1 or 2, Each of the silicon-containing particles has a region on its surface terminated by one or more of the following: a functional group containing oxygen and carbon, a functional group containing oxygen and hydrogen, a functional group containing oxygen and lithium, or a hydrogen atom.

4. In any one of claims 1 to 3, The silicon-containing particles are electrodes having amorphous silicon.

5. In any one of claims 1 to 3, The silicon-containing particles are electrodes having polycrystalline silicon.

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