Secondary battery, electronic device, power storage system, and vehicle

Abstract

Provided is a secondary battery having high capacity and little deterioration. Provided is a novel power storage device. The secondary battery includes a positive electrode and a negative electrode, the negative electrode including a first active material, a second active material, and a graphene compound, at least a part of a surface of the first active material including a region covered with the second active material, the surface of the second active material and at least a part of the surface of the first active material include a region covered with a graphene compound, the first active material contains graphite, the second active material contains silicon, and the capacity of the positive electrode is 50% or more but less than 100% of the capacity of the negative electrode.

Description

This application is a divisional application of the patent application with application number "202180083013.8", application date "December 3, 2021", and invention name "Secondary battery, electronic device, power storage system and vehicle". Technical Field

[0001] One embodiment of the present invention relates to an electrode and a method for manufacturing the same. Another embodiment of the present invention relates to an active material included in an electrode and a method for manufacturing the same. Another embodiment of the present invention relates to a secondary battery and a method for manufacturing the same. Another embodiment of the present invention relates to a mobile object, such as a vehicle, including a secondary battery, as well as a portable information terminal, an electronic device, and the like.

[0002] One embodiment of the present invention relates to an article, method, or manufacturing method. Furthermore, the present invention relates to a process, machine, product, or composition of matter. One embodiment of the present invention relates to a semiconductor device, display device, light-emitting device, power storage device, lighting device, electronic device, or a method for manufacturing the same.

[0003] Note that in this specification, electronic equipment refers to any device having a power storage device. Examples of electronic equipment include electro-optical devices and information terminal devices having a power storage device.

[0004] It should be noted that in this specification, the term "electrical storage device" refers to any element or device that has an electrical storage function. For example, electrical storage devices such as lithium-ion secondary batteries (also called secondary batteries), lithium-ion capacitors, and electric double-layer capacitors are all included in the category of electrical storage devices. Background Art

[0005] In recent years, research and development of various energy storage devices, including lithium-ion secondary batteries, lithium-ion capacitors, and air batteries, has become increasingly intense. In particular, with the development of the semiconductor industry for mobile phones, smartphones, portable information terminals such as notebook personal computers, portable music players, digital cameras, medical equipment, and next-generation clean energy vehicles such as hybrid electric vehicles (HVs), electric vehicles (EVs), and plug-in hybrid electric vehicles (PHVs), demand for high-output, high-energy-density lithium-ion secondary batteries has skyrocketed. As a rechargeable energy source, they have become essential in the modern information society. [Prior technical literature] [Patent Document]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2002-216751 [Patent Document 2] PCT International Application Translation No. 2019-522886 Summary of the Invention Technical problem to be solved by the invention

[0007] To extend driving distance, secondary batteries used in mobile vehicles such as electric vehicles and hybrid vehicles need to have higher capacities.

[0008] Furthermore, in portable terminals and the like, power consumption increases as they become more multifunctional. Furthermore, secondary batteries used in portable terminals and the like are required to be smaller and lighter. Consequently, secondary batteries used in portable terminals are also required to have higher capacities.

[0009] In addition to stability, high capacity is also crucial for secondary batteries. Alloy materials such as silicon-based materials have high capacity and are therefore expected to be used as active materials in secondary batteries. However, alloy materials with high charge and discharge capacities undergo volume changes during charge and discharge, which can lead to problems such as pulverization and detachment of the active material, hindering adequate cycle performance.

[0010] In order to solve the problems of the above-mentioned alloy materials, the combination of alloy materials with graphite or carbon materials has been studied. Patent Document 1 describes a composite material in which a coating layer composed of carbon is formed on the surface of a porous particle core formed by bonding silicon-containing particles and carbon-containing particles. Patent Document 2 describes a composite particle containing silicon (Si), lithium fluoride (LiF) and a carbon material. However, none of the above documents can fully solve the problems of micronization and separation of active materials caused by the expansion of alloy materials during charging and discharging.

[0011] For example, the electrodes of a secondary battery are composed of materials such as active materials, conductive materials, and binders. The higher the ratio of materials such as active materials that contribute to the capacity of charge and discharge, the higher the capacity of the secondary battery can be. By making the electrode include a conductive material, the conductivity of the electrode can be improved and good output characteristics can be obtained. In addition, when the active material repeatedly expands and contracts during the charge and discharge of the secondary battery, the collapse of the active material and the interruption of the conductive path sometimes occur in the electrode. In this case, by making the electrode include a conductive material and a binder, the collapse of the active material and the interruption of the conductive path can be suppressed. On the other hand, when a conductive material and a binder are used, the ratio of the active material decreases, and sometimes the capacity of the secondary battery decreases.

[0012] One object of one embodiment of the present invention is to provide an electrode having excellent properties. Another object of one embodiment of the present invention is to provide an active material having excellent properties. Another object of one embodiment of the present invention is to provide a novel electrode.

[0013] Furthermore, one of the purposes of one embodiment of the present invention is to provide a negative electrode with high mechanical strength. Furthermore, one of the purposes of one embodiment of the present invention is to provide a positive electrode with high mechanical strength. Furthermore, one of the purposes of one embodiment of the present invention is to provide a negative electrode with high capacity. Furthermore, one of the purposes of one embodiment of the present invention is to provide a positive electrode with high capacity. Furthermore, one of the purposes of one embodiment of the present invention is to provide a negative electrode with little degradation. Furthermore, one of the purposes of one embodiment of the present invention is to provide a positive electrode with little degradation.

[0014] Furthermore, one of the purposes of one embodiment of the present invention is to provide a secondary battery with less degradation. Furthermore, one of the purposes of one embodiment of the present invention is to provide a secondary battery with high safety. Furthermore, one of the purposes of one embodiment of the present invention is to provide a secondary battery with high energy density. Furthermore, one of the purposes of one embodiment of the present invention is to provide a novel secondary battery.

[0015] Note that the inclusion of the above-mentioned objectives does not preclude the existence of other objectives. Note that one embodiment of the present invention does not necessarily achieve all of the above-mentioned objectives. Furthermore, objectives other than the above-mentioned objectives may be extracted from the description, drawings, and claims. Means of solving technical problems

[0016] One embodiment of the present invention is a secondary battery comprising a positive electrode and a negative electrode, wherein the negative electrode comprises a first active material, a second active material, and a graphene compound, at least a portion of a surface of the first active material comprises an area covered by the second active material, the surface of the second active material and at least a portion of a surface of the first active material comprise an area covered by the graphene compound, the first active material comprises graphite, the second active material comprises silicon, and the capacity of the positive electrode is greater than 50% and less than 100% of the capacity of the negative electrode.

[0017] In addition, one embodiment of the present invention is a secondary battery comprising a positive electrode and a negative electrode, wherein the negative electrode comprises a first active material, a second active material and a graphene compound, at least a portion of the surface of the first active material comprises an area covered by the second active material, the surface of the second active material and at least a portion of the surface of the first active material comprise an area covered by the graphene compound, the first active material comprises graphite, the second active material comprises silicon, and the second active material has a Si-Si bond in a fully charged state.

[0018] In addition, one embodiment of the present invention is a secondary battery, which includes a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode includes a first active material, a second active material and a graphene compound, at least a portion of the surface of the first active material includes an area covered by the second active material, the surface of the second active material and at least a portion of the surface of the first active material include an area covered by the graphene compound, the first active material includes graphite, the second active material includes silicon, the capacity of the positive electrode is greater than 50% and less than 100% of the capacity of the negative electrode, and the electrolyte includes an ionic liquid.

[0019] In addition, one embodiment of the present invention is a secondary battery, which includes a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode includes a first active material, a second active material and a graphene compound, at least a portion of the surface of the first active material includes an area covered by the second active material, the surface of the second active material and at least a portion of the surface of the first active material include an area covered by the graphene compound, the first active material includes graphite, the second active material includes silicon, the second active material has a Si-Si bond in a fully charged state, and the electrolyte includes an ionic liquid.

[0020] In any of the secondary batteries described above, the ionic liquid preferably contains EMI-FSI and 2 mol / L or more of LiFSI.

[0021] In any of the above secondary batteries, preferably, the positive electrode includes lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel, and the surface layer of the lithium cobalt oxide includes a region where the concentration of one or more selected from magnesium, fluorine, and aluminum is the highest.

[0022] In any of the above-described secondary batteries, preferably, the first active material includes graphite having a particle size of 5 μm or greater, and the second active material includes silicon having a particle size of 250 nm or less.

[0023] One embodiment of the present invention is a vehicle including any of the secondary batteries described above.

[0024] One embodiment of the present invention is a power storage system including any of the secondary batteries described above.

[0025] One embodiment of the present invention is an electronic device including any of the above-described secondary batteries. Effects of the Invention

[0026] According to one embodiment of the present invention, an active material having excellent properties can be provided. In addition, according to one embodiment of the present invention, an electrode having excellent properties can be provided. In addition, according to one embodiment of the present invention, a novel electrode can be provided.

[0027] Furthermore, according to one embodiment of the present invention, a negative electrode with high mechanical strength can be provided. Furthermore, according to one embodiment of the present invention, a positive electrode with high mechanical strength can be provided. Furthermore, according to one embodiment of the present invention, a negative electrode with high capacity can be provided. Furthermore, according to one embodiment of the present invention, a positive electrode with high capacity can be provided. Furthermore, according to one embodiment of the present invention, a negative electrode with little degradation can be provided. Furthermore, according to one embodiment of the present invention, a positive electrode with little degradation can be provided.

[0028] Furthermore, one embodiment of the present invention can provide a secondary battery with less degradation. Furthermore, one embodiment of the present invention can provide a secondary battery with high safety. Furthermore, one embodiment of the present invention can provide a secondary battery with high energy density. Furthermore, one embodiment of the present invention can provide a novel secondary battery.

[0029] Note that the description of these effects does not preclude the existence of other effects. Furthermore, one embodiment of the present invention does not necessarily have all of the aforementioned effects. Furthermore, if the description of the specification, drawings, and claims clearly indicates effects other than those described above, such effects may be obtained from the description of the specification, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1A and Figure 1B This is a diagram showing an example of a cross section of an electrode. Figure 1C It is a diagram illustrating the capacity ratio of the negative electrode to the positive electrode. Figures 2A to 2C It is a diagram illustrating the capacity ratio of the negative electrode to the positive electrode and the voltage of the secondary battery. Figure 3A This is a diagram showing an example of particles included in the negative electrode. Figure 3B and Figure 3C It is a diagram showing the change in shape of particles during charge and discharge. Figure 4A and Figure 4B This is a diagram showing calculations of a negative electrode according to one embodiment of the present invention. Figure 5 This is a diagram showing calculations of a negative electrode according to one embodiment of the present invention. Figures 6A to 6C This is a diagram showing calculations of a negative electrode according to one embodiment of the present invention. Figure 7 This is a diagram showing an example of a method for manufacturing an electrode. Figure 8A and Figure 8B is an example of a model of a graphene compound. Figure 9This is a diagram showing a cross-sectional structure of a positive electrode according to one embodiment of the present invention. Figures 10A1 to 10C2 This is a diagram showing the cross-sectional structure of a positive electrode active material complex according to one embodiment of the present invention. Figure 11A is a top view of a positive electrode active material according to one embodiment of the present invention. Figure 11B and Figure 11C This is a cross-sectional view of a positive electrode active material according to one embodiment of the present invention. Figure 12 This is a diagram illustrating the crystal structure of a positive electrode active material according to one embodiment of the present invention. Figure 13 It is the XRD pattern calculated based on the crystal structure. Figure 14 A diagram illustrating the crystal structure of a positive electrode active material of a comparative example. Figure 15 It is the XRD pattern calculated based on the crystal structure. Figure 16 This is an example of a TEM image showing roughly uniform crystal orientation. Figure 17A This is an example of a STEM image showing roughly uniform crystal orientation. Figure 17B is the FFT of the rock salt type crystal RS region, Figure 17C It is the FFT of the region of layered rock salt type crystal LRS. Figure 18A This is an exploded perspective view of a coin-type secondary battery. Figure 18B This is a perspective view of a coin-type secondary battery. Figure 18C It is a cross-sectional perspective view. Figure 19A An example of a cylindrical secondary battery is shown. Figure 19B An example of a cylindrical secondary battery is shown. Figure 19C A plurality of examples of cylindrical secondary batteries are shown. Figure 19D An example of a power storage system including a plurality of cylindrical secondary batteries is shown. Figure 20A and Figure 20B is a diagram illustrating an example of a secondary battery. Figure 20C It is a diagram showing the internal state of a secondary battery. Figures 21A to 21C It is a diagram illustrating an example of a secondary battery. Figure 22A and Figure 22B It is a diagram showing the appearance of a secondary battery. Figures 23A to 23C It is a diagram explaining a method for manufacturing a secondary battery. Figures 24A to 24C is a diagram showing a structural example of a battery pack. Figure 25A and Figure 25B It is a diagram illustrating an example of a secondary battery. Figures 26A to 26C It is a diagram illustrating an example of a secondary battery. Figure 27A and Figure 27B It is a diagram illustrating an example of a secondary battery. Figure 28A is a perspective view showing a battery pack according to one embodiment of the present invention. Figure 28B is the block diagram of the battery pack, Figure 28C is a block diagram of a vehicle including an engine. 29A to 29D This is a diagram illustrating an example of a transport vehicle. Figure 30A and Figure 30B This is a diagram illustrating a power storage device according to one embodiment of the present invention. Figure 31A is a diagram showing an electric bicycle, Figure 31B is a diagram showing a secondary battery of an electric bicycle, Figure 31C This is a diagram illustrating an electric motorcycle. Figures 32A to 32D It is a diagram illustrating an example of an electronic device. Figure 33A Showing an example of a wearable device, Figure 33B showing a perspective view of a watch-type device, Figure 33C This is a diagram illustrating the side view of a wristwatch-type device. Figure 33D It is a diagram illustrating an example of wireless headphones. Figure 34A and Figure 34B is the SEM image of the electrode. Figure 35A and Figure 35B is a graph showing cycle characteristics. Figure 36A and Figure 36B is a graph showing cycle characteristics. Figure 37A and Figure 37B is a graph showing discharge characteristics. Modes for Carrying Out the Invention

[0031] The following describes embodiments of the present invention in detail with reference to the accompanying drawings. Note that the present invention is not limited to the following description, and those skilled in the art will readily appreciate that its methods and details can be modified in various forms. Furthermore, the present invention should not be construed as being limited solely to the following embodiments.

[0032] In the drawings, the size, thickness of layers, or regions may be exaggerated for clarity of description, and therefore, the present invention is not limited to the dimensions in the drawings.

[0033] In addition, in this specification and other documents, ordinal numbers such as "first" and "second" are used for convenience, but these numbers do not indicate the order of the steps or the order of stacking. Therefore, for example, "first" can be appropriately replaced with "second" or "third" to provide a more detailed description. Furthermore, the ordinal numbers used in this specification and other documents may not match the ordinal numbers used to designate one embodiment of the present invention.

[0034] In addition, in this specification, etc., the particles are not limited to spherical (circular cross-sectional shape), and the cross-sectional shape of each particle can also be elliptical, rectangular, trapezoidal, triangular, a quadrilateral with curved corners, an asymmetric shape, etc., and each particle can also be amorphous.

[0035] (Implementation Method 1) In this embodiment, an example of a secondary battery which is one embodiment of the present invention is described.

[0036] [Structural Example of Secondary Battery] A secondary battery including a positive electrode, a negative electrode, and an electrolyte is described below.

[0037] Figure 1A : is a schematic cross-sectional view showing the interior of a secondary battery according to one embodiment of the present invention. Figure 1A The negative electrode 570a, positive electrode 570b, and electrolyte 576 shown are applicable to coin-type secondary batteries, cylindrical secondary batteries, and laminated secondary batteries described in the following embodiments. The negative electrode 570a includes at least a negative electrode current collector 571a and a negative electrode active material layer 572a formed in contact with the negative electrode current collector 571a. The positive electrode 570b includes at least a positive electrode current collector 571b and a positive electrode active material layer 572b formed in contact with the positive electrode current collector 571b. Figure 1B yes Figure 1A Magnified view of the area surrounded by the dotted line C in FIG. Figure 1C It is an explanation Figure 1A Graph showing the capacity ratio of the negative electrode 570a to the positive electrode 570b in the region surrounded by the dotted line A and the dotted line B. The secondary battery may include a separator between the negative electrode 570a and the positive electrode 570b.

[0038] [Capacity ratio of negative electrode to positive electrode] Figure 1C 、 Figure 2A 、 Figure 2B and Figure 2CThe negative electrode characteristic curve 560a and the positive electrode characteristic curve 560b shown are characteristic curves showing the relationship between the capacity and potential of the negative electrode active material layer 572a and the positive electrode active material layer 572b. Figure 1A The negative electrode 570 a and the positive electrode 570 b facing each other and having the same area in the region surrounded by the dotted line A and the dotted line B include the above-mentioned negative electrode active material layer 572 a and positive electrode active material layer 572 b.

[0039] Figure 1C The capacitance C1 in the negative electrode characteristic curve 560a is the total chargeable and dischargeable capacity of the negative electrode 570a. The total chargeable and dischargeable capacity of the negative electrode 570a refers to the charge capacity under the following circumstances: For example, a half-cell including the negative electrode 570a and lithium metal is manufactured, and after constant current discharge (0.2C, lower limit voltage is 0.01V), constant voltage discharge (lower limit current density is 0.02C) is performed, and then constant current charging (0.2C, upper limit voltage is 1V) is performed. In addition, Figure 1C Capacitor C2 in the positive electrode characteristic curve 560b is the capacity of the positive electrode in the fully charged state of the secondary battery. The fully charged state of the secondary battery in this specification refers to a charged state in which the rated capacity specified in, for example, JIS C8711 (2013) is obtained.

[0040] The capacity ratio of the negative electrode 570a to the positive electrode 570b in the secondary battery shows the percentage of the capacity of the positive electrode 570b when the capacity of the negative electrode 570a is 100% in the negative electrode 570a and the positive electrode 570b having the same area. Figure 2A As shown, when the capacity of the negative electrode 570a is equal to the capacity of the positive electrode 570b, the capacity ratio of the negative electrode 570a to the positive electrode 570b is 100%.

[0041] Next, refer to Figure 1C The following describes the case where the capacity ratio of the negative electrode 570a to the positive electrode 570b is less than 100%. A capacity ratio less than 100% means that the total charge and discharge capacity of the negative electrode 570a is greater than the charge and discharge capacity of the positive electrode 570b. Figure 1C The capacitance C1 of the negative electrode 570a is shown to be greater than the capacitance C2 of the positive electrode 570b.

[0042] As described above, when the capacity ratio is less than 100%, excess capacity is generated in capacitor C1 of negative electrode 570a, but this has the advantage of easily suppressing unintended lithium ion precipitation in negative electrode 570a. Furthermore, a secondary battery including negative electrode 570a according to one embodiment of the present invention, described later, has the following characteristics: when the capacity ratio is preferably 50% or more and less than 100%, and more preferably 70% or more and less than 90%, a secondary battery with high charge-discharge capacity and excellent charge-discharge cycle characteristics can be obtained.

[0043] The voltage of a secondary battery is described below. The voltage of a secondary battery can be considered as the difference between the positive electrode potential and the negative electrode potential. For example, Figure 2A ΔVa in represents the voltage of the secondary battery when the capacity ratio of the negative electrode 570a to the positive electrode 570b is 100%. Figure 2B ΔVb in represents the voltage of the secondary battery when the capacity ratio is less than 100%. Figure 2B As shown, when the capacity ratio is lower than 100%, the secondary battery is used in a region where the operating potential range of the negative electrode 570 a is high, whereby the voltage of the secondary battery decreases.

[0044] then, Figure 2C An example is shown in which the secondary battery voltage does not decrease even when the capacity ratio of the negative electrode 570a to the positive electrode 570b is less than 100%. Figure 2C The ΔVa and ΔVc shown are the same voltage value. Figure 2B The operating potential range of the positive electrode 570b is Figure 2A The operating potential range of the positive electrode 570b is the same as that of the positive electrode 570b. As mentioned above, the secondary battery voltage ΔVb is smaller than ΔVa. Figure 2C As shown in FIG. 5 , when the operating potential range of the positive electrode 570 b is expanded to a high potential, both the secondary battery voltages ΔVc and ΔVa become high values.

[0045] like Figure 2C As shown, a secondary battery with no voltage drop can be obtained even when the capacity ratio of the negative electrode 570a to the positive electrode 570b is less than 100%. In this case, the positive electrode 570b is exposed to a relatively high potential, so the positive electrode 570b needs to have high resistance to charge and discharge at high potentials. The positive electrode active material 100 shown in one embodiment of the present invention can have a stable crystal structure under high-potential charging, making it suitable as an active material included in the positive electrode 570b. The positive electrode active material 100 will be described in detail later.

[0046] [negative electrode] Figure 1B yes Figure 1A An enlarged view of the area surrounded by the dotted line C in FIG. Figure 1B As shown, the negative electrode active material layer 572 a includes a first active material 581 , a second active material 582 , a graphene compound 583 as a sheet-like material, and an electrolyte 576 . Figure 3A This schematic diagram illustrates a graphene compound 583 in contact with a first active material 581, covering, encapsulating, or wrapping around a second active material 582 located on the surface of the first active material 581. The graphene compound 583 included in the negative electrode 570a is preferably used, for example, as a conductive material. In one embodiment of the present invention, the conductive material can wrap around the active material via hydrogen bonding, thereby achieving a highly conductive electrode.

[0047] Various materials can be used as the first active material 581 and the second active material 582. When the particles of one embodiment of the present invention, i.e., particles containing oxygen-containing functional groups or fluorine atoms on the surface or particles including regions terminated by oxygen-containing functional groups or fluorine atoms on the surface, are used as the first active material 581 and the second active material 582, the affinity between the first active material 581 and the second active material 582 and the graphene compound 583 is improved. Figure 1B and Figure 3A As shown, the graphene compound 583 can contact the first active material 581 in a manner that covers, encapsulates, or wraps around the second active material 582 located on the surface of the first active material 581. The graphene compound 583 can wrap around the first active material 581 and the second active material 582, thereby realizing an electrode with high conductivity. The state of contact in a winding manner can also be said to be a state of contact not at a point but in a close contact manner. In addition, it can also be said to be a state of contact along the surface of the particle. In addition, it can also be said to be a state of contacting multiple particles in a surface manner. The materials that can be used as the first active material 581 and the second active material 582 will be described later.

[0048] Reference Figure 3B and Figure 3C A case where an active material whose volume changes greatly due to charge and discharge is used as the second active material 582 will be described. Figure 3B The following example illustrates a first active material 581, a second active material 582, and a graphene compound 583 as a sheet-like material. The graphene compound 583 is in contact with the first active material 581, covering, enveloping, or wrapping around the second active material 582 located on the surface of the first active material 581. The second active material 582 is located between the first active material 581 and the graphene compound 583, so it can be said that the graphene compound 583 is in contact with both the first active material 581 and the second active material 582. Figure 3C Show Figure 3B The volume of the second active material 582 shown increases due to charge or discharge. Because the graphene compound 583 is in contact with the first active material 581 by covering, enveloping, or wrapping around the second active material 582 located on the surface of the first active material 581, the electrical connection between the second active material 582 and the first active material 581 is maintained even if the volume of the second active material 582 increases due to charge or discharge. This also prevents electrode collapse.

[0049] When the graphene compound 583 is in contact with the active material in a manner that is wrapped around an active material such as the first active material 581 and the second active material 582, the contact area between the graphene compound 583 and the active material increases, and the conductivity of electrons migrating through the graphene compound 583 is improved. In addition, when the volume change of the active material due to charging and discharging is large, the separation of the active material can be effectively prevented by making the graphene compound 583 contact the active material in a manner that is wrapped around the active material. These effects are more significant when the graphene compound is in contact with the active material in a manner that is closely wrapped around the active material. Here, it is preferred that the size of the pores in the graphene compound 583 is sufficient to allow Li ions to pass through, and the number of pores is large enough not to block the electronic conductivity of the graphene compound 583.

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

[0051] As carbon fibers, for example, mesophase pitch-based carbon fibers, isotropic pitch-based carbon fibers, etc. can be used. As carbon fibers, carbon nanofibers or carbon nanotubes can be used. For example, carbon nanotubes can be produced by vapor phase growth methods, etc.

[0052] Furthermore, the active material layer may contain metal powder selected from copper, nickel, aluminum, silver, gold, etc., metal fibers, conductive ceramic materials, etc. as a conductive material.

[0053] The content of the conductive material is preferably 0.5 wt % to 10 wt %, and more preferably 0.5 wt % to 5 wt %, relative to the total solid weight of the active material layer.

[0054] Unlike granular conductive agents such as carbon black, which form point contact with the active material, graphene compounds form surface contact with low contact resistance. Therefore, the conductivity between the granular active material and the graphene compound can be improved with a smaller amount of graphene compound than with conventional conductive agents. Consequently, the proportion of active material in the active material layer can be increased, thereby increasing the discharge capacity of the secondary battery.

[0055] Furthermore, the graphene compound according to one embodiment of the present invention has excellent lithium permeability, and thus can increase the charge and discharge rate of the secondary battery.

[0056] Carbon compounds in the form of particles such as carbon black and graphite and carbon compounds in the form of fibers such as carbon nanotubes can easily enter tiny spaces. For example, tiny spaces refer to areas between multiple active materials. By combining carbon compounds that can easily enter tiny spaces and sheet-like carbon compounds such as graphene that can impart conductivity to multiple particles, the density of the electrode can be increased and a good conductive path can be formed. In addition, by making the secondary battery include the electrolyte 576 of one embodiment of the present invention, the operating stability of the secondary battery can be improved. That is, the secondary battery of one embodiment of the present invention can have both high energy density and stability, and is very effective as a vehicle-mounted secondary battery. When the increase in the number of secondary batteries increases the weight of the vehicle, the energy required for movement increases, and thus the cruising range becomes shorter. By using high-density secondary batteries, the cruising range can be extended even if the weight of the secondary batteries installed on the vehicle is the same, that is, the total weight of the vehicle is the same.

[0057] As the capacity of a vehicle's secondary battery increases, more charging power is required, so charging is preferably completed quickly. Furthermore, since charging is performed under high-rate charging conditions during so-called regenerative charging, where temporary power is generated when the vehicle brakes and used for charging, vehicle secondary batteries require excellent rate characteristics.

[0058] By using the electrolyte 576 of one embodiment of the present invention, a secondary battery for use in a vehicle having a wide operating temperature range can be obtained.

[0059] Furthermore, the secondary battery of one embodiment of the present invention can be miniaturized due to its high energy density, and can be rapidly charged due to its high conductivity. Therefore, the structure of the secondary battery of one embodiment of the present invention is also effective in portable information terminals.

[0060] The negative electrode active material layer 572a preferably includes a binder (not shown). The binder, for example, binds or secures the electrolyte 576 and the active material. Furthermore, the binder can bind or secure the electrolyte 576 and the carbon-based material, the active material and the carbon-based material, multiple active materials and each other, or multiple carbon-based materials.

[0061] As adhesives, it is preferred to use materials such as polystyrene, polymethyl acrylate, 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.

[0062] Polyimide has very good and stable properties in terms of heat, mechanical and chemical aspects. In addition, when polyimide is used as a binder, a dehydration reaction and a cyclization (imidization) reaction are caused. These reactions can be caused, for example, by heat treatment. If a graphene having a functional group containing oxygen is used as a graphene compound in an electrode of one embodiment of the present invention, and polyimide is used as a binder, the graphene compound can be reduced by the heat treatment, thereby simplifying the process. In addition, because it has high heat resistance, it can be heat-treated at a heating temperature of 200°C or more, for example. By heat-treating at a heating temperature of 200°C or more, the reduction reaction of the graphene compound can be fully caused, thereby further improving the conductivity of the electrode.

