Method for fabricating electrodes

Abstract

One aspect of the present invention addresses the problem of achieving a manufacturing method that can achieve a high capacity density of a secondary battery. Another aspect of the present invention also addresses the problem of providing a method for manufacturing a secondary battery with high safety or high reliability. Provided is a method for manufacturing an electrode (positive electrode, negative electrode) for a secondary battery, the method comprising a vibration treatment step for applying vibration to the electrode, and a pressing step for pressing the electrode and compressing an active material layer of the electrode, wherein the vibration treatment step is performed before the pressing step.

Description

[Technical Field]

[0001] This relates to secondary batteries and methods for manufacturing them; methods and apparatus for manufacturing electrodes; or to portable information terminals, vehicles, etc., that have secondary batteries.

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

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

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

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

[0006] Lithium-ion rechargeable batteries use lithium cobalt oxide (LiCoO2) and lithium nickel-cobalt-manganate (LiNi 1-x-y Co x Mn y It consists of a positive electrode containing a positive electrode active material such as O2 or lithium iron phosphate (LiFePO4), a negative electrode containing a negative electrode active material such as a carbon material like graphite that can intercalate and deintercalate lithium, and an electrolyte containing an organic solvent such as ethylene carbonate (EC) or diethyl carbonate (DEC).

[0007] Furthermore, lithium-ion secondary batteries are required to have high capacity density, high performance, and safety in various operating environments.

[0008] Patent Document 1 discloses a method for manufacturing electrodes that can increase the capacity density of secondary batteries. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] WO2020 / 128699 pamphlet [Overview of the project] [Problems that the invention aims to solve]

[0010] The objective is to realize a manufacturing method that enables high capacity density of secondary batteries. Furthermore, another objective is to provide a manufacturing method for secondary batteries that is safe and reliable.

[0011] Electrodes (positive and negative electrodes) for lithium-ion secondary batteries are manufactured by coating a slurry containing particulate active material onto a metal foil called a current collector and drying it. Electrodes manufactured in this way have an active material layer on the current collector. The active material layer contains active material and voids, and minimizing the voids is necessary to increase the capacity density of secondary batteries. By using electrodes with fewer voids, a larger battery capacity can be obtained even with the same volume of secondary battery, improving the capacity density per unit volume. Electrodes with an active material layer with fewer voids are sometimes called high-density electrodes, densified electrodes, or electrodes with high film density.

[0012] To produce high-density electrodes, a process of compressing the active material layer using a roll press or similar method is often employed. Conventional methods involve applying a constant load in one direction to the electrode containing the active material layer, making it difficult to obtain sufficiently high-density electrodes. Furthermore, even when sufficiently high-density electrodes were obtained, it was unavoidable that defects such as cracks and slips would occur in the active material. Defects in the active material can lead to the leaching of transition metals from the active material during high-voltage charging, decomposition of the electrolyte, and a decrease in the stability of the active material at high temperatures, thus posing a high risk of problems in terms of safety and reliability.

[0013] Furthermore, the description of these problems does not preclude the existence of other problems. Moreover, one aspect of the present invention does not need to solve all of these problems. It is possible to extract other problems from the description in the specification, drawings, and claims. [Means for solving the problem]

[0014] One of the inventions disclosed herein is a pressing method for use on either a positive electrode or a negative electrode, or both, comprising a mechanism or pre-process for applying vibrations such as ultrasonic waves, which can reduce defects occurring in the active material at a sufficiently high-density electrode.

[0015] Furthermore, one of the inventions disclosed herein is a method for manufacturing an electrode to be used as either a positive electrode or a negative electrode, or both, the method for manufacturing an electrode using a pressing method having a mechanism or a pre-process for applying vibrations such as ultrasound, which can reduce defects occurring in the active material in a sufficiently high-density electrode.

[0016] Furthermore, one of the inventions disclosed herein is a high-density electrode with few defects in the active material, a high-density electrode secondary battery with few defects in the active material, and a method for manufacturing the same. A high-density electrode with few defects in the active material makes it possible to realize a superior secondary battery that satisfies high capacity density, high performance, and safety in various operating environments.

[0017] One aspect of the present invention is a method for manufacturing electrodes for a secondary battery, comprising a vibration treatment step of applying vibration to the electrodes and a pressing step of applying pressure to the electrodes to compress the active material layer of the electrodes, wherein the vibration treatment step is performed before the pressing step.

[0018] Furthermore, one aspect of the present invention is a method for manufacturing electrodes for a secondary battery, comprising a vibration treatment step of applying a first vibration to the electrode, and a pressing step of applying pressure to the electrode to compress the active material layer of the electrode, wherein a second vibration is applied to the electrode simultaneously with the pressurization, and the vibration treatment step is performed before the pressing step.

[0019] Furthermore, one aspect of the present invention is a method for manufacturing electrodes for a secondary battery, comprising a vibration treatment step of applying vibration to the electrodes to adjust the temperature, and a pressing step of applying pressure to the electrodes to compress the active material layer of the electrodes, wherein the vibration treatment step is performed before the pressing step.

[0020] Furthermore, one aspect of the present invention is a method for manufacturing electrodes for a secondary battery, comprising a vibration treatment step of applying a first vibration to the electrode to adjust its temperature, and a pressing step of applying pressure to the electrode to compress the active material layer of the electrode, wherein a second vibration is applied to the electrode simultaneously with the pressurization, and the vibration treatment step is performed before the pressing step.

[0021] In the electrode manufacturing method described in any one of the above, the electrode may be either a positive electrode or a negative electrode, or both.

[0022] In the electrode manufacturing method described in any one of the above, it is preferable that the temperature adjustment in the vibration treatment step and / or pressing step is adjusted so that the electrode reaches a temperature of 80°C or higher and 150°C or lower. [Effects of the Invention]

[0023] This method enables the creation of secondary batteries with high capacity density. Furthermore, it provides a method for creating safe and reliable secondary batteries. Alternatively, it enables a method for reducing defects in the active material in sufficiently high-density electrodes. High-density electrodes with fewer active material defects enable the creation of superior secondary batteries that meet high capacity density, high performance, and safety requirements in various operating environments. [Brief explanation of the drawing]

[0024] Figure 1 shows an example of an electrode fabrication apparatus illustrating one aspect of the present invention. Figures 2A and 2B are schematic cross-sectional diagrams of an electrode, illustrating an example of the effect of the electrode manufacturing method according to one aspect of the present invention. Figure 2C is an example showing a cross-section of an electrode according to one aspect of the present invention. Figures 3A and 3B show an example of an electrode fabrication apparatus illustrating one aspect of the present invention. Figure 4 shows an example of an electrode fabrication apparatus illustrating one aspect of the present invention. Figure 5A is a top view of a positive electrode active material according to one embodiment of the present invention, and Figures 5B and 5C are cross-sectional views of a positive electrode active material according to one embodiment of the present invention. Figure 6 is a diagram illustrating the crystal structure of a positive electrode active material according to one embodiment of the present invention. Figure 7 shows the XRD pattern calculated from the crystal structure. Figure 8 illustrates the crystal structure of the positive electrode active material in the comparative example. Figure 9 shows the XRD pattern calculated from the crystal structure. Figure 10 is a schematic cross-sectional view of positive electrode active material particles. Figure 11A is a STEM image of the particles after pressing, and Figures 11B and 11C are schematic cross-sectional views. Figure 12A is an exploded perspective view of a coin-type rechargeable battery, Figure 12B is a perspective view of a coin-type rechargeable battery, and Figure 12C is a cross-sectional perspective view thereof. Figure 13A shows an example of a cylindrical secondary battery. Figure 13B shows an example of a cylindrical secondary battery. Figure 13C shows an example of multiple cylindrical secondary batteries. Figure 13D shows an example of an energy storage system with multiple cylindrical secondary batteries. Figures 14A and 14B illustrate examples of secondary batteries, while Figure 14C shows the inside of a secondary battery. Figures 15A to 15C illustrate examples of secondary batteries. Figures 16A and 16B show the external appearance of a secondary battery. Figures 17A to 17C illustrate the method for manufacturing a secondary battery. Figures 18A to 18C show examples of battery pack configurations. Figures 19A and 19B illustrate an example of a secondary battery. Figures 20A to 20C illustrate examples of secondary batteries. Figures 21A and 21B illustrate an example of a secondary battery. Figure 22A is a perspective view of a battery pack showing one embodiment of the present invention, Figure 22B is a block diagram of the battery pack, and Figure 22C is a block diagram of a vehicle having a motor. Figures 23A to 23D illustrate an example of a transport vehicle. Figures 24A and 24B illustrate an energy storage device according to one aspect of the present invention. Figure 25A shows an electric bicycle, Figure 25B shows the secondary battery of an electric bicycle, and Figure 25C is a diagram illustrating an electric motorcycle. Figures 26A to 26D illustrate an example of an electronic device. Figure 27A shows an example of a wearable device, Figure 27B shows a perspective view of a wristwatch-type device, and Figure 27C is a diagram illustrating the side view of a wristwatch-type device. Figure 27D is a diagram illustrating an example of wireless earphones. [Modes for carrying out the invention]

[0025] Embodiments of the present invention will be described in detail below with reference to the drawings. However, it will be readily apparent to those skilled in the art that the present invention is not limited to the following description, and its form and details can be modified in various ways. Furthermore, the present invention is not to be interpreted as being limited to the embodiments described below.

[0026] In this specification, the term "complex oxide" refers to an oxide that contains multiple types of metal atoms in its structure.

[0027] Furthermore, in this specification, crystal planes and directions are indicated by Miller indices. In crystallography, crystal planes and directions are indicated by superscripts above the numbers, but in this specification, due to limitations in patent application notation, a minus sign (-) may be placed before the number instead of a superscript above it. Individual orientations indicating directions within a crystal are indicated by [ ], aggregate orientations indicating all equivalent directions are indicated by < >, individual planes indicating crystal planes are indicated by ( ), and aggregate planes with equivalent symmetry are indicated by {}. In addition, for trigonal and hexagonal crystals, including R-3m, (hkl) may be used as well as (hkil) for Miller indices, where i is -(h+k).

[0028] Furthermore, in this specification, the layered rock salt-type crystal structure of a composite oxide containing lithium and a transition metal refers to a crystal structure having a rock salt-type ionic arrangement in which cations and anions are arranged alternately, and in which the transition metal and lithium are regularly arranged to form a two-dimensional plane, thereby enabling two-dimensional diffusion of lithium. Defects such as vacancies in cations or anions may be present. Also, strictly speaking, a layered rock salt-type crystal structure may have a distorted lattice structure of the rock salt-type crystal.

[0029] Furthermore, in this specification, a rock salt-type crystal structure refers to a structure in which cations and anions are arranged alternately. Note that there may be vacancies of cations or anions in part of the crystal structure.

[0030] In addition, in this specification and the like, the theoretical capacity of the positive electrode active material refers to the amount of electricity when all the insertable and removable lithium in the positive electrode active material has been removed. For example, the theoretical capacity of LiFePO4 is 170 mAh / g, the theoretical capacity of LiCoO2 is 274 mAh / g, the theoretical capacity of LiNiO2 is 275 mAh / g, and the theoretical capacity of LiMn2O4 is 148 mAh / g.

[0031] In addition, the degree to which lithium that can be inserted and removed remains in the positive electrode active material is represented by x in the composition formula, for example, x in Li x CoO2, or x in Li x M1O2. Li x CoO2 in this specification can be appropriately read as Li x M1O2. x can be referred to as the occupancy rate. In the case of the positive electrode active material in the secondary battery, x = (theoretical capacity - charge capacity) / theoretical capacity may be used. For example, when a secondary battery using LiCoO2 as the positive electrode active material is charged to 219.2 mAh / g, it can be said that Li 0.2 CoO2 or x = 0.2. A small x in Li x CoO2 means, for example, 0.1 < x ≤ 0.24.

