Method for manufacturing secondary battery

Abstract

To provide an active material layer having a high filling factor and high density by using a small amount of a conductive assistant in manufacturing the active material layer.SOLUTION: The first carbon material and the second carbon material which is more likely to aggregate than the first carbon material are contained in the positive electrode active material layer and mixed so that the weight of the second carbon material is greater than or equal to 1.5 times and less than or equal to 20 times that of the first carbon material, whereby aggregation of the second carbon material and aggregation of the first carbon material can be prevented and the proportion of the aggregation portion can be reduced.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an object, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, a manufacture, or a composition of matter. In particular, one embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a secondary battery, a power storage device, a memory device, a driving method thereof, or a manufacturing method thereof. In particular, one embodiment of the present invention relates to a secondary battery, a power storage device, and a manufacturing method thereof. Another embodiment of the present invention relates to a vehicle having a secondary battery, or a vehicle electronic device provided in a vehicle.

[0002] In this specification, the term "secondary battery" or "power storage device" generally refers to elements and devices having a power storage function. [Background technology]

[0003] In recent years, there has been active development of various types of power storage devices, such as lithium-ion secondary batteries, lithium-ion capacitors, air batteries, and all-solid-state batteries. Demand for high-power, high-energy-density lithium-ion secondary batteries, in particular, has rapidly expanded alongside the development of the semiconductor industry, and they are now essential to the modern information society as a rechargeable energy source, thanks to their high output and high energy density, and are used in a variety of applications, including mobile phones, smartphones, tablets, and notebook computers, as well as portable music players, digital cameras, medical devices, drones, and next-generation clean-energy vehicles, such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs).

[0004] In addition, electric vehicles (EVs) are vehicles that are driven solely by electric motors, but there are also hybrid vehicles that have both an internal combustion engine and an electric motor. Multiple secondary batteries used in automobiles are grouped into a single battery pack, and multiple sets of battery packs are placed under the automobile.

[0005] Electronic devices carried by users or worn by users operate using primary or secondary batteries, which are examples of power storage devices, as their power source. It is desirable for electronic devices carried by users to be used for long periods of time, and for this reason, large-capacity secondary batteries are used. However, incorporating a large-capacity secondary battery into an electronic device poses the problem of its large size and weight. Therefore, development is underway to develop small or thin, large-capacity secondary batteries that can be incorporated into portable electronic devices.

[0006] As described above, lithium ion secondary batteries are used in a variety of fields and applications, and among these, the characteristics required of lithium ion secondary batteries include high energy density, high cycle characteristics, and safety in various operating environments.

[0007] In particular, lithium cobalt composite oxide (LiCoO2) is widely used as a positive electrode active material for secondary batteries because it can provide a high voltage of 4 V. Carbon black is also widely used as a conductive additive. Patent Document 1 discloses a positive electrode for a nonaqueous secondary battery that uses graphene oxide, which can form an active material layer with high electronic conductivity with a small amount of conductive additive. Patent Document 2 also discloses a method for producing a storage battery electrode that uses graphene oxide and acetylene black. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-7141 [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-63032 Summary of the Invention [Problem to be solved by the invention]

[0009] A secondary battery includes at least an outer casing, a current collector, an active material (positive electrode active material or negative electrode active material), a conductive additive, and a binder. It also includes an electrolyte solution in which a lithium salt or the like is dissolved. If it is a solid-state battery, it also includes a solid electrolyte.

[0010] The current collector is a metal foil, and the electrode is formed by applying a slurry to the metal foil and drying it. After drying, the foil may be pressed further. The electrode is formed by forming an active material layer on the current collector.

[0011] The term "slurry" refers to a liquid material used to form an active material layer on a current collector, and includes at least active material particles, a binder, and a solvent, preferably with a conductive additive added. The slurry is sometimes called an electrode slurry or an active material slurry. When forming a positive electrode active material layer, a positive electrode slurry is used, and when forming a negative electrode active material layer, a negative electrode slurry is used.

[0012] The conductive additive, also called a conductivity-imparting agent or conductive material, is made of a carbon material. By attaching the conductive additive between multiple active material particles, the active material particles are electrically connected to each other, thereby increasing conductivity. The term "attachment" does not only refer to physical adhesion between the active material particles and the conductive additive, but also encompasses cases where a covalent bond is formed, bonding due to van der Waals forces, the conductive additive covering part of the surface of the active material particles, the conductive additive fitting into the surface irregularities of the active material particles, and electrical connection even when the particles are not in contact with each other.

[0013] Carbon black (furnace black, acetylene black, graphite, etc.) is a typical carbon material used as a conductive additive. Carbon black is a bulky particle with an average particle size of several tens to several hundreds of nanometers, making it difficult to form surface contact with other materials, and tends to form point contact. Therefore, when an active material is mixed with carbon black, the contact resistance between the active material and the carbon black increases. If a large amount of carbon black is used to reduce the contact resistance, the ratio of active material to the entire electrode decreases, resulting in a decrease in the discharge capacity of the secondary battery.

[0014] Furthermore, carbon black is a material that tends to agglomerate, making it difficult to mix so that it is uniformly dispersed.

[0015] Furthermore, graphene monolayers or multilayers are known as carbon materials used as conductive additives. Graphene has remarkable electrical, mechanical, and chemical properties, making it a promising carbon material for applications in a variety of fields, such as graphene-based field-effect transistors and solar cells. However, graphene is known to be difficult to disperse. To utilize graphene as a conductive additive, it is necessary to disperse the graphene. Graphene has a high specific surface area, making it difficult to disperse, and the graphene may aggregate. When aggregated graphene is used as a conductive additive, it is difficult to ensure that it functions satisfactorily as a conductive additive.

[0016] A binder (resin) is mixed into the positive electrode of a secondary battery to bond the active material to a current collector such as metal foil. Binders are also called binding agents. Binders are polymeric materials, and if too much binder is added, the proportion of active material in the positive electrode decreases, reducing the discharge capacity of the secondary battery. Therefore, the amount of binder mixed is kept to a minimum.

[0017] It is an object of the present invention to provide an active material layer having a high filling rate and high density by using a small amount of a conductive additive when forming the active material layer. That is, it is an object of one embodiment of the present invention to provide a novel method for forming an electrode slurry.

[0018] Another object of one embodiment of the present invention is to provide a method for manufacturing a novel positive electrode. Another object is to increase the density of an active material layer to increase the capacity. Another object is to improve the rate characteristics of a secondary battery. Another object is to improve the energy density of a secondary battery. Another object is to improve the cycle characteristics of a secondary battery. Another object is to provide a novel positive electrode.

[0019] Another object of one embodiment of the present invention is to provide a novel secondary battery, a novel electronic device, etc. Another object of one embodiment of the present invention is to provide a manufacturing method of the novel secondary battery.

[0020] Another goal is to provide a vehicle equipped with a secondary battery and with a long driving range, specifically a vehicle that can travel over 500 km on a single charge.

[0021] Note that the description of these problems does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily solve all of these problems. Note that problems other than these can be extracted from the description of the specification, drawings, and claims. [Means for solving the problem]

[0022] By including a first carbon material and a second carbon material that is more likely to aggregate than the first carbon material in the positive electrode active material layer and mixing them so that the weight of the second carbon material is 1.5 to 20 times, preferably 2 to 9.5 times, that of the first carbon material, it is possible to prevent aggregation of the second carbon material and the first carbon material and reduce the proportion of aggregated portions. The tendency to aggregate, i.e., the degree of aggregation, is determined by the apparent state when a cross-section is observed.

[0023] The first carbon material is graphene, also known as single-layer or multilayer graphene, and the second carbon material is carbon black. Both function as conductive additives (also called conductivity-imparting agents or conductive materials). When graphene is mixed with carbon black and used as a conductive additive in an electrode, it improves uniformity and enables the formation of a highly conductive network within the electrode. Because graphene has a thin, planar shape, it can form efficient conductive paths with a smaller amount than other conductive additives, allowing for a higher proportion of active material, thereby improving the capacity per volume of the electrode. This enables the miniaturization and high-capacity development of secondary batteries. Furthermore, the use of graphene can suppress capacity loss during rapid charging and discharging.

[0024] The method disclosed in this specification is a method for producing a secondary battery, comprising: a first step of mixing graphene, carbon black, and a binder to obtain a first mixture; a second step of mixing a positive electrode active material with the first mixture to obtain a second mixture; a third step of mixing a dispersion medium with the second mixture to obtain an electrode slurry; a fourth step of applying the electrode slurry to a positive electrode current collector; a fifth step of drying the electrode slurry to form a positive electrode; and a sixth step of stacking the positive electrode and the negative electrode to form a secondary battery, wherein the weight of the carbon black mixed in the first mixing step is 1.5 to 20 times, preferably 2 to 9.5 times, the weight of the graphene.

[0025] In the above configuration, if further pressing is performed after the fifth step, and the pressing linear pressure is set to 700 kN / m or more, a high-density positive electrode can be obtained. Specifically, the density of the positive electrode active material layer measured by weight can be set to a value higher than 3.5 g / cc. Increasing the electrode density increases the filling amount in the battery container, thereby increasing the energy density per volume.

[0026] The positive electrode active material layer obtained by the above method has the following characteristics, and a secondary battery having at least a positive electrode using the positive electrode active material layer can have an increased capacity.

[0027] Furthermore, when the mixture of graphene and carbon black is within the above range, the dispersion stability of the carbon black is excellent and agglomerations are less likely to occur during slurry preparation.

[0028] Furthermore, a secondary battery produced using the above-described method is also one aspect of the present invention. This secondary battery has a positive electrode active material layer including positive electrode active material particles containing lithium and cobalt, a first carbon material, a second carbon material, and a resin, and a negative electrode active material layer overlapping the positive electrode active material layer, and the weight of the second carbon material is 1.5 to 20 times, preferably 2 to 9.5 times, the weight of the first carbon material.

[0029] In the above configuration, the positive electrode active material layer has aggregated portions, and the proportion of the aggregated portions in the positive electrode active material layer as determined by image analysis is less than 14%.

[0030] Another configuration is a secondary battery having a positive electrode active material layer including positive electrode active material particles containing lithium and cobalt, a first carbon material, a second carbon material, and a resin, and a negative electrode active material layer overlapping the positive electrode active material layer, in which image analysis reveals that the proportion of aggregated portions in the positive electrode active material layer is less than 14%.

[0031] In the above configuration, the weight of the second carbon material is 1.5 to 20 times, preferably 2 to 9.5 times, that of the first carbon material.

[0032] In each of the above structures, the first carbon material is single-layer graphene or multi-layer graphene, and the second carbon material is carbon black. Multi-layer graphene refers to a material having a plurality of graphene layers, and indicates 2 to 100 graphene layers.

[0033] In each of the above configurations, the resin used as the binder is polyvinylidene fluoride.

[0034] In each of the above configurations, the secondary battery may be a secondary battery having an electrolytic solution or an all-solid-state secondary battery having a solid electrolyte. In the case of a secondary battery having an electrolytic solution, a separator is provided between the positive electrode and the negative electrode. In the case of an all-solid-state secondary battery, a solid electrolyte is provided between the positive electrode and the negative electrode, and a separator is not provided.

[0035] In this specification, the term "aggregate portion" refers to a region containing aggregates of one or more types of conductive additives, and is disposed between multiple active materials. FIG. 1A shows a cross-sectional photograph of an electrode having the above-described range of the mixture of the first carbon material and the second carbon material. For clarity, the aggregate portion 10 is shown in FIG. 1A with a bold line. Also shown in FIG. 1A is a cross-sectional photograph of the same portion as FIG. 1A, showing the state before the bold line is added.

[0036] The area occupied by the agglomeration portions can be less than 14% of the electrode surface. A small area is preferable. The porosity refers to the area ratio of voids (also called pores or holes) in the cross section of the electrode layer. In this specification, the porosity is the average value calculated from 180 images taken with a Hitachi High-Tech XVision 210B (Focused Ion Beam-Scanning Electron Microscope) at an accelerating voltage of 2.0 kV. The voids include those present as pores or holes inside active material particles and may also refer to the gaps between active material particles. The area occupied by the voids can be 3.4% to 7% of the electrode surface. The voids are necessary for the electrolyte to penetrate, so it is preferable to maintain them within the above range. These areas can be measured using the slice and view technique, which uses a scanning electron microscope (SEM), a measurement method based on image analysis.

[0037] The slice-and-view technique involves repeatedly acquiring image data within the FIB-SEM in the order of cross-section processing and SEM observation, thereby obtaining multiple SEM images with gradually changing depth information, and then stitching these together to obtain information equivalent to three-dimensional information.

[0038] Figure 2A shows an example of multiple cross-sectional images arranged using the slice-and-view technique. Figure 2B shows a rectangular parallelepiped (180 SEM images in total) created by stitching them together. The arrow in Figure 2B indicates the observation direction, and the plane perpendicular to the observation direction represents the cross section of the electrode. The rectangular parallelepiped consisting of the collection of SEM images has a base of 36 μm (width) × 38.5 μm (depth) and a height of 14.2 μm. Figure 2C shows a photograph of one of the SEM images. The black area in Figure 3A is extracted as the active material area, the void area in Figure 3B is extracted, and the conductive additive agglomeration area in Figure 3C is extracted. The area ratio of each area can be calculated. The average area of ​​each pixel in the SEM image is approximately 60 nm. If the difference between the conductive additive agglomeration area and the void area is clear, the agglomeration area and the void area can be distinguished from each other at approximately 60 nm. The area ratio is calculated based on the average value of 180 SEM images. A larger ratio of the active material region is preferable because it results in a larger capacity. It can be said that the positive electrode structure of a secondary battery preferably has a large ratio of the active material region when the slice and view technique is used, a small area occupied by agglomerates, and an area occupied by voids of 3.4% to 7%.