[0063] As the binder, a fluorine-containing polymer, specifically, polyvinylidene fluoride (PVDF), etc. can be used. PVDF is a resin having a melting point in the range of 134° C. to 169° C. and has excellent thermal stability.

[0064] Furthermore, as the adhesive, preferably used are rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene-propylene-diene copolymer. Fluororubber can also be used as the adhesive.

[0065] In addition, as the binder, for example, a water-soluble polymer is preferably used. As the water-soluble polymer, for example, polysaccharides can also be used. As the polysaccharides, cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, regenerated cellulose, or starch can be used. More preferably, these water-soluble polymers and the above-mentioned rubber material are used in combination.

[0066] As the binder, a plurality of the above-mentioned materials may be used in combination.

[0067] Furthermore, the graphene compound 583 is flexible and can wrap around the first active material 581 and the second active material 582 like natto. Furthermore, for example, the first active material 581 and the second active material 582 can be compared to soybeans, and the graphene compound 583 can be compared to a viscous component such as polyglutamic acid. By placing the graphene compound 583 between the electrolyte 576, multiple active materials, multiple carbon-based materials, and other materials included in the negative electrode active material layer 572a, not only can a good conductive path be formed in the negative electrode active material layer 572a, but the graphene compound 583 can also be used to constrain or fix these materials. Furthermore, for example, by forming a three-dimensional mesh structure or a polygonal arrangement structure such as a honeycomb structure with hexagonal shapes arranged in a matrix, and arranging the electrolyte 576, multiple active materials, multiple carbon-based materials, and other materials in a mesh-like manner, the graphene compound 583 not only forms a three-dimensional conductive path but also prevents the electrolyte 576 from detaching from the current collector. Furthermore, in the aforementioned polygonal arrangement structure, polygons with different numbers of sides can be mixed. Therefore, the graphene compound 583 is sometimes used as both a conductive material and a binder in the negative electrode active material layer 572a. The graphene compound 583 has pores with nine or more rings, so even if it covers the active material, it does not hinder the movement of Li particles. Therefore, it is particularly preferred as a conductive material for the negative electrode active material layer 572a.

[0068] [Negative electrode active material] The first active material 581 and the second active material 582 can have various shapes such as a rounded shape, a shape with corners, etc. In addition, in the cross section of the electrode, the first active material 581 and the second active material 582 can have various cross-sectional shapes, such as a circle, an ellipse, a curved shape, a polygon, etc. For example, Figure 1B and Figure 3A Although the first active material 581 and the second active material 582 have rounded cross sections, the first active material 581 and the second active material 582 may have corners. Alternatively, they may have a partially rounded shape and a partially cornered shape.

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

[0070] Silicon can be used as the negative electrode active material. In the negative electrode 570 a , particles containing silicon are preferably used as the second active material 582 .

[0071] Furthermore, a metal or compound containing one or more elements selected from tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium can be used as the negative electrode active material included in the second active material 582. Examples of alloy compounds using such elements include Mg2Si, Mg2Ge, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, and SbSn.

[0072] In addition, a material that achieves low resistance by adding impurity elements such as phosphorus, arsenic, boron, aluminum, gallium, etc. to silicon can also be used. In addition, a silicon material pre-doped with lithium can also be used. As a pre-doping method, there is a method of mixing lithium fluoride, lithium carbonate, etc. with silicon for annealing, a method of mechanical alloying between lithium metal and silicon, etc. In addition, after forming a first electrode with silicon as an active material, it is also possible to dope lithium into the silicon in the first electrode by combining it with a second electrode such as lithium metal to cause a charge and discharge reaction, so as to combine the doped first electrode and an electrode serving as a counter electrode (for example, a positive electrode relative to the pre-doped negative electrode) to manufacture a secondary battery.

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

[0074] Nano silicon particles may have a spherical shape, a flat spherical shape, or a rectangular parallelepiped shape with rounded corners. For example, the D50 measured by laser diffraction particle size distribution measurement is preferably 5 nm or more and less than 1 μm in size (particle diameter) of the nano silicon particles, more preferably 10 nm or more and 300 nm or less, and even more preferably 10 nm or more and 100 nm or less. Here, D50 is the particle diameter when the cumulative amount accounts for 50% in the cumulative particle amount curve of the particle size distribution measurement result, that is, the median. The measurement of particle size is not limited to laser diffraction particle size distribution measurement, and the major axis of the particle cross section can also be measured by analysis using SEM (Scanning Electron Microscope: scanning electron microscope) or TEM (Transmission Electron Microscope: transmission electron microscope).

[0075] The nano-silicon particles preferably contain amorphous silicon. In addition, the nano-silicon particles preferably contain polycrystalline silicon. The nano-silicon particles preferably contain amorphous silicon and polycrystalline silicon. In addition, the nano-silicon particles may also include a crystalline region and an amorphous region.

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

[0077] As a material containing silicon, for example, a method of containing multiple grains within a single particle can be used. For example, a method of containing one or more silicon grains within a single particle can be used. In addition, the single particle can also contain silicon oxide around the silicon grains. In addition, the silicon oxide can also be amorphous. In addition, a particle can also be formed in which silicon secondary particles are surrounded by graphene compound 583.

[0078] In addition, as a compound containing silicon, for example, Li2SiO3 and Li4SiO4 can be contained. Li2SiO3 and Li4SiO4 can be crystalline or amorphous.

[0079] Compounds containing silicon can be analyzed by NMR, XRD, Raman spectroscopy, SEM, TEM, EDX, and the like.

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

[0081] The first active material 581 is more preferably a material that causes a small volume change due to charge and discharge.

[0082] As for the volume change of the first active material 581 caused by charging or discharging, when the minimum volume during charging or discharging is 1, the maximum volume during charging or discharging is preferably 2 or less, more preferably 1.5 or less, and even more preferably 1.1 or less.

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

[0084] For example, the D50 of the first active material 581 measured by laser diffraction particle size distribution measurement is preferably 1.5 times or more and less than 1000 times the D50 of the second active material 582, more preferably 2 times or more and less than 500 times, and even more preferably 10 times or more and less than 100 times. Here, D50 is the particle size at which the cumulative amount accounts for 50% in the cumulative particle amount curve of the particle size distribution measurement result, that is, the median value. In addition, the measurement of particle size is not limited to laser diffraction particle size distribution measurement, and the diameter of the particle cross section can also be measured by analysis such as SEM or TEM.

[0085] As the first active material 581 , for example, a carbon material such as graphite, graphitizable carbon, non-graphitizable carbon, carbon nanotubes, carbon black, or graphene compound 583 that undergoes a small volume change due to charge and discharge can be used.

[0086] Alternatively, as the first active material 581 , for example, an oxide containing one or more elements selected from titanium, niobium, tungsten, and molybdenum can be used.

[0087] As the first active material 581 , a plurality of the above-mentioned metals, materials, compounds, etc. may be combined.

[0088] For example, as the first active material 581, oxides such as SnO, SnO2, titanium dioxide (TiO2), lithium titanium oxide (Li4Ti5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), molybdenum oxide (MoO2), etc.

[0089] Alternatively, a material that causes a conversion reaction may be used for the first active material 581. For example, a transition metal oxide that does not react with lithium to form an alloy, such as cobalt oxide (CoO), nickel oxide (NiO), or iron oxide (FeO), may be used for the first active material 581. Examples of materials that cause a conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3. CoS 0.89 Sulfides such as NiS, CuS, nitrides such as Zn3N2, Cu3N, Ge3N4, phosphides such as NiP2, FeP2, CoP3, fluorides such as FeF3, BiF3. In addition, the above fluorides have high potentials, so they can also be used as positive electrode materials.

[0090] [Calculation of negative electrode 1] In the negative electrode 570 a according to one embodiment of the present invention, graphite is used as the first active material 581 and silicon is used as the second active material 582 . A first principle calculation was performed on the diffusion coefficients of lithium in the first active material 581 and the second active material 582 .

[0091] Figure 4A Shown for graphite (Li 0.25 C6) calculated crystal structure model, Figure 4B Shown for silicon (Li 1.25 Calculated crystal structure model of Si).

[0092] The calculations were performed using the first-principles electronic state calculation program VASP. The specific calculation conditions used were those shown in Table 1.

[0093] [Table 1]

[0094] At each temperature Figure 4A and Figure 4B The crystal structure model shown was subjected to volume relaxation calculations, followed by MD (molecular dynamics) calculations under fixed volume conditions. MD calculations were performed in multiple steps, and the diffusion coefficient was derived from the relationship between the displacement of lithium and the elapsed time in each step.

[0095] Figure 5 Show Figure 4A 、 Figure 4B The calculated results are shown in Table 1. The calculated results show that the diffusion coefficient of lithium in graphite is higher than that in silicon.

[0096] The relationship between the redox potentials of graphite and silicon is known to be 0.05 V (vs. Li) for graphite and 0.4 V (vs. Li) for Si. The redox potential is related to the voltage at which charging (lithium absorption) begins. When considering the priority of lithium insertion during charging, it is believed that lithium is preferentially absorbed into Si, which has a higher redox potential.

[0097] Combine Figure 5 Based on the calculated results of the diffusion coefficient shown in the figure and the relationship between the redox potential, it is speculated that the following is possible: due to the difference in redox potential, lithium is preferentially absorbed into silicon at the beginning of charging, but as charging progresses, due to the difference in lithium absorption rate, lithium is gradually preferentially absorbed into graphite with a large diffusion coefficient (fast absorption rate). From this, it can be speculated that when the capacity is limited in the negative electrode 570a of one embodiment of the present invention, the graphite of the first active material 581 absorbs lithium until the theoretical capacity of the graphite is approached, and the silicon of the second active material 582 absorbs the remaining lithium. In other words, when the capacity is limited in the negative electrode 570a of one embodiment of the present invention, it is possible that the graphite of the first active material 581 is preferentially used for charging and discharging compared to the silicon of the second active material 582, and the effect of capacity limitation mainly affects the silicon of the second active material 582.

[0098] [Calculation of negative electrode 2] Figure 6A shows silicon crystals that do not contain lithium, Figure 6B and Figure 6C The structure of silicon in a charged state (a state alloyed with Li) is shown.

[0099] Figure 6B The structure when Li / Si=1.714 is shown, and it can be seen that Si-Si bonds remain in the structure. Figure 6CThe crystal structure of Li / Si=4.4 shown above has a high Li ratio and no Si-Si bond in the structure. The above Li / Si=4.4 is the limit value in theoretical capacity. It is known that the crystal structure of silicon collapses and becomes amorphous and thinner during repeated charge and discharge. However, for example, in the fully charged state of a secondary battery, some silicon remains. Figure 6B When the Si-Si bond shown in FIG. 1 is formed, it is considered that the structure is likely to be maintained to a certain extent even if charge and discharge are repeated. Figure 6B When the lithium ratio (molar ratio) of Li / Si=1.714 or less is used, it is possible to exhibit good charge and discharge cycle characteristics.

[0100] [Capacity limitation of negative electrode] The negative electrode 570a of one embodiment of the present invention is preferably used in a secondary battery with a capacity lower than the theoretical capacity of the first active material 581 and the second active material 582. As a capacity limitation for the negative electrode 570a, for example, the capacity ratio is preferably 50% or more and less than 100% of the theoretical capacity of the first active material 581 and the second active material 582, and more preferably 70% or more and less than 90%. This is preferred because a secondary battery with high charge-discharge capacity and excellent charge-discharge cycle characteristics can be obtained.

[0101] [Method for manufacturing negative electrode] Figure 7 This is a flowchart illustrating an example of a method for manufacturing the negative electrode 570 a according to one embodiment of the present invention.

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

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

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

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

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

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

[0108] Next, in step S81, the mixture E-2 and the graphene compound 583 prepared in step S80 are mixed, and the mixture is recovered in step S82. The recovered mixture is preferably in a state of high viscosity. When the viscosity of the mixture is high, dry-mixing (mixing at high viscosity) can be performed in the next step S83.

[0109] Next, dry-mixing is performed in step S83. Dry-mixing can be performed using, for example, a spatula. Dry-mixing can form a mixture in which silicon-containing particles and the graphene compound 583 are well mixed and the graphene compound 583 has good dispersion.

[0110] Next, in step S84, a solvent is added to the dry-kneaded mixture and mixed. For example, a kneader can be used for mixing. In step S85, the mixed mixture is recovered.

[0111] The steps from step S83 to step S85 are preferably repeated n times for the mixture recovered in step S85. n is, for example, a natural number of 2 or more and 10 or less. Furthermore, when the mixture is dry in step S83, it is preferable to add a solvent. On the other hand, adding too much solvent decreases the viscosity, thereby reducing the effect of dry-mixing.

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

[0113] Next, in step S87, an adhesive is prepared. The above materials can be used as the adhesive, and polyimide is particularly preferred. Note that in step S87, a precursor of the adhesive material may be prepared. For example, a polyimide precursor may be prepared.

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

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

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

[0117] Next, in step S94, the mixture E-4 is applied to the current collector prepared in step S93. Application can be performed using, for example, a slot die method, a gravure method, a blade method, or a combination thereof. Alternatively, application can be performed using a continuous coater or the like.

[0118] Next, in step S95, first heating is performed. The solvent is volatilized by the first heating. The first heating is performed at a temperature of 40°C to 200°C, preferably 50°C to 150°C. The first heating is sometimes referred to as drying.

[0119] For example, the first heating may be performed by heating at a temperature of 30°C to 70°C in an atmospheric atmosphere using a hot plate for 10 minutes or more, and then heating at a temperature of room temperature to 100°C in a reduced pressure environment for 1 hour to 10 hours.

[0120] Alternatively, the heat treatment may be performed using a drying furnace, etc. When a drying furnace is used, the heat treatment may be performed at a temperature of 30° C. to 120° C. for 30 seconds to 2 hours, for example.

[0121] Alternatively, the temperature may be increased in stages. For example, a heat treatment may be performed at a temperature of 60° C. or lower for 10 minutes or less, and then a heat treatment may be performed at a temperature of 65° C. or higher for 1 minute or more.

[0122] Next, a second heating is performed in step S96. When polyimide is used as an adhesive, a cycloaddition reaction of the polyimide is preferably caused by the second heating. In addition, a dehydration reaction of the polyimide may sometimes occur by the second heating. Alternatively, a dehydration reaction of the polyimide may occur by the first heating. In addition, a cyclization reaction of the polyimide may also occur in the first heating. In addition, a reduction reaction of the graphene compound 583 is preferably caused in the second heating. The second heating is sometimes referred to as imidization heat treatment, reduction heat treatment, or thermal reduction treatment.

[0123] Note that, by performing the press treatment before the second heating, the electrode density can be increased without degrading the battery characteristics, and therefore, it is preferable to perform the press treatment before step S96.

[0124] The second heating is performed in a temperature range of 150° C. to 500° C., preferably 200° C. to 450° C.

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

[0126] In step S97 , a negative electrode 570 a having an active material layer disposed on a current collector is obtained. The thickness of the active material layer formed by the above steps is preferably 5 μm to 300 μm, more preferably 10 μm to 150 μm. The active material loading of the active material layer is preferably 2 mg / cm 2 Above and 50mg / cm 2 the following.

[0127] The active material layer may be formed on both sides of the current collector or only on one side of the current collector. Alternatively, the active material layer may be partially formed on both sides of the current collector.

[0128] After the solvent is volatilized from the active material layer, the layer may be pressed using a compression method such as a roller pressing method or a plate pressing method. Heating may be applied during the pressing.

[0129] [positive electrode] The positive electrode 570b includes at least a positive electrode current collector 571b and a positive electrode active material layer 572b formed in contact with the positive electrode current collector 571b. The positive electrode 570b will be described in detail in the following embodiments.

[0130] [Conductive materials] Conductive materials, also known as conductivity-imparting agents or conductive additives, use carbon materials. By attaching the conductive agent between multiple active materials, the active materials become electrically connected, improving conductivity. Note that "attachment" does not mean that the active material and conductive agent are physically in close contact. Rather, it encompasses situations such as covalent bonding, van der Waals bonding, covering a portion of the active material's surface, embedding the conductive agent in the surface irregularities of the active material, and even electrical connection without contact.

[0131] As the conductive material, for example, any one or two or more of carbon black such as acetylene black and furnace black, graphite such as artificial graphite and natural graphite, carbon fibers such as carbon nanofibers and carbon nanotubes, and graphene compounds 583 can be used.

[0132] To secure the current collector 571b (e.g., metal foil) and the active material, the secondary battery's positive electrode 570b is mixed with a binder (resin). This binder is also called a bonding agent. A binder is a polymer material. Excessive amounts of binder decrease the ratio of active material in the positive electrode active material layer 572b, reducing the discharge capacity of the secondary battery. Therefore, a minimum amount of binder is used.

[0133] Graphene is a carbon material that has been expected to be applied in various technological fields, such as field-effect transistors and solar cells, due to its excellent electrical, mechanical, and chemical properties.

[0134] In addition, carbon fibers can be used as the conductive material. For example, carbon fibers such as mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers can be used. As carbon fibers, carbon nanofibers or carbon nanotubes can be used. For example, carbon nanotubes can be produced by vapor phase growth methods.

[0135] [Graphene compounds] The graphene compound 583 in this specification and the like includes 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. The graphene compound 583 refers to a compound containing carbon and having a flat plate, sheet, or other shape having a two-dimensional structure formed by a carbon 6-membered ring. In addition, the two-dimensional structure formed by the carbon 6-membered ring can also be referred to as a carbon sheet. The graphene compound 583 can also have a functional group containing oxygen. In addition, the graphene compound 583 preferably has a curved shape. In addition, the graphene compound 583 can also be curled up like a carbon nanofiber.

[0136] Furthermore, in this specification and the like, graphene oxide refers to, for example, a graphene compound containing carbon and oxygen, having a sheet-like shape, and including a functional group, particularly an epoxy group, a carboxyl group, or a hydroxyl group.

[0137] In this specification, reduced graphene oxide, for example, contains carbon and oxygen, has a sheet-like shape, and has a two-dimensional structure formed using a six-membered carbon ring. Reduced graphene oxide may also be referred to as a carbon sheet. A single layer of reduced graphene oxide is sufficient, but a stacked structure may also be employed. Reduced graphene oxide preferably has a portion with a carbon concentration greater than 80 atomic percent and an oxygen concentration of 2 atomic percent to 15 atomic percent. By having these carbon and oxygen concentrations, even a small amount of reduced graphene oxide can function as a highly conductive agent. Furthermore, the intensity ratio G / D of the G band to the D band in the Raman spectrum of reduced graphene oxide is preferably greater than 1. Even a small amount of reduced graphene oxide having this intensity ratio can function as a highly conductive agent.

[0138] By reducing graphene oxide, pores may be formed in the reduced graphene.

[0139] Furthermore, as the graphene compound, a material in which the end portion of graphene is terminated with fluorine may be used.

[0140] In a longitudinal cross-section of the active material layer, flake-shaped graphene compounds 583 are dispersed approximately uniformly within the inner region of the active material layer. Since the graphene compounds are formed to partially cover or adhere to the surfaces of the active material particles, the graphene compounds are in surface contact with the active material particles.

[0141] Here, by combining a plurality of graphene compounds 583 with each other, a mesh-shaped graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net) can be formed. When the graphene net covers the active material, the graphene net can be used as an adhesive to combine the active materials with each other. Therefore, the amount of adhesive can be reduced or no adhesive is used, thereby increasing the ratio of the active material to the electrode volume and the electrode weight. In other words, the charge and discharge capacity of the secondary battery can be increased.

[0142] Here, it is preferred to use graphene oxide as the graphene compound 583, mix the graphene oxide with an active material to form a layer to become the active material layer, and then reduce the graphene oxide. In other words, the completed active material layer preferably contains reduced graphene oxide. By using graphene oxide with extremely high dispersibility in a polar solvent when forming the active material layer containing the graphene compound 583, the graphene compound 583 can be dispersed roughly uniformly within the internal region of the active material layer.

[0143] After applying a dispersion of graphene oxide uniformly dispersed in a solvent to a current collector and removing the solvent by evaporation, the graphene oxide is reduced to produce an active material layer. The graphene compound 583 contained in the active material layer partially overlaps. In this manner, if the reduced graphene oxide is dispersed in surface contact with each other, a three-dimensional conductive path can be formed. Alternatively, the graphene oxide can be reduced, for example, by heat treatment or the use of a reducing agent.

[0144] Furthermore, a conductive path can be formed by previously covering the surface of the active material with a graphene compound to form a conductive film on the surface of the active material and electrically connecting the active materials using the graphene compound.

[0145] The graphene compound 583 of one embodiment of the present invention preferably has pores in a portion of the carbon sheet. In the graphene compound 583 of 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 carrier ions can be easily inserted and removed from the surface of the active material covered by the graphene compound 583, thereby improving the rate characteristics of the secondary battery. The pores provided in a portion of the carbon sheet are sometimes referred to as vacancies, defects, or voids.

[0146] The graphene compound 583 of one embodiment of the present invention preferably has a hole provided by a plurality of carbon atoms and one or more fluorine atoms. In addition, the plurality of carbon atoms are preferably bonded in a ring shape, and one or more of the plurality of carbon atoms bonded in a ring shape are preferably terminated by the fluorine atom. Fluorine has high electronegativity and is easily negatively charged. When positively charged lithium ions approach, interactions occur and the energy becomes stable, thereby reducing the energy barrier (barrier energy) for lithium ions to pass through the hole. Therefore, by making the hole of the graphene compound 583 contain fluorine, lithium ions easily pass through smaller holes, and a graphene compound 583 with good conductivity can be achieved. In addition, one or more of the plurality of carbon atoms bonded in a ring shape can also be terminated by hydrogen.

[0147] Figure 8A and Figure 8B An example of the structure of a graphene compound 583 including holes is shown. Figure 8A and Figure 8B The illustrated graphene compound 583 including pores is also referred to as graphene including pores or reduced graphene including pores.

[0148] Figure 8A The structure shown includes a 22-membered ring, 8 of which are terminated by hydrogen. Figure 8A The graphene compound 583 has a structure in which two linked six-membered rings are removed and the carbon atoms bonded to the removed six-membered rings are terminated with hydrogen.

[0149] Figure 8B The structure shown includes a 22-membered ring, of which 6 of the 8 carbon atoms are terminated by hydrogen and 2 by fluorine. Figure 8B The graphene compound 583 has a structure in which two linked six-membered rings are removed, and the carbon atoms bonded to the removed six-membered rings are terminated with hydrogen or fluorine.

[0150] The silicon terminated with hydroxyl groups has a strong interaction with the graphene compound 583 including pores because hydrogen contained in the hydroxyl groups on the silicon surface forms hydrogen bonds with hydrogen atoms contained in the graphene compound 583 or fluorine atoms contained in the graphene compound 583 .

[0151] The graphene compound 583 contains not only hydrogen but also fluorine. Therefore, in addition to the hydrogen bonds between the oxygen atoms of the hydroxyl group and the hydrogen atoms of the graphene compound 583, hydrogen bonds are also formed between the hydrogen atoms of the hydroxyl group and the fluorine atoms of the graphene compound 583. Therefore, it can be considered that the interaction between the particles containing silicon and the graphene compound 583 is stronger and more stable.

[0152] When the graphene compound 583 has pores, it is possible to observe a spectrum based on characteristics attributable to the pores, for example, by Raman spectroscopy mapping measurement. Furthermore, it is possible to observe the bonds and functional groups constituting the pores by ToF-SI MS. Furthermore, it is possible to observe and analyze the vicinity of the pores and the periphery of the pores by TEM.

[0153] [Adhesive] In this specification and other publications, the term "binder" refers to a polymer compound added solely to bond active materials, conductive agents, and the like to the 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 copolymers; fluororubber, polystyrene, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, and ethylene-propylene-diene polymers.

[0154] Because lithium-ion conductive polymers are high-molecular compounds, thoroughly mixing them for use in the active material layer allows the active material and conductive agent to be bonded to the current collector. Therefore, electrodes can be manufactured without a binder. Binders are materials that do not contribute to the charge and discharge reactions. Therefore, the less binder used, the more active material, electrolyte, and other materials that contribute to charge and discharge can be added. This allows for a secondary battery with improved discharge capacity and cycle characteristics.

[0155] In order to make the electrolyte 576 an electrolyte layer containing no organic solvent or very little organic solvent, it is preferable to fully dry the electrolyte layer. Note that in this specification, a weight change of the electrolyte layer of less than 5% when dried under reduced pressure at 90°C for 1 hour is considered to be fully dried.

[0156] Note that nuclear magnetic resonance (NMR) can be used, for example, to identify materials such as lithium-ion conductive polymers, lithium salts, binders, and additives included in secondary batteries. Furthermore, analysis results from 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) can also be used as a basis for judgment. Preferably, the active material layer is suspended in a solvent, the active material is separated from other materials, and then an NMR analysis is performed.

[0157] In each of the above structures, the negative electrode 570a may further include a solid electrolyte material to improve flame retardancy. As the solid electrolyte material, an oxide-based solid electrolyte is preferably used.

[0158] As oxide-based solid electrolytes, LiPON, Li2O, Li2CO3, Li2MoO4, Li3PO4, Li3VO4, Li4SiO4, LLT(La 2 / 3-x Li 3x TiO3), LLZ(Li7La3Zr2O 12 ) and other lithium composite oxides and lithium oxide materials.

[0159] LLZ is a garnet-type oxide containing Li, La, and Zr, and may be a compound further containing Al, Ga, or Ta.

[0160] Alternatively, a polymer solid electrolyte such as PEO (polyethylene oxide) formed by a coating method may be used. Since such a polymer solid electrolyte can also be used as a binder, the number of electrode components and manufacturing costs can be reduced when using a polymer solid electrolyte.

[0161] [current collector] As the positive electrode current collector 571b and the negative electrode current collector 571a, materials with high conductivity such as stainless steel, gold, platinum, zinc, iron, copper, aluminum, titanium, and their alloys, which do not alloy with carrier ions such as lithium, can be used. In addition, aluminum alloys added with elements such as silicon, titanium, neodymium, scandium, and molybdenum to improve heat resistance can be used. In addition, metal elements that react with silicon to form silicides can also be used. As the metal elements that react with silicon to form silicides, there are zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, etc. As the current collector, shapes such as sheet, mesh, punched metal mesh, and drawn metal mesh can be appropriately used. The thickness of the current collector is preferably 10 mm or more and 30 mm or less.

[0162] In addition, as the negative electrode current collector 571a, a material that does not alloy with carrier ions such as lithium is preferably used.

[0163] As the current collector, a titanium compound can also be provided in a manner laminated on the above metal element. As the titanium compound, for example, one or more selected from titanium nitride, titanium oxide, oxynitride titanium (TiO x N y , 0 < x < 2, 0 < y < 1), and titanium oxide in which a part of oxygen is replaced by nitrogen can be mixed or laminated and used. Among them, titanium nitride is particularly preferred because it has high conductivity and a high oxidation inhibition function. By providing the titanium compound on the surface of the current collector, for example, the reaction between the material contained in the active material layer formed on the current collector and the metal can be suppressed. When the active material layer contains a compound containing 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 following graphene oxide is used to form the active material layer, there is a concern about the oxidation reaction between the oxygen contained in the graphene oxide and aluminum. In this case, by providing a titanium compound on the aluminum, the oxidation reaction between the current collector and the graphene oxide can be suppressed.