[0032] When lithium cobaltate approximately satisfies the stoichiometric ratio, it is LiCoO2, and the occupancy rate of Li in the lithium site is x = 1. Also, a secondary battery after discharge is completed is also LiCoO2, and it can be said that x = 1. Here, the completion of discharge means, for example, a state where the voltage becomes 2.5 V (vs. lithium counter electrode) or less at a current of 100 mA / g. In a lithium-ion secondary battery, when the occupancy rate of lithium in the lithium site becomes x = 1 and no more lithium can enter, the voltage drops rapidly. At this time, it can be said that the discharge is completed. Generally, in a lithium-ion secondary battery using LiCoO2, since the discharge voltage drops rapidly until the discharge voltage reaches 2.5 V, it is assumed that the discharge is completed under the above conditions.

[0033] Furthermore, in this specification, the charging depth when all insertable and detachable lithium is inserted into the positive electrode active material is sometimes referred to as 0, and the charging depth when all insertable and detachable lithium in the positive electrode active material has been detached is sometimes referred to as 1.

[0034] (Embodiment 1) This embodiment describes a method for manufacturing an electrode according to one aspect of the present invention.

[0035] An example of a method for manufacturing electrodes according to one aspect of the present invention will be explained with reference to Figures 1 to 4.

[0036] [Manufacturing Method 1] The electrodes (positive electrode, negative electrode) have an active material layer and a current collector. An electrode in which the active material layer is provided on one side of the current collector is called a single-sided coated electrode, and an electrode in which the active material layer is provided on both sides of the current collector is called a double-sided coated electrode. One embodiment of the present invention is a method for manufacturing electrodes that can be applied to both single-sided coated electrodes and double-sided coated electrodes. The active material layer may contain an active material, a conductive material, and a binder. For the materials such as the active material of the positive electrode and the active material of the negative electrode, the materials described in the following embodiments may be used.

[0037] The electrode manufacturing method preferably includes a slurry manufacturing step, a coating step, a vibration treatment step, and a pressing step. The apparatus 10 shown in Figure 1 can be used for the vibration treatment step and the pressing step.

[0038] <Slurry preparation process> In the slurry preparation process, the active material is dispersed in a dispersion medium to prepare the slurry. For example, when PVDF (polyvinylidene fluoride) is used as the binder, NMP (N-methyl-2-pyrrolidone) or the like can be used as the dispersion medium. If necessary, the slurry may contain a conductive material and a binder.

[0039] <Coating process> In the coating process, a slurry is applied to the current collector. Slot die application, gravure application, blade application, and combinations thereof can be used for the slurry. After coating, the coated electrode 1 can be obtained by volatilizing the dispersion medium. The volatilization process of the dispersion medium (also called the drying process) is preferably carried out in a temperature range of 50°C to 200°C, preferably 80°C to 150°C. An example of the coated electrode 1 after the coating process is shown in Figure 2A. Immediately after the coating process, the active material layer 3, which has the active material 5 formed on the current collector 2, has many voids 4 within the active material layer 3, as schematically shown in electrode 1a in Figure 2A. Note that the contour lines showing the active material layer 3 in Figures 2A to 2C indicate the region that can be considered as the volume of the active material layer 3 when calculating the film density of the active material layer 3 (mass per unit volume of the active material layer).

[0040] <Vibration treatment process> In the vibration processing step, the vibration processing unit 20 of the apparatus 10 shown in Figure 1 can be used. The apparatus 10 has an electrode roll unwinding section 41 and a winding section 42, a vibration processing unit 20, and a pressing section 30. The electrode 1 is in contact with the surface of the roll 21 of the vibration processing unit 20 between the unwinding section 41 and the pressing section 30. By having the electrode 1 in contact with the surface of the roll 21, the vibration and heat described later can be easily transmitted to the electrode 1. The vibration processing unit 20 has a roll 21 in contact with the electrode 1 and a support 22, the support 22 having a vibrator 23. The vibrator 23 is electrically connected to an oscillator 25, and the oscillator 25 controls the vibrator 23 to vibrate at a predetermined frequency. The vibration is transmitted to the electrode 1 via the roll 21. The vibration has vertical vibration (Z direction in Figure 1) and / or lateral vibration (X and / or Y direction in Figure 1). The vibrations applied to electrode 1 allow the active material 5 in the active material layer 3 to move to a stable position, making it possible to increase the film density with a lower press pressure in the subsequent pressing process. Furthermore, it is preferable that roll 21 has a heating element such as a sheath heater inside, and that the temperature of roll 21 is adjusted in the vibration processing process so that electrode 1 is at a temperature of 50°C to 200°C, preferably 80°C to 150°C. The structure of roll 21 can be the same as that shown in Figure 3B below. Heating electrode 1 to the above temperature and applying vibrations is highly preferable because it allows the active material 5 in the active material layer 3 to move to a more stable position and provides the effect of preheating for the pressing process.

[0041] For example, a piezoelectric ceramic resonator can be used as the resonator. A Langevin-type structure can be used for the piezoelectric ceramic resonator, which has a pyramidal piezoelectric ceramic section with polarization in the thickness direction, sandwiched between two annular electrode sections. For example, piezoelectric ceramics such as PZT (lead zirconate titanate) may be used as the piezoelectric ceramic.

[0042] <Pressing Process> In the pressing process, the pressing section 30 of the apparatus 10 shown in Figure 1 can be used. The pressing section 30 has an upper roll 31, an upper support 32, a lower roll 33, and a lower support 34. The upper roll 31 has a heating section such as a sheath heater inside, and it is preferable that the temperature of the upper roll 31 is adjusted so that the electrode 1 is at a temperature of 50°C to 200°C, preferably 80°C to 150°C, during the pressing process. The electrode 1 is pressurized by the upper roll 31 and the lower roll 33, and the thickness of the active material layer 3 on the electrode 1 is reduced. In other words, the voids 4 in the active material layer 3 are reduced, and the film density of the active material layer 3 (mass per unit volume of the active material layer) is increased.

[0043] As mentioned above, Figure 2A schematically shows the state of electrode 1a immediately after the coating process, and the active material layer 3 has many voids 4. Since secondary batteries are desirable to have a high capacity per unit volume, it is desirable that the voids 4 in the active material layer 3 be as small as possible (high film density). For this reason, conventionally, electrode 1 was pressurized with a very strong force to increase the film density of the active material layer 3. However, when electrode 1 is pressurized with a very strong force, as shown schematically in Figure 2B (electrode 1b), the active material 5 cannot withstand the pressure, resulting in defects such as cracks 6 and slips 7. On the other hand, in one embodiment of the present invention, by having a vibration treatment process, it is possible to obtain an active material layer 3 with a high film density even when electrode 1 is pressurized with a smaller force than in the conventional method. In this case, as shown schematically in Figure 2C (electrode 1c), the occurrence of defects such as cracks 6 and slips 7 is greatly reduced, and an active material layer 3 with a high film density can be obtained.

[0044] [Preparation Method 2] Furthermore, in another aspect of the present invention, the vibration treatment process and the pressing process shown in manufacturing method 1 may be performed integrally using the apparatus 11 shown in Figure 3A. The method of performing the vibration treatment process and the pressing process integrally can be called vibration pressing. The upper roll 31 shown in Figure 3A, like the upper roll 31 in Figure 1, has a heating section 37 such as a sheath heater inside, and it is preferable that the temperature of the upper roll 31 is adjusted so that the electrode 1 is at a temperature of 50°C to 200°C, preferably 80°C to 150°C, during the vibration treatment process. An example of the heating section 37 of the roll is shown in Figure 3B. Figure 3B is a schematic diagram of the upper part of the vibration pressing section in Figure 3A, viewed from the X direction in the figure (the direction of movement of the electrode 1). The upper support 32 shown in Figure 3B holds the axis of the upper roll 31 at two holding sections 32b, and has vibrators 35 (35a, 35b) between the main body 32a and the holding sections 32b of the upper support 32. The vibrator 35 is connected to the oscillator 36. The upper roll 31 has a gear 38 and receives rotational power from another gear (not shown). The upper roll 31 may have a heating section 37 near its central axis. Although vibrators 35a and 35b may each be connected to separate oscillators, it is desirable that the vibrations emitted by vibrators 35a and 35b have the same amplitude, frequency, and phase.

[0045] [Method 3 of preparation] Furthermore, in another aspect of the present invention, the apparatus 12 shown in Figure 4, which combines the vibration treatment process shown in manufacturing method 1 and the vibration pressing process shown in manufacturing method 2, can be used. The structure of the roll 21 and upper roll 31 shown in Figure 4 can be the same as that of Figure 3B described above.

[0046] This embodiment can be used in appropriate combination with other embodiments.

[0047] (Embodiment 2) This embodiment describes an example of a secondary battery according to one aspect of the present invention. It is desirable that either the positive electrode or the negative electrode, or both, be manufactured using the manufacturing method shown in Embodiment 1.

[0048] <Example of a secondary battery configuration> The following explanation uses a secondary battery, in which the positive electrode, negative electrode, and electrolyte are enclosed in an outer casing, as an example.

[0049] [Positive electrode] The positive electrode comprises a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer contains a positive electrode active material and may also contain a conductive material and a binder as described later.

[0050] [Negative electrode] The negative electrode comprises a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer contains a negative electrode active material and may also contain a conductive material as described later and the binder described above.

[0051] [Current collector] As the positive electrode current collector and negative electrode current collector, materials with high conductivity that do not alloy with carrier ions such as lithium can be used, such as metals like stainless steel, gold, platinum, zinc, iron, copper, aluminum, and titanium, and their alloys. The current collector can be in the shape of a sheet, mesh, perforated metal, expanded metal, etc., as appropriate. The current collector should preferably have a thickness of 10 μm to 30 μm.

[0052] Furthermore, it is preferable to use a material for the negative electrode current collector that does not alloy with carrier ions such as lithium.

[0053] A titanium compound may be laminated on top of the metals mentioned above as a current collector. Examples of titanium compounds include titanium nitride, titanium oxide, titanium nitride in which some of the nitrogen is replaced with oxygen, titanium oxide in which some of the oxygen is replaced with nitrogen, and titanium oxynitride (TiO2). x N yOne selected from (0 < x < 2, 0 < y < 1), or two or more can be mixed or laminated and used. Among them, titanium nitride is particularly preferable because it has high conductivity and a high function of suppressing oxidation. By providing a titanium compound on the surface of the current collector, for example, the reaction between the material of the active material layer formed on the current collector and the metal can be suppressed. When the active material layer contains a compound having oxygen, the oxidation reaction between the metal and oxygen can be suppressed. For example, when aluminum is used as the current collector and the active material layer is formed using graphene oxide described later, there is a concern about the oxidation reaction between the oxygen in graphene oxide and aluminum. In such a case, by providing a titanium compound on aluminum, the oxidation reaction between the current collector and graphene oxide can be suppressed.

[0054] [Conductive material] The conductive material, also called a conductivity-imparting agent or a conductive aid, is a carbon material. By attaching the conductive material between a plurality of active materials, the plurality of active materials are electrically connected to each other, and the conductivity is enhanced. Note that "attachment" does not only refer to the physical adhesion of the active material and the conductive material, but also includes cases where a covalent bond occurs, cases where they are bonded by van der Waals forces, cases where the surface of the active material is covered by the conductive material, cases where the conductive material fits into the surface irregularities of the active material, and cases where they are electrically connected even if they are not in contact with each other.