[0039] By setting the carbon black content within the above range, even if pressing is performed during the electrode fabrication process, voids remain for the electrolyte to penetrate when the electrolyte is later added. Increasing the electrode density by pressing reduces the void ratio, resulting in a shortage of electrolyte to penetrate the voids, hindering smooth lithium ion movement and increasing resistance to lithium ion diffusion within the positive electrode. This results in a problem of reduced rate characteristics. Furthermore, increasing the void ratio and allowing sufficient electrolyte to penetrate results in a problem of reduced electrode density and reduced energy characteristics. Thus, achieving both good rate characteristics and high energy density has traditionally been difficult. By adjusting the weight of the carbon black to be mixed to 1.5 to 20 times, preferably 2 to 9.5 times, the weight of graphene and then pressing, it is possible to achieve both good rate characteristics and high energy density.

[0040] In each of the above configurations, the porosity of the positive electrode active material layer determined by image analysis is 3.4% or more and 7% or less.

[0041] Furthermore, by mixing the first carbon material (graphene) and the second carbon material (carbon black) within the above range, it is possible to achieve a higher electrode density than a positive electrode using only carbon black as a conductive additive. Increasing the electrode density allows for a larger capacity per unit weight.

[0042] In each of the above configurations, the density of the positive electrode active material layer measured gravimetrically can be made higher than 3.5 g / cc.

[0043] Powder packing density (hereinafter referred to as PPD) is calculated by filling a pellet die with powder of weight W, gradually applying uniaxial pressure, and determining the volume V when a predetermined pressure is reached (the following formula (1)).

[0044]

number

[0045] Furthermore, when graphene is used solely as a conductive additive in a positive electrode, the capacity drops significantly under rapid charging conditions (high-rate charging conditions). Although a positive electrode using graphene alone as a conductive additive can increase electrode density, it is not suitable for secondary batteries that require rapid charging.

[0046] Although the electrode density is lower than that of a positive electrode that uses only graphene as a conductive additive, by mixing the first carbon material (graphene) and the second carbon material (carbon black) within the above range, it can be used for rapid charging.

[0047] The loading amount is the amount of active material per electrode area. The loading amount is a value that can be calculated because each material is measured and mixed before making the slurry. It may also be possible to measure the loading amount by disassembling the secondary battery and dissolving the binder. The loading amount can be increased by increasing the proportion of the active material to be blended (also called mixing) or by increasing the layer thickness. However, increasing the loading amount can increase the resistance of the electrode or increase the distance to the current collector, which can easily degrade battery performance.

[0048] When a secondary battery is made using a positive electrode that uses only graphene as a conductive additive, the capacity drops significantly under rapid charging conditions (high-rate charging conditions). By keeping the mixture of the first carbon material (graphene) and the second carbon material (carbon black) within the above range, rapid charging is possible even when the loading amount is increased.

[0049] These features are effective for use as a secondary battery for vehicles.

[0050] Increasing the number of secondary batteries and increasing the vehicle's weight reduces the driving range because the energy required to move increases. By using high-density secondary batteries, the driving range can be maintained with almost no change in the total weight of the vehicle equipped with the same weight of secondary batteries.

[0051] Furthermore, as vehicle secondary batteries reach high capacity, they require more power for charging, so it is desirable to complete charging in a short time.Furthermore, charging is performed under high-rate charging conditions during so-called regenerative charging, in which temporary power is generated when the vehicle brakes are applied and the power is charged, so good rate characteristics are required for vehicle secondary batteries.

[0052] By optimizing the mixture ratio of carbon black and graphene, it is possible to achieve both high electrode density and the creation of the appropriate gaps necessary for ion conduction, resulting in a secondary battery for automotive use with high energy density and good output characteristics.

[0053] This configuration is also effective for portable information terminals, and by optimizing the mixture ratio of carbon black and graphene, it is possible to reduce the size of the secondary battery and achieve high capacity. Also, by optimizing the mixture ratio of carbon black and graphene, it is possible to rapidly charge the portable information terminal.

[0054] In this specification, the term "particles" refers not only to spherical particles but also to particles with various cross-sectional shapes. If the particle size of the positive electrode active material particles is too large, problems such as difficulty in diffusing lithium and excessive roughness of the surface of the active material layer when applied to the current collector may occur. On the other hand, if the particle size 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 referred to as median diameter) is preferably 1 μm to 100 μm, more preferably 2 μm to 40 μm, and even more preferably 5 μm to 30 μm. Alternatively, 1 μm to 40 μm is preferred. Alternatively, 1 μm to 30 μm is preferred. Alternatively, 2 μm to 100 μm is preferred. Alternatively, 2 μm to 30 μm is preferred. Alternatively, 5 μm to 100 μm is preferred. Alternatively, 5 μm to 40 μm is preferred.

[0055] The median diameter D50 can be measured by a particle size distribution analyzer using a laser diffraction / scattering method, etc. The specific surface area can be measured by a specific surface area measuring device using a gas adsorption method based on a constant volume method, for example.

[0056] Furthermore, when observing a cross section, if no aggregation occurs, the particle size of the primary particles will be as measured. However, if the primary particles aggregate to form secondary particles, care must be taken because the particle size distribution analyzer will measure the particle size of the aggregated primary particles, i.e., the secondary particles.

[0057] The carbon materials contained in secondary batteries can be identified by analyzing their crystalline state using Raman spectroscopy or X-ray diffraction. For example, graphene and carbon black can sometimes be detected and identified.

[0058] In each of the above configurations, the aggregation portion of the positive electrode active material layer is a region where a profile indicating graphene or a profile indicating carbon black is measured by X-ray diffraction.

[0059] In each of the above configurations, the aggregation portion of the positive electrode active material layer is a region where a profile indicating graphene or a profile indicating carbon black is measured by Raman spectroscopy.

[0060] In each of the above configurations, the positive electrode active material may further contain nickel, which can increase capacity.

[0061] In each of the above-described configurations, the positive electrode active material may further contain manganese, which can improve structural stability.

[0062] In each of the above-described configurations, the positive electrode active material may further contain titanium, which can improve structural stability or heat resistance.

[0063] In each of the above configurations, the positive electrode active material may further contain aluminum, which can improve heat resistance.

[0064] In each of the above configurations, the surface layer of the positive electrode active material may contain fluorine. By containing fluorine in the surface layer of the positive electrode active material, it becomes easier to insert or extract lithium ions on the positive electrode surface, and good rate characteristics can be obtained. The rate characteristics are also called charge / discharge rate characteristics, and are one of the evaluation methods that serve as an index of rapid charge / discharge. [Effects of the Invention]

[0065] By using both graphene and carbon black as conductive additives and optimizing the blending ratio, a high-density electrode can be realized. Furthermore, a secondary battery can be realized that can suppress capacity loss and maintain high capacity even when the electrode layer is thickened and the loading amount is increased. This is particularly effective for secondary batteries used in vehicles, and can provide vehicles with a long driving range, specifically a driving distance of 500 km or more per charge, without increasing the weight ratio of the secondary battery to the total vehicle weight. [Brief explanation of the drawings]

[0066] [Figure 1] 1A and 1B are cross-sectional photographs showing one embodiment of the present invention. [Figure 2] 2A and 2B are diagrams illustrating the slice-and-view technique, and FIG. 2C is a diagram showing an SEM image. [Figure 3] 3A, 3B, and 3C are processed SEM images. [Figure 4] 4A to 4C are diagrams illustrating an example of a manufacturing method according to one embodiment of the present invention. [Figure 5] FIG. 5 is a graph showing the electrode in-plane ratio. [Figure 6] FIG. 6A is a graph showing the relationship between capacity and loading amount at a 0.2C rate, and FIG. 6B is a graph showing the relationship between capacity and loading amount at a 1C rate. [Figure 7] FIG. 7A is a perspective view of a coin-type secondary battery, FIG. 7B is a cross-sectional perspective view thereof, and FIG. 7C is a cross-sectional schematic view thereof during charging. [Figure 8] Fig. 8A shows an example of a cylindrical secondary battery. Fig. 8B shows an example of a cylindrical secondary battery. Fig. 8C shows an example of multiple cylindrical secondary batteries. Fig. 8D shows an example of a power storage system having multiple cylindrical secondary batteries. [Figure 9] 9A and 9B are diagrams illustrating an example of a secondary battery, and FIG. 9C is a diagram showing the inside of the secondary battery. [Figure 10] 10A, 10B, and 10C are diagrams illustrating examples of secondary batteries. [Figure 11] 11A and 11B are diagrams showing the external appearance of a secondary battery. [Figure 12] 12A, 12B, and 12C are diagrams illustrating a method for producing a secondary battery. [Figure 13] Figure 13A shows an example of the configuration of a battery pack, Figure 13B shows an example of the configuration of a battery pack, and Figure 13C shows an example of the configuration of a battery pack. [Figure 14] FIG. 14A is a perspective view of a battery pack showing one embodiment of the present invention, FIG. 14B is a block diagram of the battery pack, and FIG. 14C is a block diagram of a vehicle having a motor. [Figure 15] 15A to 15D are diagrams illustrating an example of a transportation vehicle. [Figure 16] 16A and 16B illustrate a power storage device according to one embodiment of the present invention. [Figure 17] FIG. 17A is a diagram showing an electric bicycle, FIG. 17B is a diagram showing a secondary battery of the electric bicycle, and FIG. 17C is a diagram explaining an electric motorcycle. [Figure 18] 18A to 18D are diagrams illustrating an example of an electronic device. [Figure 19] FIG. 19A shows an example of a wearable device, FIG. 19B shows a perspective view of a wristwatch-type device, and FIG. 19C is a diagram illustrating a side view of the wristwatch-type device. [Figure 20]20A and 20B are cross-sectional SEM photographs showing one embodiment of the present invention, and FIG. 20C is a cross-sectional SEM photograph showing a comparative example. [Figure 21] 21A and 21B are cross-sectional SEM photographs showing a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0067] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be readily understood by those skilled in the art that various modifications can be made to the embodiments and details. Furthermore, the present invention should not be interpreted as being limited to the description of the embodiments shown below.

[0068] (Embodiment 1) A method for manufacturing a positive electrode of a lithium-ion secondary battery according to one embodiment of the present invention will be described with reference to Fig. 4. In this embodiment, the case where graphene (also referred to as G) and acetylene black (also referred to as AB) are used as conductive additives will be described.

[0069] First, a binder and carbon black (acetylene black in this embodiment) are prepared (Step S01 in FIG. 4). These are mixed (Step S02 in FIG. 4) to obtain a mixture 101 (Step S03 in FIG. 4). Graphene is also prepared and mixed with the mixture 101 (Step S12 in FIG. 4) to obtain a mixture 102 (Step S13 in FIG. 4).

[0070] 4 has been described, the order is not particularly limited, and for example, graphene and a binder may be mixed first, and then acetylene black may be added and mixed. Furthermore, in order to reduce the number of steps, the binder, acetylene black, and graphene may be mixed simultaneously.

[0071] The mixing amounts of graphene (first carbon material) and acetylene black (second carbon material) are important in the process enclosed by the dotted line in Figure 4. Acetylene black has the property of being more prone to aggregation than graphene.

[0072] Graphene is a type of graphene compound. Graphene compounds may have excellent electrical properties, such as high conductivity, and excellent physical properties, such as high flexibility and high mechanical strength. Graphene compounds also have a planar shape. Graphene compounds enable surface contact with low contact resistance. Even when thin, they may have very high conductivity, allowing a small amount to efficiently form a conductive path within an active material layer. Therefore, using a graphene compound as a conductive additive is preferable because it can increase the contact area between the active material and the conductive additive. It is also preferable because it can sometimes reduce electrical resistance. Examples of graphene compounds include graphene, multilayer graphene, multigraphene, graphene oxide, multilayer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multi-graphene oxide, graphene quantum dots, etc.

[0073] By mixing acetylene black in an amount 1.5 to 20 times, preferably 2 to 9.5 times, the weight of graphene, it is possible to prevent aggregation and reduce the proportion of aggregates in the electrode that is formed later. When the mixture of graphene and acetylene black is within the above range, the dispersion stability of acetylene black is excellent during slurry preparation, and aggregates are less likely to occur. In this embodiment, the weight ratio of graphene to acetylene black is set to 2:8 (i.e., 1:4).

[0074] Examples of binders that can be used include polyvinylidene fluoride (PVDF), polyimide, polytetrafluoroethylene, polyvinyl chloride, ethylene propylene diene polymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluororubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, and nitrocellulose.

[0075] Next, an active material is prepared (step S21 in FIG. 4), mixed with the mixture 102 (step S22 in FIG. 4), and then kneaded (step S23 in FIG. 4). Kneading here refers to stirring or mixing using a kneader, but is broadly synonymous with mixing. Therefore, mixing performed in other steps may also be performed using a kneader. After kneading, the mixture 103 is obtained (step S24 in FIG. 4).