[0164] [Separator] A separator is disposed between the positive electrode 570b and the negative electrode 570a. As the separator, for example, the following materials can be used: fibers having cellulose such as paper, non-woven fabric, glass fiber, ceramic, or synthetic fibers including nylon (polyamide), vinylon (polyvinyl alcohol fiber), polyester, acrylic resin, polyolefin, and polyurethane. The separator is preferably processed into a bag shape and disposed so as to surround either the positive electrode 570b or the negative electrode 570a.

[0165] The separator is a porous material having pores with a diameter of about 20 nm, preferably having pores with a diameter of 6.5 nm or more, and more preferably having pores with a diameter of at least 2 nm. In the case of the above semi-solid secondary battery, the separator can also be omitted.

[0166] The separator can have a multilayer structure. For example, a thin film of an organic material such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture of these materials. 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 aromatic polyamides (meta-aramid and para-aramid).

[0167] Applying ceramic materials can improve oxidation resistance, thereby suppressing separator degradation during high-voltage charging and discharging, thereby improving the reliability of the secondary battery. Applying fluorine-based materials facilitates close contact between the separator and the electrode, thereby improving output characteristics. Applying polyamide materials (especially aromatic polyamide) can improve heat resistance, thereby improving the safety of the secondary battery.

[0168] For example, a mixture of aluminum oxide and aramid can be coated on both sides of the polypropylene film. Alternatively, the surface of the polypropylene film in contact with the positive electrode 570b can be coated with a mixture of aluminum oxide and aramid, while the surface in contact with the negative electrode 570a can be coated with a fluorine-based material.

[0169] By adopting a separator having a multi-layer structure, the safety of the secondary battery can be ensured even if the thickness of the separator as a whole is small, and thus the capacity per unit volume of the secondary battery can be increased.

[0170] [Electrolytes] In addition, when a liquid electrolyte 576 is used as a secondary battery, for example, as the electrolyte 576, one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, vinyl chloride 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, cyclopentane, sultone, etc. can be used, or two or more of the above can be mixed in any combination and ratio and used.

[0171] In addition, by using one or more ionic liquids (room temperature molten salts) with flame retardancy and low volatility as the solvent of the electrolyte 576, even if the internal area of ​​the secondary battery is short-circuited or overcharged, the temperature of the internal area is increased, and the rupture or fire of the secondary battery can be prevented. The ionic liquid is composed of cations and anions, including organic cations and anions. As organic cations, aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations and quaternary phosphonium cations and aromatic cations such as imidazolium cations and pyridinium cations can be cited. In addition, as anions, monovalent amide anions, monovalent methylated anions, fluorosulfonic acid anions, perfluoroalkyl sulfonic acid anions, tetrafluoroborate anions, perfluoroalkyl borate anions, hexafluorophosphate anions or perfluoroalkyl phosphate anions can be cited.

[0172] In the secondary battery of one embodiment of the present invention, it is particularly preferable to use a liquid electrolyte 576 containing an ionic liquid when silicon is used as the second active material 582 included in the negative electrode 570 a .

[0173] The carrier ions of the secondary battery as one embodiment of the present invention include, for example, one or more of the following ions: alkali metal ions such as lithium ion, sodium ion, and potassium ion; and alkaline earth metal ions such as calcium ion, strontium ion, barium ion, beryllium ion, and magnesium ion.

[0174] When lithium ions are used as carrier ions, the electrolyte contains a lithium salt. For example, as lithium salts, LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl 10 、Li2B 12 Cl 12 , LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, etc.

[0175] Furthermore, the electrolyte preferably contains fluorine. As a fluorine-containing electrolyte, for example, an electrolyte containing one or more fluorinated cyclic carbonates and lithium ions can be used. Fluorinated cyclic carbonates can improve flame retardancy and enhance the safety of lithium-ion secondary batteries.

[0176] As fluorinated cyclic carbonate, fluorinated ethylene carbonate can be used, for example, monofluoroethylene carbonate (fluoroethylene carbonate, FEC, F1EC), bisfluoroethylene carbonate (DFEC, F2EC), trifluoroethylene carbonate (trifluoroethylene carbonate) (F3EC) or tetrafluoroethylene carbonate (tetrafluoroethylene carbonate) (F4EC) etc. can be used. In addition, as DFEC, there are isomers such as cis-4,5, trans-4,5. From the viewpoint of working at low temperatures, it is important to use one or more fluorinated cyclic carbonates to solvate lithium ions and transmit the lithium ions in the electrolyte included in the electrode during charge and discharge. By making the fluorinated cyclic carbonate contribute to the lithium ion transmission during charge and discharge without playing the role of a small amount of additive, it is possible to achieve work at low temperatures. In the secondary battery, lithium ions migrate in a block of more than a few and dozens of pieces.

[0177] By using a fluorinated cyclic carbonate as an electrolyte, the desolvation energy required for lithium ions solvated in the electrolyte included in the electrode to enter the active material particles can be reduced. If the desolvation energy can be reduced, it is easy for lithium ions to be embedded in or separated from the active material particles even in a low temperature range. In addition, lithium ions sometimes migrate in a solvated state, and sometimes a hopping phenomenon occurs in which solvent molecules coordinated with lithium ions are exchanged. When desolvation from lithium ions becomes easier, migration using the hopping phenomenon sometimes becomes easier, and the migration of lithium ions becomes easier. Since the decomposition products of the electrolyte entangle the surface of the active material during the charge and discharge of the secondary battery, the decomposition products of the secondary battery may deteriorate. However, when the electrolyte contains fluorine, the electrolyte is not sticky, and the decomposition products of the electrolyte are not easy to adhere to the surface of the active material. Therefore, the deterioration of the secondary battery can be suppressed.

[0178] Sometimes, a plurality of solvated lithium ions form clusters in the electrolyte, and the clusters migrate within the negative electrode 570 a , between the positive electrode 570 b and the negative electrode 570 a , within the positive electrode 570 b , and the like.

[0179] In this specification, electrolyte is a general term including solid, liquid or semi-solid materials and the like.

[0180] The interface existing in the secondary battery, such as the interface between the active material and the electrolyte, is prone to degradation. In the secondary battery of one embodiment of the present invention, by including an electrolyte containing fluorine, it is possible to prevent degradation that may occur at the interface between the active material and the electrolyte, typically the deterioration of the electrolyte or the high viscosity of the electrolyte. In addition, it is also possible to have a structure in which an electrolyte containing fluorine is wrapped with an adhesive or a graphene compound, or a structure in which an electrolyte containing fluorine holds an adhesive or a graphene compound. By having this structure, a state in which the viscosity of the electrolyte is reduced can be maintained, in other words, a non-sticky state of the electrolyte can be maintained, thereby improving the reliability of the secondary battery. Compared with FEC bonded to one fluorine, DFEC bonded to two fluorines and F4EC bonded to four fluorines have lower viscosity and are less sticky, and have weaker coordination bonds with lithium. Thus, it is possible to suppress the adhesion of high-viscosity decomposition products to active material particles. When high-viscosity decomposition products adhere to active material particles or when high-viscosity decomposition products wrap around active material particles, lithium ions are not easy to migrate at the interface of the active material particles. Fluorine-containing electrolytes mitigate the generation of decomposition products that adhere to the surface of the active material (positive electrode active material or negative electrode active material) by being solvated. Furthermore, by preventing the adhesion of decomposition products, the generation and growth of dendrites can be prevented by using fluorine-containing electrolytes.

[0181] Another feature is that an electrolyte containing fluorine is used as a main component. The electrolyte containing fluorine is 5 vol.% or more, 10 vol.% or more, and preferably 30 vol.% or more and 100 vol.% or less.

[0182] In this specification, the main component of the electrolyte refers to the component that accounts for 5% or more of the total electrolyte in the secondary battery. Here, "5% or more of the total electrolyte in the secondary battery" refers to the proportion of the component in the total electrolyte measured during the manufacture of the secondary battery. Furthermore, when a secondary battery is disassembled after manufacture, it is difficult to quantify the individual proportions of multiple electrolytes. However, it is possible to determine whether a particular organic compound accounts for 5% or more of the total electrolyte.

[0183] By using an electrolyte containing fluorine, a secondary battery operable in a wide temperature range can be realized. Specifically, a secondary battery operable in a temperature range of -40°C to 150°C, preferably -40°C to 85°C, can be realized.

[0184] In addition, additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), lithium bis(oxaloyl borate) (LiBOB), or dinitrile compounds such as succinonitrile and adiponitrile may be added to the electrolyte. The concentration of the additives may be set to, for example, 0.1 vol.% or more and less than 5 vol.% of the total electrolyte.

[0185] Furthermore, the electrolyte may contain one or more aprotic organic solvents such as γ-butyrolactone, acetonitrile, ethylene glycol dimethyl ether, and tetrahydrofuran in addition to the above.

[0186] Furthermore, the electrolyte containing a gelled polymer material improves safety against leakage, etc. Typical examples of gelled polymer materials include silicone glue, acrylic glue, acrylonitrile glue, polyethylene oxide glue, polypropylene oxide glue, and fluorine polymer glue.

[0187] As polymer materials, for example, polymers having a polyoxyalkylene structure such as polyethylene oxide (PEO), PVDF and polyacrylonitrile, and copolymers thereof can be used. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. In addition, the formed polymer may also have a porous shape.

[0188] Furthermore, although the above examples illustrate secondary batteries using liquid electrolytes, the present invention is not limited thereto and, for example, semi-solid batteries and all-solid batteries may also be manufactured.

[0189] In this specification, the layer between the positive electrode 570b and the negative electrode 570a is referred to as the electrolyte layer, regardless of whether the secondary battery uses a liquid electrolyte or the semi-solid battery. The electrolyte layer of a semi-solid battery can be said to be a layer formed by deposition and can be distinguished from the liquid electrolyte layer.

[0190] In addition, in this specification, etc., a semi-solid battery refers to a battery in which at least one of the electrolyte layer, the positive electrode 570b, and the negative electrode 570a contains a semi-solid material. Here, semi-solid does not mean that the proportion of solid material is 50%. Semi-solid means having solid properties such as small volume change, and a portion thereof has properties close to liquid, such as flexibility. When having the above properties, a single material or multiple materials can be used. For example, a material in which a liquid material is impregnated with a solid material having a porous shape can also be used.

[0191] In this specification, a polymer electrolyte secondary battery refers to a secondary battery in which the electrolyte layer between the positive electrode 570b and the negative electrode 570a contains a polymer. Polymer electrolyte secondary batteries include dry (or intrinsic) polymer electrolyte batteries and polymer gel electrolyte batteries.

[0192] The electrolyte 576 includes a lithium ion conductive polymer and a lithium salt.

[0193] In this specification and other contexts, a lithium-ion conductive polymer refers to a polymer that conducts cations such as lithium. More specifically, a lithium-ion conductive polymer is a polymer compound having polar groups capable of coordinating cations. Preferred polar groups include ether groups, ester groups, nitrile groups, carbonyl groups, and siloxane groups. As the lithium ion conductive polymer, for example, polyethylene oxide (PEO), a derivative having polyethylene oxide as a main chain, polypropylene oxide, polyacrylate, polymethacrylic acid, polysiloxane, polyphosphazene, or the like can be used.

[0194] The lithium-ion conductive polymer may be branched or cross-linked. Furthermore, the lithium-ion conductive polymer may be a copolymer. The molecular weight is preferably 10,000 or greater, more preferably 100,000 or greater.

[0195] In lithium-ion conductive polymers, lithium ions migrate while replacing interacting polar groups through the partial movement of the polymer chain (also known as segmental movement). For example, in PEO, lithium ions migrate while replacing interacting oxygen groups through the segmental movement of the ether chain. At temperatures near or above the melting point or softening point of the lithium-ion conductive polymer, the crystalline regions dissolve, the amorphous regions increase, and the movement of the ether chains becomes more active, thereby increasing ion conductivity. Therefore, when using PEO as a lithium-ion conductive polymer, it is preferable to perform charging and discharging at temperatures above 60°C.

[0196] According to Shannon's ionic radius (Shannon et al., Acta A 32 (1976) 751.), the radii of monovalent lithium ions in tetracoordinate, hexacoordinate, and octacoordinate positions are 0.0590 nm, 0.076 nm, and 0.092 nm, respectively. In addition, the radii of divalent oxygen ions in dicoordinate, tricoordinate, tetracoordinate, hexacoordinate, and octacoordinate positions are 0.135 nm, 0.136 nm, 0.138 nm, 0.140 nm, and 0.142 nm, respectively. The distance between the polar groups of adjacent lithium ion conductive polymer chains is preferably greater than the distance at which lithium ions and anions of the polar groups can stably exist while maintaining the above-mentioned ionic radius. Furthermore, the distance is preferably a distance at which the interaction between lithium ions and polar groups fully occurs. Note that, as described above, since segment motion occurs, it is not necessary to maintain a fixed distance at all times. It is sufficient as long as there is an appropriate distance when lithium ions pass through.

[0197] In addition, as lithium salts, for example, a compound containing lithium and at least one of phosphorus, fluorine, nitrogen, sulfur, oxygen, chlorine, arsenic, boron, aluminum, bromine and iodine can be used. For example, LiPF6, LiN(FSO2)2 (lithium bis(fluorosulfonyl)imide, LiFSI), LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl 10 、Li2B 12 Cl 12 , one or more of lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2 (lithium bis(trifluoromethanesulfonyl)amide, LiTFSA), LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, and lithium bis(oxaloyl)borate (LiBOB).

[0198] When using LiFSI, the low-temperature characteristics are improved, so it is particularly preferred. In addition, compared with LiP F6 and the like, LiFSI and LiTFSA are less likely to react with water. Therefore, it is easy to control the dew point when manufacturing electrodes and electrolyte layers using LiFSI. For example, in addition to inert atmospheres such as argon that exclude moisture as much as possible and drying chambers that control the dew point, it can also be processed under a general atmospheric atmosphere. Therefore, productivity is improved, so it is preferred. In addition, when using Li salts with high dissociation and plasticizing effects such as LiFSI and LiTFSA, lithium conduction through segmental movement of the ether chain can be used in a wider temperature range, so it is particularly preferred.

[0199] When there is no organic solvent or the organic solvent is very small, a secondary battery that is less likely to cause ignition or fire can be realized, thereby improving safety, which is preferred.

[0200] [Outer packaging] As the outer packaging body included in the secondary battery, metal materials such as aluminum and resin materials can be used, for example. In addition, a film-like outer packaging body can also be used. As the film, for example, the following three-layer structure can be used: a metal film with excellent flexibility such as aluminum, stainless steel, copper, nickel, etc. is provided on a film composed of materials such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc., and an insulating synthetic resin film such as polyamide resin and polyester resin can also be provided on the metal film as the outer surface of the outer packaging body. In addition, a fluororesin film is preferably used as the film. Fluororesin film has high stability to acids, alkalis, organic solvents, etc., and can suppress side reactions and corrosion caused by the reaction of the secondary battery, thereby realizing an excellent secondary battery. Examples of fluororesin films include PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxyalkane: a copolymer of tetrafluoroethylene and perfluoroalkylvinylether), FEP (perfluoroethylenepropene copolymer: a copolymer of tetrafluoroethylene and hexafluoropropylene), and ETFE (ethylenetetrafluoroethylene copolymer: a copolymer of tetrafluoroethylene and ethylene).

[0201] This embodiment mode can be used in combination with other embodiment modes as appropriate.

[0202] (Implementation Method 2) In this embodiment, a positive electrode and a positive electrode active material complex according to one embodiment of the present invention are described.

[0203] Figure 9 An example of a positive electrode 570b according to one embodiment of the present invention is shown. The positive electrode 570b includes a positive electrode current collector 571b and a positive electrode active material layer 572b. The positive electrode active material layer 572b includes a positive electrode active material complex 100z. Figure 10A1 and Figure 10A2 As shown, the positive electrode active material complex 100z includes, for example, a first active material 100x and a second active material 100y that can occlude and release carrier ions. Figure 9 The example using the graphene compound 102 and the carbon black 103 as the conductive material is shown, but when the positive electrode active material complex 100z has sufficient electron conductivity, the conductive material may not be used in the positive electrode active material layer 572b. Figure 9 In the examples shown, either graphene compounds, carbon black, or carbon fibers such as carbon nanotubes can be used alone, or carbon fibers such as carbon nanotubes and carbon black can be used in combination. Figure 9As shown in FIG, the positive electrode active material layer 572b preferably includes a binder. As the binder, a polymer material such as polyvinylidene fluoride and a molecular crystalline electrolyte such as Li(FSI)(SN)2 can be used.

[0204] The positive electrode active material complex 100z is arranged in a state capable of transferring electrons with the positive electrode current collector 571b. In other words, the positive electrode active material complex 100z is in electrical contact with the positive electrode current collector 571b. Alternatively, an undercoat layer may be provided on the positive electrode current collector 571b. In this case, the positive electrode active material complex 100z is in electrical contact with the positive electrode current collector 571b via the undercoat layer. Alternatively, the positive electrode active material complex 100z may be in electrical contact with the positive electrode current collector 571b via a conductive material.

[0205] Note that the density of the positive electrode active material layer 572 b is preferably 3.0 g / cm 3 More than 3.5 g / cm 3 More preferably, 3.8 g / cm 3 Therefore, pressure treatment can be performed to increase the density of the positive electrode active material layer 572 b. Note that when performing pressure treatment, it is preferable to appropriately set the pressure treatment conditions so as not to damage the structures of the first active material 100 x and the positive electrode active material complex 100 z described later.

[0206] [Positive electrode active material complex] Figures 10A1 to 10C2 1 is a schematic cross-sectional view illustrating the positive electrode active material complex 100z.

[0207] Figure 10A1 and Figure 10A2 This is a diagram illustrating a positive electrode active material complex 100z, which includes a first active material 100x serving as a positive electrode active material and a second active material 100y covering at least a portion of the first active material 100x. Figure 10A1 Although a structure in which one first active material 100 x is covered with the second active material 100 y is shown, the present invention is not limited thereto, and a structure in which a plurality of first active materials 100 x are covered with the second active material 100 y may be employed.

[0208] For example, Figure 10A2 As shown, a structure may be adopted in which at least a portion of the first active material 100xa and the first active material 100xb is covered with the second active material 100y. Figure 10A2The figure shows a situation where at least a portion of the first active material 100xa and the first active material 100xb are in contact, but the first active material 100xa and the first active material 100xb do not need to be in direct contact. When at least a portion (preferably almost the entirety) of the particle surface of the particulate first active material 100x used as the positive electrode active material is covered with the second active material 100y, the area of ​​the first active material 100x directly in contact with the electrolyte 576 is reduced, which can inhibit the separation of transition metal elements and / or oxygen from the first active material 100x under high-voltage charging conditions, thereby inhibiting the capacity reduction caused by repeated charge and discharge. In addition, by being covered with the second active material 100y, which is electrochemically stable even under high-temperature and high-voltage charging conditions, a secondary battery using the positive electrode active material complex 100z of one embodiment of the present invention can achieve the following effects: improved stability at high temperatures; improved fire resistance; etc.

[0209] Figure 10B1 and Figure 10B2 This is a diagram illustrating a positive electrode active material complex 100z, which includes a first active material 100x serving as a positive electrode active material and a glass 101 covering at least a portion of the first active material 100x. Figure 10B1 Although a structure in which one first active material 100 x is covered by the glass 101 is shown, the present invention is not limited thereto, and a structure in which a plurality of first active materials 100 x are covered by the glass 101 may also be employed.

[0210] For example, Figure 10B2 As shown, a structure in which at least a portion of the first active material 100xa and the first active material 100xb is covered with the glass 101 may be employed. Figure 10B2 The figure shows a situation where at least a portion of the first active material 100xa and the first active material 100xb are in contact, but the first active material 100xa and the first active material 100xb do not need to be in direct contact. When at least a portion (preferably almost the entirety) of the particle surface of the particulate first active material 100x used as the positive electrode active material is covered by the glass 101, the area of ​​the first active material 100x that is in direct contact with the electrolyte 576 is reduced, which can inhibit the transition metal element and / or oxygen from being separated from the first active material 100x under high voltage charging conditions, thereby inhibiting the capacity drop caused by repeated charge and discharge. In addition, by being covered with the glass 101 that is electrochemically stable even under high temperature and high voltage charging conditions, a secondary battery using the positive electrode active material complex 100z of one embodiment of the present invention can obtain the following effects: improved stability at high temperatures; improved fire resistance; etc.

[0211] Figure 10C1 and Figure 10C2This figure illustrates a positive electrode active material complex 100z, which includes a first active material 100x serving as a positive electrode active material and a second active material 100y in contact with the first active material 100x via a glass 101 covering at least a portion of the first active material 100x. Note that Figure 10C1 Although a structure in which one first active material 100 x is covered by the glass 101 is shown, the present invention is not limited thereto, and a structure in which a plurality of first active materials 100 x are covered by the glass 101 may also be employed.

[0212] For example, Figure 10C2 As shown, a structure in which at least a portion of the first active material 100xa and the first active material 100xb is covered with the glass 101 may be employed. Figure 10C2 The diagram shows at least partial contact between the first active material 100xa and the first active material 100xb. However, the first active material 100xa and the first active material 100xb do not necessarily need to be in direct contact. When at least a portion (preferably substantially the entirety) of the particle surface of the particulate first active material 100x serving as the positive electrode active material is covered by the glass 101, in a positive electrode active material composite 100z including the second active material 100y in contact with the first active material 100x via the glass 101, the area of ​​the first active material 100x in direct contact with the electrolyte 576 is reduced. This can suppress the separation of transition metal elements and / or oxygen from the first active material 100x during high-voltage charging, thereby suppressing capacity degradation caused by repeated charge and discharge. In addition, by being covered with glass 101 that is electrochemically stable even under high temperature and high voltage conditions and a second active material 100y that is stable even under high charging voltage conditions, a secondary battery using a positive electrode active material complex 100z of one embodiment of the present invention can achieve the following effects: improved stability at high temperatures; improved fire resistance; etc.

[0213] exist Figures 10A1 to 10C2 In the illustrated positive electrode active material complex 100z, by using materials with excellent stability under high-voltage charging conditions as the first active material 100x, such as lithium cobalt oxide containing magnesium and fluorine, lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel, or nickel-cobalt-manganese oxide with molar ratios of nickel:cobalt:manganese = 8:1:1 and nickel:cobalt:manganese = 9:0.5:0.5, the durability and stability of the positive electrode active material complex 100z under high-voltage charging can be further improved. Furthermore, the heat resistance and / or fire resistance of a secondary battery using the positive electrode active material complex 100z can be further improved.

[0214] Note that lithium cobalt oxide containing magnesium, fluorine, aluminum and nickel has the characteristics of containing a large amount of magnesium, fluorine or aluminum in the surface portion of the positive electrode active material and nickel is widely distributed throughout the particles, and the repeated characteristics of charge and discharge at high voltage are very good, so it is a particularly preferred material as the first active material 100x. When a large amount of magnesium, fluorine or aluminum is contained in the surface portion of the positive electrode active material, for example, in the line analysis of STEM-EDX, the count of characteristic X-rays originating from magnesium, fluorine or aluminum in the surface portion becomes the maximum. Here, the surface portion refers to the area within about 10nm from the surface of the positive electrode active material. Note that the crack portion of the positive electrode active material also includes the surface portion, and the crack portion generated before the step of adding magnesium, fluorine or aluminum in the positive electrode active material manufacturing process includes the surface portion containing a large amount of magnesium, fluorine or aluminum.

[0215] By using at least the first active material 100x and the second active material 100y for composite processing, it is possible to obtain Figure 10A1 and Figure 10A2 The positive electrode active material complex 100z shown in the figure. As a composite treatment, for example, any one or more of the following composite treatments can be used: composite treatments using mechanical energy such as mechanochemical method, mechanical fusion method and ball mill method; composite treatments using liquid phase reaction such as coprecipitation method, hydrothermal method and sol-gel method; and composite treatments using gas phase reaction such as barrel sputtering method, ALD (Atomic Layer Deposition) method, evaporation method and CVD (Chemical Vapor Deposition) method. In addition, it is preferred to perform one or more heating treatments in the composite treatment. In addition, in this specification, composite treatment is sometimes also referred to as surface coating treatment or coating treatment.

[0216] In addition, by using at least the first active material 100x and the glass 101 for composite processing, Figure 10B1 and Figure 10B2 The positive electrode active material complex 100z shown in FIG. For example, the composite treatment may include one or more of the following: composite treatments utilizing mechanical energy, such as mechanochemical methods, mechanofusion methods, and ball mill methods; composite treatments utilizing liquid-phase reactions, such as coprecipitation methods, hydrothermal methods, and sol-gel methods; and composite treatments utilizing gas-phase reactions, such as barrel sputtering, ALD methods, vapor deposition methods, and CVD methods. Furthermore, one or more heat treatments are preferably performed during the composite treatment.

[0217] Furthermore, by using at least the first active material 100x, the second active material 100y and the glass 101 for composite processing, a Figure 10C1 and Figure 10C2The positive electrode active material complex 100z shown in FIG. For example, the composite treatment may include one or more of the following: composite treatments utilizing mechanical energy, such as mechanochemical methods, mechanofusion methods, and ball mill methods; composite treatments utilizing liquid-phase reactions, such as coprecipitation methods, hydrothermal methods, and sol-gel methods; and composite treatments utilizing gas-phase reactions, such as barrel sputtering, ALD methods, vapor deposition methods, and CVD methods. Furthermore, one or more heat treatments are preferably performed during the composite treatment.

[0218] As described above, the first active material 100x in the positive electrode active material complex 100z of one embodiment of the present invention is not in contact with the electrolyte 576, so the degradation of the first active material 100x caused by the electrolyte can be suppressed. This degradation is sometimes caused by defects generated in the first active material 100x, such as defects called pits. Pits refer to areas where the main components of the first active material 100x such as cobalt and oxygen are deintercalated in several layers during the charge and discharge cycle test. For example, it can be considered that cobalt sometimes dissolves into the electrolyte. As the charge and discharge cycle test proceeds, the pits develop toward the interior of the active material. Note that the opening shape of the pit is not circular but has a deep groove-like shape. Due to the structure in which the electrolyte 576 is not in contact with the first active material 100x, the development of the above-mentioned defects can be suppressed, and in particular, the generation and development of pits can be suppressed.

[0219] When the positive electrode active material complex 100z includes the second active material 100y in contact with the first active material 100x via the glass 101, it can be said that the positive electrode active material complex 100z has a double structure on the surface. Note that the positive electrode active material complex 100z of one embodiment of the present invention is not limited to a double structure of the glass 101 and the second active material 100y. As another example of the positive electrode active material complex 100z of one embodiment of the present invention, a structure in which a glass active material mixed layer including the glass 101 and the second active material 100y covers at least a portion of the surface of the first active material 100x can also be employed.

[0220] Furthermore, the positive electrode active material complex 100z as one embodiment of the present invention may include a graphene compound 102 in its surface layer or glass active material mixed layer. In place of the graphene compound 102, carbon black or carbon fibers such as carbon nanotubes may be used.

[0221] As the glass 101, a material having an amorphous portion can be used. As a material having an amorphous portion, for example, a material containing one or more selected from SiO2, SiO, Al2O3, TiO2, Li4SiO4, Li3PO4, Li2S, SiS2, B2S3, GeS4, AgI, Ag2O, Li2O, P2O5, B2O3, and V2O5, etc., Li7P3S 11 or Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 < x < 2, 0 < y < 3,) etc. The material having an amorphous portion can be used in an entirely amorphous state or in a state of crystallized glass (also called glass-ceramics) in which a part is crystallized. The glass 101 preferably has lithium ion conductivity. Lithium ion conductivity can also be said to have lithium ion diffusivity and lithium ion penetrability. Additionally, the melting point of the glass 101 is preferably 800 °C or lower, more preferably 500 °C or lower. Further, the glass 101 preferably has electron conductivity. Additionally, the softening point of the glass 101 is preferably 800 °C or lower. For example, Li2O-B2O3-SiO2 type glass can be used.