[0055] Active material layers such as the positive electrode active material layer and the negative electrode active material layer preferably have a conductive material. [[ID=ll]]

[0056] As the conductive material, for example, any one or two or more of carbon black such as acetylene black and furnace black, graphite such as artificial graphite and natural graphite, carbon fibers such as carbon nanofibers and carbon nanotubes, and graphene compounds can be used.

[0057] As carbon fibers, for example, mesophase pitch carbon fibers and isotropic pitch carbon fibers can be used. Alternatively, carbon nanofibers or carbon nanotubes can be used. Carbon nanotubes can be fabricated, for example, by vapor deposition.

[0058] The active material layer may also contain metal powders or metal fibers such as copper, nickel, aluminum, silver, or gold, or conductive ceramic materials as conductive materials.

[0059] The content of the conductive additive relative to the total amount of the active material layer is preferably 1 wt% to 10 wt%, and more preferably 1 wt% to 5 wt%.

[0060] Unlike granular conductive materials such as carbon black, which make point contact with the active material, graphene compounds enable surface contact with low contact resistance. Therefore, a smaller amount of graphene compound can improve the electrical conductivity between the granular active material and the graphene compound compared to conventional conductive materials. Consequently, the ratio of the active material in the active material layer can be increased. This, in turn, can increase the discharge capacity of the secondary battery.

[0061] Particulate carbon-containing compounds such as carbon black and graphite, or fibrous carbon-containing compounds such as carbon nanotubes, readily penetrate minute spaces. These minute spaces refer, for example, to regions between multiple active materials. By combining a carbon-containing compound that readily penetrates minute spaces with a sheet-like carbon-containing compound such as graphene, which can impart conductivity across multiple particles, the electrode density can be increased, and excellent conductive paths can be formed. A secondary battery obtained by the manufacturing method according to one embodiment of the present invention can have high capacity density and stability, making it effective as a secondary battery for automotive use.

[0062] [Binder] The active material layer preferably has a binder (not shown). The binder binds or fixes, for example, the electrolyte and the active material. The binder can also bind or fix the electrolyte and a carbon-based material, the active material and a carbon-based material, multiple active materials to each other, multiple carbon-based materials, etc.

[0063] It is preferable to use materials such as polystyrene, methyl polyacrylate, polymethyl methacrylate (polymethyl methacrylate, PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, and nitrocellulose as binders.

[0064] Polyimides possess excellent thermal, mechanical, and chemical stability.

[0065] Fluorine-containing polymer materials, specifically polyvinylidene fluoride (PVDF), can be used. PVDF is a resin with a melting point in the range of 134°C to 169°C, and is a material with excellent thermal stability.

[0066] Furthermore, it is preferable to use rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, or ethylene-propylene-diene copolymer as a binder. Fluororubber can also be used as a binder.

[0067] Furthermore, it is preferable to use a water-soluble polymer as the binder. Examples of water-soluble polymers include polysaccharides. Examples of polysaccharides include cellulose derivatives such as carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, diacetylcellulose, and regenerated cellulose, or starch. It is even more preferable to use these water-soluble polymers in combination with the aforementioned rubber material.

[0068] You may use a combination of several of the binders mentioned above.

[0069] <Graphene compound> In this specification, graphene compounds include graphene, multilayer graphene, multigraphene, graphene oxide, multilayer graphene oxide, multigraphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multigraphene oxide, graphene quantum dots, etc. A graphene compound is a material having carbon, having a plate-like or sheet-like shape, and having a two-dimensional structure formed by a six-membered carbon ring. The two-dimensional structure formed by the six-membered carbon ring may also be called a carbon sheet. Graphene compounds may have functional groups. Furthermore, graphene compounds preferably have a bent shape. Furthermore, graphene compounds may be rolled up to resemble carbon nanofibers.

[0070] In this specification, graphene oxide refers to, for example, a material having carbon and oxygen, having a sheet-like structure, and having functional groups, particularly epoxy groups, carboxyl groups, or hydroxyl groups.

[0071] In this specification, reduced graphene oxide refers to, for example, a material having carbon and oxygen, having a sheet-like shape, and possessing a two-dimensional structure formed by a six-membered carbon ring. It may also be called a carbon sheet. Reduced graphene oxide can function as a single sheet, but multiple sheets may be laminated together. It is preferable that reduced graphene oxide has a portion where the carbon concentration is greater than 80 atomic%, and the oxygen concentration is between 2 atomic% and 15 atomic%. By having such carbon and oxygen concentrations, it can function as a highly conductive material even in small quantities. Furthermore, it is preferable that the intensity ratio of the G band to the D band in the Raman spectrum of reduced graphene oxide is 1 or greater. Reduced graphene oxide with such an intensity ratio can function as a highly conductive material even in small quantities.

[0072] In some cases, pores can be created in graphene compounds by reducing graphene oxide.

[0073] Alternatively, a material in which the ends of graphene are terminated with fluorine may be used.

[0074] In the longitudinal section of the active material layer, sheet-like graphene compounds are dispersed approximately uniformly within the internal region of the active material layer. Multiple graphene compounds are formed to partially cover multiple granular active materials or to adhere to the surfaces of multiple granular active materials, and thus are in surface contact with one another.

[0075] Here, multiple graphene compounds can bond together to form a mesh-like graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net). When the active material is coated with the graphene net, the graphene net can also function as a binder that binds the active materials together. Therefore, the amount of binder can be reduced or eliminated, thereby improving the ratio of active material to electrode volume or electrode weight. In other words, the charge and discharge capacity of the secondary battery can be increased.

[0076] Here, it is preferable to use graphene oxide as the graphene compound, mix it with the active material to form a layer that will become the active material layer, and then reduce it. In other words, it is preferable that the completed active material layer has reduced graphene oxide. By using graphene oxide, which has extremely high dispersibility in polar solvents, for the formation of the graphene compound, the graphene compound can be dispersed approximately uniformly within the internal region of the active material layer. By volatilizing and removing the solvent from the dispersion medium containing the uniformly dispersed graphene oxide and reducing the graphene oxide, the graphene compounds remaining in the active material layer partially overlap and are dispersed to the extent that they are in surface contact with each other, thereby forming three-dimensional conductive paths. The reduction of graphene oxide may be carried out, for example, by heat treatment or by using a reducing agent.

[0077] Furthermore, by using a spray-drying device beforehand, a graphene compound, which is a conductive material, can be formed as a coating to cover the entire surface of the active material, and then the active material particles can be electrically connected with the graphene compound to form conductive paths.

[0078] Furthermore, the active material layer may be made by mixing the graphene compound with the material used to form the graphene compound. For example, particles used as a catalyst when forming the graphene compound may be mixed together with the graphene compound. Examples of catalysts used when forming the graphene compound include silicon dioxide (SiO2, SiO2). x Examples of particles include those having (x<2), aluminum oxide, iron, nickel, ruthenium, iridium, platinum, copper, germanium, etc. Preferably, the average particle diameter (D50: also called the median diameter) of the particles is 1 μm or less, and more preferably 100 nm or less.

[0079] [Separator] A separator is placed between the positive and negative electrodes. The separator can be made from materials such as cellulose fibers including paper, nonwoven fabrics, glass fibers, ceramics, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, or polyurethane. It is preferable that the separator be processed into a bag shape and positioned to enclose either the positive or negative electrode.

[0080] The separator is a porous material having pores with a diameter of about 20 nm, preferably pores with a diameter of 6.5 nm or more, and more preferably pores with a diameter of at least 2 nm.

[0081] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture thereof. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aramid (meta-aramid, para-aramid).

[0082] Coating with ceramic materials improves oxidation resistance, suppressing separator degradation during high-voltage charging and discharging, and thus improving the reliability of secondary batteries. Coating with fluorine-based materials improves adhesion between the separator and electrodes, thereby improving output characteristics. Coating with polyamide materials, particularly aramid, improves heat resistance, thus enhancing the safety of secondary batteries.

[0083] For example, a polypropylene film may be coated on both sides with a mixture of aluminum oxide and aramid. Alternatively, the side of the polypropylene film in contact with the positive electrode may be coated with a mixture of aluminum oxide and aramid, and the side in contact with the negative electrode may be coated with a fluorine-based material.

[0084] By using a multi-layered separator, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, thus increasing the capacity per unit volume of the secondary battery.

[0085] [Electrolyte] When using a liquid electrolyte in a secondary battery, for example, one of the following can be used as the electrolyte: ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc., or two or more of these can be used in any combination and ratio.

[0086] Furthermore, by using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as the solvent for the electrolyte, it is possible to prevent the secondary battery from rupturing or igniting even if the internal temperature rises due to a short circuit or overcharging in the internal region of the secondary battery. Ionic liquids consist of cations and anions, and include organic cations and anions. Examples of organic cations include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, as well as aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions include monovalent amide anions, monovalent methide anions, fluorosulfonic acid anions, perfluoroalkyl sulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, or perfluoroalkyl phosphate anions.

[0087] In particular, in a secondary battery according to one aspect of the present invention, when silicon is used as the second active material of the negative electrode, it is preferable to use a liquid electrolyte having an ionic liquid.

[0088] A secondary battery according to one aspect of the present invention has, for example, alkali metal ions such as sodium ions and potassium ions, or alkaline earth metal ions such as calcium ions, strontium ions, barium ions, beryllium ions, and magnesium ions as carrier ions.

[0089] When lithium ions are used as carrier ions, the electrolyte, for example, contains a lithium salt. Examples of lithium salts include LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, and Li2B. 10 Cl 10 Li2B 12 Cl 12 LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, etc. can be used.

[0090] Furthermore, the electrolyte preferably contains fluorine. As a fluorine-containing electrolyte, for example, an electrolyte having one or more types of fluorinated cyclic carbonates and lithium ions can be used. Fluorinated cyclic carbonates can improve flammability and enhance the safety of lithium-ion secondary batteries.

[0091] As fluorinated cyclic carbonates, fluorinated ethylene carbonates such as monofluoroethylene carbonate (fluoroethylene carbonate, FEC, F1EC), difluoroethylene carbonate (DFEC, F2EC), trifluoroethylene carbonate (F3EC), and tetrafluoroethylene carbonate (F4EC) can be used. Note that DFEC has isomers such as cis-4,5 and trans-4,5. As an electrolyte, it is important to solvate lithium ions using one or more types of fluorinated cyclic carbonates and transport them within the electrolyte contained in the electrodes during charging and discharging in order to operate at low temperatures. By contributing to the transport of lithium ions during charging and discharging, rather than using fluorinated cyclic carbonates as small additives, low-temperature operation becomes possible. In secondary batteries, lithium ions move in clusters of several to several dozen ions.

[0092] By using fluorinated cyclic carbonates as the electrolyte, the desolvation energy required for lithium ions solvated within the electrolyte to enter the active material particles is reduced. Reducing this desolvation energy makes it easier for lithium ions to insert into or detach from the active material particles, even at low temperatures. While lithium ions may move while remaining solvated, a hopping phenomenon can occur where the coordinating solvent molecules are replaced. Easier desolvation of lithium ions can facilitate hopping, thus improving lithium ion movement. There is a concern that the decomposition products of the electrolyte during charging and discharging of secondary batteries can adhere to the surface of the active material, leading to battery degradation. However, when the electrolyte contains fluorine, the electrolyte is fluid, making it difficult for the decomposition products to adhere to the surface of the active material. Therefore, battery degradation can be suppressed.