[0076] The active material is preferably a positive electrode active material having a metal (hereinafter referred to as element A) that serves as a carrier ion. As element A, for example, alkali metals such as lithium, sodium, and potassium, and Group 2 elements such as calcium, beryllium, and magnesium can be used.

[0077] In a positive electrode active material, carrier ions are desorbed from the positive electrode active material during charging. The greater the desorption of element A, the greater the number of ions that contribute to the capacity of the secondary battery, resulting in an increased capacity. On the other hand, the greater the desorption of element A, the more likely the crystal structure of the compound contained in the positive electrode active material is to be deformed. The destructive effect of the crystal structure of the positive electrode active material may lead to a decrease in discharge capacity with charge-discharge cycles. When the positive electrode active material of one embodiment of the present invention contains element X, the destructive effect of the crystal structure caused by desorption of carrier ions during charging of the secondary battery may be suppressed. For example, a portion of element X is substituted at the position of element A. Elements such as magnesium, calcium, zirconium, lanthanum, and barium can be used as element X. Furthermore, elements such as copper, potassium, sodium, and zinc can be used as element X. Furthermore, two or more of the elements listed above may be used in combination as element X.

[0078] Furthermore, the positive electrode active material preferably contains a halogen in addition to the element X. Preferably, the positive electrode active material contains a halogen such as fluorine or chlorine. When the positive electrode active material contains the halogen, substitution of the element X at the position of the element A may be promoted.

[0079] When the positive electrode active material contains the element X, or when it contains a halogen in addition to the element X, the electrical conductivity on the surface of the positive electrode active material may be suppressed.

[0080] The positive electrode active material also contains a metal (hereinafter referred to as element M) whose valence changes with charging and discharging of the secondary battery. The element M is, for example, a transition metal. The positive electrode active material contains, for example, one or more of cobalt, nickel, and manganese as the element M, and particularly contains cobalt. Furthermore, the position of element M may contain an element such as aluminum that does not change valence and can have the same valence as element M, more specifically, a trivalent typical element. The aforementioned element X may, for example, be substituted at the position of element M. Furthermore, when the positive electrode active material is an oxide, element X may be substituted at the position of oxygen.

[0081] As the positive electrode active material, for example, a lithium composite oxide having a layered rock salt crystal structure is preferably used. More specifically, examples of the lithium composite oxide having a layered rock salt crystal structure include lithium cobalt oxide, lithium nickel oxide, lithium composite oxide containing nickel, manganese, and cobalt, and lithium composite oxide containing nickel, cobalt, and aluminum. Furthermore, these positive electrode active materials are preferably represented by the space group R-3m.

[0082] In a positive electrode active material having a layered rock-salt crystal structure, increasing the depth of charge can cause the crystal structure to collapse. Here, the collapse of the crystal structure refers to, for example, layer misalignment. If the collapse of the crystal structure is irreversible, repeated charging and discharging can cause a decrease in the capacity of the secondary battery.

[0083] The positive electrode active material contains element X, which suppresses the above-mentioned layer misalignment, even at deep charge depths. Suppressing this misalignment can reduce volume changes during charge and discharge. Therefore, the positive electrode active material can achieve excellent cycle characteristics. Furthermore, the positive electrode active material can adopt a stable crystal structure at high-voltage charge states. The crystal structure at a charge depth of 0 (discharged state) is R-3m (O3), but at fully charged charge depths, the material has a crystal structure different from the H1-3 crystal structure. This structure belongs to the R-3m space group, and ions such as cobalt and magnesium occupy six oxygen coordination positions. The symmetry of the CoO2 layers in this structure is the same as that of the O3 type. Therefore, this structure is referred to herein as an O3' type crystal structure or a pseudospinel type crystal structure. In both the O3 type and O3' type crystal structures, it is preferable for magnesium to be present in a dilute form between the CoO2 layers, i.e., at the lithium sites. It is also preferable that fluorine is present randomly and dilutely at the oxygen sites.

[0084] In the O3'-type crystal structure, light elements such as lithium may occupy the oxygen tetracoordination position.

[0085] The O3'-type crystal structure is preferably represented by a unit cell using one cobalt and one oxygen. This indicates that the symmetry between cobalt and oxygen differs between the O3'-type structure and the H1-3-type structure, and the O3'-type structure exhibits a smaller change from the O3-type structure than the H1-3-type structure. The unit cell that is more preferably used to represent the crystal structure of the positive electrode active material can be selected, for example, so that the GOF (goodness of fit) value is smaller in Rietveld analysis of XRD.

[0086] The O3' type crystal structure can show the coordinates of cobalt and oxygen in the unit cell as Co(0,0,0.5), O(0,0,x), with 0.20≦x≦0.25.

[0087] The positive electrode active material has the chemical formula AM y OZ (y>0, z>0). For example, lithium cobalt oxide may be expressed as LiCoO2. Also, for example, lithium nickel oxide may be expressed as LiNiO2. Materials with a layered rock salt type crystal structure, such as lithium cobalt oxide (LiCoO2), are known to have a high discharge capacity and are excellent as positive electrode active materials for secondary batteries. An example of a material with a layered rock salt type crystal structure is a composite oxide expressed as LiMO2.

[0088] Lithium cobalt oxide at a depth of charge of 0 (discharged state) has a region with a crystal structure of space group R-3m, in which lithium occupies octahedral sites and there are three CoO2 layers in the unit cell. For this reason, this crystal structure is sometimes called an O3-type crystal structure. Note that a CoO2 layer is an octahedral structure in which cobalt is coordinated with six oxygen atoms, and the layers are connected in a plane with edge sharing.

[0089] At a charge depth of 1, the crystal structure is of the space group P-3m1, with one CoO2 layer in the unit cell. Therefore, this crystal structure is sometimes called an O1-type crystal structure.

[0090] Furthermore, when the depth of charge is about 0.8, lithium cobalt oxide has a crystal structure of the space group R-3m. This structure can be thought of as a structure in which CoO2 structures such as P-3m1(O1) and LiCoO2 structures such as R-3m(O3) are alternately stacked. For this reason, this crystal structure is sometimes called the H1-3 crystal structure. In fact, the H1-3 crystal structure has twice the number of cobalt atoms per unit cell of other structures.

[0091] The O3' crystal structure exhibits diffraction peaks at 2θ = 19.30 ± 0.20° (19.10° to 19.50°) and 2θ = 45.55 ± 0.10° (45.45° to 45.65°). More specifically, sharp diffraction peaks appear at 2θ = 19.30 ± 0.10° (19.20° to 19.40°) and 2θ = 45.55 ± 0.05° (45.50° to 45.60°).

[0092] On the other hand, peaks do not appear at these positions in the H1-3 crystal structure and CoO2(P-3m1, O1). Therefore, the appearance of peaks at 2θ=19.30±0.20° and 2θ=45.55±0.10° when charged at a high voltage is characteristic of a positive electrode active material with an O3' crystal structure.

[0093] Although the positive electrode active material of one embodiment of the present invention has an O3'-type crystal structure when charged at a high voltage, not all of the particles need to have the O3'-type crystal structure. Other crystal structures may be included, or some particles may be amorphous. However, when Rietveld analysis is performed on the XRD pattern, the O3'-type crystal structure is preferably 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more. When the O3'-type crystal structure is 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more, the positive electrode active material can have sufficiently excellent cycle characteristics.

[0094] Furthermore, even after 100 or more charge / discharge cycles from the start of measurement, when Rietveld analysis is performed, the O3' type crystal structure is preferably 35 wt% or more, more preferably 40 wt% or more, and even more preferably 43 wt% or more.

[0095] Note that increasing the magnesium concentration above the desired value may reduce the effect on stabilizing the crystal structure. This is thought to be because magnesium occupies not only the lithium site but also the cobalt site. The number of magnesium atoms in the positive electrode active material of one embodiment of the present invention is preferably 0.001 to 0.1 times the number of atoms of the transition metal M, more preferably more than 0.01 to less than 0.04, and even more preferably about 0.02. Alternatively, it is preferably 0.001 to 0.04. Alternatively, it is preferably 0.01 to 0.1 times. The magnesium concentration shown here may be, for example, a value obtained by performing elemental analysis of the entire particles of the positive electrode active material using ICP-MS or the like, or may be based on the value of the raw material composition during the production process of the positive electrode active material.

[0096] The number of nickel atoms in the positive electrode active material is preferably more than 0% but not more than 7.5% of the number of cobalt atoms, preferably 0.05% to 4%, preferably 0.1% to 2%, and more preferably 0.2% to 1%. Alternatively, more than 0% but not more than 4% is preferred. Alternatively, more than 0% but not more than 2% is preferred. Alternatively, 0.05% to 7.5% is preferred. Alternatively, 0.05% to 2% is preferred. Alternatively, 0.1% to 7.5% is preferred. Alternatively, 0.1% to 4% is preferred. The nickel concentration shown here may be a value obtained by performing elemental analysis of the entire particles of the positive electrode active material using, for example, GD-MS, ICP-MS, or the like, or may be based on the value of the raw material composition during the production process of the positive electrode active material.

[0097] The positive electrode active material is not limited to the materials listed above.

[0098] For example, a composite oxide having a spinel crystal structure can be used as the positive electrode active material. Also, for example, a polyanion-based material can be used as the positive electrode active material. Examples of polyanion-based materials include materials having an olivine crystal structure and Nasicon-based materials. Also, for example, a material containing sulfur can be used as the positive electrode active material.

[0099] As a material having a spinel-type crystal structure, for example, a composite oxide represented by LiM2O4 can be used. It is preferable to have Mn as the element M. For example, LiMn2O4 can be used. Furthermore, by having Ni in addition to Mn as the element M, the discharge voltage of the secondary battery can be improved and the energy density can be improved, which is preferable. Furthermore, a lithium-containing material having a spinel-type crystal structure containing manganese, such as LiMn2O4, can be mixed with a small amount of lithium nickel oxide (LiNiO2 or LiNi 1-x M x Mixing O2 (M=Co, Al, etc.) is preferable because it can improve the characteristics of the secondary battery.

[0100] An example of a polyanion-based material that can be used is a composite oxide containing oxygen, metal A, metal M, and element Z. Metal A is one or more of Li, Na, and Mg, metal M is one or more of Fe, Mn, Co, Ni, Ti, V, and Nb, and element Z is one or more of S, P, Mo, W, As, and Si.

[0101] As a material having an olivine-type crystal structure, for example, a composite material (general formula LiMPO4 (M is one or more of Fe(II), Mn(II), Co(II), and Ni(II))) can be used. Representative examples of the general formula LiMPO4 include LiFePO4, LiNiPO4, LiCoPO4, LiMnPO4, and 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 less than 1, 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 ePO4 (where c + d + e ≤ 1, 0 < c < 1, 0 < d < 1, 0 < e < 1), LiFe f Ni g Co h Mn i PO4 (where f + g + h + i ≤ 1, 0 < f < 1, 0 < g < 1, 0 < h < 1, 0 < i < 1), etc. can be used as lithium compounds.

[0102] Also, composite materials such as general formula Li (2-j) MSiO4 (M is one or more of Fe(II), Mn(II), Co(II), Ni(II), 0 ≤ j ≤ 2), etc. can be used. For the general formula Li (2-j) Representative examples of MSiO4 include Li (2-j) FeSiO4, Li (2-j) NiSiO4, Li (2-j) CoSiO4, Li (2-j) MnSiO4, Li (2-j) Fe k Ni l SiO4, Li (2-j) Fe k Co l SiO4, Li (2-j) Fe k Mn l SiO4, Li (2-j) Ni k Co l SiO4, Li (2-j) Ni k Mn l SiO4 (where k + l ≤ 1, 0 < k < 1, 0 < l < 1), Li (2-j) Fe m Ni n Co q SiO4, Li (2-j) Fe m Ni n Mn q SiO4, Li (2-j) Ni m Co n Mn q SiO4 (where m + n + q ≤ 1, 0 < m < 1, 0 < n < 1, 0 < q < 1), Li (2-j) Fe r Ni s Co t Mn uLithium compounds such as SiO4 (where r + s + t + u ≤ 1, 0 < r < 1, 0 < s < 1, 0 < t < 1, 0 < u < 1) can be used as materials.

[0103] Also, A x NASICON-type compounds represented by the general formula M2(XO4)3 (A = Li, Na, Mg, M = Fe, Mn, Ti, V, Nb, X = S, P, Mo, W, As, Si) can be used. Examples of NASICON-type compounds include Fe2(MnO4)3, Fe2(SO4)3, Li3Fe2(PO4)3, etc. Also, as the positive electrode active material, compounds represented by the general formula Li2MPO4F, Li2MP2O7, Li5MO4 (M = Fe, Mn) can be used.

[0104] Also, as the positive electrode active material, perovskite-type fluorides such as NaFeF3, FeF3, metal chalcogenides (sulfides, selenides, tellurides) such as TiS2, MoS2, oxides having an inverse spinel-type crystal structure such as LiMVO4, vanadium oxide-based (V2O5, V6O 13 , LiV3O8, etc.), manganese oxides, organic sulfur compounds, and other materials may be used.