[0222] The glass 101 preferably has electron conductivity. However, when the electron conductivity of the glass 101 is low, the glass 101 can be made to have electron conductivity by mixing carbon fiber conductive materials such as graphene compounds, carbon black, or carbon nanotubes into the glass 101.

[0223] Note that a structure in which at least a part of the surface of the positive electrode active material complex 100z is covered with a graphene compound can also be adopted. Preferably, a structure in which the particle surface of the positive electrode active material complex 100z and / or more than 80% of the aggregates containing the positive electrode active material complex 100z are covered with a graphene compound is adopted. The graphene compound will be described later.

[0224] Further, the positive electrode active material complex 100z preferably has a structure covered with a molecular crystalline electrolyte. The molecular crystalline electrolyte can be used as an adhesive for the positive electrode active material layer 572b. The molecular crystalline electrolyte is preferably a material with high ion conductivity. Carrier ions can be exchanged between the positive electrode active material complex 100z covered with the molecular crystalline electrolyte and the electrolyte 576.

[0225] [Positive electrode active material] As the first active material 100x, a composite oxide represented by LiM1O2 (M1 is one or more selected from Fe, Ni, Co, and Mn) having a layered rock salt type crystal structure can be used. In addition, as the first active material 100x, a material obtained by adding an additive element X to a composite oxide represented by LiM1O2 can be used. As the additive element X contained in the first active material 100x, it is preferred to use one or more selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. These elements sometimes further stabilize the crystal structure of the first active material 100x. Specifically, the first active material 100x may include lithium cobalt oxide containing magnesium and fluorine, lithium cobalt oxide containing magnesium, fluorine, aluminum, and nickel, lithium cobalt oxide containing magnesium, fluorine, and titanium, lithium nickel-cobalt oxide containing magnesium and fluorine, lithium cobalt-aluminate containing magnesium and fluorine, lithium nickel-cobalt-aluminate, lithium nickel-cobalt-aluminate containing magnesium and fluorine, or lithium nickel-cobalt-manganese oxide containing magnesium and fluorine. Note that the transition metal ratio of the nickel-cobalt-manganese oxide is preferably a high nickel ratio. For example, a molar ratio of nickel:cobalt:manganese = 8:1:1 or nickel:cobalt:manganese = 9:0.5:0.5 is preferred. Furthermore, the nickel-cobalt-manganese oxide preferably includes nickel-cobalt-manganese oxide containing calcium.

[0226] Alternatively, as the first active material 100x, a material in which secondary particles of a composite oxide represented by LiM1O2 (M1 is one or more selected from Fe, Ni, Co, and Mn) are covered with a metal oxide may be used. As the metal oxide, oxides of one or more metals selected from Al, Ti, Nb, Zr, La, and Li may be used. For example, as the first active material 100x, a metal oxide-covered composite oxide may be used, in which secondary particles of a composite oxide represented by LiM1O2 (M1 is one or more selected from Fe, Ni, Co, and Mn) are covered with aluminum oxide. For example, a metal oxide-covered composite oxide may be used, in which secondary particles of nickel-cobalt-manganese oxide having a molar ratio of nickel:cobalt:manganese = 8:1:1 or nickel:cobalt:manganese = 9:0.5:0.5 are covered with aluminum oxide. The covering layer is preferably thin, for example, from 1 nm to 200 nm, more preferably from 1 nm to 100 nm. Furthermore, the nickel-cobalt-manganese oxide preferably contains calcium.

[0227] As the first active material 100 x , the positive electrode active material 100 described in the embodiment below can be used.

[0228] As the second active material 100y, one or more of oxides and LiM2PO4 having an olivine-type crystal structure (M2 is one or more selected from Fe, Ni, Co, and Mn) can be used. As the oxide, for example, there are alumina, zirconia, hafnium oxide, niobium oxide, and the like. In addition, as LiM2PO4, for example, there are LiFePO4, LiNiPO4, LiCoPO4, LiMnPO4, LiFe a Ni b PO4, LiFe a Co b PO4, LiFe a Mn b PO4, LiNi a Co b PO4, LiNi a Mn b PO4 (a + b is 1 or less, 0 < a < 1, 0 < b < 1), LiFe c Ni d Co e PO4, LiFe c Ni d Mn e PO4, LiNi c Co d Mn e PO4 (c + d + e is 1 or less, 0 < c < 1, 0 < d < 1, 0 < e < 1), LiFe f Ni g Co h Mn i PO4 (f + g + h + i is 1 or less, 0 < f < 1, 0 < g < 1, 0 < h < 1, 0 < i < 1), etc. In addition, the particle surface of the second active material 100y may also include a carbon coating layer.

[0229] As the conductive material, for example, any one or two or more of carbon blacks such as acetylene black and furnace black, graphites such as artificial graphite and natural graphite, carbon fibers such as carbon nanofibers and carbon nanotubes, and graphene compounds can be used.

[0230] This embodiment can be used in appropriate combination with other embodiments.

[0231] (Embodiment 3) In this embodiment, one mode of the positive electrode active material of the present invention will be described with reference to FIGS. 11 to 17.

[0232] In the present specification and the like, crystal planes and orientations are expressed by Miller indices. However, in the present specification and the like, due to the symbol limitations in patent applications, sometimes a minus sign (-) is attached before a number to represent crystal planes and orientations, instead of attaching a superscript horizontal line to the number. In addition, "[ ]" represents an individual orientation showing the orientation within a crystal, "<>" represents a set orientation showing all equivalent crystal directions, "()" represents an individual plane showing a crystal plane, and "{}" represents a set plane having equivalent symmetry. In addition, for Miller indices of trigonal and hexagonal crystal systems such as R-3m, in addition to (hkl), (hkil) is also used. Here, i is -(h + k).

[0233] In addition, in the present specification and the like, the layered rock salt-type crystal structure of a composite oxide containing lithium and a transition metal refers to the following crystal structure: having a rock salt-type ionic arrangement in which cations and anions are alternately arranged, and the transition metal and lithium are regularly arranged to form a two-dimensional plane, so that lithium can diffuse two-dimensionally therein. In addition, it may also include defects such as vacancies of cations or anions. Strictly speaking, the layered rock salt-type crystal structure is sometimes a structure formed by lattice deformation of a rock salt-type crystal.

[0234] In addition, in the present specification and the like, the rock salt-type crystal structure refers to a structure in which cations and anions are alternately arranged. In addition, it may also include vacancies of cations or anions in a part of the crystal structure.

[0235] In addition, in the present specification and the like, the theoretical capacity of a positive electrode active material refers to the amount of electricity when all lithium ions that can be intercalated and deintercalated in the positive electrode active material are deintercalated. For example, the theoretical capacity of LiFePO4 is 170 mAh / g, the theoretical capacity of LiCoO2 is 274 mAh / g, the theoretical capacity of LiNiO2 is 275 mAh / g, and the theoretical capacity of LiMn2O4 is 148 mAh / g.

[0236] In addition, for x in the composition formula, for example, x in Li x CoO2 or x in Li x MO2 represents the amount of lithium remaining in the positive electrode active material that can be intercalated and deintercalated. In the present specification, Li x CoO2 can be appropriately replaced with Li x MO2. It can be said that x represents the occupancy rate. When explaining the positive electrode active material in a secondary battery, x can also be (theoretical capacity - charging capacity) / theoretical capacity. For example, when charging a secondary battery using LiCoO2 as the positive electrode active material to 219.2 mAh / g, it can be said that the secondary battery is Li 0.2 CoO2 or it can be said that x = 0.2. A smaller x in Li x CoO2, for example, means a case where 0.1 < x ≤ 0.24.

[0237] When lithium cobalt oxide roughly satisfies the stoichiometric ratio, it is LiCoO2 and the occupancy rate of Li at the lithium position is x=1. In addition, a secondary battery at the end of discharge can also be said to be LiCoO2 and x=1. Here, "end of discharge" refers to a state where the current is 100mA / g and the voltage is 2.5V (to the electrode lithium) or less. In a lithium-ion secondary battery, the voltage drops sharply when the occupancy rate of lithium at the lithium position is x=1 and other lithium cannot be embedded in the positive electrode active material. It can be said that the discharge is ended at this time. Generally speaking, the discharge voltage of a lithium-ion secondary battery using LiCoO2 drops sharply before reaching 2.5V, so it is assumed that the discharge is ended under the above conditions.

[0238] In this specification and other documents, the depth of charge when all lithium ions that can be inserted into or desorbed from the positive electrode active material are all inserted is sometimes referred to as 0, and the depth of charge when all lithium ions that can be inserted into and desorbed from the positive electrode active material are all desorbed is sometimes referred to as 1.

[0239] [Positive electrode active material] Refer to Figures 11 to Figure 15 A positive electrode active material according to one embodiment of the present invention will be described.

[0240] Figure 11A This is a schematic top view of a positive electrode active material 100 according to one embodiment of the present invention. Figure 11B Shown along Figure 11A Schematic diagram of the cross section of AB in FIG.

[0241] <Contained elements and distribution> The positive electrode active material 100 contains lithium, a transition metal, oxygen, and an additional element X. The positive electrode active material 100 can be said to be a material obtained by adding the additional element X to a composite oxide represented by LiM1O2 (M1 is one or more selected from Fe, Ni, Co, and Mn).

[0242] As the transition metal contained in the positive electrode active material 100, it is preferred to use a metal that can form a layered rock salt type composite oxide belonging to the space group R-3m together with lithium. For example, at least one of manganese, cobalt and nickel can be used. That is, as the transition metal contained in the positive electrode active material 100, either only cobalt or nickel can be used, or two kinds of cobalt and manganese, or cobalt and nickel can be used, or three kinds of cobalt, manganese and nickel can be used. That is, the positive electrode active material 100 can include composite oxides containing lithium and transition metals such as lithium cobaltate, lithium nickelate, lithium cobaltate in which a part of the cobalt is substituted by manganese, lithium cobaltate in which a part of the cobalt is substituted by nickel, and nickel-manganese-lithium cobaltate. When cobalt and nickel are included as transition metals, the crystal structure sometimes becomes more stable when charged at a high voltage, so it is preferred.

[0243] As the added element X contained in the positive electrode active material 100, it is preferred to use one or more selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron and arsenic. These elements sometimes further stabilize the crystal structure of the positive electrode active material 100. In other words, the positive electrode active material 100 may include lithium cobaltate containing magnesium and fluorine, lithium cobaltate containing magnesium, fluorine and titanium, nickel-lithium cobaltate containing magnesium and fluorine, cobalt-lithium aluminum oxide containing magnesium and fluorine, nickel-cobalt-lithium aluminum oxide, nickel-cobalt-lithium aluminum oxide containing magnesium and fluorine, nickel-manganese-lithium cobalt oxide containing magnesium and fluorine, etc. In addition, in this specification, the added element X may also be referred to as a mixture, a part of a raw material, etc.

[0244] like Figure 11B As shown, the positive electrode active material 100 includes a surface portion 100a and an inner portion 100b. The concentration of the added element X in the surface portion 100a is preferably higher than that in the inner portion 100b. Figure 11B As shown by the gradient in FIG, the added element X preferably has a concentration gradient that increases from the inside to the surface. In this specification, etc., the surface portion 100a refers to the area within a depth of about 10 nm from the surface of the positive electrode active material 100. The surface generated by cracks and / or fissures can also be called the surface, such as Figure 11C As shown, the area from the surface to a depth of approximately 10 nm is referred to as the surface portion 100c. Furthermore, the area of ​​the positive electrode active material 100 deeper than the surface portion 100a and the surface portion 100c is referred to as the interior portion 100b. When the positive electrode active material 100 forms a positive electrode active material composite 100z, it is preferable that the surface resulting from the crack is also covered by the glass 101.

[0245] In the positive electrode active material 100 according to one embodiment of the present invention, the surface layer portion 100 a having a high concentration of the added element X, i.e., the outer periphery of the particle, is reinforced to prevent the layered structure formed by the octahedrons of cobalt and oxygen from being destroyed even when lithium is released from the positive electrode active material 100 during charging.

[0246] Furthermore, the concentration gradient of the added element X is preferably uniformly distributed throughout the surface portion 100a of the positive electrode active material 100. This is because, even if the strength of a portion of the surface portion 100a is enhanced, if there are areas where the strength is not enhanced, stress may concentrate in those areas, which is not desirable. When stress concentrates in a portion of the particle, defects such as cracks may form in that area, potentially leading to damage to the positive electrode active material and a decrease in charge-discharge capacity.

[0247] Magnesium is divalent, and in a layered rock salt crystal structure, magnesium is more stable at the lithium site than at the transition metal site, making it easier for it to enter the lithium site. When magnesium is present at an appropriate concentration at the lithium site in the surface portion 100a, the layered rock salt crystal structure can be easily maintained. Furthermore, magnesium has a strong bond with oxygen, so it can prevent oxygen from escaping to the surrounding area. An appropriate magnesium concentration is preferred because it does not negatively impact the insertion and removal of lithium during charging and discharging. However, excess magnesium may negatively impact the insertion and removal of lithium.

[0248] Aluminum is trivalent and can exist as a transition metal in the layered rock salt crystal structure. Aluminum can inhibit the dissolution of surrounding cobalt. Furthermore, aluminum's strong bonding with oxygen prevents oxygen from escaping from the surrounding area. Therefore, the inclusion of aluminum as the additive element X allows for the production of a positive electrode active material 100 whose crystal structure is less susceptible to collapse even during repeated charge and discharge.

[0249] In addition, fluorine is a monovalent anion, and when a portion of oxygen in the surface portion 100a is replaced by fluorine, the lithium separation energy is reduced. This is because the valence of the cobalt ions accompanying lithium separation changes as follows: in the absence of fluorine, the cobalt ions change from trivalent to tetravalent, and in the presence of fluorine, the cobalt ions change from divalent to trivalent, and the redox potential of the cobalt ions is different. Therefore, when a portion of oxygen in the surface portion 100a of the positive electrode active material 100 is replaced by fluorine, it can be said that the separation and insertion of lithium ions near fluorine occur smoothly. As a result, the charge and discharge characteristics and rate characteristics can be improved when used in a secondary battery, so it is preferred.

[0250] Titanium oxide is known to have super-hydrophilic properties. Therefore, by manufacturing a positive electrode active material 100 containing titanium oxide in the surface portion 100a, wettability with highly polar solvents can be improved. This improves interfacial contact between the positive electrode active material 100 and the highly polar electrolyte during secondary battery manufacturing, potentially suppressing increases in internal resistance. Note that in this specification, the term "electrolyte" refers to a liquid electrolyte.

[0251] Generally, as the charging voltage of a secondary battery increases, the voltage of the positive electrode also increases. The positive electrode active material of one embodiment of the present invention has a stable crystal structure even at high voltages. The stable crystal structure of the positive electrode active material in the charged state can suppress the decrease in capacitance due to repeated charge and discharge.

[0252] In addition, a short circuit in a secondary battery can cause not only defects in the charging and / or discharging operations of the secondary battery, but also heat and fire. In order to achieve a safe secondary battery, it is preferable to suppress the short-circuit current even at a high charging voltage. The positive electrode active material 100 of one embodiment of the present invention can also suppress the short-circuit current even at a high charging voltage. Therefore, a secondary battery that achieves both high capacity and safety can be manufactured.

[0253] A secondary battery using the positive electrode active material 100 according to one embodiment of the present invention preferably achieves high capacity, excellent charge-discharge cycle characteristics, and safety simultaneously.

[0254] For example, the concentration gradient of the added element X can be evaluated using energy dispersive X-ray spectroscopy (EDX). In EDX measurement, a method that scans an area while performing measurements to perform two-dimensional evaluation is sometimes referred to as EDX surface analysis. Furthermore, a method that extracts data from a linear region from EDX surface analysis to evaluate the atomic concentration distribution within the positive electrode active material particles is sometimes referred to as line analysis.

[0255] EDX surface analysis (e.g., element mapping) can quantitatively analyze the concentration of the added element X in the surface portion 100a, interior portion 100b, and near the grain boundaries of the positive electrode active material 100. Furthermore, EDX line analysis can analyze the concentration distribution of the added element X.

[0256] When EDX line analysis is performed on the positive electrode active material 100, the magnesium concentration peak (the position where the concentration reaches the maximum value) of the surface portion 100a preferably appears at a depth of 3 nm from the surface of the positive electrode active material 100 toward the center, more preferably appears at a depth of 1 nm, and further preferably appears at a depth of 0.5 nm.

[0257] Furthermore, the distribution of fluorine contained in the positive electrode active material 100 preferably overlaps with the distribution of magnesium. Therefore, when performing EDX line analysis, the fluorine concentration peak (the position where the concentration reaches the maximum value) of the surface portion 100a preferably appears at a depth of 3 nm from the surface of the positive electrode active material 100 toward the center, more preferably at a depth of 1 nm, and even more preferably at a depth of 0.5 nm.

[0258] Note that not all added elements X may have the same concentration distribution. For example, when aluminum is included as the added element X, the positive electrode active material 100 preferably has a slightly different distribution than magnesium and fluorine. For example, during EDX line analysis, it is preferred that the magnesium concentration peak (the location where the concentration reaches its maximum value) in the surface portion 100a is closer to the surface than the aluminum concentration peak (the location where the concentration reaches its maximum value). For example, the aluminum concentration peak preferably appears from the surface of the positive electrode active material 100 toward the center to a depth of 0.5 nm or more and 20 nm or less, and more preferably appears at a depth of 1 nm or more and 5 nm or less.

[0259] When the positive electrode active material 100 is subjected to line analysis or surface analysis, the ratio of the added element X to the transition metal M1 near the grain boundary (X / M1) is preferably 0.020 or more and 0.50 or less. More preferably, it is 0.025 or more and 0.30 or less. Even more preferably, it is 0.030 or more and 0.20 or less. For example, when the added element X is magnesium and the transition metal M1 is cobalt, the atomic ratio of magnesium to cobalt (Mg / Co) is preferably 0.020 or more and 0.50 or less. More preferably, it is 0.025 or more and 0.30 or less. Even more preferably, it is 0.030 or more and 0.20 or less.

[0260] As mentioned above, if the positive electrode active material 100 contains an excessive amount of the additive element X, there is a concern that this may negatively affect the insertion and extraction of lithium. Furthermore, there is a concern that this may lead to increased resistance or decreased capacity when used in a secondary battery. On the other hand, if the additive element X is insufficient, the additive element X may not be distributed throughout the entire surface portion 100a, and the effect of maintaining the crystal structure may not be achieved sufficiently. Therefore, the concentration of the additive element X is adjusted to achieve an appropriate concentration in the positive electrode active material 100.

[0261] Therefore, for example, the positive electrode active material 100 may have regions where excess additive element X is concentrated. The presence of these regions allows excess additive element X to be removed from other regions, allowing an appropriate concentration of additive element X to be set throughout the interior and majority of the surface of the positive electrode active material 100. By achieving an appropriate concentration of additive element X throughout the interior and majority of the surface of the positive electrode active material 100, resistance increases and capacity decreases can be suppressed during secondary battery manufacturing. Suppressing resistance increases in secondary batteries is an extremely desirable characteristic for high-rate charging and discharging.

[0262] Furthermore, in the positive electrode active material 100 having a region where the excess additive element X is concentrated, a certain amount of excess additive element X may be mixed in during the manufacturing process. This is preferable because it increases the degree of freedom in production.

[0263] In this specification, etc., the term "localization" refers to a state in which the concentration of a certain element is different between region A and region B. It may also refer to uneven precipitation, precipitation, unevenness, deviation, high concentration, or low concentration.

[0264] <Crystal Structure> Materials with a layered rock salt crystal structure, such as lithium cobalt oxide (LiCoO2), have high discharge capacity and are considered excellent positive electrode active materials for secondary batteries. Examples of materials with a layered rock salt crystal structure include composite oxides represented by LiM1O2 (where M1 is one or more selected from Fe, Ni, Co, and Mn).

[0265] The magnitude of the Jahn-Teller effect in transition metal compounds is believed to vary depending on the number of electrons in the d orbital of the transition metal.

[0266] Nickel-containing compounds can sometimes be prone to distortion due to the Jahn-Teller effect. Consequently, when LiNiO2 is charged and discharged at high voltages, there is a concern that this distortion may cause crystal structure collapse. LiCoO2 is preferred because it has less negative effects from the Jahn-Teller effect and sometimes offers better resistance to high-voltage charge and discharge.

[0267] Reference Figure 12 Figure 17 illustrates the structure of the positive electrode active material. Figure 12 17 , the case where cobalt is used as the transition metal contained in the positive electrode active material is described.

[0268] <Existing Positive Electrode Active Materials> Figure 14 The positive electrode active material shown is lithium cobalt oxide (LiCoO2, LCO) without the addition of halogen and magnesium. Figure 14 The crystal structure of lithium cobalt oxide shown changes depending on the depth of charge. In other words, when expressed as LixCoO2, the crystal structure changes depending on the lithium occupancy rate x at the lithium site.

[0269] like Figure 14 As shown, lithium cobalt oxide in the x = 1 state (discharge state) includes a region having a crystal structure belonging to the space group R-3m, including three CoO2 layers in the unit cell. Therefore, this crystal structure is sometimes referred to as an O3-type crystal structure. Note that the CoO2 layer refers to a structure in which cobalt is coordinated to six oxygen atoms in an octahedral structure, maintaining a state of edge sharing in one plane direction.

[0270] When x = 0, it has a crystal structure belonging to the space group P-3m1, and the unit cell includes one CoO2 layer. Therefore, this crystal structure is sometimes called an O1-type crystal structure.

[0271] When x=0.12 or so, lithium cobalt oxide has a crystal structure belonging to the space group R-3m. This structure can also be regarded as a structure in which a CoO2 structure such as a structure belonging to P-3m1(O1) and a LiCoO2 structure such as a structure belonging to R-3m(O3) are alternately stacked. Therefore, this crystal structure is sometimes called an H1-3 type crystal structure. Note that the actual insertion and extraction of lithium will be uneven, so the H1-3 type crystal structure is observed experimentally from about x=0.25. In fact, the number of cobalt atoms in the unit cell of the H1-3 type crystal structure is twice that of other structures. However, in the case of Figure 14 In this specification, for easy comparison with other structures, the c-axis of the H1-3 type crystal structure is 1 / 2 of the unit cell.

[0272] As an example of an H1-3 type crystal structure, the coordinates of cobalt and oxygen in the unit cell can be represented by 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 both oxygen atoms. In this way, the H1-3 type crystal structure is represented by a unit cell using one cobalt and two oxygens. On the other hand, as described below, it is preferred to represent the O3' type crystal structure of one embodiment of the present invention by a unit cell using one cobalt and one oxygen. This means that the difference between the O3' type crystal structure and the H1-3 type structure lies in the symmetry of cobalt and oxygen, and the O3' type crystal structure has less change from the O3 structure than the H1-3 type structure. For example, any unit cell can be selected under the condition that the GOF (goodness of fit) value when the XRD pattern is subjected to Rietveld analysis is as small as possible to more appropriately represent the crystal structure of the positive electrode active material.

[0273] When high-voltage charging with a charging voltage of 4.6 V or more relative to the redox potential of lithium metal or deep charging and discharging with x = 0.24 or less is repeatedly performed, the crystal structure of lithium cobalt oxide repeatedly changes between the H1-3 type crystal structure and the structure belonging to R-3m (O3) in the discharged state (i.e., non-equilibrium phase transition).

[0274] However, the CoO2 layers of the two crystal structures mentioned above deviate greatly. Figure 14 As shown by the dotted line and double arrows, in the H1-3 type crystal structure, the CoO2 layer deviates significantly from the R-3m(O3) structure. This dynamic structural change can negatively impact the stability of the crystal structure.

[0275] Furthermore, the volume difference is also significant. When compared per the same number of cobalt atoms, the volume difference between the H1-3 type crystal structure and the O3 type crystal structure in the discharged state is 3.0% or more.

[0276] In addition to the above, the structure of the H1-3 type crystal structure having a continuous CoO2 layer, such as the structure belonging to P-3m1(O1), is likely to be unstable.

[0277] Therefore, the crystal structure of lithium cobalt oxide collapses during repeated high-voltage charge and discharge. This crystal structure collapse leads to deterioration in cycle characteristics. This is believed to be because the crystal structure collapse reduces the number of sites where lithium can stably exist, making lithium insertion and extraction difficult.

[0278] <Positive Electrode Active Material of One Embodiment of the Present Invention> <Inside> The positive electrode active material 100 of one embodiment of the present invention can reduce the deviation of the CoO2 layer even if high voltage charging and discharging are repeated. Furthermore, the volume change can be reduced. Therefore, the positive electrode active material of one embodiment of the present invention can achieve good cycle characteristics. In addition, the positive electrode active material of one embodiment of the present invention can also have a stable crystal structure in a state of high voltage charging. Therefore, sometimes the positive electrode active material of one embodiment of the present invention is not prone to short circuit when maintaining a high voltage charging state. In this case, the stability is further improved, so it is preferred.

[0279] The positive electrode active material of one embodiment of the present invention has a small change in crystal structure between a fully discharged state and a high voltage charged state, and a small volume difference per the same number of transition metal atoms when compared.

[0280] Figure 12 The crystal structure of the positive electrode active material 100 before and after charge and discharge is shown. The positive electrode active material 100 is a composite oxide containing lithium, cobalt as a transition metal, and oxygen. Preferably, magnesium is included as the additive element X in addition to the above. Furthermore, a halogen such as fluorine or chlorine is preferably included as the additive element X.

[0281] Figure 12 The crystal structure of x=1 (discharge state) is the same as Figure 14 The same structure belongs to R-3m (O3). However, the positive electrode active material 100 of one embodiment of the present invention has a crystal structure different from the H1-3 type crystal structure when it has a fully charged depth of charge. This structure belongs to the space group R-3m, in which ions such as cobalt and magnesium occupy six oxygen positions. In addition, the symmetry of the CoO2 layer of 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. In addition, in order to illustrate the symmetry of the cobalt atom and the symmetry of the oxygen atom, Figure 12 Although lithium is omitted in the diagram of the O3′ type crystal structure, lithium actually exists between the CoO 2 layers in an amount of, for example, 20 atomic % or less relative to cobalt.

[0282] Furthermore, in the O3' type crystal structure, light elements such as lithium may occupy the positions coordinated to the four oxygen atoms.

[0283] In addition, although the O3' type crystal structure contains lithium irregularly between layers, it can also have a crystal structure similar to the CdCl2 type crystal structure. This crystal structure similar to the CdCl2 type is similar to the crystal structure of lithium nickelate charged to a depth of charge of 0.94 (Li 0.06 However, pure lithium cobaltate or layered rock salt-type positive electrode active materials containing a large amount of cobalt generally do not have such a crystal structure.

[0284] In the positive electrode active material 100 according to one embodiment of the present invention, the change in the crystal structure during high voltage charging, that is, when a large amount of lithium is released, is suppressed compared to conventional positive electrode active materials. Figure 12 As shown by the middle dashed line, there is almost no deviation of the CoO2 layer in the above crystal structure.