[0093] Solvated lithium ions may form clusters in the electrolyte and move within the negative electrode, between the positive and negative electrodes, within the positive electrode, etc.

[0094] In this specification, electrolytes are a general term that includes solid, liquid, or semi-solid materials.

[0095] Degradation is prone to occur at interfaces within secondary batteries, such as the interface between the active material and the electrolyte. In one embodiment of the present invention, the presence of a fluorine-containing electrolyte prevents degradation that may occur at the interface between the active material and the electrolyte, typically resulting in alteration of the electrolyte or increased viscosity of the electrolyte. Alternatively, a binder or graphene compound may be attached to or retained on the fluorine-containing electrolyte. This configuration makes it possible to maintain a state where the viscosity of the electrolyte is reduced, in other words, a free-flowing state of the electrolyte, thereby improving the reliability of the secondary battery. DFEC with two fluorine atoms and F4EC with four fluorine atoms have lower viscosity and are freer than FEC with one fluorine atom, resulting in weaker coordination bonds with lithium. Therefore, the adhesion of highly viscous decomposition products to the active material particles can be reduced. When highly viscous decomposition products adhere to or cling to the active material particles, lithium ions become less able to move at the interface of the active material particles. Fluorine-containing electrolytes mitigate the formation of decomposition products that adhere to the surface of the active material (positive electrode active material or negative electrode active material) through solvation. Furthermore, by using an electrolyte containing fluorine, the formation and growth of dendrites can be prevented by preventing the adhesion of decomposition products.

[0096] Another characteristic is the use of an electrolyte containing fluorine as the main component, with the fluorine-containing electrolyte being 5% or more by volume, 10% or more by volume, preferably 30% to 100% by volume.

[0097] In this specification, the main component of the electrolyte refers to a component that accounts for 5% or more by volume of the total electrolyte of the secondary battery. Furthermore, "5% or more by volume of the total electrolyte of the secondary battery" here refers to the proportion of the total electrolyte measured during the manufacturing of the secondary battery. In addition, when a secondary battery is disassembled after its manufacture, it is difficult to quantify the proportion of each of the multiple types of electrolytes, but it is possible to determine whether a particular organic compound accounts for 5% or more by volume of the total electrolyte.

[0098] By using an electrolyte containing fluorine, a secondary battery capable of operating over a wide temperature range, specifically from -40°C to 150°C, preferably from -40°C to 85°C, can be realized.

[0099] Furthermore, additives such as vinylene carbonate, propanesultone (PS), tert-butylbenzene (TBB), lithium bis(oxalate)borate (LiBOB), and dinitrile compounds such as succinonitrile and adiponitrile may be added to the electrolyte. The concentration of the additive should be, for example, 0.1% or more and less than 5% by volume relative to the total electrolyte.

[0100] In addition to the above, the electrolyte may also contain one or more aprotic organic solvents such as γ-butyrolactone, acetonitrile, dimethoxyethane, and tetrahydrofuran.

[0101] Furthermore, the presence of a polymer material that gels the electrolyte enhances safety against leakage and other issues. Typical examples of polymer materials that gel include silicone gels, acrylic gels, acrylonitrile gels, polyethylene oxide gels, polypropylene oxide gels, and fluorine-based polymer gels.

[0102] As polymer materials, for example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, and polyacrylonitrile, as well as copolymers containing these, can be used. For example, PVDF-HFP, which is a copolymer of PVDF and hexafluoropropylene (HFP), can be used. Furthermore, the polymer formed may have a porous structure.

[0103] Furthermore, the above configuration is an example of a secondary battery using a liquid electrolyte, but is not particularly limited. For example, semi-solid-state batteries and all-solid-state batteries can also be fabricated.

[0104] In this specification, whether it is a secondary battery using a liquid electrolyte or a semi-solid battery, the layer placed between the positive and negative electrodes will be referred to as the electrolyte layer. The electrolyte layer of a semi-solid battery is a layer formed by film deposition and can be distinguished from the liquid electrolyte layer.

[0105] Furthermore, in this specification, a semi-solid battery refers to a battery having a semi-solid material in at least one of its components: the electrolyte layer, the positive electrode, and the negative electrode. Here, "semi-solid" does not mean that the solid material makes up 50% of the battery. "Semi-solid" means possessing solid properties, such as small volume change, while also having some liquid-like properties, such as flexibility. As long as these properties are met, the battery may consist of a single material or multiple materials. For example, a liquid material may be impregnated into a porous solid material.

[0106] Furthermore, in this specification, a polymer electrolyte secondary battery refers to a secondary battery having a polymer in the electrolyte layer between the positive electrode and the negative electrode. Polymer electrolyte secondary batteries include dry (or intrinsic) polymer electrolyte batteries and polymer gel electrolyte batteries.

[0107] The electrolyte comprises a lithium-ion conductive polymer and a lithium salt.

[0108] In this specification, a lithium-ion conductive polymer is a polymer that has the conductivity of a cation such as lithium. More specifically, it is a polymer compound having a polar group to which a cation can coordinate. Preferably, the polar group is an ether group, ester group, nitrile group, carbonyl group, siloxane, etc.

[0109] Examples of lithium-ion conductive polymers that can be used include polyethylene oxide (PEO), derivatives having polyethylene oxide as the main chain, polypropylene oxide, polyacrylic acid esters, polymethacrylate esters, polysiloxanes, and polyphosphazenes.

[0110] The lithium-ion conductive polymer may be branched, crosslinked, or copolymerized. Its molecular weight is preferably, for example, 10,000 or more, and more preferably 100,000 or more.

[0111] In lithium-ion conductive polymers, lithium ions move while changing the polar groups they interact with through partial motion (also called segmental motion) of the polymer chains. For example, in PEO, lithium ions move while changing the oxygen groups they interact with through segmental motion of the ether chains. When the temperature is close to or higher than the melting or softening point of the lithium-ion conductive polymer, the crystalline region dissolves and the amorphous region increases, and the motion of the ether chains becomes more active, resulting in higher ionic conductivity. Therefore, when using PEO as a lithium-ion conductive polymer, it is preferable to perform charging and discharging at 60°C or higher.

[0112] According to Shannon et al., Acta A 32(1976)751, the radius of a monovalent lithium ion is 0.590 × 10⁻⁶ in the 4-coordinate state. -1 nm, 0.76 × 10 for 6-coordinate. -1 nm, 0.92 × 10 for 8-coordinate. -1 It is in nm. The radius of a divalent oxygen ion is 1.35 × 10⁻⁶ when it is two-coordinate. -1 nm, 1.36 × 10 for 3-coordinate.-1 nm, 1.38 × 10 for 4-coordinate. -1 nm, 1.40 × 10 for 6-coordinate. -1 nm, 1.42 × 10 for 8-coordinate. -1 The distance is in nm. The distance between polar groups in adjacent lithium-ion conductive polymer chains is preferably greater than or equal to the distance at which lithium ions and anions from the polar groups can stably exist while maintaining the ionic radius described above. Furthermore, it is preferable that the distance is sufficient for sufficient interaction between lithium ions and polar groups. However, as mentioned above, segmental motion occurs, so it is not necessary to maintain a constant distance at all times. It is sufficient if the distance is appropriate when lithium ions pass through.

[0113] Furthermore, as lithium salts, compounds can be used that contain lithium along with at least one of the following: phosphorus, fluorine, nitrogen, sulfur, oxygen, chlorine, arsenic, boron, aluminum, bromine, and iodine. For example, LiPF6, LiN(FSO2)2 (lithium bis(fluorosulfonyl)imide, LiFSI), LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, Li2B 10 Cl 10 Li2B 12 Cl 12 Lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, lithium bis(oxalate) borate (LiBOB), etc., can be used individually or in any combination and ratio of two or more of these.

[0114] In particular, using LiFSI is preferable because it exhibits good low-temperature characteristics. Furthermore, LiFSI and LiTFSA are less reactive with water compared to LiPF6, etc. Therefore, it is easier to control the dew point when fabricating electrodes and electrolyte layers using LiFSI. For example, they can be handled not only in an inert atmosphere such as argon with moisture removed as much as possible, and in a dry room with controlled dew point, but also in a normal atmospheric atmosphere. This improves productivity, which is preferable. Moreover, using Li salts with high dissociability and plasticizing effects, such as LiFSI and LiTFSA, is particularly preferable when using lithium conduction utilizing the segmental motion of the ether chain, because it can be used over a wide temperature range.

[0115] The absence or very low amount of organic solvents makes it possible to create a secondary battery that is less likely to ignite or burn, thus improving safety, which is preferable. Furthermore, if the electrolyte layer has no organic solvents or very little organic solvents, it can have sufficient strength to electrically insulate the positive and negative electrodes even without a separator. Because a separator is not required, a highly productive secondary battery can be created. If the electrolyte layer contains both an electrolyte and an inorganic filler, the strength is further increased, resulting in a secondary battery with even greater safety.

[0116] [Exterior] The outer casing of a secondary battery can be made of metal materials such as aluminum or resin materials. A film-like outer casing can also be used. As a film, for example, a three-layer film can be used, in which a highly flexible metal thin film such as aluminum, stainless steel, copper, or nickel is provided on a film made of materials such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as polyamide resin or polyester resin is provided on the metal thin film as the outer surface of the outer casing. Furthermore, it is preferable to use a fluororesin film as the film. Fluororesin films have high stability against acids, alkalis, organic solvents, etc., and suppress side reactions, corrosion, etc. associated with the reactions of the secondary battery, thereby realizing a superior secondary battery. Examples of fluororesin films include PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxyalkane: copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether), FEP (perfluoroethylenepropene copolymer: copolymer of tetrafluoroethylene and hexafluoropropylene), and ETFE (ethylenetetrafluoroethylene copolymer: copolymer of tetrafluoroethylene and ethylene).

[0117] <An example of a negative electrode active material> It is preferable to use materials as the negative electrode active material that can react with carrier ions in a secondary battery, materials that can insert and remove carrier ions, materials that can react with metals that become carrier ions, and materials that can dissolve and precipitate metals that become carrier ions.

[0118] An example of a negative electrode active material is described below.

[0119] Furthermore, as the negative electrode active material, a metal or compound having one or more elements selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium can be used. Examples of alloy compounds using such elements include Mg2Si, Mg2Ge, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, and SbSn.

[0120] Furthermore, materials with reduced resistance may be used by adding impurity elements such as phosphorus, arsenic, boron, aluminum, and gallium to silicon. Alternatively, lithium-predoped silicon materials may be used. Methods of predoping include annealing silicon with lithium fluoride, lithium carbonate, etc., and mechanical alloying of lithium metal and silicon. Alternatively, after forming an electrode containing silicon (silicon electrode), lithium can be doped (predoped) by a charge-discharge reaction in combination with an electrode made of lithium metal, etc. Subsequently, a secondary battery may be fabricated by combining the doped silicon electrode with a counter electrode (for example, a positive electrode relative to a predoped negative electrode).

[0121] For example, silicon nanoparticles can be used as the negative electrode active material. The average particle size D50 of the silicon nanoparticles is preferably 5 nm or more and less than 1 μm, more preferably 10 nm or more and 300 nm or less, and even more preferably 10 nm or more and 100 nm or less.

[0122] Silicon nanoparticles may be crystalline. Furthermore, silicon nanoparticles may have both crystalline and amorphous regions.

[0123] For example, a material containing silicon is SiO x A material represented by (where x is preferably less than 2, and more preferably between 0.5 and 1.6) can be used.

[0124] Furthermore, carbon-based materials such as graphite, easily graphitizable carbon, poorly graphitizable carbon, carbon nanotubes, carbon black, and graphene compounds can be used as the negative electrode active material.