[0105] Also, as the positive electrode active material, borate-based materials represented by the general formula LiMBO3 (M is Fe(II), Mn(II), Co(II)) may be used.

[0106] Examples of materials containing sodium include sodium-containing oxides such as NaFeO2 or Na 2 / 3 [Fe 1 / 2 Mn 1 / 2 O2, Na 2 / 3 [Ni 1 / 3 Mn 2 / 3 O2, Na2Fe2(SO4)3, Na3V2(PO4)3, Na2FePO4F, NaVPO4F, NaMPO4 (M is Fe(II), Mn(II), Co(II), Ni(II)), Na2FePO4F, Na4Co3(PO4)2P2O7, etc., which can be used as the positive electrode active material.

[0107] Alternatively, lithium-containing metal sulfides such as Li2TiS3 and Li3NbS4 may be used as the positive electrode active material.

[0108] As the positive electrode active material of one embodiment of the present invention, two or more of the materials listed above may be mixed and used.

[0109] In this embodiment, a lithium composite oxide is used as the positive electrode active material, and the lithium composite oxide contains Ni, Co, and Mn in a composition ratio of 8:1:1 (also called NCM). NCM is widely used due to its cost benefits and high capacity, and graphene, which is added later, plays an important role in maximizing the performance of this NCM.

[0110] Next, the remaining binder is prepared (step S31 in FIG. 4 ), and the mixture 103 and the binder are mixed (step S32 in FIG. 4 ) to obtain a mixture 104 (step S34 in FIG. 4 ). In this embodiment, the same binder is mixed twice, in steps S01 and S31. The total amount of binder mixed in steps S01 and S31 can be set depending on the amounts of acetylene black, graphene, and active material, and may be added to the electrode slurry in an amount of 1 wt % to 5 wt %. By mixing the binder while graphene is dispersed so as to be in surface contact with multiple active material particles, the active material and graphene can be bound together while maintaining the dispersed state. Mixing the binder can improve the strength of the electrode.

[0111] Next, a dispersion medium is prepared (step S41 in FIG. 4), and the dispersion medium is added to and mixed with the mixture 104 until a predetermined viscosity is reached (step S42 in FIG. 4).

[0112] It is preferable to use a polar solvent as the dispersion medium. Examples of the polar solvent that can be used include N-methyl-2-pyrrolidone (abbreviation: NMP), N,N-dimethylformamide (abbreviation: DMF), and dimethyl sulfoxide (abbreviation: DMSO). In this embodiment, the viscosity is adjusted by mixing NMP as the dispersion medium to prepare a slurry.

[0113] Through the above steps, electrode slurry can be prepared (step S44 in FIG. 4).

[0114] Next, a current collector is prepared (step S51 in FIG. 4), and the electrode slurry prepared in step S44 is applied to one or both surfaces of the current collector by a coating method such as a roll coating method using an applicator roll or the like, a screen printing method, a doctor blade method, a spin coating method, or a bar coating method (step S52 in FIG. 4).

[0115] When preparing a positive electrode, a positive electrode current collector is used. Highly conductive materials, such as metals such as stainless steel, gold, platinum, aluminum, and titanium, and alloys thereof, can be used as the positive electrode current collector. It is preferable that the material used for the positive electrode current collector does not dissolve at the potential of the positive electrode. Aluminum alloys containing elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, and molybdenum, can also be used. The positive electrode current collector may also be made of a metal element that reacts with silicon to form silicide. Examples of metal elements that react with silicon to form silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collector can be in the form of a foil, plate (sheet), mesh, punched metal, expanded metal, or other suitable shape. It is preferable to use a current collector with a thickness of 5 μm to 30 μm.

[0116] The electrode slurry applied to the current collector is dried by ventilation drying, reduced pressure (vacuum) drying, or other methods (step S53 in FIG. 4). This drying may be carried out using hot air at a temperature of 50°C to 170°C for a period of 1 minute to 10 hours, preferably 1 minute to 1 hour. This step evaporates the dispersion medium contained in the electrode slurry. The drying atmosphere is not particularly limited.

[0117] Through the above steps, an electrode that contains graphene and acetylene black as a conductive additive and functions as a positive electrode can be fabricated (Step S54 in FIG. 4).

[0118] While a larger amount of active material increases the capacity of the resulting positive electrode, the content of the conductive additives graphene and acetylene black decreases. Too little conductive additive results in low conductivity and poor battery performance. Therefore, the active material and conductive additive are preferably mixed in an amount that maximizes the amount of active material while ensuring sufficient conductivity. Specifically, when preparing the electrode slurry described below, the weight ratio of graphene is preferably 0.1 wt% to 10 wt%, more preferably 0.2 wt% to 6 wt%, based on the total weight (wt%) of the active material, conductive additive, and binder. Furthermore, within this range, acetylene black is mixed in an amount 1.5 to 20 times, preferably 2 to 9.5 times, the weight of graphene. In this embodiment, the active material, graphene, acetylene black, and binder are mixed in a ratio of 95:0.6:2.4:2.

[0119] Lithium-ion secondary batteries function through the movement of electrons and Li ions. The movement of electrons is promoted by a conductive additive (in this embodiment, both graphene and acetylene black). To promote the movement of Li ions, fluorine or the like may be contained in a region of the positive electrode active material up to about 10 nm from the surface toward the interior, i.e., in the surface layer.

[0120] Furthermore, when fluorine is contained in the surface layer, it is preferable that the fluorine and cobalt are bonded together. As a result, some of the Co atoms adjacent to the fluorine atoms are bonded together. 3+ Co 2+ It is preferable that:

[0121] The valence of cobalt can be analyzed using, for example, electron spin resonance (ESR). Cobalt in the layered rock salt crystal structure is 3+ is diamagnetic, Co 2+ indicates paramagnetism. In diamagnetic materials, the magnetic susceptibility χ does not change with temperature. In contrast, in paramagnetic materials, the magnetic susceptibility χ increases as the temperature decreases, and the amount of spin observed in ESR increases.

[0122] Therefore, the spin amount of cobalt observed by ESR was compared at room temperature (about 300 K) and at low temperature (about 113 K), and the difference in spin amount was found to be 1.0 × 10 12 If the surface layer contains more than 100 spins / g, it can be assumed that at least a portion of the material is paramagnetic cobalt. 2+ It is believed to have a bond between fluorine and cobalt. 2+ When the compound has the above structure, the lithium ions may be easily inserted and extracted, which may result in a positive electrode active material with improved rate characteristics, which is preferable.

[0123] The area of ​​the void regions of the electrode obtained in this embodiment was extracted using the slice-and-view technique, and the area ratio (also called void ratio or porosity) was calculated to be 6.87%. The results are shown in Figure 5. The area occupied by the active material (NCM ratio) was 79.27%, and the ratio of the aggregated portion containing the conductive additive was 13.87%.

[0124] The figure also shows an example in which the weight ratio of acetylene black to graphene used as the conductive additive was 7:3. The void ratio was 3.46%, the NCM ratio was 83.08%, and the ratio of the aggregated portion containing the conductive additive was 13.47%.

[0125] From the results in FIG. 5, it can be seen that by mixing acetylene black in an amount 1.5 to 20 times, preferably 2 to 9.5 times, the weight of graphene, aggregation of acetylene black and aggregation of graphene can be prevented and the proportion of aggregates can be reduced. The area occupied by the aggregates within the electrode surface can be less than 14%. It is preferable that the area occupied by the aggregates is small. Furthermore, the area occupied by voids can be 3.4 to 7% of the area within the electrode surface.

[0126] For comparison, an example in which only acetylene black was used as the conductive additive and an example in which only graphene was used as the conductive additive are also shown in Figure 5. In these two comparative examples, the active material, the conductive additive (graphene or acetylene black), and the binder were mixed in a ratio of 95:3:2.

[0127] FIG. 6 shows a graph in which the horizontal axis represents the amount of support and the vertical axis represents the capacity using the electrode of this embodiment.

[0128] Figure 6A shows the loading dependence of discharge characteristics measured at a 0.2C rate, and all results are the same. Figure 6B shows the loading dependence of discharge characteristics measured at a 1C rate, and the capacity significantly decreased when graphene only was used.

[0129] Here, we will explain charge and discharge rates. The charge rate is the relative value of the current during constant current charging relative to the battery capacity, i.e., the value of the charging current [A] divided by the battery capacity [Ah]. It is also called the C rate. It is expressed in units of C. For example, if a battery with a capacity of 10 Ah is charged at a constant current of 2 A, it is said to have been charged at a rate of 0.2 C. A charge rate of 1 C is the amount of current required to charge the battery to its full capacity in one hour. The higher the charge rate, the faster the charging rate. The discharge rate is the relative value of the current during constant current discharge relative to the battery capacity, i.e., the value of the discharging current [A] divided by the battery capacity [Ah]. It is also called the C rate. It is expressed in units of C. For example, if a battery with a capacity of 10 Ah is discharged at a constant current of 2 A, it is said to have been discharged at a rate of 0.2 C. A discharge rate of 1 C is the amount of current required to discharge the battery to its full capacity in one hour. The higher the discharge rate, the faster the discharging rate.

[0130] The average electrode density was measured to be approximately 3.74 g / cc for the comparative example in which the conductive additive was graphene alone, approximately 3.56 g / cc for the comparative example in which the conductive additive was acetylene black alone, and approximately 3.62 g / cc for the comparative example in which the conductive additive was graphene and acetylene black.

[0131] The comparative example in which only graphene was used as a conductive additive had a high electrode density, but the loading dependency at 1C rate was poor, making it unsuitable for thickening the electrode, for example. The comparative example in which only graphene was used as a conductive additive had poor output characteristics.

[0132] Furthermore, in the comparative example in which the only conductive additive was acetylene black, it was difficult to increase the electrode density.

[0133] 5 and 6, it can be seen that the use of both graphene and acetylene black as conductive additives results in a higher electrode density and maintains output characteristics compared to the comparative example. The use of both graphene and acetylene black as conductive additives improves the dispersibility of the conductive additive, suppresses the generation of aggregates of the conductive additive, and has the synergistic effect of suppressing the reduction of voids for the electrolyte to penetrate.

[0134] This embodiment is particularly effective for the positive electrode of a secondary battery used in a vehicle. The positive electrode active material layer of the secondary battery used in a vehicle is an electrode having a thickness of more than 50 μm, i.e., an electrode with a high loading, and by using both graphene and acetylene black as a conductive additive, there is an advantage that the charge / discharge characteristics are not deteriorated even at a high density and a high loading.

[0135] (Embodiment 2) In this embodiment, a lithium-ion secondary battery including a positive electrode manufactured by a manufacturing method of one embodiment of the present invention will be described. The lithium-ion secondary battery includes at least a positive electrode, a negative electrode, a separator, and an electrolyte.

[0136] [Positive electrode] The positive electrode includes a positive electrode active material layer and a positive electrode current collector, and is preferably manufactured by the manufacturing method described in Embodiment 1.

[0137] [Negative electrode] The negative electrode includes a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer may also include a conductive additive and a binder.

[0138] <Negative electrode active material> As the negative electrode active material, for example, an alloy material or a carbon material can be used.

[0139] The negative electrode active material can be an element capable of undergoing charge-discharge reactions through alloying and dealloying reactions with lithium. For example, materials containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium can be used. These elements have a larger capacity than carbon, and silicon, in particular, has a high theoretical capacity of 4200 mAh / g. For this reason, silicon is preferred as the negative electrode active material. Compounds containing these elements can also be used. Examples include SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, and SbSn. Here, elements that can undergo charge-discharge reactions by alloying / dealloying reactions with lithium, and compounds containing such elements, are sometimes called alloy-based materials.

[0140] In this specification, SiO refers to, for example, silicon monoxide. Alternatively, SiO refers to SiO x Here, x preferably has a value of 1 or close to 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

[0141] As the carbon material, graphite, easily graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon nanotubes, graphene, carbon black, etc. may be used.

[0142] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape and is preferred. Furthermore, it is relatively easy to reduce the surface area of ​​MCMB, and this may be preferred. Examples of natural graphite include flake graphite and spherical natural graphite.

[0143] When lithium ions are inserted into graphite (when lithium-graphite intercalation compounds are formed), graphite exhibits a low potential similar to that of metallic lithium (0.05 V to 0.3 V vs. Li / Li + ) This allows lithium-ion secondary batteries to exhibit high operating voltages. Furthermore, graphite is preferred because it has advantages such as a relatively high capacity per unit volume, a relatively small volume expansion, low cost, and a higher level of safety compared to lithium metal.

[0144] In addition, titanium dioxide (TiO2), lithium titanium oxide (Li4Ti5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), molybdenum oxide (MoO2), and other oxides can be used.

[0145] In addition, the negative electrode active material is a composite nitride of lithium and transition metals, Li3N-type 3-x M x N (M=Co, Ni, Cu) can be used. For example, Li 2.6 Co 0.4 N3 has a large charge / discharge capacity (900mAh / g, 1890mAh / cm 3 ) and is preferred.

[0146] When a composite nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, and therefore it can be preferably combined with a material that does not contain lithium ions, such as V2O5 or Cr3O8, as the positive electrode active material. Even when a material containing lithium ions is used as the positive electrode active material, the composite nitride of lithium and a transition metal can be used as the negative electrode active material by first desorbing the lithium ions contained in the positive electrode active material.