[0285] In more detail, the positive electrode active material 100 of one embodiment of the present invention has high structural stability even when charged at a high voltage. For example, even if the existing positive electrode active material becomes a charging voltage of the H1-3 type crystal structure, for example, a voltage of about 4.6V based on the potential of lithium metal is also included in the region where the charging voltage of the crystal structure belonging to R-3m (O3) can be maintained, and in a region with a higher charging voltage, for example, a voltage of about 4.65V to 4.7V based on the potential of lithium metal is also included in the region where the O3' type crystal structure can be maintained. When the charging voltage is further increased, H1-3 type crystallization is observed. For example, when graphite is used as the negative electrode active material of a secondary battery, even at a voltage of a secondary battery of 4.3V or more and 4.5V or less, a charging voltage of the crystal structure of R-3m (O3) is also included, and in a region with a higher charging voltage, for example, a voltage of 4.35V or more and 4.55V or less relative to the potential of lithium metal is also included in the region where the O3' type crystal structure can be maintained.

[0286] Therefore, even when high-voltage charge and discharge are repeated, the crystal structure of the positive electrode active material 100 according to one embodiment of the present invention is unlikely to collapse.

[0287] In the positive electrode active material 100 , the volume difference per unit cell between the O3 type crystal structure with x=1 and the O3′ type crystal structure with x=0.2 is 2.5% or less, specifically 2.2% or less.

[0288] The coordinates of cobalt and oxygen in the unit cell of the O3'-type crystal structure can be represented by Co(0, 0, 0.5) and O(0, 0, x) (0.20≤x≤0.25), respectively.

[0289] Additive elements X such as magnesium, which are irregularly present in small amounts between the CoO2 layers, i.e., at the lithium positions, have the effect of suppressing the deviation of the CoO2 layers. Thus, when magnesium is present between the CoO2 layers, an O3' type crystal structure is easily obtained. Therefore, magnesium is distributed in at least a portion of the surface portion of the positive electrode active material 100 of one embodiment of the present invention, and preferably is also distributed in the entire surface portion of the positive electrode active material 100. In addition, in order to distribute magnesium in the entire surface portion of the positive electrode active material 100, it is preferred to perform a heat treatment during the manufacturing process of the positive electrode active material 100 of one embodiment of the present invention.

[0290] However, if the heat treatment temperature is too high, cation mixing occurs, increasing the likelihood that additive elements (X) such as magnesium will intrude into the cobalt sites. Magnesium present at the cobalt sites is not effective in maintaining the R-3m structure during high-voltage charging. Furthermore, if the heat treatment temperature is too high, there is a concern that adverse effects such as cobalt reduction to divalent form and lithium evaporation may occur.

[0291] Therefore, it is preferable to add a halogen compound such as a fluorine compound to the lithium cobalt oxide before performing the heat treatment to distribute magnesium throughout the surface of the positive electrode active material 100. The addition of the halogen compound lowers the melting point of the lithium cobalt oxide. This lowering of the melting point facilitates the distribution of magnesium throughout the surface of the positive electrode active material 100 at a temperature where cation mixing is less likely to occur. Furthermore, the presence of the fluorine compound can be expected to improve corrosion resistance against hydrofluoric acid generated by decomposition of the electrolyte.

[0292] Note that when the magnesium concentration is set to a desired value or more, the effect of stabilizing the crystal structure sometimes becomes smaller. This is because magnesium not only enters the lithium position but also the cobalt position. The number of atoms of magnesium contained in the positive electrode active material of one embodiment of the present invention is preferably greater than 0.001 times and less than 0.1 times the number of atoms of a transition metal such as cobalt, more preferably greater than 0.01 times and less than 0.04 times, and further preferably about 0.02 times. The magnesium concentration shown here can be, for example, a value obtained by elemental analysis of the positive electrode active material as a whole using ICP-MS (Inductively Coupled Plasma Mass Spectrometer) or the like, or a value obtained by mixing raw materials in the manufacturing process of the positive electrode active material 100.

[0293] For example, it is preferred to add one or more metals selected from nickel, aluminum, manganese, titanium, vanadium and chromium as a metal other than cobalt (hereinafter referred to as the additive element X) to lithium cobaltate, and it is particularly preferred to add one or more of nickel and aluminum. Manganese, titanium, vanadium and chromium are sometimes stable when they become tetravalent, and sometimes they are very helpful in stabilizing the structure. By adding the additive element X, the crystal structure in the high-voltage charging state can be made more stable. Here, it is preferred that the additive element X is added to the positive electrode active material of one embodiment of the present invention at a concentration that does not greatly change the crystallinity of the lithium cobaltate. For example, the amount of the additive element X added is preferably such that it does not cause the above-mentioned Jan-Taylor effect, etc.

[0294] Transition metals such as nickel and manganese, and aluminum are preferably present at the cobalt position, but some of them may be present at the lithium position. Furthermore, magnesium is preferably present at the lithium position. A portion of the oxygen may be substituted with fluorine.

[0295] An increase in the magnesium concentration in the positive electrode active material of one embodiment of the present invention may sometimes reduce the capacity of the positive electrode active material. This may be mainly because, for example, magnesium enters the position of lithium, reducing the amount of lithium that contributes to charging and discharging. When the positive electrode active material of one embodiment of the present invention contains nickel as an added element X in addition to magnesium, the charge-discharge cycle characteristics may be improved. In addition, when the positive electrode active material of one embodiment of the present invention contains aluminum as an added element X in addition to magnesium, the charge-discharge cycle characteristics may be improved. In addition, when the positive electrode active material of one embodiment of the present invention includes magnesium, nickel, and aluminum as an added element X, the charge-discharge cycle characteristics may be improved.

[0296] The following considers the concentration of elements in the positive electrode active material according to one embodiment of the present invention containing magnesium, nickel, and aluminum as the added element X.

[0297] The number of nickel atoms contained in the positive electrode active material of one embodiment of the present invention is preferably 10% or less of the number of cobalt atoms, more preferably 7.5% or less, further preferably 0.05% or more and 4% or less, and particularly preferably 0.1% or more and 2% or less. The nickel concentration shown here can be, for example, a value obtained by elemental analysis of the entire positive electrode active material particle using ICP-MS or the like, or a value obtained based on the raw material mixing during the production process of the positive electrode active material.

[0298] When a high voltage charge state is maintained for a long time, the components of the positive electrode active material dissolve in the electrolyte, which may cause the crystal structure to collapse. However, by containing nickel at the above ratio, the dissolution of the components of the positive electrode active material 100 can sometimes be suppressed.

[0299] The number of aluminum atoms contained in the positive electrode active material of one embodiment of the present invention is preferably 0.05% or more and 4% or less of the number of cobalt atoms, and more preferably 0.1% or more and 2% or less. The aluminum concentration shown here can be, for example, a value obtained by elemental analysis of the entire positive electrode active material using ICP-MS or the like, or a value obtained based on the raw material mixing during the production process of the positive electrode active material.

[0300] In the positive electrode active material containing the additional element X according to one embodiment of the present invention, phosphorus is preferably used as the additional element X. In addition, the positive electrode active material according to one embodiment of the present invention more preferably contains a compound containing phosphorus and oxygen.

[0301] The positive electrode active material of one embodiment of the present invention contains a compound containing phosphorus as the additional element X, thereby suppressing short circuits even when a high-temperature and high-voltage charging state is maintained for a long period of time.

[0302] When the positive electrode active material of one embodiment of the present invention contains phosphorus as the additional element X, hydrogen fluoride generated by decomposition of the electrolyte may react with phosphorus to reduce the concentration of hydrogen fluoride in the electrolyte.

[0303] When the electrolyte contains LiPF6 as a lithium salt, hydrogen fluoride may be generated by hydrolysis. Furthermore, hydrogen fluoride may be generated by the reaction of PVDF, a component of the positive electrode, with a base. Reducing the hydrogen fluoride concentration in the electrolyte can sometimes suppress current collector corrosion and / or film peeling. Furthermore, it can sometimes prevent a decrease in adhesion due to gelation and / or insolubility of PVDF.

[0304] When the positive electrode active material 100 according to one embodiment of the present invention includes phosphorus and magnesium as the added element X, its stability under high-voltage charging is extremely high. When phosphorus and magnesium are included as the added element X, the atomic number of phosphorus is preferably 1% or more and 20% or less of the atomic number of cobalt, more preferably 2% or more and 10% or less, and even more preferably 3% or more and 8% or less. Furthermore, the atomic number of magnesium is preferably 0.1% or more and 10% or less of the atomic number of cobalt, more preferably 0.5% or more and 5% or less, and even more preferably 0.7% or more and 4% or less. The phosphorus and magnesium concentrations shown here can be values ​​obtained by elemental analysis of the entire positive electrode active material 100 using, for example, ICP-MS, or values ​​obtained by mixing raw materials during the production process of the positive electrode active material 100.

[0305] When the positive electrode active material 100 has cracks, if phosphorus, more specifically, a compound containing phosphorus and oxygen, is present therein, the expansion of the cracks may be suppressed.

[0306] Note that from Figure 12The symmetry of the oxygen atoms in the O3-type crystal structure and the O3'-type crystal structure differs slightly. Specifically, the oxygen atoms in the O3-type crystal structure are arranged along the dashed line, while the oxygen atoms in the O3'-type crystal structure are not strictly aligned. This is because in the O3'-type crystal structure, as the amount of tetravalent cobalt increases with the decrease in lithium, the strain caused by the Jahn-Teller effect increases, causing the octahedral structure of CoO6 to become distorted. Furthermore, this is due to the increased repulsion between the oxygen atoms in the CoO2 layer as the amount of lithium decreases.

[0307] <<Surface Layer 100a>> Magnesium is preferably distributed throughout the entire surface portion of the positive electrode active material 100 of one embodiment of the present invention. However, in addition to this, the magnesium concentration in the surface portion 100a is preferably higher than the average of the entire surface. For example, the magnesium concentration in the surface portion 100a measured by XPS or the like is preferably higher than the average magnesium concentration of the entire surface measured by ICP-MS or the like.

[0308] In addition, when the positive electrode active material 100 of one embodiment of the present invention contains an element other than cobalt, such as one or more metals selected from aluminum, manganese, iron, and chromium, the concentration of the metal near the particle surface is preferably higher than the average concentration of the entire particle. For example, the concentration of the element other than cobalt in the particle surface portion 100a measured by XPS or the like is preferably higher than the average concentration of the element in the entire particle measured by ICP-MS or the like.

[0309] The surface of the positive electrode active material 100 is full of crystal defects, and due to lithium extraction and insertion from the surface during charging, the lithium concentration in the surface tends to be lower than that in the interior. Consequently, it tends to be unstable, and the crystal structure is easily disrupted. A high magnesium concentration in the surface 100a can more effectively suppress changes in the crystal structure. Furthermore, a high magnesium concentration in the surface 100a is expected to improve corrosion resistance to hydrofluoric acid generated by electrolyte decomposition.

[0310] Furthermore, the concentration of halogens such as fluorine in the surface portion 100a of the positive electrode active material 100 of one embodiment of the present invention is preferably higher than the overall average. The presence of halogens in the surface portion 100a in the area in contact with the electrolyte effectively improves corrosion resistance to hydrofluoric acid.

[0311] Thus, it is preferred that the surface portion 100a of the positive electrode active material 100 of one embodiment of the present invention preferably has a composition different from that of the interior, that is, the concentration of added elements such as magnesium and fluorine is higher than that of the interior 100b. In addition, the surface portion 100a preferably has a crystal structure that is stable at room temperature. Thus, the surface portion 100a may also have a crystal structure different from that of the interior 100b. For example, at least a portion of the surface portion 100a of the positive electrode active material 100 of one embodiment of the present invention may have a rock salt type crystal structure. Note that when the surface portion 100a has a crystal structure different from that of the interior 100b, the orientation of the crystals of the surface portion 100a and the interior 100b is preferably roughly the same.

[0312] The anions of layered rock salt type crystals and rock salt type crystals form cubic closest packing structures (face-centered cubic lattice structures) respectively. It can be inferred that the anions in O3' type crystals also have cubic closest packing structures. In this specification, the structure in which the A layer, B layer and C layer comprising anions deviate from each other and are stacked like ABCABC is called a cubic closest packing structure. Therefore, the anions may not strictly be a cubic lattice. At the same time, in fact, crystallization has defects, so the analysis results may not be based on theory. For example, spots may also appear on positions slightly different from the theoretical positions in the FFT (Fast Fourier Transform) of electron diffraction or TEM images. For example, when the difference in orientation from the theoretical position is less than 5 degrees or less than 2.5 degrees, it can be said that the structure has a cubic closest packing structure.

[0313] When layered rock salt type crystals come into contact with rock salt type crystals, there are crystal planes with consistent orientation in the cubic closest packing structure formed by the anions.

[0314] In addition, it can be explained as follows. The anions on the (111) plane of the cubic crystal structure have a triangular lattice. The layered rock salt type has a rhombus structure belonging to the space group R-3m, but in order to facilitate the understanding of the structure, it is usually expressed as a composite hexagonal lattice, and the (0001) plane of the layered rock salt type has a hexagonal lattice. The triangular lattice of the cubic crystal (111) has the same atomic arrangement as the hexagonal lattice of the (0001) plane of the layered rock salt type. The state in which the lattices of the two are integrated can be said to be a state in which the orientation of the cubic closest packing structure is consistent.

[0315] Note that 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 the crystal planes that satisfy the above conditions differ between layered rock salt crystals and O3'-type crystals and rock salt crystals. In this specification, the state in which the orientation of the cubic closest packing structure formed by anions in layered rock salt crystals, O3'-type crystals, and rock salt crystals is consistent may refer to a state in which the crystal orientation is approximately consistent.

[0316] Whether the crystal orientations of two regions are roughly aligned can be determined using TE images, STEM (Scanning Transmission Electron Microscope) images, HAADF-STEM (High-angle Annular Dark Field Scanning TEM) images, ABF-STEM (Annular Bright-Field Scanning Transmission Electron Microscope) images, electron diffraction, FFT of TEM images, and the like. X-ray diffraction (XRD) and neutron diffraction can also be used as a basis for determination.

[0317] Figure 16 An example of a TEM image showing that the orientations of layered rock salt crystals LRS and rock salt crystals RS are substantially aligned is shown. TEM images, STEM images, HAADF-STEM images, ABF-STEM images, and other images can reflect the crystal structure.

[0318] For example, the contrast derived from the crystal plane can be obtained from high-resolution TEM images. Due to the diffraction and interference of the electron beam, for example, when the electron beam is incident perpendicular to the c-axis of the layered rock salt type composite hexagonal lattice, the repetition of bright and dark lines derived from the contrast of the (0003) plane can be obtained. Therefore, the repetition of bright and dark lines is observed in the TEM image, and between the bright lines (for example, Figure 16 L in RS and L LRS When the angle between the dark lines is less than 5 degrees or less than 2.5 degrees, it can be judged that the crystal planes are roughly consistent, that is, the crystal orientations are roughly consistent. Similarly, when the angle between the dark lines is less than 5 degrees or less than 2.5 degrees, it can also be judged that the crystal orientations are roughly consistent.

[0319] In addition, in the HAADF-STEM image, a contrast ratio proportional to the atomic number is obtained, and the larger the atomic number of the element, the brighter it is observed. For example, when using a layered rock salt type lithium cobalt oxide belonging to the space group R-3m, the atomic number of cobalt (atomic number 27) is the largest, so the electron beam is scattered more strongly at the position of the cobalt atom, so that the arrangement of the cobalt atoms is observed as an arrangement of bright lines or high-brightness points. Therefore, when observing lithium cobalt oxide with a layered rock salt type crystal structure in a direction perpendicular to the c-axis, the arrangement of cobalt atoms is observed as bright lines or arrangements of higher-brightness points in the direction perpendicular to the c-axis, and the arrangement of lithium atoms and oxygen atoms is observed as dark lines or areas with lower brightness. The same is true when fluorine (atomic number 9) and magnesium (atomic number 12) are included as additive elements in lithium cobalt oxide.

[0320] Therefore, in HAADF-STEM images, if a repetition of bright and dark lines is observed between two regions with different crystal structures, and the angle between the bright lines is 5 degrees or less, or 2.5 degrees or less, it can be determined that the atomic arrangement is roughly consistent, that is, the crystal orientation is roughly consistent. Similarly, if the angle between the dark lines is 5 degrees or less, or 2.5 degrees or less, it can also be determined that the crystal orientation is roughly consistent.

[0321] In addition, in ABF-STEM, elements with smaller atomic numbers appear brighter, but similarly to HAADF-STEM, a contrast corresponding to the atomic number can be obtained, so the orientation of the crystal can be determined similarly to the HAADF-STEM image.

[0322] Figure 17A An example of a STEM image showing that the orientations of the layered rock salt type crystals LRS and the rock salt type crystals RS are substantially aligned is shown. Figure 17B FFT of the region showing rock salt type crystal RS, Figure 17C FFT of a region showing layered rock salt type crystals LRS. Figure 17B and Figure 17C The left side shows the literature value, and the right side shows the measured value. The spot with O indicates the zero-order diffraction.

[0323] exist Figure 17B The spots marked with A in the figure are from the 11-1 reflection of the cubic crystal. Figure 17C The spots marked with A are from the 0003 reflection of the layered rock salt type. Figure 17B The straight line of AO and the line passing through Figure 17C The straight lines of AO are roughly parallel. In other words, it can be seen that Figure 17B and Figure 17C It can be seen that the orientation of the cubic 11-1 reflection is substantially consistent with the orientation of the layered rock salt type 0003 reflection. The terms "substantially consistent" and "substantially parallel" herein refer to angles of 5 degrees or less or 2.5 degrees or less.

[0324] As described above, in FFT and electron diffraction, when the orientations of the layered rock salt type crystals and the rock salt type crystals are roughly the same, the layered rock salt type crystals may be <0003> The orientation or its equivalent plane orientation is substantially consistent with the <11-1> orientation or its equivalent plane orientation of the rock salt type. In this case, the reciprocal points are preferably spot-shaped, i.e., not continuous with other reciprocal points. The reciprocal points being spot-shaped and not continuous with other reciprocal points indicates high crystallinity.

[0325] Furthermore, as described above, when the orientation of the 11-1 reflection of the cubic crystal is approximately the same as the orientation of the 0003 reflection of the layered rock salt, a spot that does not originate from the 0003 reflection of the layered rock salt may be observed in the reciprocal space in a direction different from that of the 0003 reflection of the layered rock salt, depending on the incident orientation of the electron beam. Figure 17C The spot in the figure B is from the 10-14 reflection of the layered rock salt type. This spot is sometimes located at the inverse grid point ( Figure 17C Observe at a location where the difference in orientation between the two points (A) is 52° to 56° (i.e., ∠AOB is 52° to 56°) and d is 0.19 nm to 0.21 nm. Note that the above index is only an example and does not necessarily need to be consistent with it. For example, reciprocal grid points equivalent to 0003 and 1014 can also be used.

[0326] Similarly, spots not originating from cubic 11-1 are sometimes observed in a reciprocal space at an orientation different from that of cubic 11-1. Figure 17B The spots in the image B come from the 200 reflection of the cubic crystal. Sometimes, the reflections of 11-1 ( Figure 17B Diffraction spots are observed at locations where the difference in azimuth between the two points (A) is 54° to 56° (i.e., ∠AOB is 54° to 56°). Note that the above indices are only examples and do not necessarily need to be consistent with them. For example, reciprocal grid points equivalent to 11-1 and 200 can also be used.

[0327] Note that layered rock salt-type positive electrode active materials, such as lithium cobalt oxide, are known to readily exhibit crystal planes on the (0003) plane and its equivalent, as well as the (10-14) plane and its equivalent. Therefore, when carefully observing the shape of the positive electrode active material using an SEM or other method, for example, using a TEM or other method with an electron beam incident at [1-210], the sample is thinned using a FIB (Focused Ion Beam) or other method to facilitate observation of the (0003) plane. When determining the uniformity of crystal orientation, thinning is preferably performed to facilitate observation of the (0003) plane of the layered rock salt.

[0328] However, if the surface portion 100a consists solely of MgO or a solid solution of MgO and CoO(II), lithium insertion and removal are difficult. Therefore, the surface portion 100a must contain at least cobalt and also lithium during discharge to provide pathways for lithium insertion and removal. Furthermore, the cobalt concentration is preferably higher than the magnesium concentration.

[0329] Furthermore, the additive element X is preferably located on the surface layer 100a of the particles of the positive electrode active material 100 of one embodiment of the present invention. For example, the positive electrode active material 100 of one embodiment of the present invention may be covered with a film containing the additive element X.

[0330] <Grain Boundary> The additional element X contained in the positive electrode active material 100 according to one embodiment of the present invention may be randomly present in a small amount inside, but it is more preferable that a part of the additional element X be segregated at the grain boundaries.

[0331] In other words, the concentration of the added element X in the grain boundaries and the vicinity of the positive electrode active material 100 according to one embodiment of the present invention is preferably higher than that in other regions inside the positive electrode active material 100 .

[0332] Grain boundaries can be considered surface defects. Therefore, like particle surfaces, they tend to be unstable and easily initiate changes in the crystal structure. Therefore, a higher concentration of the added element X at and near the grain boundaries effectively suppresses changes in the crystal structure.

[0333] Furthermore, when the concentration of the added element X is high at the grain boundaries and in the vicinity thereof, even when cracks are generated along the grain boundaries of the particles of the positive electrode active material 100 according to one embodiment of the present invention, the concentration of the added element X is high near the surface where the cracks are generated. Therefore, the corrosion resistance of the positive electrode active material to hydrofluoric acid can be improved even after the cracks are generated.

[0334] Note that in this specification and the like, the vicinity of a grain boundary refers to a region ranging from the grain boundary to approximately 10 nm.

[0335] <Particle size> If the particle size of the positive electrode active material 100 in one embodiment of the present invention is too large, problems such as difficulty in lithium diffusion and excessively rough surface of the active material layer when applied to the current collector may occur. On the other hand, if the particle size of the positive electrode active material 100 is too small, problems such as difficulty in supporting the active material layer when applied to the current collector and excessive reaction with the electrolyte may occur. Therefore, the average particle size (D50, also known as the median particle size) is preferably 1 μm to 100 μm, more preferably 2 μm to 40 μm, and even more preferably 5 μm to 30 μm.

[0336] <Analysis Method> To determine whether a particular positive electrode active material is the positive electrode active material 100 according to one embodiment of the present invention that exhibits an O3'-type crystal structure when charged at a high voltage, a positive electrode containing the positive electrode active material charged at a high voltage can be analyzed using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), or other methods. XRD is particularly preferred due to its advantages: it can analyze the symmetry of transition metals such as cobalt contained in the positive electrode active material at high resolution; it can compare the degree of crystallinity and the orientation of the crystals; it can analyze the periodic distortion of the crystal lattice and the grain size; and it can achieve sufficient accuracy even when directly measuring the positive electrode obtained by disassembling a secondary battery.

[0337] As described above, the positive electrode active material 100 according to one embodiment of the present invention is characterized by minimal changes in crystal structure between the high-voltage charged and discharged states. Materials containing 50% or more of a crystal structure that significantly changes between high-voltage charged and discharged states are not preferred because they cannot withstand high-voltage charging and discharging. Note that sometimes the desired crystal structure cannot be achieved simply by adding additive elements. For example, in a positive electrode active material such as lithium cobalt oxide containing magnesium and fluorine, when charged at a high voltage, the O3'-type crystal structure sometimes accounts for more than 60% of the material, and the H1-3-type crystal structure sometimes accounts for more than 50% of the material. Furthermore, when a specified voltage is used, the O3'-type crystal structure accounts for almost 100% of the material, and when the specified voltage is further increased, the H1-3-type crystal structure sometimes develops. Therefore, to determine whether the positive electrode active material 100 is according to one embodiment of the present invention, crystal structure analysis using methods such as XRD is necessary.

[0338] However, the crystal structure of the positive electrode active material in a high-voltage charged or discharged state may change when exposed to air. For example, it may change from an O3'-type crystal structure to an H1-3-type crystal structure. Therefore, all samples are preferably processed under an inert atmosphere such as argon.

[0339] <Charging method> For high voltage charging to determine whether a composite oxide is the positive electrode active material 100 according to one embodiment of the present invention, for example, a coin battery (CR2032 type, 20 mm in diameter, 3.2 mm in height) using lithium as a counter electrode can be prepared and charged.

[0340] More specifically, as the positive electrode, a positive electrode obtained by applying a slurry obtained by mixing a positive electrode active material, a conductive material, and a binder to a positive electrode current collector of aluminum foil can be used.

[0341] Lithium metal can be used as the counter electrode. Note that when a material other than lithium metal is used as the counter electrode, the potential of the positive electrode differs from that of a secondary battery. Unless otherwise specified, the voltage and potential in this specification refer to the potential of the positive electrode.

[0342] The electrolyte contained in the electrolytic solution was 1 mol / L lithium hexafluorophosphate (LiPF6). An organic solvent mixed with ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC = 3:7 and 2 wt% vinylene carbonate (VC) was used as the electrolyte.

[0343] A polypropylene film with a thickness of 25 μm can be used as the separator.

[0344] The positive electrode can and the negative electrode can may be formed of stainless steel (SUS).

[0345] The coin cell manufactured under the above conditions is charged at a constant current of 4.6V and 0.5C, and then charged at a constant voltage until the current value reaches 0.01C. Note that 1C here is 137mA / g. The temperature is 25°C. After charging in this way, the coin cell is disassembled in an argon atmosphere glove box and the positive electrode is removed, thereby obtaining a positive electrode active material charged at a high voltage. When performing various analyses later, it is preferably sealed under an argon atmosphere to prevent reactions with external components. For example, XRD can be performed under the condition of a sealed container sealed in an argon atmosphere.

[0346] <xrd> Figure 13 and Figure 15 The ideal powder XRD pattern obtained by CuKα1 radiation calculated from the model of O3' type crystal structure and H1-3 type crystal structure is shown. In addition, for comparison, the ideal XRD pattern calculated from the crystal structure of LiCoO2(O3) with x=1 and CoO2(O1) with x=0 is also shown. The patterns of LiCoO2(O3) and CoO2(O1) were made by using Reflex Powder Diffraction, one of the modules of Materials Studio (BIOVIA), from the crystal structure information obtained from ICSD (Inorganic Crystal Structure Database). The range of 2θ was set to 15° to 75°, Step size = 0.01, and wavelength λ1 = 1.540562×10 -10 m and λ2 were not set, and Monochromator was set to single. The pattern of the O3'-type crystal structure was prepared by inferring the crystal structure from the XRD pattern of the positive electrode active material according to one embodiment of the present invention and fitting it using TOPAS ver.3 (crystal structure analysis software manufactured by Bruker). XRD patterns were prepared in the same manner as for other structures.

[0347] like Figure 13 As shown in FIG. 1 , in the O3' type crystal structure, diffraction peaks appear at 2θ of 19.30±0.20° (19.10° to 19.50°) and 2θ of 45.55±0.10° (45.45° to 45.65°). More specifically, sharp diffraction peaks appear at 2θ of 19.30±0.10° (19.20° to 19.40°) and 2θ of 45.55±0.05° (45.50° to 45.60°). However, as Figure 15 As shown, the H1-3 type crystal structure and CoO2 (P-3m1, O1) do not have peaks at the above positions. Therefore, it can be said that the presence of peaks at 2θ of 19.30±0.20° and 2θ of 45.55±0.10° under high voltage charging is a characteristic of the positive electrode active material 100 of one embodiment of the present invention.

[0348] It can be said that the positions of the diffraction peaks observed by XRD are close to those of the crystal structure with x = 1 and the crystal structure in the high-voltage charging state. More specifically, it can be said that the position difference between two or more, preferably three or more, of the main diffraction peaks of the two is less than 2θ = 0.7, and more preferably less than 2θ = 0.5.