[0125] Furthermore, as the negative electrode active material, for example, an oxide having one or more elements selected from titanium, niobium, tungsten, and molybdenum can be used.

[0126] Multiple metals, materials, compounds, etc., as described above can be used in combination as the negative electrode active material.

[0127] Examples of negative electrode active materials include SnO, SnO2, titanium dioxide (TiO2), and lithium titanium oxide (Li4Ti5O2). 12 ), lithium-graphite intercalation compound (Li x Oxides such as C6, niobium pentoxide (Nb2O5), tungsten oxide (WO2), and molybdenum oxide (MoO2) can be used.

[0128] Furthermore, as the negative electrode active material, a Li3N type structure is used, which is a lithium and transition metal binitride. 3-x M x N(M=Co, Ni, Cu) can be used. For example, Li 2.6 Co 0.4 N3 is preferable because it exhibits a large charge / discharge capacity (900mAh / g).

[0129] When lithium and transition metal binitrides are used as the negative electrode material, it is preferable that they be combined with lithium-ion-free materials such as V2O5 and Cr3O8 as the positive electrode material. Even when a lithium-ion-containing material is used as the positive electrode material, lithium and transition metal binitrides can be used as the negative electrode material by removing the lithium ions contained in the positive electrode material beforehand.

[0130] In addition, materials in which a conversion reaction occurs can also be used as the negative electrode active material. For example, transition metal oxides that do not undergo an alloying reaction with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may be used as the negative electrode active material. Examples of materials in which a conversion reaction occurs further include oxides such as Fe2O3, CuO, Cu2O, RuO2, and Cr2O3, CoS 0.89 Conversion reactions also occur with sulfides such as NiS, CuS, nitrides such as Zn3N2, Cu3N, and Ge3N4, phosphides such as NiP2, FeP2, and CoP3, and fluorides such as FeF3 and BiF3. Since the potential of the above fluorides is high, they may be used as the positive electrode material.

[0131] <An example of the positive electrode active material> Examples of the positive electrode active material include composite oxides containing lithium having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure.

[0132] It is preferable to use a positive electrode active material having a layered crystal structure as the positive electrode active material of one aspect of the present invention.

[0133] Examples of the layered crystal structure include a layered rock salt-type crystal structure. Examples of the composite oxide having a layered rock salt-type crystal structure include LiM x O y (where x > 0 and y > 0, more specifically, for example, y = 2 and 0.8 < x < 1.2). Here, M is a metal element, preferably one or more selected from cobalt, manganese, nickel, and iron. Alternatively, M is, for example, two or more selected from cobalt, manganese, nickel, iron, aluminum, titanium, zirconium, lanthanum, copper, and zinc.

[0134] LiM x O y Examples of the composite oxide represented by LiCoO2, LiNiO2, LiMnO2, etc. Also, NiCo-based represented by LiNi x Co 1-x O2 (0 < x < 1), LiM x Oy As the composite oxide represented by, for example, LiNi x Mn 1-x O2 (0 < x < 1), a NiMn-based one and the like are exemplified.

[0135] Further, as the composite oxide represented by LiMO2, for example, LiNi x Co y Mn z O2 (x > 0, y > 0, 0.8 < x + y + z < 1.2), a NiCoMn-based one (also referred to as NCM) is exemplified. Specifically, for example, it is preferable to satisfy 0.1x < y < 8x and 0.1x < z < 8x. As an example, x, y, and z preferably satisfy x:y:z = 1:1:1 or values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 5:2:3 or values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 8:1:1 or values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 6:2:2 or values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 1:4:1 or values in the vicinity thereof.

[0136] Further, as the composite oxide having a layered rock salt-type crystal structure, for example, Li2MnO3, Li2MnO3-LiMeO2 (Me is Co, Ni, Mn), etc. are exemplified.

[0137] When using a positive electrode active material having a layered crystal structure represented by the above composite oxide, a secondary battery with a large lithium content per volume and a high capacity per volume may be realized. In such a positive electrode active material, the amount of lithium desorbed per volume during charging is also large, and in order to perform stable charge and discharge, stabilization of the crystal structure after desorption is required. Also, in charge and discharge, the crystal structure may collapse, which may inhibit high-speed charging or high-speed discharging.

[0138] A lithium-containing material having a spinel-type crystal structure containing manganese such as LiMn2O4 as a positive electrode active material is preferably mixed with lithium nickelate (LiNiO2 or LiNi 1-x M x O2 (0 < x < 1) (M = Co, Al, etc.)). By adopting this configuration, the characteristics of the secondary battery can be improved.

[0139] Further, as the positive electrode active material, a lithium manganese composite oxide represented by the composition formula Li a Mn b M c O d can be used. Here, the element M is preferably a metal element selected from those other than lithium and manganese, or silicon or phosphorus, and more preferably nickel. Further, when measuring the entire particles of the lithium manganese composite oxide, it is preferable to satisfy 0 < a / (b + c) < 2, c > 0, and 0.26 ≦ (b + c) / d < 0.5 during discharge. The composition of metals, silicon, phosphorus, etc. in the entire particles of the lithium manganese composite oxide can be measured using, for example, ICP-MS (inductively coupled plasma mass spectrometer). Also, the oxygen composition of the entire particles of the lithium manganese composite oxide can be measured using, for example, EDX (energy dispersive X-ray analysis method). Further, it can be obtained by using valence evaluation of melting gas analysis and XAFS (X-ray absorption fine structure) analysis in combination with ICPMS analysis. The lithium manganese composite oxide refers to an oxide containing at least lithium and manganese, and may contain at least one element selected from the group consisting of chromium, cobalt, aluminum, nickel, iron, magnesium, molybdenum, zinc, indium, gallium, copper, titanium, niobium, silicon, and phosphorus.

[0140] [Structure of Positive Electrode Active Material] The positive electrode active material of one aspect of the present invention will be described with reference to FIGS. 5 to 9.

[0141] FIG. 5A is a top view schematic diagram of a positive electrode active material 100 which is one aspect of the present invention. The cross-sectional schematic diagram at A - B in FIG. 5A is shown in FIG. 5B.

[0142] <Elemental composition and distribution> The positive electrode active material 100 comprises lithium, a transition metal M1, oxygen, and an additive element X. The positive electrode active material 100 can also be described as a composite oxide represented by LiM1O2 (where M1 is one or more selected from Fe, Ni, Co, and Mn) to which the additive element X is added.

[0143] It is preferable to use a metal that can form a layered rock salt type composite oxide belonging to space group R-3m together with lithium as the transition metal in the positive electrode active material 100. For example, at least one of manganese, cobalt, and nickel can be used. In other words, the positive electrode active material 100 may use only cobalt as the transition metal, only nickel, two types of cobalt and manganese, two types of cobalt and nickel, or three types of cobalt, manganese, and nickel. In other words, the positive electrode active material 100 can have composite oxides containing lithium and a transition metal, such as lithium cobalt oxide, lithium nickel oxide, lithium cobalt oxide in which part of the cobalt is substituted with manganese, lithium cobalt oxide in which part of the cobalt is substituted with nickel, and nickel-manganese-lithium cobalt oxide. It is preferable to have nickel in addition to cobalt as the transition metal because the crystal structure may become more stable in the charged state at high voltage.

[0144] The additive element X in the positive electrode active material 100 is preferably one or more selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. These elements may further stabilize the crystal structure of the positive electrode active material 100. In other words, the positive electrode active material 100 can include lithium cobalt oxide having magnesium and fluorine, lithium cobalt oxide having magnesium, fluorine and titanium, lithium nickel-cobalt oxide having magnesium and fluorine, lithium cobalt-aluminate having magnesium and fluorine, lithium nickel-cobalt-aluminate having magnesium and fluorine, lithium nickel-manganese-cobalt oxide having magnesium and fluorine, etc. In this specification, the additive element X may be referred to as a mixture, part of a raw material, etc.

[0145] As shown in Figure 5B, the positive electrode active material 100 has a surface layer 100a and an interior layer 100b. It is preferable that the surface layer 100a has a higher concentration of the added element X than the interior layer 100b. Also, as shown by the gradient in Figure 5B, it is preferable that the added element X has a concentration gradient that increases from the interior to the surface. In this specification, the surface layer 100a refers to the region of the positive electrode active material 100 from the surface down to about 10 nm. A surface created by cracks and / or fissures may also be called a surface, and as shown in Figure 5C, the region from such a surface down to about 10 nm is called the surface layer 100c. Furthermore, the region of the positive electrode active material 100 that is deeper than the surface layer 100a and the surface layer 100c is called the interior layer 100b.

[0146] In one embodiment of the present invention, the positive electrode active material 100 is reinforced by a surface layer 100a, i.e., the outer periphery of the particles, which has a high concentration of the added element X, so that even if lithium is removed from the positive electrode active material 100 due to charging, the layered structure consisting of octahedrons of cobalt and oxygen does not break down.

[0147] Furthermore, it is preferable that the concentration gradient of the additive element X is uniformly distributed throughout the entire surface layer 100a of the positive electrode active material 100. This is because even if there is reinforcement in a part of the surface layer 100a, if there are unreinforced areas, stress may concentrate in those areas, which is undesirable. If stress concentrates in a part of the particles, defects such as cracks may occur from that point, which may lead to cracking of the positive electrode active material and a decrease in charge / discharge capacity.

[0148] Magnesium is divalent and is more stable in lithium sites than transition metal sites in layered rock salt crystal structures, thus readily occupying lithium sites. The presence of magnesium at an appropriate concentration in the lithium sites of the surface layer 100a facilitates the maintenance of the layered rock salt crystal structure. Furthermore, magnesium has a strong binding affinity for oxygen, which can suppress the desorption of oxygen from its surroundings. At appropriate concentrations, magnesium is preferable as it does not adversely affect lithium insertion and desorption during charging and discharging. However, excessive magnesium may adversely affect lithium insertion and desorption.

[0149] Aluminum is trivalent and can exist at transition metal sites in layered rock salt crystal structures. Aluminum can suppress the leaching of surrounding cobalt. Furthermore, because aluminum has a strong bonding force with oxygen, it can suppress the desorption of oxygen from around the aluminum. Therefore, by including aluminum as the additive element X, a positive electrode active material 100 can be made that is less prone to crystal structure collapse even after repeated charging and discharging.

[0150] Fluorine is a monovalent anion, and if some of the oxygen in the surface layer 100a is replaced by fluorine, the lithium desorption energy decreases. This is because the change in the valence of cobalt ions associated with lithium desorption differs depending on the presence or absence of fluorine. For example, without fluorine, the valence changes from trivalent to tetravalent, while with fluorine, it changes from divalent to trivalent, resulting in a different oxidation-reduction potential for cobalt ions. Therefore, if some of the oxygen in the surface layer 100a of the positive electrode active material 100 is replaced by fluorine, the desorption and insertion of lithium ions near the fluorine can occur more smoothly. This is preferable because it improves charge-discharge characteristics, rate characteristics, etc., when used in a secondary battery.

[0151] Titanium oxide is known to be superhydrophilic. Therefore, by using a positive electrode active material 100 having titanium oxide in its surface layer 100a, it is possible to improve wettability with highly polar solvents. When used in a secondary battery, good contact at the interface between the positive electrode active material 100 and the highly polar electrolyte may be achieved, potentially suppressing an increase in resistance. In this specification, the term "electrolyte" refers to a liquid electrolyte.

[0152] As the charging voltage of a secondary battery increases, the voltage at the positive electrode generally rises. The positive electrode active material according to one aspect of the present invention has a stable crystal structure even at high voltages. The stability of the crystal structure of the positive electrode active material in the charged state suppresses the decrease in capacity associated with repeated charging and discharging.