[0147] In addition, materials that undergo a conversion reaction can also be used as the negative electrode active material. For example, transition metal oxides that do not form alloys with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), can be used as the negative electrode active material. Materials that undergo a conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, and CoS 0.89 It also occurs with sulfides such as NiS and CuS, nitrides such as Zn3N2, Cu3N and Ge3N4, phosphides such as NiP2, FeP2 and CoP3, and fluorides such as FeF3 and BiF3.

[0148] As the conductive additive and binder that can be contained in the negative electrode active material layer, the same materials as the conductive additive and binder that can be contained in the positive electrode active material layer can be used.

[0149] <Negative electrode current collector> The negative electrode current collector may be made of the same material as the positive electrode current collector, but it is preferable that the negative electrode current collector be made of a material that does not alloy with carrier ions such as lithium.

[0150] [Separator] A separator is placed between the positive electrode and the negative electrode. The separator can be made of, for example, cellulose-containing fibers such as paper, nonwoven fabric, glass fiber, ceramics, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, or polyurethane. The separator is preferably processed into a bag shape and placed so as to encase either the positive electrode or the negative electrode.

[0151] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine-based material, a polyamide material, or a mixture of these. Examples of ceramic materials that can be used include aluminum oxide particles and silicon oxide particles. Examples of fluorine-based materials that can be used include PVDF and polytetrafluoroethylene. Examples of polyamide materials that can be used include nylon and aramid (meta-aramid, para-aramid).

[0152] Coating with ceramic materials improves oxidation resistance, suppressing separator degradation during high-voltage charging and discharging and improving the reliability of secondary batteries. Coating with fluorine-based materials also improves adhesion between the separator and electrodes, improving output characteristics. Coating with polyamide materials, especially aramid, improves heat resistance, improving the safety of secondary batteries.

[0153] For example, both sides of a polypropylene film may be coated with a mixed material of aluminum oxide and aramid, or the surface of the polypropylene film that contacts the positive electrode may be coated with a mixed material of aluminum oxide and aramid, and the surface that contacts the negative electrode may be coated with a fluorine-based material.

[0154] When a separator with a multilayer structure is used, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, and therefore the capacity per volume of the secondary battery can be increased.

[0155] [Electrolyte] The electrolytic solution contains a solvent and an electrolyte. The solvent for the electrolytic solution is preferably an aprotic organic solvent, such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, or sultone, or any combination and ratio of two or more of these.

[0156] Furthermore, by using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as the solvent for the electrolyte, it is possible to prevent the electricity storage device from exploding or catching fire even if the internal temperature rises due to an internal short circuit or overcharging of the electricity storage device. Ionic liquids are composed of cations and anions, including organic cations and anions. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.

[0157] Examples of the electrolyte to be dissolved in the solvent include LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, and Li2B 10 Cl 10 , Li2B12 Cl 12 Lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, etc. can be used alone or in any combination and ratio of two or more of these.

[0158] The electrolyte used in the electricity storage device is preferably a highly purified electrolyte with a low content of granular waste or elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities"). Specifically, the weight ratio of impurities to the electrolyte is preferably 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0159] The electrolyte may also contain additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalato)borate (LiBOB), or dinitrile compounds such as succinonitrile and adiponitrile. The concentration of the additive may be, for example, 0.1 wt % to 5 wt % of the total solvent.

[0160] Alternatively, a polymer gel electrolyte may be used in which a polymer is swollen with an electrolytic solution.

[0161] The use of a polymer gel electrolyte improves safety against leakage, etc. It also enables the secondary battery to be made thinner and lighter.

[0162] Examples of polymers that can be gelled include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, and fluorine-based polymer gel. For example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing these can be used. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The polymer formed may also have a porous shape.

[0163] In addition, instead of an electrolyte solution, a solid electrolyte containing inorganic materials such as sulfides or oxides, or a solid electrolyte containing polymeric materials such as polyethylene oxide (PEO) can be used. When a solid electrolyte is used, the installation of a separator or spacer is unnecessary. Furthermore, since the entire battery can be solidified, there is no risk of leakage, dramatically improving safety.

[0164] Therefore, the positive electrode slurry or electrode manufactured by the manufacturing method of one embodiment of the present invention can be applied to an all-solid-state battery. By applying the positive electrode slurry or electrode to an all-solid-state battery, an all-solid-state battery with high safety and excellent characteristics can be obtained.

[0165] (Embodiment 3) In this embodiment mode, examples of a plurality of shapes of secondary batteries each having a positive electrode or a negative electrode manufactured by the manufacturing method described in the previous embodiment will be described.

[0166] [Coin-type secondary battery] An example of a coin-type secondary battery will be described below: Fig. 7A is an external view of a coin-type (single-layer flat) secondary battery, and Fig. 7B is a cross-sectional view thereof.

[0167] In a coin-type secondary battery 300, a positive electrode can 301, which also serves as a positive electrode terminal, and a negative electrode can 302, which also serves as a negative electrode terminal, are insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with the positive electrode current collector. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with the negative electrode current collector.

[0168] It is to be noted that the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 each only need to have an active material layer formed on one side.

[0169] For the positive electrode can 301 and the negative electrode can 302, metals such as nickel, aluminum, titanium, or alloys thereof, or alloys of these with other metals (e.g., stainless steel), which are corrosion-resistant to the electrolyte, can be used. Furthermore, to prevent corrosion by the electrolyte, it is preferable to coat them 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.

[0170] These negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte, and as shown in FIG. 7B, positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are stacked in this order with positive electrode can 301 facing downwards, and positive electrode can 301 and negative electrode can 302 are crimped together via gasket 303 to produce coin-type secondary battery 300.

[0171] By using the manufacturing method described in the above embodiment for the positive electrode 304, the coin-type secondary battery 300 can have a high capacity.

[0172] Here, we will use Figure 7C to explain the current flow during charging of a secondary battery. When a lithium-based secondary battery is considered as a closed circuit, the movement of lithium ions and the flow of current are in the same direction. In lithium-based secondary batteries, the anode (positive electrode) and cathode (negative electrode) are interchanged during charging and discharging, and the oxidation and reduction reactions alternate. Therefore, the electrode with the higher reaction potential is called the positive electrode, and the electrode with the lower reaction potential is called the negative electrode. Therefore, in this specification, whether during charging, discharging, when a reverse pulse current is applied, or when a charging current is applied, the positive electrode will be called the "positive electrode" or "+ electrode," and the negative electrode will be called the "negative electrode" or "- electrode." Using the terms anode (positive electrode) or cathode (negative electrode), which are related to oxidation and reduction reactions, may lead to confusion because they are reversed during charging and discharging. Therefore, the terms anode (positive electrode) and cathode (negative electrode) will not be used in this specification. If the terms anode (positive electrode) or cathode (negative electrode) are used, it should be clearly stated whether they are used during charging or discharging, and whether they correspond to the positive electrode (plus pole) or negative electrode (minus pole).

[0173] A charger is connected to the two terminals shown in Fig. 7C to charge the secondary battery 300. As the charging of the secondary battery 300 progresses, the potential difference between the electrodes increases.

[0174] [Cylindrical secondary battery] An example of a cylindrical secondary battery will be described with reference to Fig. 8A. As shown in Fig. 8A, a cylindrical secondary battery 400 has a positive electrode cap (battery lid) 401 on the top surface, and a battery can (external can) 402 on the side and bottom surfaces. The positive electrode cap 401 and the battery can (external can) 402 are insulated by a gasket (insulating packing) 410.

[0175] Fig. 8B is a diagram showing a schematic cross section of a cylindrical secondary battery. The cylindrical secondary battery shown in Fig. 8B has a positive electrode cap (battery lid) 601 on the top surface and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap and battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0176] A battery element is provided inside a hollow cylindrical battery can 602, in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 sandwiched between them. Although not shown, the battery element is wound around a center pin. One end of the battery can 602 is closed and the other end is open. The battery can 602 can be made of a metal such as nickel, aluminum, or titanium, or an alloy of these metals or an alloy of these metals with other metals (e.g., stainless steel), which are corrosion-resistant to the electrolyte. To prevent corrosion by the electrolyte, the battery can 602 is preferably coated with nickel, aluminum, or the like. Inside the battery can 602, the wound battery element, in which the positive electrode, negative electrode, and separator are wound, is sandwiched between a pair of opposing insulating plates 608 and 609. A nonaqueous electrolyte (not shown) is poured into the battery can 602, in which the battery element is provided. The nonaqueous electrolyte may be the same as that used in coin-type secondary batteries.

[0177] Because the positive and negative electrodes used in cylindrical storage batteries are wound, it is preferable to form active materials on both sides of the current collector. A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be made of a metal material such as aluminum. The positive electrode terminal 603 is resistance-welded to a safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 613 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 is a thermosensitive resistor whose resistance increases as the temperature rises, and the increased resistance limits the amount of current to prevent abnormal heat generation. Barium titanate (BaTiO3) based semiconductor ceramics or the like can be used for the PTC element.

[0178] 8C shows an example of a power storage system 415. The power storage system 415 has a plurality of secondary batteries 400. The positive electrodes of the respective secondary batteries are in contact with and electrically connected to conductors 424 separated by insulators 425. The conductors 424 are electrically connected to a control circuit 420 via wiring 423. The negative electrodes of the respective secondary batteries are electrically connected to the control circuit 420 via wiring 426. The control circuit 420 may be a charge / discharge control circuit that performs charging / discharging or the like, or a protection circuit that prevents overcharging or overdischarging.

[0179] 8D shows an example of a power storage system 415. The power storage system 415 has a plurality of secondary batteries 400, which are sandwiched between a conductive plate 413 and a conductive plate 414. The plurality of secondary batteries 400 are electrically connected to the conductive plate 413 and the conductive plate 414 by wiring 416. The plurality of secondary batteries 400 may be connected in parallel, in series, or in parallel and then further connected in series. By configuring the power storage system 415 to have a plurality of secondary batteries 400, a large amount of power can be extracted.

[0180] A plurality of secondary batteries 400 may be connected in parallel and then further connected in series.

[0181] A temperature control device may be provided between the multiple secondary batteries 400. When the secondary batteries 400 are overheated, they can be cooled by the temperature control device, and when the secondary batteries 400 are too cold, they can be heated by the temperature control device. This makes it difficult for the performance of the power storage system 415 to be affected by the outside air temperature.

[0182] 8D, the power storage system 415 is electrically connected to a control circuit 420 via wiring 421 and wiring 422. The wiring 421 is electrically connected to the positive electrodes of the plurality of secondary batteries 400 via a conductive plate 413, and the wiring 422 is electrically connected to the negative electrodes of the plurality of secondary batteries 400 via a conductive plate 414.

[0183] [Other examples of secondary battery structures] An example of the structure of the secondary battery will be described with reference to FIGS.

[0184] A secondary battery 913 shown in FIG. 9A has 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 contacts the housing 930, and the terminal 951 is not in contact with the housing 930 by using an insulating material or the like. Note that in FIG. 9A, for convenience, the housing 930 is shown separated, but in reality, the wound body 950 is covered by the housing 930, and the terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (e.g., aluminum) or a resin material.

[0185] 9B, the housing 930 shown in Fig. 9A may be formed from a plurality of materials. For example, the secondary battery 913 shown in Fig. 9B has housings 930a and 930b bonded together, and a wound body 950 is provided in the area surrounded by the housings 930a and 930b.

[0186] The housing 930a can be made of an insulating material such as organic resin. In particular, by using a material such as organic resin on the surface on which the antenna is formed, it is possible to prevent the secondary battery 913 from blocking the electric field. Note that if the electric field blocking effect of the housing 930a is small, the antenna may be provided inside the housing 930a. The housing 930b can be made of, for example, a metal material.

[0187] 9C shows the structure of wound body 950. Winding body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. Winding body 950 is a wound body in which negative electrode 931 and positive electrode 932 are stacked on top of each other with separator 933 sandwiched therebetween, and the resulting laminated sheet is wound. Note that multiple stacks of negative electrode 931, positive electrode 932, and separator 933 may be stacked one on top of the other.

[0188] Alternatively, a secondary battery 913 may be provided having a wound body 950a as shown in FIG. 10. The wound body 950a shown in FIG. 10A has a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 has a negative electrode active material layer 931a. The positive electrode 932 has a positive electrode active material layer 932a. The separator 933 has a width greater 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. From the standpoint of safety, it is preferable that the negative electrode active material layer 931a be wider than the positive electrode active material layer 932a. A wound body 950a having such a shape is preferable because of its high safety and productivity.

[0189] 10B, negative electrode 931 is electrically connected to terminal 951. Terminal 951 is electrically connected to terminal 911a. Positive electrode 932 is electrically connected to terminal 952. Terminal 952 is electrically connected to terminal 911b.

[0190] 10C, wound body 950a and the electrolyte are covered by casing 930 to form secondary battery 913. It is preferable to provide casing 930 with a safety valve, an overcurrent protection element, etc. The safety valve is a valve that opens when the inside of casing 930 reaches a predetermined internal pressure to prevent the battery from exploding.