[0349] In addition, the positive electrode active material 100 of one embodiment of the present invention has an O3'-type crystal structure when charged at a high voltage, but the positive electrode active material 100 as a whole does not need to have an O3'-type crystal structure. It can have other crystal structures, and a part can be amorphous. Note that when the XRD pattern is subjected to Rietveld analysis, the O3'-type crystal structure is preferably 50 wt% or more, more preferably 60 wt% or more, and further preferably 66 wt% or more. When the O3'-type crystal structure is 50 wt% or more, more preferably 60 wt% or more, and further preferably 66 wt% or more, a positive electrode active material with sufficiently excellent cycle characteristics can be achieved.

[0350] Furthermore, the O3′-type crystal structure as determined by Rietveld analysis after 100 or more charge and discharge cycles from the start of measurement is preferably 35 wt % or more, more preferably 40 wt % or more, and even more preferably 43 wt % or more.

[0351] Furthermore, the grain size of the O3'-type crystal structure possessed by the particles of the positive electrode active material is only about 1 / 10 that of the discharged LiCoO2(O3). Therefore, even under the same XRD measurement conditions as for the positive electrode before charge and discharge, a distinct peak of the O3'-type crystal structure can be confirmed in the high-voltage charged state. On the other hand, even if a portion of pure LiCoO2 has a structure similar to the O3'-type crystal structure, the grain size will be smaller, and the peak will be broader and smaller. The grain size can be determined from the half-width of the XRD peak.

[0352] As described above, the positive electrode active material of one embodiment of the present invention is preferably not susceptible to the Jahn-Teller effect. The positive electrode active material of one embodiment of the present invention preferably has a layered rock salt crystal structure and primarily contains cobalt as a transition metal. Furthermore, the positive electrode active material of one embodiment of the present invention may contain the aforementioned additional element X other than cobalt, within a range that minimizes the influence of the Jahn-Teller effect.

[0353] When examining the preferred range of the lattice constant, it is found that in the positive electrode active material of one embodiment of the present invention, the lattice constant of the a-axis in the layered rock salt type crystal structure contained in the particles of the positive electrode active material in the non-charged or discharged state, which can be inferred from the XRD pattern, is preferably greater than 2.814×10 -10 m and less than 2.817×10 -10 m, and the lattice constant of the c-axis is preferably greater than 14.05×10 -10 m and less than 14.07×10 -10 The state without charge and discharge may refer to, for example, the state of powder before the positive electrode of the secondary battery is produced.

[0354] Alternatively, the value of the a-axis lattice constant divided by the c-axis lattice constant (a-axis / c-axis) in the layered rock salt type crystal structure contained in the positive electrode active material in the non-charged or discharged state is preferably greater than 0.20000 and less than 0.20049.

[0355] Alternatively, in a layered rock salt-type crystal structure contained in a positive electrode active material in a state without charge or discharge or in a discharged state, when XRD analysis is performed, a first peak at 2θ of 18.50° or more and 19.30° or less is sometimes observed, and a second peak at 2θ of 38.00° or more and 38.80° or less is sometimes observed.

[0356] The peaks appearing in the powder XRD pattern reflect the crystal structure of the interior 100b of the positive electrode active material 100, which occupies most of the volume of the positive electrode active material 100. The crystal structure of the surface layer 100a and the like can be analyzed by electron diffraction or the like on a cross section of the positive electrode active material 100.

[0357] <xps> X-ray photoelectron spectroscopy (XPS) can analyze from the surface to a depth of approximately 2 to 8 nm (typically around 5 nm), allowing quantitative analysis of the concentration of each element in approximately half of the surface layer 100a. Furthermore, by performing narrow scan analysis, the bonding state of the elements can be analyzed. XPS measurement accuracy is generally around ±1 at%, and although it varies depending on the element, the detection limit is around 1 at%.

[0358] When performing XPS analysis, for example, monochromated aluminum is used as the X-ray source, and the extraction angle is, for example, 45°.

[0359] In addition, when the positive electrode active material 100 of one embodiment of the present invention is analyzed by XPS, it is preferred that the peak showing the bond energy between fluorine and other elements is 682eV or more and less than 685eV, more preferably about 684.3eV. This value is different from the 685eV bond energy of lithium fluoride and the 686eV bond energy of magnesium fluoride. In other words, when the positive electrode active material 100 of one embodiment of the present invention contains fluorine, it is preferably a bond other than lithium fluoride and magnesium fluoride.

[0360] In addition, when the positive electrode active material 100 of one embodiment of the present invention is analyzed using XPS, the peak showing the bond energy between magnesium and other elements is preferably 1302 eV or more and less than 1304 eV, more preferably around 1303 eV. This value is different from the 1305 eV bond energy of magnesium fluoride and is close to the bond energy value of magnesium oxide. In other words, when the positive electrode active material 100 of one embodiment of the present invention contains magnesium, a bond other than magnesium fluoride is preferred.

[0361] As the added element X such as magnesium and aluminum, which is preferably present in a large amount in the surface portion 100a, the concentration measured by XPS is preferably higher than the concentration of magnesium and aluminum measured by ICP-MS (inductively coupled plasma mass spectrometry) or GD-MS (glow discharge mass spectrometry).

[0362] When the cross section is exposed by machining and analyzed using TEM-EDX, the concentration of magnesium and aluminum in the surface portion 100a is preferably higher than that in the inner portion 100b. Machining can be performed using, for example, FIB.

[0363] Preferably, the number of magnesium atoms is 0.4 to 1.5 times the number of cobalt atoms when analyzed by XPS (X-ray photoelectron spectroscopy). In addition, the ratio of magnesium atoms, Mg / Co, is preferably 0.001 to 0.06 when analyzed by ICP-MS.

[0364] On the other hand, nickel included in the transition metal is preferably distributed throughout the particles of the positive electrode active material 100 rather than being concentrated in the surface layer 100a. Note that even if there is a region where the excess added element X is concentrated, this is not the only limitation.

[0365] <Surface roughness and specific surface area> The positive electrode active material 100 according to one embodiment of the present invention preferably has a smooth surface with minimal irregularities. This smooth surface with minimal irregularities is a factor indicative of a good distribution of the additive element X in the surface portion 100a. Note that during the manufacturing process of the positive electrode active material 100, when initial heating of lithium cobalt oxide or lithium nickel-cobalt-manganese oxide is performed before the addition of the additive element X, the high-voltage charge and discharge cycle characteristics are extremely excellent, making this material particularly preferred as the positive electrode active material 100.

[0366] Furthermore, by making the surface of the positive electrode active material 100 smooth and having few irregularities, it is possible to improve the stability of the surface of the positive electrode active material 100 and suppress the occurrence of pits.

[0367] For example, whether the surface is smooth and has few irregularities can be determined by referring to a cross-sectional SEM image or a cross-sectional TEM image of the positive electrode active material 100 , the specific surface area of ​​the positive electrode active material 100 , and the like.

[0368] For example, as shown below, the surface smoothness can be quantified from a cross-sectional SEM image of the positive electrode active material 100 .

[0369] First, the positive electrode active material 100 is processed by FIB or the like to expose its cross section. At this time, it is preferred to cover the positive electrode active material 100 with a protective film, a protective agent, or the like. Next, an SEM image of the interface between the protective film or the like and the positive electrode active material 100 is taken. The SEM image is subjected to noise processing using image processing software. For example, after Gaussian Blur (σ=2), binarization is performed. Furthermore, the interface is extracted using image processing software. Furthermore, the interface line between the protective film or the like and the positive electrode active material 100 is selected using a magic hand tool or the like, and the data is extracted to a spreadsheet software or the like. The root mean square (RMS) surface roughness is calculated using the function of the spreadsheet software or the like as described below, that is, correction is performed based on a regression curve (quadratic regression), and the parameters for calculating the roughness are calculated from the tilt-corrected data, thereby calculating the standard deviation. In addition, the surface roughness is the surface roughness of at least 400 nm around the outer periphery of the positive electrode active material particles.

[0370] The surface of the positive electrode active material 100 particles of this embodiment has a root mean square (RMS) surface roughness, which is an indicator of roughness, of preferably 10 nm or less, less than 3 nm, more preferably less than 1 nm, and even more preferably less than 0.5 nm.

[0371] Note that there are no particular limitations on image processing software for noise processing, interface extraction, etc., and for example, "ImageJ" can be used. Furthermore, there are no particular limitations on spreadsheet software, and for example, Microsoft Office Excel can be used.

[0372] For example, the actual specific surface area A measured by the constant volume gas adsorption method can also be used. R Compared with the ideal specific surface area A i The ratio of quantifies the surface smoothness of the positive electrode active material 100.

[0373] Ideal specific surface area A i The value is calculated based on the assumption that all particles have the same diameter and D50, the same weight, and are perfectly spherical in shape.

[0374] The median diameter D50 can be measured by a particle size distribution analyzer using a laser diffraction and scattering method, etc. The specific surface area can be measured by a specific surface area measuring device using a constant volume gas adsorption method, etc.

[0375] In the positive electrode active material 100 of one embodiment of the present invention, the ideal specific surface area A obtained from the median diameter D50 is preferably i Compared with the actual specific surface area A R The ratio of A R / A i It is 1 or more and 2 or less.

[0376] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0377] (Implementation 4) In this embodiment, various shapes of secondary batteries including a positive electrode or a negative electrode manufactured by the manufacturing method described in the above embodiment will be described.

[0378] [Coin-type secondary battery] An example of a coin-type secondary battery will be described. Figure 18A This is an exploded perspective view of a coin-type (single-layer flat) secondary battery. Figure 18B This is its appearance picture. Figure 18C Coin-type secondary batteries are mainly used in small electronic devices. In this specification, etc., coin-type batteries include button-type batteries.

[0379] In order to easily understand the overlapping relationship of components (upper and lower relationship and position relationship), Figure 18A A schematic diagram is used. Therefore, Figure 18A Not with Figure 18B Exactly the same picture.

[0380] exist Figure 18A In the stack, the positive electrode 304, separator 310, negative electrode 307, spacer 322, and gasket 312 are stacked. Then, the negative electrode can 302 and the positive electrode can 301 are sealed. Figure 18A The sealing gasket is not shown. Spacers 322 and gaskets 312 are used to protect the interior of the positive electrode can 301 and the negative electrode can 302 or to secure the position of the cans when they are pressed together. Spacers 322 and gaskets 312 are made of stainless steel or an insulating material.

[0381] A stacked structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305 is referred to as a positive electrode 304 .

[0382] In order to prevent short circuits between the positive and negative electrodes, separator 310 and annular insulator 313 are arranged to cover the side and top surfaces of positive electrode 304. The plane area of ​​separator 310 is larger than that of positive electrode 304.

[0383] Figure 18B It is a perspective view of the manufactured coin-type secondary battery.

[0384] In a coin-type secondary battery 300, a positive electrode can 301, which also serves as a positive terminal, and a negative electrode can 302, which also serves as a negative terminal, are insulated and sealed by a gasket 303 made of, for example, polypropylene. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 disposed in contact therewith. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 disposed in contact therewith. The negative electrode 307 is not limited to a laminated structure; lithium metal foil or a lithium-aluminum alloy foil may also be used.

[0385] In the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 , the active material layer may be formed on one surface respectively.

[0386] For the positive electrode can 301 and the negative electrode can 302, metals such as nickel, aluminum, and titanium, alloys thereof, and alloys of these with other metals (e.g., stainless steel) that are resistant to electrolyte corrosion can be used. Furthermore, to prevent corrosion from the electrolyte, the positive electrode can 301 and the negative electrode can 302 are preferably covered with nickel, aluminum, or the like. 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.

[0387] By immersing the negative electrode 307, the positive electrode 304 and the separator 310 in an electrolyte, Figure 18C As shown, the positive electrode can 301 is placed at the bottom, and the positive electrode 304, separator 310, negative electrode 307 and negative electrode can 302 are stacked in this order. The positive electrode can 301 and negative electrode can 302 are press-fitted with a gasket 303 interposed therebetween to manufacture the coin-type secondary battery 300.

[0388] By adopting the above structure, a coin-type secondary battery 300 with high capacity, high charge and discharge capacity, and good cycle characteristics can be manufactured. In addition, when a secondary battery including a solid electrolyte layer between the negative electrode 307 and the positive electrode 304 is used, the separator 310 may not be provided.

[0389] [Cylindrical secondary battery] Next, refer to Figure 19A and Figure 19B An example of a cylindrical secondary battery will be described. Figure 19B : is a diagram schematically showing a cross section of a cylindrical secondary battery. Figure 19A and Figure 19B As shown, the top surface of the cylindrical secondary battery 616 includes a positive electrode cover (battery cover) 601, and its side and bottom surfaces include a battery can (external can) 602. The positive electrode cover 601 and the battery can (external can) 602 are insulated by a gasket (insulating gasket) 610.

[0390] A battery element is provided inside the hollow cylindrical battery can 602, in which a strip-shaped positive electrode 604 and a strip-shaped negative electrode 606 are wound with a separator 605. Although not shown in the figure, the battery element is wound around the central axis. One end of the battery can 602 is closed and the other end is open. As the battery can 602, metals such as nickel, aluminum, titanium, etc. that are resistant to corrosion by the electrolyte, their alloys, and alloys of these and other metals (such as stainless steel, etc.) can be used. In addition, in order to prevent corrosion caused by the electrolyte, the battery can 602 is preferably covered with nickel, aluminum, etc. Inside the battery can 602, the battery element in which the positive electrode, negative electrode and separator are wound is sandwiched by a pair of opposing insulating plates 608 and insulating plates 609. In addition, a non-aqueous electrolyte (not shown) is injected into the interior of the battery can 602 in which the battery element is provided. As the non-aqueous electrolyte, the same electrolyte as that of a coin-type secondary battery can be used.

[0391] Since the positive and negative electrodes used in cylindrical storage batteries are wound, it is preferable that the active material is formed on both sides of the current collector. 19A to 19D Although the secondary battery 616 is shown as having a cylinder height greater than its diameter, the present invention is not limited thereto. Alternatively, a secondary battery having a cylinder diameter greater than its height may be used. By adopting the above structure, for example, a miniaturized secondary battery can be achieved.

[0392] By using the negative electrode 570a obtained in the above embodiment as the negative electrode 606, a cylindrical secondary battery 616 having high capacity, high charge-discharge capacity, and good cycle characteristics can be manufactured. Furthermore, by using the positive electrode active material complex 100z obtained in the above embodiment as the positive electrode 604, a cylindrical secondary battery 616 having high capacity, high charge-discharge capacity, and good cycle characteristics can be manufactured.

[0393] The positive electrode 604 is connected to the positive terminal (positive electrode current collecting lead) 603, while the negative electrode 606 is connected to the negative terminal (negative electrode current collecting lead) 607. Both the positive terminal 603 and the negative terminal 607 can be made of metal materials such as aluminum. The positive terminal 603 is resistance-welded to the safety valve mechanism 613, while the negative 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. When the internal pressure of the battery rises above a specified threshold, the safety valve mechanism 613 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604. The PTC element 611 is a thermally sensitive resistor whose resistance increases as the temperature rises. This increase in resistance limits the current flow to prevent abnormal heating. Barium titanate (BaTiO3)-based semiconductor ceramics, for example, can be used as PTC elements.

[0394] Figure 19C An example of a power storage system 615 is shown. Power storage system 615 includes multiple secondary batteries 616. The positive electrode of each secondary battery contacts a conductor 624 separated by an insulator 625, and the positive electrodes are electrically connected to each other. Conductor 624 is electrically connected to a control circuit 620 via wiring 623. Furthermore, the negative electrode of each secondary battery is electrically connected to control circuit 620 via wiring 626. A protection circuit, etc., that prevents overcharging or overdischarging can be used as control circuit 620.

[0395] Figure 19D An example of a power storage system 615 is shown. Power storage system 615 includes multiple secondary batteries 616 sandwiched between a conductive plate 628 and a conductive plate 614. Multiple secondary batteries 616 are electrically connected to conductive plate 628 and conductive plate 614 via wiring 627. Multiple secondary batteries 616 can be connected in parallel or in series. By configuring power storage system 615 including multiple secondary batteries 616, large amounts of power can be obtained.

[0396] Alternatively, a plurality of secondary batteries 616 may be connected in parallel and then connected in series.

[0397] Furthermore, a temperature control device may be provided between the plurality of secondary batteries 616. The temperature control device can be used to cool the secondary batteries 616 when they are overheated, and can be used to heat the secondary batteries 616 when they are overcooled. Therefore, the performance of the power storage system 615 is less susceptible to the effects of the external temperature.

[0398] In addition, Figure 19D In FIG, the power 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 electrodes of the plurality of secondary batteries 616 via a conductive plate 628, and wiring 622 is electrically connected to the negative electrodes of the plurality of secondary batteries 616 via a conductive plate 614.

[0399] [Other structural examples of secondary batteries] An example of the structure of a secondary battery will be described using FIG. 20 and FIG. 21 .

[0400] Figure 20A The secondary battery 913 shown includes a wound body 950 provided with terminals 951 and 952 inside a housing 930. The wound body 950 is immersed in an electrolyte inside the housing 930. The terminal 952 is in contact with the housing 930, and the terminal 951 is prevented from contacting the housing 930 by an insulating material. Note that for the sake of convenience, although Figure 20A Frame 930 is shown separated in the figure, but in reality, wound body 950 is covered by frame 930, and terminals 951 and 952 extend outside frame 930. Frame 930 can be made of a metal material (eg, aluminum) or a resin material.

[0401] In addition, if Figure 20B As shown, multiple materials can also be used to form Figure 20A For example, in the Figure 20B In the secondary battery 913 shown, a frame body 930 a and a frame body 930 b are bonded together, and a wound body 950 is provided in a region surrounded by the frame bodies 930 a and 930 b.

[0402] Frame 930a can be made of an insulating material such as organic resin. In particular, using materials such as organic resin to form the antenna surface can reduce shielding by the electric field of secondary battery 913. Alternatively, if the electric field shielding caused by frame 930a is minimal, the antenna can be placed inside frame 930a. Frame 930b can be made of, for example, a metal material.

[0403] Furthermore, Figure 20C The structure of a wound body 950 is shown. The wound body 950 includes a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 and the positive electrode 932 are stacked with the separator 933 interposed therebetween to form a laminated sheet. The wound body 950 is a wound body formed by winding this laminated sheet. Alternatively, multiple layers of the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked.

[0404] Alternatively, you can use Figures 21A to 21C A secondary battery 913 including a wound body 950a is shown. Figure 21A The wound body 950a shown includes a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 includes a negative electrode active material layer 931a, and the positive electrode 932 includes a positive electrode active material layer 932a.

[0405] By using the negative electrode 570a obtained in the above embodiment as the negative electrode 606, a cylindrical secondary battery 616 having high capacity, high charge-discharge capacity, and excellent cycle characteristics can be manufactured. Furthermore, by using the positive electrode active material complex 100z obtained in the above embodiment as the positive electrode 932, a secondary battery 913 having high capacity, high charge-discharge capacity, and excellent cycle characteristics can be manufactured.

[0406] The separator 933 is wider than the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap the negative electrode active material layer 931a and the positive electrode active material layer 932a. Furthermore, from a safety perspective, it is preferable that the negative electrode active material layer 931a be wider than the positive electrode active material layer 932a. The wound body 950a of this shape is preferred because it offers excellent safety and productivity.

[0407] like Figure 21B As shown, the negative electrode is electrically connected to terminal 951. Terminal 951 is electrically connected to terminal 911a. In addition, the positive electrode is electrically connected to terminal 952. Terminal 952 is electrically connected to terminal 911b.

[0408] like Figure 21C As shown, the wound body 950a and the electrolyte are covered by the frame 930 to form the secondary battery 913. The frame 930 is preferably provided with a safety valve, an overcurrent protection element, etc. The safety valve is a valve that opens the inside of the frame 930 at a specified internal pressure to prevent battery rupture.

[0409] like Figure 21B As shown, the secondary battery 913 may also include a plurality of winding bodies 950a. By using a plurality of winding bodies 950a, a secondary battery 913 with a larger charge and discharge capacity can be realized. Figure 21A and Figure 21B For other components of the secondary battery 913 shown, please refer to 20A to 20C The secondary battery 913 is shown.

[0410] <Laminated secondary battery> then, Figure 22A and Figure 22B 1 is an external view showing an example of a laminated secondary battery. Figure 22A and Figure 22B A positive electrode 503 , a negative electrode 506 , a separator 507 , an outer package 509 , a positive electrode lead electrode 510 , and a negative electrode lead electrode 511 are all shown.

[0411] Figure 23A It is an appearance diagram of the positive electrode 503 and the negative electrode 506. The positive electrode 503 includes a positive electrode current collector 501, and a positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. In addition, the positive electrode 503 has an area where the positive electrode current collector 501 is partially exposed (hereinafter referred to as the tab area). The negative electrode 506 includes a negative electrode current collector 504, and a negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. In addition, the negative electrode 506 has an area where the negative electrode current collector 504 is partially exposed, namely the tab area. The area and shape of the tab area of ​​the positive electrode and the negative electrode are not limited to Figure 23A Example shown.

[0412] <Method for Manufacturing Laminated Secondary Battery> Here, refer to Figure 23B and Figure 23C Right Figure 22A An example of a method for manufacturing a laminated secondary battery will be described, with its appearance shown in FIG.

[0413] First, the negative electrode 506 , the separator 507 , and the positive electrode 503 are stacked. Figure 23B The stacked negative electrode 506, separator 507, and positive electrode 503 are shown. Here, an example using five negative electrode sets and four positive electrode sets is shown. This is also referred to as a stack consisting of negative electrodes, separators, and positive electrodes. Next, the tab regions of the positive electrodes 503 are bonded together, and the positive electrode lead electrode 510 is bonded to the outermost tab region of the positive electrode. This bonding can be accomplished using, for example, ultrasonic welding. Similarly, the tab regions of the negative electrodes 506 are bonded together, and the negative electrode lead electrode 511 is bonded to the outermost tab region of the negative electrode.

[0414] Next, the negative electrode 506 , the separator 507 , and the positive electrode 503 are placed on the outer package 509 .

[0415] Below, as Figure 23C As shown, the outer packaging 509 is folded along the portion indicated by the dotted line. Then, the outer periphery of the outer packaging 509 is bonded. For example, heat compression bonding can be used as the bonding method. At this time, an area (hereinafter referred to as an inlet) that is not bonded to a portion (or one edge) of the outer packaging 509 is provided for subsequent injection of the electrolyte.

[0416] Next, the electrolyte is introduced into the inner side of the outer packaging body 509 through an inlet provided in the outer packaging body 509. The electrolyte is preferably introduced under a reduced pressure atmosphere or an inert gas atmosphere. Finally, the inlet is joined. In this way, the laminated secondary battery 500 can be manufactured.

[0417] By using the negative electrode 570a obtained in the above embodiment as the negative electrode 606, a cylindrical secondary battery 616 having high capacity, high charge-discharge capacity, and good cycle characteristics can be manufactured. Furthermore, by using the positive electrode active material complex 100z obtained in the above embodiment as the positive electrode 503, a secondary battery 500 having high capacity, high charge-discharge capacity, and good cycle characteristics can be manufactured.

[0418] [Battery pack example] use Figures 24A to 24C An example of a secondary battery pack according to one embodiment of the present invention that can be wirelessly charged using an antenna will be described.

[0419] Figure 24A 1 is a diagram showing the appearance of a secondary battery pack 531 having a thin rectangular parallelepiped shape (or a relatively thick flat plate shape). Figure 24B 5 is a diagram illustrating the structure of a secondary battery pack 531. The secondary battery pack 531 includes a circuit board 540 and a secondary battery 513. A label 529 is attached to the secondary battery 513. The circuit board 540 is secured by a sealing tape 515. The secondary battery pack 531 also includes an antenna 517.

[0420] The interior of the secondary battery 513 may have a structure including a wound body or a structure including a stacked body.

[0421] like Figure 24B As shown, in the secondary battery pack 531, a control circuit 590 is provided on, for example, a circuit board 540. Furthermore, the circuit board 540 is electrically connected to the terminal 514. Furthermore, the circuit board 540 is electrically connected to the antenna 517, one of the positive and negative lead wires 551 of the secondary battery 513, and the other of the positive and negative lead wires 552.

[0422] In addition, if Figure 24C As shown, the circuit board 540 may include a circuit system 590 a disposed on the circuit board 540 and a circuit system 590 b electrically connected to the circuit board 540 through the terminal 514 .

[0423] In addition, the shape of antenna 517 is not limited to a coil shape, and can be, for example, linear or plate-shaped. In addition, antennas such as planar antennas, aperture antennas, traveling wave antennas, EH antennas, magnetic field antennas, or dielectric antennas can also be used. Alternatively, antenna 517 can also be a flat conductor. The flat conductor can also be used as one of the conductors for electric field coupling. In other words, antenna 517 can also be used as one of the two conductors of a capacitor. In this way, not only electromagnetic and magnetic fields can be used, but also electric fields can be used to exchange power.

[0424] The secondary battery pack 531 includes a layer 519 between the antenna 517 and the secondary battery 513. The layer 519 has a function of, for example, shielding the electromagnetic field from the secondary battery 513. As the layer 519, for example, a magnetic material can be used.

[0425] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0426] (Implementation 5) In this embodiment, an example of manufacturing an all-solid-state battery using the positive electrode active material complex 100z obtained in the above embodiment is described.

[0427] like Figure 25A As shown, a secondary battery 400 according to one embodiment of the present invention includes a positive electrode 410 , a solid electrolyte layer 420 , and a negative electrode 430 .

[0428] The positive electrode 410 includes a positive electrode current collector 413 and a positive electrode active material layer 414. The positive electrode active material layer 414 includes a positive electrode active material 411 and a solid electrolyte 421. The positive electrode active material complex 100z obtained in the above embodiment is used as the positive electrode active material 411. The positive electrode active material layer 414 may also include a conductive material and a binder.

[0429] The solid electrolyte layer 420 includes a solid electrolyte 421 . The solid electrolyte layer 420 is located between the positive electrode 410 and the negative electrode 430 , and does not include either the positive electrode active material 411 or the negative electrode active material 431 .

[0430] The negative electrode 430 includes a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 includes a negative electrode active material 431 and a solid electrolyte 421. In addition, the negative electrode active material layer 434 may also include a conductive material and a binder. Note that when metallic lithium is used for the negative electrode active material 431, it is not necessary to use particles, so Figure 25B As shown, the negative electrode 430 may be formed without the solid electrolyte 421. When metallic lithium is used for the negative electrode 430, the energy density of the secondary battery 400 can be increased, which is preferable.

[0431] As the solid electrolyte 421 included in the solid electrolyte layer 420 , for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, or the like can be used.

[0432] Sulfide solid electrolytes include thio-LISICON (Li 10 GeP2S 12 、Li 3.25 Ge 0.25 P 0.75 S4, etc.), sulfide glass (70Li2S·30P2S5, 30Li2S·26B2S3·44LiI, 63Li2S·38SiS2·1Li3PO4, 57Li2S·36SiS2·5Li4SiO4, 50Li2S·50GeS2, etc.), sulfide crystallized glass (Li7P3S 11 、Li 3.25 P 0.95 S4, etc.) Sulfide-based solid electrolytes have the following advantages: they are highly conductive materials; they can be synthesized at low temperatures; they are relatively soft, making it easy to maintain a conductive path even after charge and discharge; etc.

[0433] Oxide-based solid electrolytes include materials with a perovskite crystal structure (La 2 / 3-x Li 3x TiO3, etc.), materials with NASICON crystal structure (Li 1-Y Al Y Ti 2-Y (PO4)3, etc.), materials with garnet crystal structure (Li7La3Zr2O 12 etc.), materials with LISICON crystal structure (Li 14 ZnGe4O 16 etc.), LLZO(Li7La3Zr2O 12 ), oxide glass (Li3PO4-Li4SiO4, 50Li4SiO4·50Li3BO3, etc.), oxide crystal glass (Li 1.07 Al 0.69 Ti 1.46 (PO4)3、Li 1.5 Al 0.5 Ge 1.5 (PO4)3, etc.) The advantage of oxide-based solid electrolytes is that they are stable in the atmosphere.