[0153] Furthermore, a short circuit in a secondary battery can not only cause malfunctions in the charging and / or discharging operations of the secondary battery, but also lead to overheating and ignition. To realize a safe secondary battery, it is preferable that the short-circuit current is suppressed even at high charging voltages. The positive electrode active material 100 in one aspect of the present invention suppresses the short-circuit current even at high charging voltages. Therefore, it is possible to create a secondary battery that achieves both high capacity and safety.

[0154] A secondary battery using the positive electrode active material 100 according to one embodiment of the present invention preferably satisfies high capacity, excellent charge-discharge cycle characteristics, and safety simultaneously.

[0155] The concentration gradient of the added element X can be evaluated, for example, using energy dispersive X-ray spectroscopy (EDX). Among EDX measurements, the method of scanning within a region to evaluate it in two dimensions is sometimes called EDX surface analysis. Furthermore, the method of extracting linear region data from EDX surface analysis and evaluating the distribution of atomic concentrations within the positive electrode active material particles is sometimes called line analysis.

[0156] EDX surface analysis (e.g., elemental mapping) allows for the quantitative analysis of the concentration of added element X in the surface layer 100a, interior 100b, and near grain boundaries of the positive electrode active material 100. Furthermore, EDX radiation analysis allows for the analysis of the concentration distribution of added element X.

[0157] When EDX radiation analysis is performed on the positive electrode active material 100, the magnesium concentration peak (the position where the concentration is maximum) in the surface layer 100a is preferably located within a depth of 3 nm from the surface toward the center of the positive electrode active material 100, more preferably within a depth of 1 nm, and even more preferably within a depth of 0.5 nm.

[0158] Furthermore, it is preferable that the distribution of fluorine in the positive electrode active material 100 overlaps with the distribution of magnesium. Therefore, when EDX radiation analysis is performed, the peak of fluorine concentration in the surface layer 100a (the position where the concentration is maximum) is preferably located within a depth of 3 nm from the surface toward the center of the positive electrode active material 100, more preferably within a depth of 1 nm, and even more preferably within a depth of 0.5 nm.

[0159] It should be noted that not all additive elements X have the same concentration distribution. For example, if the positive electrode active material 100 contains aluminum as additive element X, it is preferable that the distribution is slightly different from that of magnesium and fluorine. For example, when EDX radiation analysis is performed, it is preferable that the peak of magnesium concentration is closer to the surface than the peak of aluminum concentration in the surface layer 100a. For example, it is preferable that the peak of aluminum concentration is located at a depth of 0.5 nm to 20 nm from the surface toward the center of the positive electrode active material 100, and more preferably at a depth of 1 nm to 5 nm.

[0160] Furthermore, when EDX radiation analysis or EDX surface analysis is performed on the positive electrode active material 100, the ratio of the number of atoms of the added element X to the number of atoms of the transition metal M1 (X / M1) near the grain boundary is preferably 0.020 or more and 0.50 or less. More preferably 0.025 or more and 0.30 or less. More preferably 0.030 or more and 0.20 or less. For example, when the added element X is magnesium and the transition metal M1 is cobalt, the ratio of the number of atoms of magnesium to the number of atoms of cobalt (Mg / Co) near the grain boundary is preferably 0.020 or more and 0.50 or less. More preferably 0.025 or more and 0.30 or less. More preferably 0.030 or more and 0.20 or less.

[0161] As mentioned above, if the additive elements in the positive electrode active material 100 are in excess, they may adversely affect the insertion and removal of lithium. Furthermore, when used in a secondary battery, they may lead to increased resistance and decreased capacity. On the other hand, if they are insufficient, they may not be distributed throughout the entire surface layer 100a, resulting in insufficient maintenance of the crystal structure. Therefore, the concentration of additive element X in the positive electrode active material 100 is adjusted to an appropriate level.

[0162] Therefore, for example, the positive electrode active material 100 may have regions where excess additive element X is unevenly distributed. The presence of such regions removes excess additive element X from other regions, allowing for an appropriate concentration of additive element X in most of the interior and surface of the positive electrode active material 100. By achieving an appropriate concentration of additive element X in most of the interior and surface of the positive electrode active material 100, it is possible to suppress increases in resistance and decreases in capacity when used as a secondary battery. The ability to suppress increases in the resistance of a secondary battery is an extremely desirable characteristic, especially during high-rate charging and discharging.

[0163] Furthermore, in positive electrode active material 100 having regions where excess additive element X is unevenly distributed, it is permissible to mix in a certain degree of excess additive element X during the manufacturing process. This is preferable as it widens the margin in production.

[0164] In this specification, "non-uniformity" refers to a difference in the concentration of an element between a region A and a region B. Other terms that may be used include segregation, precipitation, heterogeneity, bias, high concentration, or low concentration.

[0165] <Crystal structure> Materials with a layered rock salt crystal structure, such as lithium cobalt oxide (LiCoO2), are known to have high discharge capacity and are excellent as positive electrode active materials for secondary batteries. Examples of materials with a layered rock salt crystal structure include composite oxides represented as LiM1O2 (where M1 is one or more elements selected from Fe, Ni, Co, and Mn).

[0166] It is known that the Jahn-Teller effect in transition metal compounds differs in strength depending on the number of electrons in the d orbitals of the transition metal.

[0167] In nickel-containing compounds, distortion can easily occur due to the Jahn-Teller effect. Therefore, when LiNiO2 is charged and discharged at high voltages, there is a concern that the crystal structure may collapse due to distortion. In LiCoO2, the effect of the Jahn-Teller effect is suggested to be smaller, and it may have better resistance to high-voltage charging and discharging, making it preferable.

[0168] The positive electrode active material will be explained using Figures 6 to 9. Figures 6 to 9 describe the case where cobalt is used as the transition metal in the positive electrode active material.

[0169] <Conventional positive electrode active material> The positive electrode active material shown in Figure 8 is lithium cobalt oxide (LiCoO2, LCO) without halogens or magnesium. The crystal structure of the lithium cobalt oxide shown in Figure 8 changes depending on the depth of charge. In other words, when denoted as LixCoO2, the crystal structure changes depending on the lithium occupancy rate x of the lithium sites.

[0170] As shown in Figure 8, lithium cobalt oxide in the x=1 state (discharge state) has a region with a crystal structure of space group R-3m, and there are three CoO2 layers in the unit cell. For this reason, this crystal structure is sometimes called an O3 type crystal structure. The CoO2 layer refers to a structure in which octahedral structures, in which oxygen atoms are coordinated to cobalt in a 6-coordinate manner, are continuous in the planar direction with shared edges.

[0171] Furthermore, when x=0, it has a crystal structure of space group P-3m1, with one CoO2 layer present in the unit cell. For this reason, this crystal structure is sometimes called an O1 type crystal structure.

[0172] Furthermore, lithium cobalt oxide at x=0.12 has a crystal structure with space group R-3m. This structure can be described as a structure in which CoO2 structures like P-3m1(O1) and LiCoO2 structures like R-3m(O3) are alternately stacked. For this reason, this crystal structure is sometimes called the H1-3 type crystal structure. Because actual lithium insertion and deinsertion can be uneven, the H1-3 type crystal structure is experimentally observed from x=0.25. In reality, the H1-3 type crystal structure has twice the number of cobalt atoms per unit cell compared to other structures. However, in this specification, including Figure 8, the c-axis of the H1-3 type crystal structure is shown as half the unit cell for easier comparison with other structures.

[0173] As an example, the H1-3 type crystal structure can be represented by the coordinates of cobalt and oxygen in a unit cell as follows: Co(0,0,0.42150±0.00016), O1(0,0,0.27671±0.00045), and O2(0,0,0.11535±0.00045). O1 and O2 are oxygen atoms, respectively. Thus, the H1-3 type crystal structure is represented by a unit cell using one cobalt and two oxygen atoms. On the other hand, as will be described later, the O3' type crystal structure in one aspect of the present invention is preferably represented by a unit cell using one cobalt and one oxygen atom. This indicates that the symmetry between cobalt and oxygen differs between the O3' type crystal structure and the H1-3 type structure, and that the O3' type crystal structure shows less variation from the O3 structure compared to the H1-3 type structure. The choice of which unit cell is preferable to represent the crystal structure of the positive electrode active material can be made, for example, by selecting the unit cell that results in a smaller GOF (goodness of fit) value in Rietveld analysis of the XRD pattern.

[0174] When high-voltage charging occurs, such as when the charging voltage is 4.6V or higher relative to the oxidation-reduction potential of lithium metal, or when deep charging occurs, such as when x = 0.24 or less, and discharging is repeated, lithium cobalt oxide undergoes repeated changes in its crystal structure (i.e., non-equilibrium phase changes) between the H1-3 type crystal structure and the R-3m(O3) structure in the discharged state.

[0175] However, these two crystal structures exhibit a significant displacement of the CoO2 layer. As shown by the dotted line and arrows in Figure 8, in the H1-3 type crystal structure, the CoO2 layer is significantly shifted from R-3m(O3). Such dynamic structural changes can negatively affect the stability of the crystal structure.

[0176] Furthermore, the volume difference is also significant. When comparing the same number of cobalt atoms, the volume difference between the H1-3 type crystal structure and the O3 type crystal structure in the discharged state is more than 3.0%.

[0177] In addition, the H1-3 type crystal structure, which consists of continuous CoO2 layers such as P-3m1(O1), is likely to be unstable.

[0178] Therefore, repeated high-voltage charging and discharging causes the crystal structure of lithium cobalt oxide to break down. This breakdown of the crystal structure leads to a deterioration of the cycle characteristics. This is thought to be because the breakdown of the crystal structure reduces the number of sites where lithium can exist stably, and also makes it more difficult for lithium to be inserted and removed.

[0179] <Positive electrode active material according to one aspect of the present invention> <Internal> The positive electrode active material 100 according to one aspect of the present invention can reduce the displacement of the CoO2 layer during repeated high-voltage charging and discharging. Furthermore, it can reduce the change in volume. Therefore, the positive electrode active material according to one aspect of the present invention can achieve excellent cycle characteristics. In addition, the positive electrode active material according to one aspect of the present invention can adopt a stable crystal structure in a high-voltage charged state. Therefore, the positive electrode active material according to one aspect of the present invention may be less prone to short circuits when a high-voltage charged state is maintained. In such cases, safety is further improved, which is preferable.

[0180] In one embodiment of the present invention, the change in crystal structure and the difference in volume per unit number of transition metal atoms between a fully discharged state and a high-voltage charged state are small.

[0181] Figure 6 shows the crystal structure of the positive electrode active material 100 before and after charging and discharging. The positive electrode active material 100 is a composite oxide containing lithium, cobalt as a transition metal, and oxygen. In addition to the above, it is preferable to have magnesium as an additive element X. Furthermore, it is preferable to have halogens such as fluorine and chlorine as additive element X.

[0182] The crystal structure at x=1 (discharge state) in Figure 6 is the same R-3m(O3) as in Figure 8. On the other hand, the positive electrode active material 100 of one embodiment of the present invention has a crystal structure different from the H1-3 type crystal structure when it is in a fully charged state. This structure belongs to the space group R-3m, and ions such as cobalt and magnesium occupy the oxygen 6 coordination positions. Furthermore, the symmetry of the CoO2 layer in this structure is the same as that of the O3 type. Therefore, this structure is referred to as the O3' type crystal structure in this specification. Note that in the diagram of the O3' type crystal structure shown in Figure 6, the representation of lithium is omitted in order to explain the symmetry of the cobalt atom and the symmetry of the oxygen atom, but in reality, lithium of, for example, less than 20 atomic percent relative to cobalt is present between the CoO2 layers. Furthermore, in both the O3 type crystal structure and the O3' type crystal structure, it is preferable that magnesium is present dilutely between the CoO2 layers, i.e., at the lithium sites. It is also preferable that halogens such as fluorine are present randomly and dilutely at the oxygen sites.