[0191] As shown in Fig. 10B, the secondary battery 913 may have multiple wound bodies 950a. Using multiple wound bodies 950a can result in a secondary battery 913 with a larger charge / discharge capacity. For other elements of the secondary battery 913 shown in Figs. 10A and 10B, the descriptions of the secondary battery 913 shown in Figs. 9A to 9C can be referred to.

[0192] By using the positive electrode described in the above embodiment for the positive electrode 932, the secondary battery 913 can have high charge / discharge capacity and excellent cycle characteristics.

[0193] <Laminated secondary battery> 11A and 11B show examples of external views of a laminated secondary battery, which includes a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0194] FIG. 12A shows the appearance of a positive electrode 503 and a negative electrode 506. The positive electrode 503 has 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. The positive electrode 503 also has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as a tab region). The negative electrode 506 has a negative electrode current collector 504, and a negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. The negative electrode 506 also has a region where the negative electrode current collector 504 is partially exposed, i.e., a tab region. The area or shape of the tab regions of the positive electrode and negative electrode are not limited to the example shown in FIG. 12A.

[0195] <Method for manufacturing laminated secondary batteries> Here, an example of a method for producing the laminated secondary battery whose external view is shown in FIG. 11A will be described with reference to FIGS. 12B and 12C.

[0196] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. FIG. 12B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example is shown in which five pairs of negative electrodes and four pairs of positive electrodes are used. This can also be called a laminate consisting of a negative electrode, a separator, and a positive electrode. Next, the tab regions of the positive electrodes 503 are joined together, and a positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For example, ultrasonic welding or the like may be used for joining. Similarly, the tab regions of the negative electrodes 506 are joined together, and a negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0197] Next, the negative electrode 506 , the separator 507 and the positive electrode 503 are placed on the exterior body 509 .

[0198] Next, as shown in Fig. 12C, the exterior body 509 is folded at the portion indicated by the dashed line. Thereafter, the outer periphery of the exterior body 509 is joined. For example, thermocompression bonding may be used for the joining. At this time, an area (hereinafter referred to as an inlet) that is not joined is provided in a part (or one side) of the exterior body 509 so that an electrolyte can be introduced later.

[0199] Next, an electrolyte solution (not shown) is introduced into the inside of the exterior body 509 through an inlet provided in the exterior body 509. The introduction of the electrolyte solution is preferably carried out under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is joined. In this manner, the laminated secondary battery 500 can be produced.

[0200] By using the positive electrode described in the above embodiment for the positive electrode 503, the secondary battery 500 can have a high charge / discharge capacity and a high density positive electrode.

[0201] [Example of a battery pack] An example of a secondary battery pack according to one embodiment of the present invention, which can be wirelessly charged using an antenna, will be described with reference to FIG.

[0202] FIG. 13A is a diagram showing the appearance of secondary battery pack 531, which has a thin rectangular parallelepiped shape (which can also be called a thick flat plate shape). FIG. 13B is a diagram illustrating the configuration of secondary battery pack 531. Secondary battery pack 531 has circuit board 540 and secondary battery 513. Label 529 is attached to secondary battery 513. Circuit board 540 is fixed with sticker 515. Secondary battery pack 531 also has antenna 517.

[0203] The inside of the secondary battery 513 may have a structure including a wound body or a laminated body.

[0204] 13B, for example, a secondary battery pack 531 has a control circuit 590 on a circuit board 540. The circuit board 540 is electrically connected to a terminal 514. The circuit board 540 is also electrically connected to an antenna 517, one 551 of a positive electrode lead and a negative electrode lead of a secondary battery 513, and the other 552 of a positive electrode lead and a negative electrode lead of the secondary battery 513.

[0205] 13C , the semiconductor device may have a circuit system 590a provided on the circuit board 540 and a circuit system 590b electrically connected to the circuit board 540 via the terminals 514. For example, a portion of the control circuit is provided in the circuit system 590a, and another portion is provided in the circuit system 590b.

[0206] The antenna 517 is not limited to a coil shape, and may be, for example, a wire or plate shape. Also, antennas such as a planar antenna, an aperture antenna, a traveling wave antenna, an EH antenna, a magnetic field antenna, and a dielectric antenna may be used. Alternatively, the antenna 517 may be a flat conductor. This flat conductor can function as one of the conductors for electric field coupling. In other words, the antenna 517 may function as one of the two conductors of a capacitor. This allows power to be exchanged not only by electromagnetic fields and magnetic fields, but also by electric fields.

[0207] The secondary battery pack 531 has a layer 519 between the antenna 517 and the secondary battery 513. The layer 519 has a function of, for example, shielding an electromagnetic field caused by the secondary battery 513. The layer 519 can be made of, for example, a magnetic material.

[0208] This embodiment mode can be freely combined with other embodiment modes.

[0209] (Fourth embodiment) This embodiment is an example different from the cylindrical secondary battery shown in Fig. 8D. Fig. 14C shows an example in which the secondary battery is applied to an electric vehicle (EV).

[0210] The electric vehicle is equipped with first batteries 1301a and 1301b as main driving secondary batteries, and a second battery 1311 that supplies power to an inverter 1312 that starts a motor 1304. The second battery 1311 is also called a cranking battery (starter battery). The second battery 1311 only needs to have high output, and does not need to have a large capacity, and the capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0211] The internal structure of the first battery 1301a may be a wound type as shown in FIG. 9A, 9B, 9C, or 10A, or a stacked type as shown in FIG. 11A, 11B, 12A, 12B, or 12C.

[0212] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more may be connected in parallel. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack having multiple secondary batteries, it is possible to extract large amounts of power. The multiple secondary batteries may be connected in parallel, in series, or in series after being connected in parallel. A plurality of secondary batteries is also called a battery pack.

[0213] In addition, in order to cut off power from a plurality of secondary batteries in a vehicle, a service plug or circuit breaker that can cut off high voltage without using tools is provided in the first battery 1301a.

[0214] The power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V in-vehicle components (such as an electric power steering 1307, a heater 1308, and a defogger 1309) via a DC-DC circuit 1306. When a rear motor 1317 is provided on the rear wheels, the first battery 1301a is also used to rotate the rear motor 1317.

[0215] Furthermore, the second battery 1311 supplies power to 14V in-vehicle components (audio 1313, power windows 1314, lamps 1315, etc.) via the DCDC circuit 1310.

[0216] The first battery 1301a will be described with reference to FIG. 14A.

[0217] FIG. 14A shows an example in which nine prismatic secondary batteries 1300 are used as one battery pack 1415. Furthermore, nine prismatic secondary batteries 1300 are connected in series, with one electrode fixed by fixing portion 1413 made of an insulator and the other electrode fixed by fixing portion 1414 made of an insulator. While this embodiment shows an example in which the batteries are fixed by fixing portions 1413 and 1414, they may also be housed in a battery housing box (also called a casing). Because it is expected that a vehicle will be subjected to external vibrations or shaking (such as from the road surface), it is preferable to fix multiple secondary batteries by fixing portions 1413 and 1414 or a battery housing box. Furthermore, one electrode is electrically connected to control circuit unit 1320 by wiring 1421. Furthermore, the other electrode is electrically connected to control circuit unit 1320 by wiring 1422.

[0218] A memory circuit including a transistor using an oxide semiconductor may be used for the control circuit unit 1320. A charge control circuit or a battery control system having a memory circuit including a transistor using an oxide semiconductor may be referred to as a battery operating system (BTOS) or a battery oxide semiconductor.

[0219] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, a metal oxide such as In-M-Zn oxide (wherein M is one or more elements selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, etc.) can be used as the oxide. In particular, the In-M-Zn oxide that can be used as the oxide is preferably a C-Axis Aligned Crystal Oxide Semiconductor (CAAC-OS) or a Cloud-Aligned Composite Oxide Semiconductor (CAC-OS). Alternatively, an In-Ga oxide or an In-Zn oxide may be used as the oxide. A CAAC-OS is an oxide semiconductor having multiple crystalline regions, each of which has a c-axis aligned in a specific direction. The specific direction may be the thickness direction of the CAAC-OS film, a normal direction to the surface on which the CAAC-OS film is formed, or a normal direction to the surface of the CAAC-OS film. A crystalline region is a region in which the atomic arrangement is periodic. Considering the atomic arrangement as a lattice arrangement, a crystalline region is also a region in which the lattice arrangement is uniform. Furthermore, a CAAC-OS has a region in which multiple crystalline regions are connected in the ab-plane direction, and the region may have distortion. The distortion refers to a point in the region in which multiple crystalline regions are connected, where the lattice arrangement changes direction between a region with a uniform lattice arrangement and another region with a different uniform lattice arrangement. In other words, a CAAC-OS is an oxide semiconductor that is c-axis oriented but not clearly oriented in the ab-plane direction. A CAC-OS is, for example, a material in which elements constituting a metal oxide are unevenly distributed in a size range of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or a similar size range. Hereinafter, a metal oxide in which one or more metal elements are unevenly distributed and the regions containing the metal elements are mixed in a size range of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or a similar size range, is also referred to as a mosaic or patch structure.

[0220] Furthermore, CAC-OS has a mosaic structure in which the material is separated into first and second regions, and the first regions are distributed throughout the film (hereinafter also referred to as a cloud structure). That is, CAC-OS is a composite metal oxide having a structure in which the first and second regions are mixed.

[0221] Here, the atomic ratios of In, Ga, and Zn to the metal elements constituting the CAC-OS in the In-Ga-Zn oxide are denoted as [In], [Ga], and [Zn], respectively. For example, in the CAC-OS in the In-Ga-Zn oxide, the first region is a region where [In] is larger than [In] in the composition of the CAC-OS film. The second region is a region where [Ga] is larger than [Ga] in the composition of the CAC-OS film. Alternatively, for example, the first region is a region where [In] is larger than [In] in the second region and [Ga] is smaller than [Ga] in the second region. The second region is a region where [Ga] is larger than [Ga] in the first region and [In] is smaller than [In] in the first region.

[0222] Specifically, the first region is a region whose main component is indium oxide, indium zinc oxide, or the like. The second region is a region whose main component is gallium oxide, gallium zinc oxide, or the like. In other words, the first region can be rephrased as a region whose main component is In. The second region can be rephrased as a region whose main component is Ga.

[0223] It should be noted that there are cases where a clear boundary between the first region and the second region cannot be observed.

[0224] For example, in the case of CAC-OS in In-Ga-Zn oxide, EDX mapping obtained using EDX (Energy Dispersive X-ray spectroscopy) confirms that the CAC-OS has a structure in which a region mainly composed of In (first region) and a region mainly composed of Ga (second region) are unevenly distributed and mixed.

[0225] When CAC-OS is used in a transistor, the conductivity due to the first region and the insulating property due to the second region act in a complementary manner, thereby providing the CAC-OS with a switching function (the ability to turn on and off). In other words, CAC-OS has a conductive function in part of the material and an insulating function in part of the material, and the material as a whole functions as a semiconductor. By separating the conductive function from the insulating function, both functions can be maximized. Therefore, by using CAC-OS in a transistor, a high on-current (I on ), high field-effect mobility (μ), and good switching behavior can be achieved.

[0226] Oxide semiconductors have a variety of structures, each with different characteristics. The oxide semiconductor of one embodiment of the present invention may include two or more of an amorphous oxide semiconductor, a polycrystalline oxide semiconductor, an a-like OS, a CAC-OS, an nc-OS, and a CAAC-OS.

[0227] It can also be said that the control circuit 1320 detects the terminal voltage of the secondary battery and manages the charge / discharge state of the secondary battery. For example, to prevent overcharging, it can turn off both the output transistor and the cutoff switch of the charging circuit almost simultaneously.

[0228] FIG. 14B shows an example of a block diagram of the battery pack 1415 shown in FIG. 14A.

[0229] The control circuit unit 1320 includes a switch unit 1324 including at least a switch for preventing overcharging and a switch for preventing overdischarging, a control circuit 1322 for controlling the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 sets upper and lower voltage limits for the secondary battery used and limits the upper limit of the current from the outside or the upper limit of the output current to the outside. The range between the lower limit and the upper limit of the secondary battery's voltage is within the recommended voltage range. If the voltage falls outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit unit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent overcharging or overdischarging. For example, if the control circuit 1322 detects a voltage that could cause overcharging, it turns off the switch unit 1324 to cut off the current. A PTC element may also be provided in the charge / discharge path to provide a function for cutting off the current in response to a rise in temperature. The control circuit section 1320 also has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0230] The switch unit 1324 can be configured by combining n-channel transistors or p-channel transistors. The switch unit 1324 is not limited to a switch having a Si transistor using single crystal silicon. For example, the switch unit 1324 may be formed of a power transistor having Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), or GaOx (gallium oxide; x is a real number greater than 0). Furthermore, memory elements using OS transistors can be freely arranged by stacking them on circuits using Si transistors, facilitating integration. Furthermore, OS transistors can be fabricated using the same manufacturing equipment as Si transistors, allowing for low-cost fabrication. Specifically, a control circuit unit 1320 using OS transistors can be stacked on the switch unit 1324 and integrated into a single chip. The control circuit unit 1320 occupies a smaller volume, enabling miniaturization.