[0434] Halide-based solid electrolytes include LiAlCl4, Li3InBr6, LiF, LiCl, LiBr, LiI, etc. In addition, a composite material formed by filling the pores of porous alumina or porous silica with these halide-based solid electrolytes can also be used as a solid electrolyte.

[0435] Furthermore, different solid electrolytes may be mixed and used.

[0436] Among them, Li with NASICON crystal structure 1-x Al x Ti 2-x (PO4)3(0 < x < 1) (hereinafter referred to as LATP) contains aluminum and titanium, which are elements that can be included in the positive electrode active material of the secondary battery 400 in one embodiment of the present invention. Therefore, a multiplicative effect on improving the cycle characteristics can be expected, so it is preferred. In addition, a reduction in processes can also be expected to improve productivity. Note that in this specification, etc., the NASICON-type crystal structure refers to a structure in which the MO6 octahedron and XO4 tetrahedron in a compound represented by M2(XO4)3 (M: transition metal, X: S, P, As, Mo, W, etc.) share vertices and are three-dimensionally arranged.

[0437] [Shape of outer package and secondary battery] The outer package of the secondary battery 400 in one embodiment of the present invention can adopt various materials and shapes, and preferably, materials and shapes having a pressing function on the positive electrode, solid electrolyte layer, and negative electrode.

[0438] For example, FIG. 26 shows an example of a unit for evaluating materials for all-solid-state batteries.

[0439] Figure 26A It is a cross-sectional schematic view of the evaluation unit. The evaluation unit includes a lower member 761, an upper member 762, and fixing screws or wing nuts 764 for fixing them. The evaluation material is fixed by pressing the electrode plate 753 with the rotating pressing screw 763. An insulator 766 is provided between the lower member 761 and the upper member 762 made of a stainless steel material. In addition, an O-ring 765 for sealing is provided between the upper member 762 and the pressing screw 763.

[0440] The evaluation material is placed on the electrode plate 751, surrounded by an insulating tube 752, and pressed by the electrode plate 753 above. Figure 26B A perspective view magnifying the vicinity of the evaluation material is shown.

[0441] An example in which a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c are laminated is shown as the evaluation material. Figure 26C A cross-sectional view thereof is shown. Note that Figures 26A to 26C The same parts in [[ ]] are denoted by the same reference numerals.

[0442] The electrode plate 751 and the lower member 761 electrically connected to the positive electrode 750a can be regarded as the positive electrode terminal. The electrode plate 753 and the upper member 762 electrically connected to the negative electrode 750c can be regarded as the negative electrode terminal. In addition, the resistance, etc. can be measured by pressing the evaluation material with the electrode plate 751 and the electrode plate 753.

[0443] The secondary battery of one embodiment of the present invention preferably has an outer package that is highly airtight. For example, a ceramic package or a resin package can be used. Furthermore, the outer package is preferably sealed in a sealed atmosphere that prevents atmospheric ingress, such as in a glove box.

[0444] Figure 27A 26 is a perspective view showing a secondary battery according to one embodiment of the present invention having an outer casing and a shape different from those in FIG. 26 . Figure 27A The secondary battery includes external electrodes 771 and 772 and is sealed by an outer package having a plurality of packaging members.

[0445] Figure 27B Shown along Figure 27A An example of a cross section cut along the dotted line in FIG. The stacked body comprising positive electrode 750a, solid electrolyte layer 750b, and negative electrode 750c is surrounded and sealed by a packaging member 770a having an electrode layer 773a disposed on a flat plate, a frame-shaped packaging member 770b, and a packaging member 770c having an electrode layer 773b disposed on a flat plate. Packaging members 770a, 770b, and 770c can be made of an insulating material such as a resin or ceramic.

[0446] The external electrode 771 is electrically connected to the positive electrode 750a via the electrode layer 773a and serves as a positive electrode terminal. In addition, the external electrode 772 is electrically connected to the negative electrode 750c via the electrode layer 773b and serves as a negative electrode terminal.

[0447] By using the positive electrode active material complex 100z obtainable in the above-described embodiment, an all-solid-state secondary battery having a high energy level density and excellent output characteristics can be realized.

[0448] The contents of this embodiment can be combined with the contents of other embodiments as appropriate.

[0449] (Implementation 6) This embodiment shows Figure 19D Different examples of cylindrical secondary batteries. Figure 28C An example applicable to electric vehicles (EVs) will be described.

[0450] In an electric vehicle, the main driving secondary batteries include first batteries 1301a and 1301b, and a second battery 1311 that supplies power to an inverter 1312 that starts an engine 1304. Second battery 1311 is also called a cranking battery (also called a starting battery). High output is sufficient, not necessarily high capacity. Furthermore, second battery 1311 has a smaller capacity than first batteries 1301a and 1301b.

[0451] The internal structure of the first battery 1301a can be either Figure 20A or Figure 21C The winding type shown can also be used Figure 22A or Figure 22B The stacked type shown. Alternatively, the first battery 1301a may use the all-solid-state battery of Embodiment 5. Using the all-solid-state battery of Embodiment 5 as the first battery 1301a allows for high capacity, improved safety, and reduced size and weight.

[0452] In this embodiment, an example of connecting first batteries 1301a and 1301b in parallel is shown, but more than three batteries can be connected in parallel. In addition, as long as sufficient power can be stored in first battery 1301a, first battery 1301b can be omitted. By forming a battery pack with multiple secondary batteries, a large amount of power can be extracted. Multiple secondary batteries can be connected in parallel, in series, or in parallel and then in series. Multiple secondary batteries are sometimes referred to as a battery pack.

[0453] In order to cut off the power from the plurality of secondary batteries, the vehicle-mounted secondary battery includes a charging plug or a circuit breaker that can cut off the high voltage without using tools, which is provided on the first battery 1301a.

[0454] Furthermore, the power of the first batteries 1301a and 1301b is mainly used to rotate the engine 1304, and is also supplied to 42V series vehicle components (such as the electric power steering system (steering system) 1307, the heater 1308, and the defogger 1309) via the DC-DC circuit 1306. In the case where the rear wheels include a rear engine 1317, the first battery 1301a is used to rotate the rear engine 1317.

[0455] Furthermore, the second battery 1311 supplies power to 14V series vehicle-mounted components (audio 1313 , power windows 1314 , lights 1315 , etc.) via the DCDC circuit 1310 .

[0456] In addition, use Figure 28A The first battery 1301a will be described.

[0457] Figure 28A An example of using nine rectangular secondary batteries 1300 as a battery pack 1415 is shown. In addition, the nine rectangular secondary batteries 1300 are connected in series and one electrode is fixed using a fixing portion 1413 composed of an insulator and the other electrode is fixed using a fixing portion 1414 composed of an insulator. In this embodiment, an example of fixing using fixing portions 1413 and 1414 is shown, but it can also be stored in a battery storage box (also called a frame). Assuming that the vehicle is vibrated or shaken from the outside (road surface, etc.), it is preferable to use fixing portions 1413, 1414 and a battery storage box to fix multiple secondary batteries. In addition, one electrode is electrically connected to the control circuit unit 1320 via wiring 1421. The other electrode is electrically connected to the control circuit unit 1320 via wiring 1422.

[0458] Alternatively, a memory circuit including transistors using oxide semiconductors may be used as the control circuit portion 1320. A charge control circuit or battery control system including a memory circuit including transistors using oxide semiconductors is sometimes referred to as a BTOS (Battery Operating System).

[0459] It is preferred to use a metal oxide used as an oxide semiconductor. For example, as an oxide, it is preferred to use a metal oxide such as In-M-Zn oxide (the element M is one or more selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten and magnesium). In particular, the In-M-Zn oxide that can be applied to the oxide is preferably CAAC-OS (C-Axis Aligned Crystal Oxide Semiconductor) or CAC-OS (Cloud-Aligned Composite Oxide Semiconductor). In addition, In-Ga oxide and In-Zn oxide can also be used as the oxide. CAAC-OS is an oxide semiconductor including a plurality of crystalline regions, the c-axes of the plurality of crystalline regions being oriented in a specific direction. In addition, the specific direction refers to the thickness direction of the CAAC-OS film, the normal direction of the formed surface of the CAAC-OS film, or the normal direction of the surface of the CAAC-OS film. In addition, the crystalline region is a region having a periodic arrangement of atoms. Note that when the atomic arrangement is regarded as a lattice arrangement, the crystalline region is also a region with a uniform lattice arrangement. Furthermore, CAAC-OS has a region where a plurality of crystalline regions are connected in the ab plane direction, and sometimes the region has distortion. In addition, distortion refers to a portion where the direction of the lattice arrangement changes between a region with a uniform lattice arrangement and other regions with a uniform lattice arrangement in a region where a plurality of crystalline regions are connected. In other words, CAAC-OS refers to an oxide semiconductor that is c-axis oriented and has no obvious orientation in the ab plane direction. In addition, CAC-OS refers to, for example, a structure in which elements contained in a metal oxide are unevenly distributed, wherein the size of the material containing the unevenly distributed elements is greater than 0.5 nm and less than 10 nm, preferably greater than 1 nm and less than 3 nm, or a similar size. Note that in the following, a state in which one or more metal elements are unevenly distributed in a metal oxide and the regions containing the metal elements are mixed is also referred to as a mosaic or patch shape, and the size of the region is greater than 0.5 nm and less than 10 nm, preferably greater than 1 nm and less than 3 nm, or a similar size.

[0460] Furthermore, CAC-OS refers to a composite metal oxide having a structure in which the material is divided into a first region and a second region, forming a mosaic shape, and the first region is distributed in the film (hereinafter also referred to as a cloud shape). In other words, CAC-OS refers to a composite metal oxide having a structure in which the first region and the second region are mixed.

[0461] Here, the atomic ratios of In, Ga, and Zn relative to the metal elements constituting the CAC-OS of an In-Ga-Zn oxide are each denoted as [In], [Ga], and [Zn]. For example, in the CAC-OS of an In-Ga-Zn oxide, the first region is a region where [In] is greater than [In] in the composition of the CAC-OS film. Furthermore, the second region is a region where [Ga] is greater than [Ga] in the composition of the CAC-OS film. Furthermore, for example, the first region is a region where [In] is greater than [In] in the second region and [Ga] is less than [Ga] in the second region. Furthermore, the second region is a region where [Ga] is greater than [Ga] in the first region and [In] is less than [In] in the first region.

[0462] Specifically, the first region is a region primarily composed of indium oxide, indium zinc oxide, or the like. Furthermore, the second region is a region primarily composed of gallium oxide, gallium zinc oxide, or the like. In other words, the first region can be referred to as a region primarily composed of In. Furthermore, the second region can be referred to as a region primarily composed of Ga.

[0463] Note that a clear boundary between the first region and the second region may not be observed in some cases.

[0464] For example, in the CAC-OS of In-Ga-Zn oxide, based on the EDX surface analysis (mapping) image obtained by energy dispersive X-ray spectroscopy (EDX), it can be confirmed that the structure has a region with In as the main component (first region) and a region with Ga as the main component (second region) that are unevenly distributed and mixed.

[0465] When CAC-OS is used in transistors, the complementary effects of the conductivity of the first region and the insulation of the second region allow the CAC-OS to have a switching function (a function that controls on / off). In other words, a portion of the CAC-OS material has a conductive function and another portion has an insulating function, resulting in the entire material having a semiconductor function. By separating the conductive and insulating functions, each function can be maximized. Therefore, by using CAC-OS in transistors, a high on-state current (I on ), high field-effect mobility (μ) and good switching performance.

[0466] Oxide semiconductors have various structures and properties. The oxide semiconductor of one embodiment of the present invention may include two or more of an amorphous oxide semiconductor, a polycrystalline oxide semiconductor, a-like OS (amorphous-like oxide semiconductor), CAC-OS, nc-OS (nano crystalline oxide semiconductor), and CAAC-OS.

[0467] In addition, the control circuit unit 1320 preferably uses a transistor containing an oxide semiconductor because the transistor can be used in a high-temperature environment. In order to simplify the process, the control circuit unit 1320 can also be formed using a unipolar transistor. The operating ambient temperature range of the transistor containing an oxide semiconductor in the semiconductor layer is larger than that of the single-crystal Si transistor, that is, above -40°C and below 150°C, and the characteristic change of the secondary battery when overheated is smaller than that of the single-crystal Si transistor. The off-state current of the transistor containing an oxide semiconductor is also below the lower limit of measurement at 150°C, but the temperature dependence of the off-state current characteristics of the single-crystal Si transistor is large. For example, at 150°C, the off-state current of the single-crystal Si transistor increases, and the current switching ratio does not become sufficiently large. The control circuit unit 1320 can improve safety. In addition, by combining it with a secondary battery in which the positive electrode active material complex 100z that can be obtained in the above embodiment is used for the positive electrode, a multiplying effect of safety can be obtained.

[0468] The control circuit unit 1320, which uses a memory circuit including a transistor utilizing an oxide semiconductor, can also be used as an automatic control device for secondary batteries that are susceptible to instability such as micro-short circuits. Functions for addressing the causes of secondary battery instability include overcharge prevention, overcurrent prevention, overheating control during charging, cell balancing in a battery pack, overdischarge prevention, a capacity meter, automatic control of charging voltage and current according to temperature, charging current control according to the degree of degradation, detection of abnormal micro-short circuit behavior, and prediction of micro-short circuit anomalies. The control circuit unit 1320 has at least one of the above functions. Furthermore, the automatic control device for secondary batteries can be miniaturized.

[0469] A micro-short refers to a very small short circuit within a secondary battery. This is not a short circuit between the positive and negative electrodes of the secondary battery, preventing charging or discharging. Instead, it is a phenomenon where a small amount of short-circuit current flows through the tiny short circuit. Because even a short, tiny short circuit produces a significant voltage change, this abnormal voltage value can affect subsequent estimations.

[0470] One of the reasons for micro short circuits is believed to be that due to repeated charging and discharging, the positive electrode active material is unevenly distributed, local current concentration occurs in part of the positive electrode and part of the negative electrode, and part of the separator is rendered inoperative, or side reactions produce side reactants, leading to micro short circuits.

[0471] In addition to detecting micro-shorts, the control circuit unit 1320 also detects the terminal voltage of the secondary battery and manages the charge and discharge status of the secondary battery. For example, to prevent overcharging, the output transistor and the blocking switch of the charging circuit can be turned off almost simultaneously.

[0472] in addition, Figure 28B Show Figure 28A An example of a block diagram of a battery pack 1415 is shown.

[0473] The control circuit unit 1320 includes a switch unit 1324, which includes at least a switch to prevent overcharge and a switch to prevent overdischarge; 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 sets the upper and lower voltage limits of the secondary battery to control the input current flowing from the external device and the output current flowing to the external device. The recommended operating voltage range is above the lower voltage limit and below the upper voltage limit of the secondary battery. When the voltage falls outside this range, the switch unit 1324 activates, acting as a protection circuit. Furthermore, because the control circuit unit 1320 controls the switch unit 1324 to prevent overdischarge and overcharge, it can also be referred to as a protection circuit. For example, when the control circuit 1322 detects a voltage that could lead to overcharge, it closes the switch in the switch unit 1324, thereby blocking the current. Alternatively, a PTC element can be provided in the charge / discharge path to block the current in response to rising temperature. Furthermore, the control circuit unit 1320 includes an external terminal 1325 (+IN) and an external terminal 1326 (−IN).

[0474] The switch portion 1324 can be formed by combining n-channel transistors and p-channel transistors. In addition to switches including Si transistors using single-crystal silicon, 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), GaO x (gallium oxide; x is a real number greater than 0) constitute the switch section 1324. In addition, the storage element using the OS transistor can be freely configured by stacking it on a circuit using Si transistors, so it is easy to integrate. In addition, the OS transistor can be manufactured using the same manufacturing equipment as the Si transistor, so it can be manufactured at a low cost. That is, by stacking the control circuit section 1320 using the OS transistor on the switch section 1324 for integration, the switch section 1324 and the control circuit section 1320 can be integrated into one chip. The volume occupied by the control circuit section 1320 can be reduced, so miniaturization can be achieved.

[0475] The first batteries 1301 a and 1301 b mainly supply power to 42V series (high voltage series) on-board devices, while the second battery 1311 supplies power to 14V series (low voltage series) on-board devices.

[0476] This embodiment shows an example in which lithium-ion secondary batteries are used in both the first battery 1301a and the second battery 1311. A lead-acid battery, an all-solid-state battery, or an electric double-layer capacitor may also be used for the second battery 1311. For example, the all-solid-state battery of embodiment 5 may also be used. By using the all-solid-state battery of embodiment 5 as the second battery 1311, a high capacity can be achieved, thereby achieving miniaturization and lightweighting.

[0477] Furthermore, regenerative energy generated by the rotation of tire 1316 is transmitted to engine 1304 via transmission 1305, and is then charged from engine controller 1303 and battery controller 1302 via control circuit unit 1321 to second battery 1311. Furthermore, regenerative energy is charged from battery controller 1302 via control circuit unit 1320 to first battery 1301a. Furthermore, regenerative energy is charged from battery controller 1302 via control circuit unit 1320 to first battery 1301b. To efficiently charge regenerative energy, first batteries 1301a and 1301b are preferably capable of high-speed charging.

[0478] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b, etc. The battery controller 1302 sets the charging conditions according to the charging characteristics of the secondary battery to be used and performs high-speed charging.

[0479] In addition, although not shown in the figure, when connected to an external charger, the charger socket or the charger connection cable is electrically connected to the battery controller 1302. The power supplied from the external charger is charged to the first batteries 1301a and 1301b through the battery controller 1302. In addition, some chargers are provided with a control circuit without using the function of the battery controller 1302, but in order to prevent overcharging, it is preferred to charge the first batteries 1301a and 1301b through the control circuit unit 1320. In addition, sometimes the charger socket or the charger connection cable is provided with a control circuit. The control circuit unit 1320 is sometimes referred to as an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) provided in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. In addition, the ECU includes a microcomputer. In addition, the ECU uses a CPU or a GPU.

[0480] External chargers installed at charging stations include 100V outlets, 200V outlets, three-phase 200V 50kW outlets, etc. Furthermore, charging can be performed by supplying power from an external charging device using a contactless power supply method.

[0481] In order to charge the battery in a short time during high-speed charging, a secondary battery that can withstand charging at a high voltage is desired.

[0482] Furthermore, the secondary battery of this embodiment uses the positive electrode active material complex 100z obtained in the above-described embodiment. Furthermore, when graphene is used as the conductive material and the capacity is suppressed to maintain high capacity even when the electrode layer thickness is increased and the loading is increased, a synergistic effect is achieved, resulting in a secondary battery with significantly improved electrical characteristics. This is particularly effective for secondary batteries used in vehicles, enabling a longer driving range without increasing the weight of the secondary battery relative to the total vehicle weight. Specifically, a vehicle capable of traveling over 500 km per charge is achieved.

[0483] In particular, the secondary battery of this embodiment, by using the positive electrode active material complex 100z described in the above embodiment, can increase the operating voltage of the secondary battery, thereby increasing the usable capacity as the charging voltage increases. In addition, by using the positive electrode active material complex 100z described in the above embodiment as the positive electrode, a secondary battery for a vehicle with excellent cycle characteristics can be provided.

[0484] Next, an example in which a secondary battery as one embodiment of the present invention is mounted on a vehicle, typically a transportation vehicle, will be described.

[0485] In addition, it is possible to Figure 19D 、 Figure 21C 、 Figure 28A The secondary battery shown in any one of the above is installed in a new generation of clean energy vehicles such as hybrid electric vehicles (HV), electric vehicles (EV) or plug-in hybrid electric vehicles (PHV) in the vehicle. In addition, the secondary battery can also be installed in agricultural machinery, electric bicycles including electric-assisted bicycles, motorcycles, electric wheelchairs, electric karts, small or large ships, submarines, fixed-wing aircraft and rotary-wing aircraft, rockets, artificial satellites, space probes, planetary probes, spacecraft and other transportation vehicles. The secondary battery of one embodiment of the present invention can be a high-capacity secondary battery. Therefore, the secondary battery of one embodiment of the present invention is suitable for miniaturization and lightweighting, and can be suitable for use in transportation vehicles.

[0486] 29A to 29D A transport vehicle is shown as a moving object to which one embodiment of the present invention is applied. Figure 29A The vehicle 2001 shown is an electric vehicle that uses an electric motor as a driving power source. Alternatively, the vehicle 2001 is a hybrid vehicle that can use an electric motor or an engine as a driving power source. When installing a secondary battery in a vehicle, the secondary battery example shown in Embodiment 4 can be installed in one or more locations. Figure 29A The illustrated automobile 2001 includes a battery pack 2200 , which includes a secondary battery module in which a plurality of secondary batteries are connected. Furthermore, the battery pack preferably includes a charge control device electrically connected to the secondary battery module.

[0487] In addition, in the car 2001, the secondary battery of the car 2001 can be charged by supplying power from an external charging device using a plug-in method or a contactless power supply method. When charging, the charging method and connector specifications can be appropriately carried out according to the methods specified by CHAdeMO (a registered trademark in Japan) or the combined charging system "Combined Charging System". As a secondary battery, a charging station set up in a commercial facility or a home power supply can also be used. For example, by supplying power from the outside using plug-in technology, the storage device installed in the car 2001 can be charged. Charging can be performed by converting AC power into DC power using a conversion device such as an ACDC converter.

[0488] Although not shown, it is also possible to install a power receiving device in the vehicle and charge it by supplying power contactlessly from a ground-based power transmission device. When using a contactless power supply method, by integrating the power transmission device into the road or an exterior wall, charging can be performed not only while the vehicle is parked but also while it is in motion. Furthermore, this contactless power supply method can be used to send and receive power between two vehicles. Furthermore, solar cells can be installed on the exterior of the vehicle to charge the secondary battery while the vehicle is parked or in motion. This contactless power supply can be achieved using electromagnetic induction or magnetic field resonance.

[0489] exist Figure 29B In the diagram, a large transport vehicle 2002 including an electrically controlled engine is shown as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 is, for example, a secondary battery module having a maximum voltage of 170V, with 48 cells connected in series, each of which has a nominal voltage of 3.0V or higher and 5.0V or lower. The battery pack 2201 has the same characteristics as the battery pack 2201, except for the number of secondary batteries constituting the secondary battery module. Figure 29A The functions are the same, so the description is omitted.

[0490] exist Figure 29C In the figure, a large transport vehicle 2003 including an electrically controlled engine is shown as an example. The secondary battery module of the transport vehicle 2003 is, for example, a secondary battery module having a maximum voltage of 600V, in which more than 100 secondary batteries having a nominal voltage of 3.0V or more and 5.0V or less are connected in series. By using the negative electrode 570a that can be obtained in the above embodiment for the negative electrode, a cylindrical secondary battery 616 with high capacity, high charge and discharge capacity and good cycle characteristics can be manufactured. By using a secondary battery that uses the positive electrode active material complex 100z described in the above embodiment for the positive electrode, a secondary battery with good frequency characteristics and charge and discharge cycle characteristics can be manufactured, thereby contributing to the high performance and long life of the transport vehicle 2003. In addition, in addition to the difference in the number of secondary batteries constituting the secondary battery module, the battery pack 2202 has the same Figure 29A The functions are the same, so the description is omitted.

[0491] exist Figure 29D , an aircraft 2004 equipped with an engine that burns fuel is shown as an example. Figure 29D The aircraft 2004 shown includes wheels for taking off and landing, so it can be said that the aircraft 2004 is a type of transportation vehicle. In the aircraft 2004, multiple secondary batteries are connected to form a secondary battery module and include a battery pack 2203 having a secondary battery module and a charging control device.

[0492] The secondary battery module of the aircraft 2004 has, for example, eight 4V secondary batteries connected in series and a maximum voltage of 32V. Figure 29A The functions are the same, so the description is omitted.

[0493] The contents of this embodiment can be combined with the contents of other embodiments as appropriate.

[0494] (Implementation 7) In this embodiment, the Figure 30A and Figure 30B An example in which the secondary battery according to one embodiment of the present invention is installed in a building will be described.

[0495] Figure 30A The house shown includes a storage device 2612 having a secondary battery module according to one embodiment of the present invention and a solar panel 2610. The storage device 2612 is electrically connected to the solar panel 2610 via wiring 2611 or the like. In addition, the storage device 2612 can be electrically connected to a ground-mounted charging device 2604. The electricity obtained by the solar panel 2610 can be charged into the storage device 2612. In addition, the electricity stored in the storage device 2612 can be charged into the secondary battery included in the vehicle 2603 via the charging device 2604. The storage device 2612 is preferably arranged in the underfloor space. By being arranged in the underfloor space, the underfloor space can be effectively utilized. Alternatively, the storage device 2612 can also be arranged on the floor.

[0496] The power stored in power storage device 2612 can also be supplied to other electronic devices in the house. Therefore, even when power cannot be supplied from a commercial power source due to a power outage or the like, the electronic devices can be used by using power storage device 2612 according to one embodiment of the present invention as an uninterruptible power supply.

[0497] Figure 30B An example of a power storage device according to one embodiment of the present invention is shown. Figure 30B As shown, an electricity storage device 791 according to one embodiment of the present invention is installed in an underfloor space 796 of a building 799. Alternatively, the control circuit described in Embodiment 6 may be provided in electricity storage device 791. Furthermore, by using the negative electrode 570a obtained in the above embodiment as the negative electrode, a cylindrical secondary battery 616 with high capacity, high charge / discharge capacity, and excellent cycle characteristics can be manufactured. By using a secondary battery using the positive electrode active material complex 100z obtained in the above embodiment as the positive electrode in electricity storage device 791, a long-life electricity storage device 791 can be realized.

[0498] The power storage device 791 is provided with a control device 790 , and the control device 790 is electrically connected to the switchboard 703 , the power storage controller 705 (also referred to as a control device), the display 706 , and the router 709 through wiring.

[0499] Electric power is supplied from the commercial power source 701 to the distribution board 703 via the service line installation portion 710. Furthermore, both the electric power from the power storage device 791 and the electric power from the commercial power source 701 are supplied to the distribution board 703, which then supplies the supplied electric power to the general load 707 and the storage load 708 via outlets (not shown).

[0500] Examples of the general load 707 include electronic devices such as a television and a personal computer, and examples of the power storage load 708 include electronic devices such as a microwave oven, a refrigerator, and an air conditioner.

[0501] The power storage controller 705 includes a measuring unit 711, a forecasting unit 712, and a planning unit 713. The measuring unit 711 measures the power consumption of the general load 707 and the power storage load 708 during a single day (e.g., from midnight to midnight). The measuring unit 711 may also measure the amount of power in the power storage device 791 and the amount of power supplied from the commercial power supply 701. Furthermore, the forecasting unit 712 predicts the amount of power required to be consumed by the general load 707 and the power storage load 708 the following day based on the power consumption of the general load 707 and the power storage load 708 during a single day. Furthermore, the planning unit 713 determines a charge and discharge schedule for the power storage device 791 based on the power demand predicted by the forecasting unit 712.

[0502] The amount of power consumed by the general load 707 and the storage load 708 measured by the measuring unit 711 can be checked using the display 706. Alternatively, it can be checked using electronic devices such as a television and a personal computer via the router 709. Furthermore, it can be checked using a portable electronic terminal such as a smartphone or tablet computer via the router 709. Furthermore, the required power for each time period (or each hour) predicted by the prediction unit 712 can be checked using the display 706, an electronic device, or a portable electronic terminal.