[0183] In the O3' type crystal structure, light elements such as lithium may occupy the oxygen 4-coordinate position.

[0184] Furthermore, the O3' type crystal structure has lithium randomly distributed between layers, but it can also be said to be a crystal structure similar to the CdCl2 type crystal structure. This crystal structure similar to the CdCl2 type is found when lithium nickelate is charged to x=0.06 (Li 0.06 Although its crystal structure is similar to that of NiO2, it is known that pure lithium cobaltate or layered rock salt-type cathode active materials containing a large amount of cobalt do not usually adopt this crystal structure.

[0185] In one embodiment of the present invention, the change in crystal structure when charged at high voltage and a large amount of lithium is desorbed is suppressed compared to conventional positive electrode active materials. For example, as shown by the dotted line in Figure 6, there is almost no displacement of the CoO2 layer in these crystal structures.

[0186] More specifically, the positive electrode active material 100 according to one embodiment of the present invention exhibits high structural stability even at high charging voltages. For example, in conventional positive electrode active materials, there is a charging voltage range in which the R-3m(O3) crystal structure can be maintained even at a charging voltage that results in an H1-3 type crystal structure, for example, a voltage of about 4.6V relative to the potential of lithium metal. Furthermore, there is a range in which an O3' type crystal structure can be adopted even at a higher charging voltage, for example, a voltage of about 4.65V to 4.7V relative to the potential of lithium metal. Only when the charging voltage is further increased may an H1-3 type crystal be observed. In addition, in secondary batteries, for example, when graphite is used as the negative electrode active material, there is a charging voltage range in which the R-3m(O3) crystal structure can be maintained even when the voltage of the secondary battery is 4.3V or higher and 4.5V or lower. Furthermore, there is a range in which an O3' type crystal structure can be adopted even at a higher charging voltage, for example, a voltage of 4.35V or higher and 4.55V or lower relative to the potential of lithium metal.

[0187] Therefore, in the positive electrode active material 100 of one aspect of the present invention, the crystal structure is less likely to collapse even when repeatedly charged and discharged at high voltage.

[0188] Furthermore, in the positive electrode active material 100, the difference in volume per unit cell between the O3-type crystal structure at x=1 and the O3'-type crystal structure at x=0.2 is 2.5% or less, more specifically 2.2% or less.

[0189] Furthermore, the O3' type crystal structure can be represented by showing the coordinates of cobalt and oxygen in the unit cell as follows: Co(0,0,0.5), O(0,0,x), within the range of 0.20≦x≦0.25.

[0190] Additive element X, such as magnesium, which is randomly and dilutely present between CoO2 layers, i.e., at lithium sites, has the effect of suppressing the displacement of the CoO2 layers. Therefore, when magnesium is present between CoO2 layers, an O3' type crystal structure is more likely to be formed. For this reason, it is preferable that magnesium is distributed in at least a portion of the surface layer of the positive electrode active material 100 according to one embodiment of the present invention, and moreover, distributed throughout the entire surface layer of the positive electrode active material 100. Furthermore, in order to distribute magnesium throughout the entire surface layer of the positive electrode active material 100, it is preferable to perform a heat treatment in the manufacturing process of the positive electrode active material 100 according to one embodiment of the present invention.

[0191] However, if the heat treatment temperature is too high, cation mixing will occur, increasing the likelihood that the added element X, such as magnesium, will enter the cobalt site. Magnesium present in the cobalt site does not help maintain the R-3m structure under high-voltage charging conditions. Furthermore, if the heat treatment temperature is too high, there are concerns about adverse effects such as the reduction of cobalt to its divalent state and the evaporation of lithium.

[0192] Therefore, it is preferable to add a halogen compound such as a fluorine compound to lithium cobalt oxide before the heat treatment to distribute magnesium throughout the surface layer of the positive electrode active material 100. Adding a halogen compound causes a decrease in the melting point of lithium cobalt oxide. By lowering the melting point, it becomes easier to distribute magnesium throughout the surface layer of the positive electrode active material 100 at a temperature at which cation mixing is less likely to occur. Furthermore, if a fluorine compound is present, it can be expected that the corrosion resistance to hydrofluoric acid produced by the decomposition of the electrolyte will be improved.

[0193] Furthermore, if the magnesium concentration is increased beyond the desired value, the effect on stabilizing the crystal structure may decrease. This is thought to be because magnesium will enter not only the lithium sites but also the cobalt sites. The number of magnesium atoms in the positive electrode active material according to one embodiment of the present invention is preferably 0.001 times or more and 0.1 times or less the number of transition metal atoms such as cobalt, more preferably greater than 0.01 times and less than 0.04 times, and even more preferably about 0.02 times. The magnesium concentration shown here may be, for example, a value obtained by elemental analysis of the entire positive electrode active material using ICP-MS, or it may be based on the value of the raw material composition during the process of manufacturing the positive electrode active material 100.

[0194] Lithium cobalt oxide may be mixed with one or more metals other than cobalt (hereinafter referred to as additive element X), such as nickel, aluminum, manganese, titanium, vanadium, and chromium, and it is particularly preferable to add nickel and one or more aluminum. Manganese, titanium, vanadium, and chromium may be stable in their tetravalent state and may contribute significantly to structural stability. Adding additive element X may make the crystal structure more stable in a high-voltage charged state. In one embodiment of the present invention, it is preferable that the additive element X is added at a concentration that does not significantly change the crystallinity of lithium cobalt oxide. For example, it is preferable that the amount is such that the aforementioned Jahn-Teller effect does not occur.

[0195] Nickel, manganese, and other transition metals, as well as aluminum, are preferably present at the cobalt site, but some may be present at the lithium site. Magnesium is also preferably present at the lithium site. Oxygen may be partially substituted with fluorine.

[0196] In one embodiment of the present invention, the capacity of the positive electrode active material may decrease as the magnesium concentration increases. One possible reason for this is that the amount of lithium contributing to charging and discharging may decrease due to the presence of magnesium in the lithium sites. In one embodiment of the present invention, the charge-discharge cycle characteristics may be improved by including nickel in addition to magnesium as additive element X in the positive electrode active material. In another embodiment of the present invention, the charge-discharge cycle characteristics may be improved by including aluminum in addition to magnesium as additive element X in the positive electrode active material. Furthermore, in one embodiment of the present invention, the charge-discharge cycle characteristics may be improved by using a positive electrode active material having magnesium, nickel, and aluminum as additive element X.

[0197] Below, we examine the elemental concentrations of a positive electrode active material according to one embodiment of the present invention, in which magnesium, nickel, and aluminum are used as additive element X.

[0198] The number of nickel atoms in the positive electrode active material according to one embodiment of the present invention is preferably 10% or less of the number of cobalt atoms, more preferably 7.5% or less, even more preferably 0.05% to 4%, and particularly preferably 0.1% to 2%. The nickel concentration shown herein may be, for example, a value obtained by elemental analysis of the entire positive electrode active material using ICP-MS, or it may be based on the value of the raw material composition during the manufacturing process of the positive electrode active material.

[0199] If the positive electrode active material is charged at a high voltage for an extended period, the constituent elements of the positive electrode active material may dissolve into the electrolyte, potentially causing the crystal structure to collapse. However, by including nickel in the above proportion, it may be possible to suppress the dissolution of constituent elements from the positive electrode active material 100.

[0200] The number of aluminum atoms in the positive electrode active material according to one embodiment of the present invention is preferably 0.05% to 4% of the number of cobalt atoms, and more preferably 0.1% to 2%. The aluminum concentration shown here may be, for example, a value obtained by elemental analysis of the entire positive electrode active material using ICP-MS, or it may be based on the value of the raw material composition during the manufacturing process of the positive electrode active material.

[0201] Furthermore, in the positive electrode active material having additive element X according to one aspect of the present invention, it is preferable that phosphorus is used as the additive element X. Moreover, it is more preferable that the positive electrode active material according to one aspect of the present invention has a compound containing phosphorus and oxygen.

[0202] In one embodiment of the present invention, the positive electrode active material contains a compound with phosphorus as an additive element X, which may make it less likely for a short circuit to occur when a high-temperature and high-voltage charged state is maintained for a long period of time.

[0203] In one embodiment of the present invention, if the positive electrode active material contains phosphorus as an additive element X, the hydrogen fluoride generated by the decomposition of the electrolyte may react with the phosphorus, potentially reducing the concentration of hydrogen fluoride in the electrolyte.

[0204] When the electrolyte contains LiPF6 as a lithium salt, hydrolysis may generate hydrogen fluoride. Hydrogen fluoride may also be generated by the reaction between PVDF, used as a component of the positive electrode, and alkali. Reducing the hydrogen fluoride concentration in the electrolyte may suppress corrosion of the current collector and / or peeling of the coating. Furthermore, it may suppress the decrease in adhesion due to gelation and / or insolubilization of the PVDF.

[0205] In one embodiment of the present invention, when the positive electrode active material 100 contains phosphorus and magnesium as additive elements X, it exhibits extremely high stability in a high-voltage charged state. When phosphorus and magnesium are present as additive elements X, the number of phosphorus atoms is preferably 1% to 20% of the number of cobalt atoms, more preferably 2% to 10%, and even more preferably 3% to 8%. In addition, the number of magnesium atoms is preferably 0.1% to 10% of the number of cobalt atoms, more preferably 0.5% to 5%, and even more preferably 0.7% to 4%. The concentrations of phosphorus and magnesium shown here may be values ​​obtained by performing an overall elemental analysis of the positive electrode active material 100 using, for example, ICP-MS, or they may be based on the values ​​of the raw material composition during the manufacturing process of the positive electrode active material 100.

[0206] If the positive electrode active material 100 has cracks, the presence of phosphorus, or more specifically, a compound containing phosphorus and oxygen, within the cracks may suppress the progression of the cracks.

[0207] As shown in Figure 6, the symmetry of oxygen atoms differs slightly between the O3-type and O3'-type crystal structures. Specifically, in the O3-type crystal structure, oxygen atoms are aligned along the dotted line, whereas in the O3'-type crystal structure, oxygen atoms are not strictly aligned. This is because, in the O3'-type crystal structure, the amount of tetravalent cobalt increases as lithium decreases, leading to a larger Jahn-Teller strain and distortion of the octahedral structure of CoO6. The increased repulsion between oxygen atoms in the CoO2 layer due to the decrease in lithium also plays a role.

[0208] <Surface layer 100a> It is preferable that magnesium is distributed throughout the entire surface layer 100a of the positive electrode active material 100 according to one embodiment of the present invention, and in addition, it is preferable that the magnesium concentration in the surface layer 100a is higher than the overall average. For example, it is preferable that the magnesium concentration in the surface layer 100a measured by XPS or the like is higher than the overall average magnesium concentration measured by ICP-MS or the like.

[0209] Furthermore, in one embodiment of the present invention, when the positive electrode active material 100 contains one or more metals other than cobalt, such as nickel, aluminum, manganese, iron, and chromium, it is preferable that the concentration of the metal near the particle surface is higher than the overall average. For example, it is preferable that the concentration of elements other than cobalt in the surface layer 100a, as measured by XPS or the like, is higher than the concentration of those elements in the entire particle, as measured by ICP-MS or the like.