[0231] The first batteries 1301a and 1301b mainly supply power to 42V (high voltage) in-vehicle devices, and the second battery 1311 supplies power to 14V (low voltage) in-vehicle devices. A lead-acid battery is often used as the second battery 1311 because of its cost advantage. If the second battery 1311 that starts the inverter becomes inoperable, even if the first batteries 1301a and 1301b have remaining capacity, the motor cannot be started. To prevent this, if the second battery 1311 is a lead-acid battery, power is supplied from the first battery to the second battery, and the second battery is charged to always maintain a fully charged state.

[0232] In this embodiment, an example is shown in which lithium ion secondary batteries are used as both the first battery 1301a and the second battery 1311. The second battery 1311 may be a lead storage battery, an all-solid-state battery, or an electric double layer capacitor.

[0233] Furthermore, regenerated energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305, and is then charged into the second battery 1311 via the control circuit unit 1321 from the motor controller 1303 or the battery controller 1302. Alternatively, the first battery 1301a is charged from the battery controller 1302 via the control circuit unit 1320. Alternatively, the first battery 1301b is charged from the battery controller 1302 via the control circuit unit 1320. In order to efficiently charge the regenerated energy, it is desirable that the first batteries 1301a and 1301b be capable of being rapidly charged.

[0234] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set charging conditions according to the charging characteristics of the secondary battery used, and can perform rapid charging.

[0235] Although not shown, when an external charger is connected, the charger's outlet or the charger's connection cable is electrically connected to the battery controller 1302. The power supplied from the external charger is charged to the first batteries 1301a, 1301b via the battery controller 1302. Some chargers are provided with a control circuit, and although the function of the battery controller 1302 may not be used, it is preferable to charge the first batteries 1301a, 1301b via a control circuit unit 1320 to prevent overcharging. In some cases, the connection cable or the charger's connection cable is provided with a control circuit. The control circuit unit 1320 is also called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) provided in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU includes a microcomputer. The ECU uses a CPU or a GPU.

[0236] External chargers installed at charging stations and the like are available with 100V outlets, 200V outlets, or three-phase 200V and 50kW. Charging is also possible by receiving power from external charging equipment using a wireless power supply system, etc.

[0237] When rapid charging is performed, a secondary battery that can withstand high voltage charging is desired in order to charge in a short time.

[0238] The secondary battery of this embodiment uses both graphene and acetylene black as conductive additives and optimizes the blending ratio, thereby enabling rapid charging. This allows efficient regenerative charging and shortens the charging time.

[0239] In particular, the secondary battery of the present embodiment described above uses both graphene and acetylene black as conductive additives, and by optimizing the compounding ratio, rapid charging at low temperatures (-40°C or higher and 10°C or lower) is possible.

[0240] Furthermore, the secondary battery of the present embodiment described above uses both graphene and acetylene black as conductive additives and has a high-density positive electrode by optimizing the blending ratio. Furthermore, a secondary battery can be realized that can suppress capacity reduction and maintain high capacity even when the electrode layer is thickened and the loading amount is increased. This is particularly effective for secondary batteries used in vehicles, and can provide a vehicle with a long cruising distance, specifically, a cruising distance of 500 km or more per charge, without increasing the ratio of the weight of the secondary battery to the total weight of the vehicle.

[0241] In particular, the secondary battery of the present embodiment described above uses both graphene and acetylene black as conductive additives, and by optimizing the compounding ratio, the operating voltage of the secondary battery can be increased, and the usable capacity increases as the charging voltage increases.

[0242] Next, an example in which a secondary battery according to one embodiment of the present invention is mounted on a vehicle, typically a transportation vehicle, will be described.

[0243] Furthermore, when the secondary battery shown in any one of FIGS. 8D, 10C, and 14A is installed in a vehicle, next-generation clean energy automobiles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs) can be realized. Furthermore, the secondary battery can also be installed in transportation vehicles such as agricultural machinery, mopeds including electrically assisted bicycles, motorcycles, electric wheelchairs, electric carts, small or large ships, submarines, aircraft such as fixed-wing aircraft and rotary-wing aircraft, rockets, artificial satellites, space probes or planetary probes, and spacecraft. 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 weight reduction and can be suitably used in transportation vehicles.

[0244] 15A to 15D illustrate examples of transportation vehicles using one embodiment of the present invention. An automobile 2001 shown in FIG. 15A is an electric automobile that uses an electric motor as a power source for traveling. Alternatively, it is a hybrid automobile that can appropriately select and use an electric motor or an engine as a power source for traveling. When a secondary battery is installed in a vehicle, an example of the secondary battery described in Embodiment 3 is installed in one or more locations. The automobile 2001 shown in FIG. 15A includes a battery pack 2200, which includes a secondary battery module to which multiple secondary batteries are connected. It is preferable that the automobile further includes a charge control device electrically connected to the secondary battery module.

[0245] Furthermore, automobile 2001 can charge its secondary battery by receiving power supply from an external charging facility using a plug-in system, a contactless power supply system, or the like. Charging can be performed using a predetermined charging method or connector standard, such as CHAdeMO (registered trademark) or Combo, as appropriate. The secondary battery may be charged at a charging station provided in a commercial facility or from a household power source. For example, plug-in technology can be used to charge the secondary battery mounted on automobile 2001 using an external power supply. Charging can be performed by converting AC power to DC power via a conversion device such as an AC-DC converter.

[0246] Although not shown, a power receiving device can be mounted on a vehicle and power can be supplied contactlessly from a ground-based power transmitting device for charging. In the case of this contactless power supply method, by incorporating a power transmitting device into the road or an exterior wall, charging can be performed not only while the vehicle is stopped but also while the vehicle is moving. This contactless power supply method can also be used to transmit and receive power between two vehicles. Furthermore, a solar cell can be installed on the exterior of the vehicle, and the secondary battery can be charged while the vehicle is stopped or moving. For such contactless power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0247] 15B shows a large transport vehicle 2002 having an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 is, for example, a four-cell unit of secondary batteries of 3.5V to 4.7V, with 48 cells connected in series for a maximum voltage of 170V. Apart from the number of secondary batteries constituting the secondary battery module of the battery pack 2201, the transport vehicle 2002 has the same functions as those shown in FIG. 15A, and therefore a description thereof will be omitted.

[0248] FIG. 15C shows, as an example, a large transport vehicle 2003 having an electrically controlled motor. The secondary battery module of the transport vehicle 2003 has, for example, a maximum voltage of 600 V, with more than 100 secondary batteries connected in series, with a voltage of 3.5 V to 4.7 V. Therefore, secondary batteries with minimal variation in characteristics are required. By optimizing the mixture ratio of carbon black and graphene, the uniformity of the electrodes can be improved, and secondary batteries with stable battery characteristics can be manufactured. From the viewpoint of yield, this allows for low-cost mass production. Furthermore, except for the number of secondary batteries constituting the secondary battery module of the battery pack 2202, the same functions as those shown in FIG. 15A are provided, and therefore a description thereof will be omitted.

[0249] Fig. 15D shows, as an example, an aircraft 2004 having an engine that burns fuel. Since the aircraft 2004 shown in Fig. 15D has wheels for takeoff and landing, it can also be said to be part of a transportation vehicle, and has a battery pack 2203 that includes a secondary battery module formed by connecting multiple secondary batteries and includes the secondary battery module and a charge control device.

[0250] The secondary battery module of the aircraft 2004 has, for example, eight 4V secondary batteries connected in series to produce a maximum voltage of 32V. Other than the number of secondary batteries constituting the secondary battery module of the battery pack 2203, it has the same functions as those in Fig. 15A, and therefore a description thereof will be omitted.

[0251] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0252] (Embodiment 5) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted in a building will be described with reference to FIGS. 16A and 16B.

[0253] 16A includes a power storage device 2612 including a secondary battery of one embodiment of the present invention, and a solar panel 2610. The power storage device 2612 is electrically connected to the solar panel 2610 through a wiring 2611 or the like. The power storage device 2612 may be electrically connected to a ground-mounted charging device 2604. The power storage device 2612 can be charged with power obtained by the solar panel 2610. The power stored in the power storage device 2612 can be charged to a secondary battery included in a vehicle 2603 via the charging device 2604. The power storage device 2612 is preferably installed in an underfloor space. By installing the power storage device 2612 in the underfloor space, the space above the floor can be effectively utilized. Alternatively, the power storage device 2612 may be installed on the floor.

[0254] The power stored in the 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 power storage device 2612 of one embodiment of the present invention can be used as an uninterruptible power supply, enabling the use of electronic devices.

[0255] 16B illustrates an example of a power storage device 700 according to one embodiment of the present invention. As illustrated in FIG. 16B, a power storage device 791 according to one embodiment of the present invention is installed in an underfloor space 796 of a building 799.

[0256] A control device 790 is installed in the power storage device 791, and the control device 790 is electrically connected to a distribution board 703, a power storage controller 705 (also called a control device), a display 706, and a router 709 by wiring.

[0257] Electric power is sent from commercial power source 701 to distribution board 703 via service line attachment section 710. Electric power is also sent to distribution board 703 from power storage device 791 and commercial power source 701, and distribution board 703 supplies the sent electric power to general load 707 and power storage load 708 via an outlet (not shown).

[0258] The general load 707 is, for example, an electrical appliance such as a television or a personal computer, and the power storage load 708 is, for example, an electrical appliance such as a microwave oven, a refrigerator, or an air conditioner.

[0259] The power storage controller 705 has a measurement unit 711, a prediction unit 712, and a planning unit 713. The measurement unit 711 has a function of measuring the amount of power consumed by the general load 707 and the power storage load 708 during one day (for example, from midnight to midnight). The measurement unit 711 may also have a function of measuring the amount of power of the power storage device 791 and the amount of power supplied from the commercial power source 701. The prediction unit 712 has a function of predicting the amount of power demand to be consumed by the general load 707 and the power storage load 708 during the next day, based on the amount of power consumed by the general load 707 and the power storage load 708 during the previous day. The planning unit 713 has a function of creating a plan for charging and discharging the power storage device 791, based on the amount of power demand predicted by the prediction unit 712.

[0260] The amount of power consumed by the general load 707 and the power storage load 708 measured by the measurement unit 711 can be confirmed on the display 706. It can also be confirmed on an electrical device such as a television or a personal computer via the router 709. It can also be confirmed on a mobile electronic device such as a smartphone or a tablet via the router 709. The amount of power demand for each time period (or each hour) predicted by the prediction unit 712 can also be confirmed on the display 706, the electrical device, or the mobile electronic device.

[0261] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0262] (Sixth embodiment) In this embodiment, an example in which a power storage device according to one embodiment of the present invention is mounted on a motorcycle or a bicycle will be described.

[0263] 17A is an example of an electric bicycle using the power storage device of one embodiment of the present invention. The power storage device of one embodiment of the present invention can be applied to an electric bicycle 8700 shown in FIG. 17A. The power storage device of one embodiment of the present invention includes, for example, a plurality of storage batteries and a protection circuit.

[0264] The electric bicycle 8700 includes a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists a rider. The power storage device 8702 is portable and is shown in a state removed from the bicycle in FIG. 17B . The power storage device 8702 includes a plurality of built-in storage batteries 8701, which are included in the power storage device of one embodiment of the present invention, and the remaining battery charge and the like can be displayed on a display unit 8703. The power storage device 8702 also includes a control circuit 8704 of one embodiment of the present invention. The control circuit 8704 is electrically connected to the positive and negative electrodes of the storage batteries 8701.

[0265] 17C is an example of a two-wheeled vehicle including a power storage device of one embodiment of the present invention. A scooter 8600 shown in FIG. 17C includes a power storage device 8602, a side mirror 8601, and a turn signal light 8603. The power storage device 8602 can supply electricity to the turn signal light 8603.

[0266] 17C, the power storage device 8602 can be stored in the under-seat storage 8604. The power storage device 8602 can be stored in the under-seat storage 8604 even if the under-seat storage 8604 is small.

[0267] (Embodiment 7) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted in an electronic device will be described. Examples of electronic devices in which a secondary battery is mounted include television sets (also referred to as televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also referred to as mobile phones or mobile phone devices), portable game consoles, personal digital assistants, sound players, and large game consoles such as pachinko machines. Examples of personal digital assistants include notebook personal computers, tablet terminals, and mobile phones.

[0268] 18A shows an example of a mobile phone. Mobile phone 2100 includes a display unit 2102 built into a housing 2101, as well as operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. Mobile phone 2100 also includes a secondary battery 2107.

[0269] The mobile phone 2100 can execute various applications such as mobile phone calls, e-mail, document browsing and creation, music playback, internet communication, and computer games.

[0270] The operation button 2103 can be provided with various functions, such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, power saving mode activation / deactivation, etc. For example, the functions of the operation button 2103 can be freely set by an operating system built into the mobile phone 2100.

[0271] The mobile phone 2100 is also capable of performing standardized short-range wireless communication, and can also make hands-free calls by communicating with a wirelessly enabled headset, for example.

[0272] The mobile phone 2100 also has an external connection port 2104, which allows direct data exchange with other information terminals via a connector. Charging can also be performed via the external connection port 2104. Charging may also be performed by wireless power supply without using the external connection port 2104.

[0273] The mobile phone 2100 preferably has a sensor, such as a fingerprint sensor, a pulse sensor, a body temperature sensor, or other human body sensor, a touch sensor, a pressure sensor, or an acceleration sensor.