[0503] The contents of this embodiment can be combined with the contents of other embodiments as appropriate.

[0504] (Implementation 8) In this embodiment, an example in which the power storage device according to one embodiment of the present invention is mounted on a two-wheeled vehicle or a bicycle is described.

[0505] Figure 31A An example of an electric bicycle using the power storage device according to one embodiment of the present invention will be described. Figure 31A The electric bicycle 8700 shown can use the power storage device of one embodiment of the present invention. For example, the power storage device of one embodiment of the present invention includes a plurality of batteries and a protection circuit.

[0506] The electric bicycle 8700 includes a power storage device 8702. The power storage device 8702 supplies power to the engine that assists the rider. In addition, the power storage device 8702 is portable. Figure 31B The figure shows a power storage device 8702 taken out of a bicycle. The power storage device 8702 has a plurality of batteries 8701 included in the power storage device of one embodiment of the present invention built in, and the remaining power, etc. can be displayed on the display unit 8703. In addition, the power storage device 8702 includes the control circuit 8704 shown in Embodiment 6, which can control the charging of the secondary battery or detect abnormalities. The control circuit 8704 is electrically connected to the positive and negative electrodes of the battery 8701. In addition, a control circuit 8704 can also be provided. Figure 27A and Figure 27B The small solid secondary battery shown. Figure 27A and Figure 27B The small solid-state secondary battery shown is incorporated into the control circuit 8704, supplying power to maintain data in the memory circuitry included in the control circuit 8704 for a long period of time. Furthermore, by combining this battery with a secondary battery using the positive electrode active material complex 100z obtained in the above-described embodiment as its positive electrode, a synergistic effect in safety can be achieved. A secondary battery using the positive electrode active material complex 100z obtained in the above-described embodiment as its positive electrode, along with the control circuit 8704, significantly contributes to reducing accidents such as fires caused by secondary batteries.

[0507] Figure 31C This is an example of a two-wheeled vehicle using the power storage device according to one embodiment of the present invention. Figure 31C The illustrated scooter 8600 includes a power storage device 8602, side mirrors 8601, and turn signals 8603. The power storage device 8602 can supply power to the turn signals 8603. Furthermore, the power storage device 8602, which is equipped with a plurality of secondary batteries using the positive electrode active material complex 100z obtained in the above embodiment as the positive electrode, can have a high capacity and contribute to miniaturization.

[0508] In addition, Figure 31C In the illustrated scooter 8600, the power storage device 8602 can be housed in the under-seat storage portion 8604. Even if the under-seat storage portion 8604 is small, the power storage device 8602 can be housed in the under-seat storage portion 8604.

[0509] The contents of this embodiment can be combined with the contents of other embodiments as appropriate.

[0510] (Implementation 9) In this embodiment, an example of installing a secondary battery of one embodiment of the present invention in an electronic device is described. Examples of electronic devices equipped with a secondary battery include televisions (also referred to as televisions or television receivers), displays for computers, digital cameras, digital video cameras, digital photo frames, mobile phones (also referred to as mobile phones or mobile phone devices), portable game consoles, portable information terminals, sound reproduction devices, and large-scale game consoles such as pinball machines. Examples of portable information terminals include notebook personal computers, tablet terminals, e-book terminals, and mobile phones.

[0511] Figure 32A An example of a mobile phone is shown. Mobile phone 2100 includes a display portion 2102 mounted in a housing 2101, operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. Furthermore, mobile phone 2100 includes a secondary battery 2107. By including secondary battery 2107 using the positive electrode active material complex 100z described in the above embodiment as the positive electrode, a high capacity can be achieved, and a structure that can accommodate the space savings required for miniaturization of the housing can be realized.

[0512] The mobile phone 2100 can execute various applications such as mobile phone, e-mail, article reading and writing, music playing, Internet communication, computer games, etc.

[0513] In addition to time setting, the operation button 2103 may have various functions such as power on / off, wireless communication on / off, silent mode setting and canceling, power saving mode setting and canceling, etc. For example, the function of the operation button 2103 can be freely set by utilizing the operating system incorporated in the mobile phone 2100.

[0514] In addition, the mobile phone 2100 can perform short-range wireless communication standardized by the communication system. For example, by communicating with a headset capable of wireless communication, a hands-free call can be made.

[0515] Furthermore, the mobile phone 2100 has an external connection port 2104, which allows data to be directly transmitted to or received from other information terminals via a connector. Furthermore, the mobile phone 2100 can be charged via the external connection port 2104. Furthermore, charging can also be performed using wireless power supply, rather than using the external connection port 2104.

[0516] The mobile phone 2100 preferably includes a sensor. Examples of the sensor preferably include a fingerprint sensor, a pulse sensor, a body temperature sensor, and other human sensors, a touch sensor, a pressure sensor, and an acceleration sensor.

[0517] Figure 32B An unmanned aerial vehicle 2300 including a plurality of rotors 2302 is shown. The unmanned aerial vehicle 2300 is also referred to as a drone. The unmanned aerial vehicle 2300 includes a secondary battery 2301 according to one embodiment of the present invention, a camera 2303, and an antenna (not shown). The unmanned aerial vehicle 2300 can be remotely operated via the antenna. A secondary battery using the positive electrode active material complex 100z obtained in the above embodiment as a positive electrode has high energy density and high safety, and can be used safely for a long period of time, making it suitable as a secondary battery mounted on the unmanned aerial vehicle 2300.

[0518] Figure 32C An example of a robot is shown. Figure 32C The robot 6400 shown includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a moving mechanism 6408, a computing device, and the like.

[0519] The microphone 6402 has a function of detecting the user's voice and surrounding sounds, etc. In addition, the speaker 6404 has a function of emitting sounds. The robot 6400 can communicate with the user through the microphone 6402 and the speaker 6404.

[0520] Display unit 6405 has the function of displaying various information. Robot 6400 can display the information required by the user on display unit 6405. Display unit 6405 may also be equipped with a touch panel. Alternatively, display unit 6405 may be a detachable information terminal that can be placed in a fixed position on robot 6400 to enable charging and data transmission and reception.

[0521] The upper camera 6403 and the lower camera 6406 have the function of photographing the surrounding environment of the robot 6400. Furthermore, the obstacle sensor 6407 can detect the presence of obstacles in the direction of movement of the robot 6400 using the moving mechanism 6408. The robot 6400 can move safely by checking its surrounding environment using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0522] The internal area of ​​robot 6400 is equipped with a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or electronic component. Secondary batteries using the positive electrode active material complex 100z obtained in the above embodiment as a positive electrode have high energy density and high safety, allowing for safe and long-term use. Therefore, they are suitable as secondary batteries 6409 installed in robot 6400.

[0523] Figure 32D An example of a robot vacuum cleaner is shown. The robot vacuum cleaner 6300 includes a display unit 6302 located on the top surface of a housing 6301, multiple cameras 6303 located on the side, a brush 6304, operating buttons 6305, a secondary battery 6306, and various sensors. Although not shown, the robot vacuum cleaner 6300 also has wheels and a suction nozzle. The robot vacuum cleaner 6300 can move autonomously and detect trash 6310 and suck it into the suction nozzle located below.

[0524] For example, the sweeping robot 6300 can determine whether there are obstacles such as walls, furniture, or steps by analyzing the image captured by the camera 6303. In addition, when an object such as a wire that may be entangled with the brush 6304 is found through image analysis, the rotation of the brush 6304 can be stopped. The internal area of ​​the sweeping robot 6300 is equipped with a secondary battery 6306 and a semiconductor device or electronic component according to one embodiment of the present invention. The secondary battery using the positive electrode active material complex 100z that can be obtained in the above embodiment as the positive electrode has high energy density and high safety, so it can be used safely for a long period of time, so it is suitable as a secondary battery 6306 installed in the sweeping robot 6300.

[0525] Figure 33A An example of a wearable device is shown. A secondary battery is used as a power source for the wearable device. Furthermore, to improve splash, water, or dust resistance during daily life or outdoor use, users desire not only wired charging (with the connector partially exposed) but also wireless charging.

[0526] For example, the secondary battery of one embodiment of the present invention can be mounted on Figure 33A Spectacle-type device 4000 is shown. Spectacle-type device 4000 includes a frame 4000a and a display portion 4000b. By attaching a secondary battery to the temples of the curved frame 4000a, a lightweight, well-balanced spectacle-type device 4000 with a long continuous usage period can be achieved. A secondary battery using the positive electrode active material complex 100z obtained in the above embodiment as the positive electrode has a high energy density, enabling a structure that can meet the space-saving requirements of a smaller frame.

[0527] Alternatively, a secondary battery according to one embodiment of the present invention can be mounted on an earphone-type device 4001. Earphone-type device 4001 includes at least a microphone portion 4001a, a flexible tube 4001b, and an earphone portion 4001c. Furthermore, the secondary battery can be placed within flexible tube 4001b or within earphone portion 4001c. A secondary battery using the positive electrode active material complex 100z obtained in the above embodiment as the positive electrode has a high energy density and can achieve a space-saving structure that meets the requirements of miniaturized housings.

[0528] Furthermore, the secondary battery of one embodiment of the present invention can be incorporated into a device 4002 that can be worn directly on the body. Alternatively, the secondary battery 4002b can be incorporated into the thin housing 4002a of the device 4002. A secondary battery using the positive electrode active material complex 100z obtained in the above embodiment as the positive electrode has a high energy density and can achieve a space-saving structure that can accommodate the miniaturization of the housing.

[0529] Furthermore, the secondary battery of one embodiment of the present invention can be incorporated into a device 4003 that can be worn on clothing. Alternatively, the secondary battery 4003b can be incorporated into the thin housing 4003a of the device 4003. A secondary battery using the positive electrode active material complex 100z obtained in the above embodiment as the positive electrode has a high energy density and can achieve a space-saving structure that can accommodate the miniaturization of the housing.

[0530] Furthermore, a secondary battery according to one embodiment of the present invention can be mounted on a belt-type device 4006. The belt-type device 4006 includes a belt portion 4006a and a wireless power supply and reception portion 4006b, and the secondary battery can be mounted within the belt portion 4006a. A secondary battery using the positive electrode active material complex 100z obtained in the above embodiment as the positive electrode has a high energy density and can achieve a space-saving structure that meets the requirements for miniaturization of the housing.

[0531] Furthermore, the secondary battery of one embodiment of the present invention can be mounted on a wristwatch-type device 4005. The wristwatch-type device 4005 includes a display portion 4005a and a strap portion 4005b, and the secondary battery can be mounted on either the display portion 4005a or the strap portion 4005b. A secondary battery using the positive electrode active material complex 100z obtained in the above embodiment as a positive electrode has a high energy density and can achieve a space-saving structure that can meet the requirements of miniaturization of the housing.

[0532] The display portion 4005a can display various information such as e-mails and incoming phone calls in addition to the time.

[0533] In addition, since the watch-type device 4005 is a wearable device that is directly wrapped around the wrist, it can also be equipped with sensors for measuring the user's pulse, blood pressure, etc. This can store the user's exercise volume and health-related data for health management.

[0534] Figure 33B 4005 is a perspective view showing the watch-type device 4005 removed from the wrist.

[0535] in addition, Figure 33C It's a side view. Figure 33C The internal region includes a secondary battery 913. The secondary battery 913 is the secondary battery described in Embodiment Mode 4. The secondary battery 913 is provided at a position overlapping the display portion 4005a, and can achieve high density and high capacity while being compact and lightweight.

[0536] The wristwatch-type device 4005 needs to be small and lightweight. Therefore, by using the positive electrode active material complex 100z obtained in the above embodiment as the positive electrode of the secondary battery 913, a high energy density and small secondary battery 913 can be realized.

[0537] Figure 33D Here, a pair of wireless headphones including a main body 4100a and a main body 4100b is shown, but the main bodies do not necessarily need to be a pair.

[0538] The main bodies 4100a and 4100b include a driver unit 4101, an antenna 4102, and a secondary battery 4103. They may also include a display portion 4104. Furthermore, they preferably include a substrate on which circuits such as a wireless IC are mounted, a charging terminal, and the like. A microphone may also be included.

[0539] The storage box 4110 includes a secondary battery 4111. It also preferably includes a substrate on which circuits such as a wireless IC and a charging control IC are mounted, and charging terminals. It may also include a display unit, buttons, and the like.

[0540] Main bodies 4100a and 4100b can communicate wirelessly with other electronic devices such as smartphones. Therefore, sound data received from other electronic devices can be reproduced on main bodies 4100a and 4100b. Furthermore, if main bodies 4100a and 4100b include microphones, sound captured by the microphones can be transmitted to other electronic devices for processing, and then the sound data can be transmitted to main bodies 4100a and 4100b for reproduction. This allows for use as a translation machine, for example.

[0541] Furthermore, the secondary battery 4103 included in the main body 4100a can be charged from the secondary battery 4111 included in the storage case 4110. The coin-shaped secondary battery or cylindrical secondary battery described in the above-mentioned embodiment can be used as the secondary battery 4111 and the secondary battery 4103. The secondary battery obtained in the above-mentioned embodiment has a high energy density, and by using it in the secondary battery 4103 and the secondary battery 4111, a space-saving structure can be achieved that meets the requirements for miniaturization of wireless headphones.

[0542] This embodiment mode can be implemented in combination with other embodiment modes as appropriate. [Example 1]

[0543] In this example, a negative electrode according to one embodiment of the present invention was manufactured and evaluated.

[0544] <Manufacturing of negative electrode> according to Figure 7 The negative electrode was manufactured using the process shown. Silicon-containing particles used were nanosilicon particles manufactured by ALDRICH. Graphite-containing particles used were artificial graphite particles MCMB-G10 manufactured by Linyi Gelon New Battery Materials. Graphene oxide was used as the graphene compound. A polyimide precursor manufactured by Toray Industries, Inc. was used as the polyimide.

[0545] Electrode GS1 is manufactured as the negative electrode. Figure 7 The weight ratio of the materials prepared in steps S61, S72, S80, and S87 is set to artificial graphite particles: nano-silicon particles: graphene oxide: polyimide precursor = 82.8:9.2:5:3. Note that the weight ratio of artificial graphite particles to nano-silicon particles is 9:1.

[0546] Prepare nano-silicon particles and solvent and mix them ( Figure 7 The mixture was mixed at 2000 rpm for 3 minutes using a rotary mixer (manufactured by Awatori Rentaro, THINKY Co., Ltd.) and recovered to obtain a mixture E-1 ( Figure 7 Steps S64 and S65 in the process).

[0547] Next, artificial graphite particles were prepared and mixed with the mixture E-1 ( Figure 7 The mixture was mixed using a rotary stirrer at 2000 rpm for 3 minutes and recovered to obtain a mixture E-2 ( Figure 7 Steps S74 and S75 in the process).

[0548] Then, the mixture E-2 and the graphene compound were repeatedly mixed while adding the solvent. As the graphene compound, graphene oxide was prepared and mixed using a rotation and revolution stirrer at 2000 rpm for 3 minutes and recovered ( Figure 7 Then, the recovered mixture was dry-mixed, NMP was added appropriately, and the mixture was mixed at 2000 rpm for 3 minutes using a rotary mixer and recovered ( Figure 7 Steps S83, S84, and S85 are repeated 5 times to obtain a mixture E-3 ( Figure 7 Step S86).

[0549] Next, the mixture E-3 and the polyimide precursor were mixed ( Figure 7 The mixture was mixed using a rotary mixer at 2000 rpm for 3 minutes. NMP was then prepared and added to the mixture to adjust the viscosity ( Figure 7 The mixture was further mixed (using a rotary stirrer at 2000 rpm for 3 minutes, and the mixing was repeated twice), and recovered to obtain a mixture E-4 ( Figure 7 Steps S90, S91, S92 in the flow chart).

[0550] Next, a current collector was prepared and the mixture E-4 was applied ( Figure 7 As a current collector, a copper foil with a thickness of 18 μm was prepared, and the mixture E-4 was applied onto the copper foil using a doctor blade with a gap thickness of 100 μm.

[0551] Next, the copper foil coated with the mixture E-4 was first heated at 50° C. for 1 hour ( Figure 7 Then, a second heating is performed at 400°C for 5 hours under reduced pressure ( Figure 7 The graphene oxide is reduced by heating, and the amount of oxygen is reduced.

[0552] <sem> The surface of the manufactured electrode was observed by SEM using an S4800 manufactured by Hitachi High-Technologies Corporation at an accelerating voltage of 5 kV.

[0553] Figure 34A and Figure 34B This is an observation image of the surface of electrode GS1. In the SEM image, the contrast of the nano-silicon particles is relatively bright.

[0554] Figure 34B This is an enlarged image of the surface of electrode GS1. The following region is observed: multiple nano-silicon particles with a diameter of 50 nm to 250 nm are present on the surface of graphite particles with a particle size of 5 μm to 15 μm, and these nano-silicon particles are covered with graphene (reduced graphene oxide). In other words, electrode GS1 has a region where a mixed layer of nano-silicon particles and graphene covers the graphite particles.

[0555] <Manufacturing of Coin Batteries> Next, five CR2032-type (20 mm in diameter, 3.2 mm in height) coin cells (also referred to as coin-type secondary batteries) (GS-C1, GS-C2, GS-C3, GS-C4, and GS-C5) were manufactured using the manufactured electrode GS1.

[0556] Lithium metal was used as the counter electrode, and the electrolyte was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of EC:DEC = 3:7, with lithium hexafluorophosphate (LiPF6) at a concentration of 1 mol / L.

[0557] As the separator, a separator made of polypropylene having a thickness of 25 μm was used.

[0558] The positive electrode can and the negative electrode can are formed of stainless steel (SUS).

[0559] <Charge and discharge characteristics> The charge and discharge characteristics of the five manufactured coin cells were evaluated. Note that since lithium metal was used as the counter electrode, the electrode GS1 in the manufactured coin cell served as the positive electrode, and lithium was absorbed into the electrode during discharge and released from the electrode during charge.

[0560] In the first charge and discharge cycle, the five coin cells were subjected to a constant current discharge (0.1C, lower limit voltage 0.01V) followed by a constant voltage discharge (lower limit current density 0.01C) as the discharge condition (lithium occlusion), and a constant current charge (0.1C, upper limit voltage 1V) as the charge condition (lithium release). Subsequently, in the second charge and discharge cycle, the discharge condition (lithium occlusion) was a constant current discharge (0.2C, lower limit voltage 0.01V) followed by a constant voltage discharge (lower limit current density 0.02C), and the charge condition (lithium release) was a constant current charge (0.2C, upper limit voltage 1V). Discharge and charge were performed at 25°C. Then, in the third and subsequent charge-discharge cycle tests, as the discharge condition (lithium absorption), constant current discharge (0.2C, lower limit voltage of 0.01V) was followed by constant voltage discharge (lower limit current density of 0.02C). As the charge condition (lithium release), constant current charge (0.2C, upper limit voltage of 1V) was performed. Based on the second charge capacity, different capacity restrictions were adopted: no capacity restriction, capacity restriction of 90%, capacity restriction of 80%, capacity restriction of 70%, and capacity restriction of 60%. Discharge and charge were carried out at 25°C.

[0561] Table 2 shows the maximum charge capacity and 30 cycle retention rate of coin cells GS-C1 to GS-C5. Figure 35A and Figure 35B The results of the charge and discharge cycle test are shown.

[0562] [Table 2]

[0563] like Figure 35A and Figure 35B As shown in the figure, the effect of suppressing the deterioration of the charge capacity in the charge-discharge cycle test was confirmed in the coin cells (GS-C2 to GS-C5) with limited capacity. Note that the GS-C2 to GS-C5 were tested under different conditions of capacity limit of 60%, 70%, 80%, and 90%, but Figure 35B From the perspective of charge capacity retention, there is no significant difference between GS-C2 and GS-C5.

[0564] Next, the present experimental results will be examined together with the contents shown in Calculation 1 of Negative Electrode and Calculation 2 of Negative Electrode in the first embodiment.

[0565] Based on the contents shown in Calculation 1 of the negative electrode in Embodiment 1, the alloying ratios (Li / Si) of silicon and lithium in GS-C1 to GS-C5 were calculated using Formula 1. Table 3 shows the calculation results.

[0566] [Formula 1]

[0567] [Table 3]

[0568] As shown in Table 3, in GS-C1, which has poor charge-discharge cycle characteristics, the Li / Si ratio is calculated to be 2.22. On the other hand, in GS-C2, which has good charge-discharge cycle characteristics, the Li / Si ratio is 1.75, which is close to Figure 6B The structure shown (crystal structure when Li / Si=1.714). Figure 6B The structure shown includes Si-Si bonds, so it is considered that GS-C2 to GS-C5 can be charged and discharged within a range without losing the Si-Si bonds, which is the reason for the good charge-discharge cycle efficiency. [Example 2]

[0569] In this example, a coin cell manufactured using the electrode GS1 described in Example 1 and the ionic liquid was evaluated.

[0570] <Manufacturing of Coin Batteries> Next, a CR2032 type (20 mm in diameter, 3.2 mm in height) coin battery (also referred to as a coin-type secondary battery) (GS-C6) was manufactured using the manufactured electrode GS1.

[0571] Lithium metal was used as the counter electrode, and EMI-FSI containing LiFSI at a concentration of 2.15 mol / L was used as the electrolyte.

[0572] As the separators, a separator made of polypropylene with a thickness of 25 μm and a separator made of glass fiber with a thickness of 260 μm were laminated and used.

[0573] The positive electrode can and the negative electrode can are formed of stainless steel (SUS).

[0574] <Charge and discharge characteristics> The charge and discharge characteristics of the manufactured coin cell GS-C6 were evaluated. Note that since lithium metal was used as the counter electrode, the electrode GS1 in the manufactured coin cell served as the positive electrode, and lithium was absorbed into the electrode during discharge and released from the electrode during charge.

[0575] In the first charge and discharge cycle, the discharge conditions (lithium occlusion) of the manufactured coin cell GS-C6 were constant current discharge (0.1C, lower limit voltage 0.01V) followed by constant voltage discharge (lower limit current density 0.01C), and the charge conditions (lithium release) were constant current charge (0.1C, upper limit voltage 1V). Subsequently, in the second charge and discharge cycle, the discharge conditions (lithium occlusion) were constant current discharge (0.2C, lower limit voltage 0.01V) followed by constant voltage discharge (lower limit current density 0.02C), and the charge conditions (lithium release) were constant current charge (0.2C, upper limit voltage 1V). Then, in the third and subsequent charge-discharge cycle tests, the discharge conditions (lithium absorption) were constant current discharge (0.2C, lower voltage limit 0.01V) followed by constant voltage discharge (lower current density 0.02C). As the charge conditions (lithium release), constant current charge (0.2C, upper voltage limit 1V) was performed, with the capacity limited to 80% based on the second charge capacity. Discharge and charge were performed at 25°C.

[0576] Together with the results of GS-C2 and GS-C3 Figure 36A and Figure 36B The results of the charge-discharge cycle test of GS-C6 are shown in Figure 2. The maximum charge capacity is 468 mAh / g, and the retention rate after 30 cycles is 99.99%, which shows very good characteristics. Note that the calculation result of GS-C6 using formula 1 is Li / Si = 1.40. In addition, Figure 37A and Figure 37B The third discharge curves (the first discharge under capacity-limited conditions) of GS-C3 and GS-C6 are shown. Figure 37B yes Figure 37A An enlarged view of a portion of .

[0577] like Figure 36A and Figure 36B As shown, GS-C6 has good charge-discharge cycle characteristics. In the first embodiment, the relationship between the Li / Si ratio and the charge-discharge cycle characteristics was shown. However, even though the Li / Si ratio of GS-C6 is 1.40, which is a value between the Li / Si ratios of GS-C2 and GS-C3, Figure 36B It also shows a significant result of 99.99% degradation in charge and discharge cycles. Figure 37B As shown, the potential of GS-C6 at the end of discharge (the end of Li occlusion) is also above 0.05 V, which suggests that Li precipitation and reductive decomposition of the electrolyte may be suppressed. As described above, by using a secondary battery comprising a negative electrode according to one embodiment of the present invention and an ionic liquid under capacity-limited conditions, significant characteristic improvements that would not have been easily anticipated can be achieved. [Explanation of symbols]

[0578] 560a: Negative electrode characteristic curve, 560b: Positive electrode characteristic curve, 570a: Negative electrode, 570b: Positive electrode, 571a: Negative electrode current collector, 571b: Positive electrode current collector, 572a: Negative electrode active material layer, 572b: Positive electrode active material layer, 576: Electrolyte, 581: First active material, 582: Second active material, 583: Graphene compound.< / sem> < / xps> < / xrd>

Claims

1. A lithium-ion secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, The negative electrode comprises: a first negative electrode active material comprising silicon particles, a second negative electrode active material comprising graphite having a particle size larger than that of the silicon particles, and graphene or a graphene compound, The silicon particles are in contact with the graphite, and the graphene or graphene compound is in surface contact with the first negative electrode active material and the second negative electrode active material. The silicon particles include silicon oxide.

2. A lithium-ion secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, The negative electrode comprises: a first negative electrode active material comprising a silicon-containing compound, a second negative electrode active material comprising graphite having a larger particle size than the silicon-containing compound, and graphene or a graphene compound; The silicon-containing compound is in contact with the graphite, and the graphene or the graphene compound is in surface contact with the first negative electrode active material and the second negative electrode active material.

3. A lithium-ion secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, The negative electrode comprises: A first negative electrode active material comprising SiOx, a second negative electrode active material comprising graphite having a particle size larger than that of the SiOx, and graphene or a graphene compound, wherein x is less than 2, The SiOx is in contact with the graphite, and the graphene or the graphene compound is in surface contact with the first negative electrode active material and the second negative electrode active material.

4. A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, The negative electrode comprises: a first negative electrode active material comprising silicon particles, a second negative electrode active material comprising graphite having a particle size larger than that of the silicon particles, and a conductive additive, The silicon particles are in contact with the graphite, And the silicon particles include silicon oxide.

5. A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode comprises: a first negative electrode active material comprising a compound containing silicon, a second negative electrode active material comprising graphite having a particle size larger than that of the compound containing silicon, and a conductive additive, And the silicon-containing compound is in contact with the graphite.

6. A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, The negative electrode comprises: A first negative electrode active material comprising SiOx, a second negative electrode active material comprising graphite having a particle size larger than that of the SiOx, and a conductive additive, wherein x is less than 2, And the SiOx is in contact with the graphite.

7. A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, The negative electrode comprises: a first negative electrode active material comprising a silicon-containing compound, a second negative electrode active material comprising graphite, and a conductive additive, And the silicon-containing compound is in contact with the graphite.

8. The lithium ion secondary battery according to claim 2 or 5, The silicon-containing compound comprises Li2SiO3 or Li4SiO4.

9. The lithium ion secondary battery according to claim 1 or 4, The silicon oxide is amorphous.

10. The lithium ion secondary battery according to any one of claims 1 to 7, wherein the first negative electrode active material has a particle size of less than 250 nm, Furthermore, the second negative electrode active material has a particle size of 5 μm or more.

11. The lithium ion secondary battery according to any one of claims 1 to 7, wherein the negative electrode comprises a negative electrode current collector, And the negative electrode current collector comprises copper.

12. The lithium ion secondary battery according to any one of claims 1 to 7, The first negative electrode active material contacts the second negative electrode active material in a manner of covering, encapsulating or winding around the second negative electrode active material.

13. The lithium ion secondary battery according to any one of claims 1 to 3, The graphene or graphene compound contacts the first negative electrode active material and the second negative electrode active material in a manner of covering, encapsulating or winding the first negative electrode active material and the second negative electrode active material.

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