[0274] FIG. 18B shows an unmanned aerial vehicle 2300 having multiple rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 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 controlled via the antenna. The secondary battery according to one embodiment of the present invention is highly safe and can be used safely for a long period of time, making it suitable as a secondary battery to be installed in the unmanned aerial vehicle 2300.

[0275] Fig. 18C shows an example of a robot. A robot 6400 shown in Fig. 18C 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 movement mechanism 6408, a computing device, etc.

[0276] The microphone 6402 has a function of detecting the user's voice, environmental sounds, etc. The speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.

[0277] The display unit 6405 has a function of displaying various information. The robot 6400 can display information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a detachable information terminal, which can be installed in a fixed position on the robot 6400 to enable charging and data transfer.

[0278] The upper camera 6403 and the lower camera 6406 have the function of capturing images of the surroundings of the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0279] The robot 6400 includes a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or an electronic component in an internal region thereof. By using the secondary battery according to one embodiment of the present invention in the robot 6400, the robot 6400 can be a highly reliable electronic device with a long operating time.

[0280] 18D shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 arranged on the top surface of a housing 6301, a plurality of cameras 6303 arranged on the side surface, a brush 6304, an operation button 6305, a secondary battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust from a suction port arranged on the bottom surface.

[0281] For example, the cleaning robot 6300 can analyze an image captured by the camera 6303 to determine whether or not there is an obstacle such as a wall, furniture, or a step. Furthermore, when an object that may become entangled in the brush 6304, such as a wire, is detected through image analysis, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 includes a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or an electronic component in its internal area. By using the secondary battery 6306 according to one embodiment of the present invention in the cleaning robot 6300, the cleaning robot 6300 can be a highly reliable electronic device with a long operating time.

[0282] Figure 19A shows an example of a wearable device. The wearable device uses a secondary battery as a power source. Furthermore, to improve water resistance for indoor or outdoor use, there is a demand for wearable devices that can be charged wirelessly as well as via wired charging, with the connector exposed.

[0283] For example, a secondary battery according to one embodiment of the present invention can be mounted on an eyeglasses-type device 4000 as shown in FIG. 19A. The eyeglasses-type device 4000 includes a frame 4000a and a display unit 4000b. Mounting a secondary battery on temples of the curved frame 4000a makes it possible to provide an eyeglasses-type device 4000 that is lightweight, has a good weight balance, and can be used for a long time. The inclusion of a secondary battery according to one embodiment of the present invention makes it possible to realize a configuration that can accommodate space saving associated with a smaller housing.

[0284] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a headset device 4001. The headset device 4001 includes at least a microphone unit 4001a, a flexible pipe 4001b, and an earphone unit 4001c. The secondary battery can be provided in the flexible pipe 4001b or the earphone unit 4001c. By providing the secondary battery according to one embodiment of the present invention, a configuration that can accommodate space saving due to a miniaturized housing can be realized.

[0285] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a device 4002 that can be directly attached to the body. A secondary battery 4002b can be provided in a thin housing 4002a of the device 4002. By providing the secondary battery according to one embodiment of the present invention, a space-saving configuration can be realized that accompanies a miniaturized housing.

[0286] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a device 4003 that can be attached to clothing. A secondary battery 4003b can be provided in a thin housing 4003a of the device 4003. By providing the secondary battery according to one embodiment of the present invention, high density and high capacity can be achieved, and a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0287] Furthermore, the secondary battery of one embodiment of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 has a belt portion 4006a and a wireless power receiving portion 4006b, and the secondary battery can be mounted in an internal region of the belt portion 4006a. By including the secondary battery of one embodiment of the present invention, high density and high capacity can be achieved, and a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0288] Furthermore, the secondary battery of one embodiment of the present invention can be mounted on the wristwatch device 4005. The wristwatch device 4005 has a display portion 4005a and a belt portion 4005b, and the secondary battery can be provided on the display portion 4005a or the belt portion 4005b. By providing the secondary battery of one embodiment of the present invention, high density and high capacity can be achieved, and a configuration that can accommodate space saving due to miniaturization of the housing can be realized.

[0289] The display unit 4005a can display not only the time but also various other information such as incoming emails or phone calls.

[0290] Furthermore, since the wristwatch device 4005 is a wearable device that is worn directly on the wrist, it may be equipped with sensors that measure the user's pulse, blood pressure, etc. Data on the user's exercise volume and health can be accumulated to manage the user's health.

[0291] FIG. 19B shows a perspective view of the wristwatch type device 4005 removed from the wrist.

[0292] 19C shows a side view of the display portion 4005a. FIG. 19C shows a state in which a secondary battery 913 is built in the internal region. The secondary battery 913 is the secondary battery described in Embodiment 3. The secondary battery 913 is provided at a position overlapping with the display portion 4005a, and can have high density and high capacity, and is small and lightweight.

[0293] This embodiment mode can be implemented in appropriate combination with other embodiment modes. [Example]

[0294] In this example, a positive electrode using both graphene and acetylene black as a conductive additive was produced, and a cross-sectional SEM photograph was taken.

[0295] First, the active material, acetylene black, graphene, PVDF, and NMP are prepared and weighed out to the desired amounts.

[0296] In this example, the active material is a lithium composite oxide having a composition of Ni, Co, and Mn in a ratio of 8:1:1.

[0297] Sample 1 is an electrode in which the weight ratio of active material: graphene: acetylene black: PVDF is 95:0.6:2.4:2.

[0298] Sample 2 is an electrode in which the weight ratio of active material: graphene: acetylene black: PVDF is 95:0.9:2.1:2.

[0299] Sample 3 is an electrode in which the weight ratio of active material, graphene, acetylene black, and PVDF is 95:1.5:1.5:2. Sample 3 is one of the comparative examples, as the graphene and acetylene black are the same weight, making the ratio 1:1.

[0300] As Comparative Example 1, an electrode was prepared in which the weight ratio of active material: acetylene black: PVDF was 95:3:2.

[0301] As Comparative Example 2, an electrode was prepared in which the weight ratio of active material:graphene:PVDF was 95:3:2.

[0302] The method for producing each electrode is to prepare electrode slurry according to the flow chart in Figure 4, apply the electrode slurry to a 20 μm thick current collector (aluminum), and dry it.

[0303] When kneading, the mixture is mixed using a THINKY MIXER (product name: ARE-310, manufactured by Thinky Corporation). The kneader is not limited to the THINKY MIXER.

[0304] Next, pressing was performed, and then punching was performed to produce a positive electrode. The pressing conditions were varied in eight different conditions, and the range of the pressing linear pressure was 84 kN / m or more and 1467 kN / m or less.

[0305] Figure 20A shows a cross-sectional SEM photograph of Sample 1. Relatively few aggregates of acetylene black and graphene are observed. The loading amount of Sample 1 was 20.35 mg / cm. 2 Furthermore, when the press linear pressure was set to 1467 kN / m, the thickness of the electrode layer combined with the current collector was 76.5 μm, and the density was 3.79 g / cc. Furthermore, when the press linear pressure was set to 700 kN / m or more, the density could be increased to above 3.5 g / cc. The press linear pressure (also simply called linear pressure) is an index showing the molding pressure per unit length in the width direction of the roll used for pressing.

[0306] Figure 20B is a cross-sectional SEM photograph of Sample 2. More aggregates of acetylene black and graphene are observed than in Figure 20A. The loading amount of Sample 2 was 20.07 mg / cm. 2 is.

[0307] Figure 20C shows a cross-sectional SEM image of Sample 3. Many aggregates can be seen in Figure 20C. The loading amount of Sample 3 was 19.82 mg / cm. 2 is.

[0308] 21A is a cross-sectional SEM photograph of Comparative Example 1. In FIG. 21A, a relatively large number of aggregates of acetylene black can be observed. The loading amount of Comparative Example 1 was 18.48 mg / cm. 2 is.

[0309] 21B is a cross-sectional SEM photograph of Comparative Example 2. In FIG. 21B, a relatively large number of graphene aggregates can be observed. The loading amount of Comparative Example 2 was 18.46 mg / cm. 2 is.

[0310] These results indicate that Samples 1 and 2, which use both graphene and acetylene black, have fewer aggregates than the others, and that high-density electrodes can be fabricated. Furthermore, a secondary battery can be realized that can suppress capacity loss and maintain high capacity even when the electrode layer is thickened and the loading is increased. This is particularly effective for secondary batteries used in vehicles. [Explanation of symbols]

[0311] 10: aggregation portion, 11: void, 101: mixture, 102: mixture, 103: mixture, 104: mixture, 114: memory element, 300: secondary battery, 301: positive electrode can, 302: negative electrode can, 303: gasket, 304: positive electrode, 305: positive electrode current collector, 306: positive electrode active material layer, 307: negative electrode, 308: negative electrode current collector, 309: negative electrode active material layer, 310: separator, 400: secondary battery, 401: positive electrode cap, 413: conductive plate, 414: conductive plate, 415: power storage system, 416: wiring, 420: control circuit, 421: wiring, 422: wiring, 423: wiring, 424: conductor, 42 5: insulator, 426: wiring, 500: secondary battery, 501: positive electrode current collector, 502: positive electrode active material layer, 503: positive electrode, 504: negative electrode current collector, 505: negative electrode active material layer, 506: negative electrode, 507: separator, 509: exterior body, 510: positive electrode lead electrode, 511: negative electrode lead electrode, 513: secondary battery, 514: terminal, 515: seal, 517: antenna, 519: layer, 529: label, 531: secondary battery pack, 540: circuit board, 551: one of the positive electrode lead and the negative electrode lead, 552: the other of the positive electrode lead and the negative electrode lead, 590: control circuit, 590a: circuit system, 590b: circuit system, 601: positive electrode cap, 602: battery can, 603: positive electrode terminal, 604: positive electrode, 605: separator, 606: negative electrode, 607: negative electrode terminal, 608: insulating plate, 609: insulating plate, 611: PTC element, 613: safety valve mechanism, 700: power storage device, 701: commercial power source, 703: distribution board, 705: power storage controller, 706: display, 707: general load, 708: power storage system load, 709: router, 710: service line attachment section, 711: measurement section, 712: prediction section, 713: planning section, 790: control device, 791: power storage device, 796: underfloor space section, 79 9: building, 911a: terminal, 911b: terminal, 913: secondary battery, 930: housing, 930a: housing, 930b: housing, 931: negative electrode, 931a: negative electrode active material layer, 932: positive electrode, 932a: positive electrode active material layer, 933: separator, 950: wound body, 950a: wound body, 951: terminal, 952: terminal, 1300: prismatic secondary battery, 1301a: battery, 1301b: battery, 1302: battery controller, 1303: motor controller, 1304: motor, 1305: gear, 1306: DCDC circuit, 1307: electric power steering, 1308: heater,1309: defogger, 1310: DCDC circuit, 1311: battery, 1312: inverter, 1313: audio, 1314: power window, 1315: lamps, 1316: tire, 1317: rear motor, 1320: control circuit section, 1321: control circuit section, 1322: control circuit, 1324: switch section, 1325: external terminal, 1326: external terminal, 1413: fixing section, 1414: fixing section, 1415: battery pack, 1421: wiring, 1422: wiring, 2001: automobile, 2002: transport vehicle, 2003: transport vehicle, 2004: aircraft , 2100: mobile phone, 2101: housing, 2102: display unit, 2103: operation button, 2104: external connection port, 2105: speaker, 2106: microphone, 2107: secondary battery, 2200: battery pack, 2201: battery pack, 2202: battery pack, 2203: battery pack, 2300: unmanned aerial vehicle, 2301: secondary battery, 2302: rotor, 2303: camera, 2603: vehicle, 2604: charging device, 2610: solar panel, 2611: wiring, 2612: power storage device, 4000: eyeglass-type device, 4000a: frame, 4000 b: display unit, 4001: headset type device, 4001a: microphone unit, 4001b: flexible pipe, 4001c: earphone unit, 4002: device, 4002a: housing, 4002b: secondary battery, 4003: device, 4003a: housing, 4003b: secondary battery, 4005: watch type device, 4005a: display unit, 4005b: belt unit, 4006: belt type device, 4006a: belt unit, 4006b: wireless power supply receiving unit, 6300: cleaning robot, 6301: housing, 6302: display unit, 6303: camera, 6304: Brush, 6305: operation button, 6306: secondary battery, 6310: dust, 6400: robot, 6401: illuminance sensor, 6402: microphone, 6403: upper camera, 6404: speaker, 6405: display unit, 6406: lower camera, 6407: obstacle sensor, 6408: moving mechanism, 6409: secondary battery, 8600: scooter, 8601: side mirror, 8602: power storage device, 8603: turn signal light, 8604: under-seat storage, 8700: electric bicycle, 8701: storage battery, 8702: power storage device, 8703: display unit, 8704: control circuit,

Claims

[Claim 1] a first step of mixing graphene, carbon black, and a binder to obtain a first mixture; a second step of mixing a positive electrode active material with the first mixture to obtain a second mixture; a third step of mixing a dispersion medium with the second mixture to obtain an electrode slurry; a fourth step of applying the electrode slurry to a positive electrode current collector; a fifth step of drying the electrode slurry to prepare a positive electrode; a sixth step of stacking the positive electrode and the negative electrode to prepare a secondary battery; In the first mixing step, a weight of the carbon black to be mixed is 1.5 to 20 times a weight of the graphene.

Images