[0210] The surface layer 100a of the positive electrode active material 100 is, in essence, entirely composed of crystal defects, and during charging, lithium escapes from the surface, making it a region where the lithium concentration tends to be lower than in the interior. Therefore, it is prone to instability and the crystal structure is easily disrupted. A higher magnesium concentration in the surface layer 100a can more effectively suppress changes in the crystal structure. Furthermore, a higher magnesium concentration in the surface layer 100a can also be expected to improve corrosion resistance to hydrofluoric acid produced by the decomposition of the electrolyte.

[0211] Furthermore, it is preferable that the concentration of halogens such as fluorine in the surface layer 100a of the positive electrode active material 100 in one embodiment of the present invention is higher than the overall average. The presence of halogens in the surface layer 100a, which is the region in contact with the electrolyte, can effectively improve corrosion resistance to hydrofluoric acid.

[0212] Thus, it is preferable that the surface layer 100a of the positive electrode active material 100 in one aspect of the present invention has a different composition from the interior 100b, with a higher concentration of additive elements, such as magnesium and fluorine. Furthermore, it is preferable that the composition adopts a crystalline structure that is stable at room temperature. For this reason, the surface layer 100a may have a different crystalline structure from the interior 100b. For example, at least a part of the surface layer 100a of the positive electrode active material 100 in one aspect of the present invention may have a rock salt type crystalline structure. Also, if the surface layer 100a and the interior 100b have different crystalline structures, it is preferable that the orientation of the crystals in the surface layer 100a and the interior 100b is approximately the same.

[0213] Layered rock salt crystals and the anions in rock salt crystals adopt a cubic close-packed structure (face-centered cubic lattice structure). It is also presumed that the anions in O3' type crystals adopt a cubic close-packed structure. In this specification, if the anions have a structure in which three layers are stacked with a slight offset from each other, such as ABCABC, then it will be called a cubic close-packed structure. Therefore, the anions do not have to be strictly a cubic lattice. At the same time, since real crystals always have defects, the analytical results do not necessarily conform to theory. For example, in FFT (Fast Fourier Transform) such as electron diffraction or TEM images, spots may appear at positions slightly different from the theoretical positions. For example, if the orientation from the theoretical position is 5 degrees or less, or 2.5 degrees or less, it can be said that it adopts a cubic close-packed structure.

[0214] When layered rock salt crystals are in contact with other rock salt crystals, there exists a crystal plane in which the orientation of the cubic close-packed structure composed of anions is aligned.

[0215] Alternatively, it can be explained as follows: In the cubic crystal structure, anions in the (111) plane have a triangular arrangement. The layered rock salt type has a space group R-3m and a rhombohedral structure, but to facilitate understanding of the structure, it is generally represented by a composite hexagonal lattice, and the (0001) plane of the layered rock salt type has a hexagonal lattice. The triangular lattice of the cubic (111) has a similar atomic arrangement to the hexagonal lattice of the (0001) plane of the layered rock salt type. The consistency between the two lattices can be described as the orientation of the cubic close-packed structure being aligned.

[0216] However, the space group of layered rock salt crystals and O3'-type crystals is R-3m, which differs from the space groups Fm-3m (the space group of typical rock salt crystals) and Fd-3m (the space group of rock salt crystals with the simplest symmetry). Therefore, the Miller indices of crystal planes satisfying the above conditions differ between layered rock salt crystals, O3'-type crystals, and rock salt crystals. In this specification, it is sometimes said that the crystal orientations are approximately the same when the orientations of the cubic close-packed structure composed of anions are aligned in layered rock salt crystals, O3'-type crystals, and rock salt crystals.

[0217] The approximate agreement of crystal orientation in two regions can be determined from TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle scattering annular dark-field scanning transmission electron microscope) images, ABF-STEM (annular bright-field scanning transmission electron microscope) images, electron diffraction, FFT of TEM images, etc. X-ray diffraction (XRD) and neutron diffraction can also be used as criteria for determination.

[0218] <Grain boundary> The additive element X in the positive electrode active material 100 according to one aspect of the present invention may be present randomly and dilutely within the material, but it is more preferable that a portion of it is segregated at the grain boundaries.

[0219] In other words, it is preferable that the concentration of the added element X at the grain boundaries and in the vicinity thereof of the positive electrode active material 100 in one embodiment of the present invention is higher than that of other regions inside.

[0220] Grain boundaries can be considered as surface defects. Therefore, like particle surfaces, they are prone to instability and easily initiate changes in crystal structure. Consequently, increasing the concentration of additive element X at and near the grain boundaries can more effectively suppress changes in crystal structure.

[0221] Furthermore, if the concentration of additive element X is high at and near the grain boundaries, even if cracks occur along the grain boundaries of the particles of the positive electrode active material 100 according to one embodiment of the present invention, the concentration of additive element X will be high near the surface created by the cracks. Therefore, the corrosion resistance to hydrofluoric acid can be improved even in the positive electrode active material after cracks have occurred.

[0222] In this specification, the term "near the grain boundary" refers to the region extending approximately 10 nm from the grain boundary.

[0223] <Particle size> If the particle size of the positive electrode active material 100 in one aspect of the present invention is too large, problems arise such as difficulty in lithium diffusion or the surface of the active material layer becoming too rough when coated onto the current collector. On the other hand, if the particle size is too small, problems arise such as difficulty in supporting the active material layer when coating onto the current collector or excessive reaction with the electrolyte. For this reason, the average particle size D50 is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less.

[0224] <Analysis method> Whether a certain positive electrode active material is a positive electrode active material 100 according to one embodiment of the present invention that exhibits an O3' type crystal structure when charged with a high voltage can be determined by analyzing the positive electrode charged with a high voltage using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. XRD is particularly preferable because it can analyze the symmetry of transition metals such as cobalt in the positive electrode active material with high resolution, compare the crystallinity and crystal orientation, analyze the periodic distortion of the lattice and the crystallite size, and can obtain sufficient accuracy even when measuring a positive electrode obtained by disassembling a secondary battery.

[0225] As described above, the positive electrode active material 100 according to one aspect of the present invention has the characteristic of showing little change in crystal structure between a high-voltage charged state and a discharged state. Materials in which the crystal structure that shows a large change from the discharged state accounts for 50 wt% or more when charged at high voltage are undesirable because they cannot withstand high-voltage charging and discharging. It is important to note that simply adding additive elements may not result in the desired crystal structure. For example, even if they are both magnesium and lithium cobaltate containing fluorine, there are cases where the O3' type crystal structure accounts for 60 wt% or more when charged at high voltage, and cases where the H1-3 type crystal structure accounts for 50 wt% or more. Furthermore, at a predetermined voltage, the O3' type crystal structure may account for almost 100 wt%, and if the predetermined voltage is further increased, the H1-3 type crystal structure may be generated. Therefore, in order to determine whether or not a material is the positive electrode active material 100 according to one aspect of the present invention, analysis of the crystal structure, including XRD, is necessary.

[0226] However, positive electrode active materials in a high-voltage charged or discharged state may undergo changes in their crystal structure when exposed to air. For example, they may change from an O3' type crystal structure to an H1-3 type crystal structure. Therefore, it is preferable to handle all samples in an inert atmosphere such as an argon atmosphere.

[0227] <Charging method> High-voltage charging to determine whether a certain composite oxide is the positive electrode active material 100 according to one aspect of the present invention can be performed, for example, by fabricating a coin cell (CR2032 type, 20 mm in diameter and 3.2 mm in height) with lithium as the counter electrode and then charging it.

[0228] More specifically, the positive electrode can be made by coating an aluminum foil positive electrode current collector with a slurry of a mixture of positive electrode active material, conductive material, and binder.

[0229] Lithium metal can be used for the counter electrode. However, if a material other than lithium metal is used for the counter electrode, the potential of the secondary battery and the potential of the positive electrode will differ. In this specification, the voltage and potential refer to the potential of the positive electrode unless otherwise specified.

[0230] The electrolyte in the electrolyte solution may be 1 mol / L lithium hexafluoride phosphate (LiPF6), and the electrolyte solution may be a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of EC:DEC=3:7, and vinylene carbonate (VC) at 2 wt%.

[0231] Polypropylene with a thickness of 25 μm can be used for the separator.

[0232] The positive electrode and negative electrode cans can be made of stainless steel (SUS).

[0233] The coin cell prepared under the above conditions is charged with a constant current of 4.6V and 0.5C, and then charged with a constant voltage until the current value becomes 0.01C. Here, 1C is defined as 137mA / g. The temperature is set to 25℃. After charging in this manner, the coin cell is disassembled in a glove box under an argon atmosphere, and the positive electrode is removed to obtain a positive electrode active material charged at high voltage. When performing various analyses thereafter, it is preferable to seal it under an argon atmosphere to suppress reactions with external components. For example, XRD can be performed by sealing it in a sealed container under an argon atmosphere.

[0234] <xrd> The ideal powder XRD patterns for the O3’-type crystal structure and the H1-3-type crystal structure calculated from the models, using CuKα1 radiation, are shown in FIGS. 7 and 9. Also shown for comparison are the ideal XRD patterns calculated from the crystal structures of LiCoO2 (O3) with x = 1 and CoO2 (O1) with x = 0. The patterns of LiCoO2 (O3) and CoO2 (O1) were created using Reflex Powder Diffraction, which is one of the modules of Materials Studio (BIOVIA), based on the crystal structure information obtained from the ICSD (Inorganic Crystal Structure Database). The range of 2θ was set from 15° to 75°, Step size = 0.01, wavelength λ1 = 1.540562×10-10 m, λ2 was not set, and the Monochromator was set to single. The pattern of the O3’-type crystal structure was estimated from the XRD pattern of the cathode active material of one aspect of the present invention, and was fitted using TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker), and the XRD pattern was created in the same manner as the others.

[0235] As shown in FIG. 7, in the O3’-type crystal structure, diffraction peaks appear at 2θ = 19.30 ± 0.20° (19.10° or more and 19.50° or less) and 2θ = 45.55 ± 0.10° (45.45° or more and 45.65° or less). More specifically, sharp diffraction peaks appear at 2θ = 19.30 ± 0.10° (19.20° or more and 19.40° or less) and 2θ = 45.55 ± 0.05° (45.50° or more and 45.60° or less). However, as shown in FIG. 9, peaks do not appear at these positions in the H1-3-type crystal structure and CoO2 (P-3m1, O1). Therefore, it can be said that the appearance of peaks at 2θ = 19.30 ± 0.20° and 2θ = 45.55 ± 0.10° in the state of being charged at a high voltage is a characteristic of the cathode active material 100 of one aspect of the present invention.

[0236] It can also be said that the crystal structure at x = 1 and the crystal structure in the high-voltage charged state have positions where XRD diffraction peaks appear that are close. More specifically, for two or more, more preferably three or more, of the main diffraction peaks of both, the difference in the positions where the peaks appear is 2θ = 0.7° or less, more preferably 2θ = 0.5° or less.

[0237] Note that the positive electrode active material 100 of one aspect of the present invention has an O3'-type crystal structure when charged at a high voltage, but not all of the positive electrode active material 100 needs to have an O3'-type crystal structure. It may contain other crystal structures or a part thereof may be amorphous. However, when performing Rietveld analysis on the XRD pattern, it is preferable that the O3'-type crystal structure is 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more. If the O3'-type crystal structure is 50 wt% or more, more preferably 60 wt% or more, and even more preferably 66 wt% or more, a positive electrode active material with excellent cycle characteristics can be obtained.

[0238] Also, even after 100 cycles or more of charge and discharge from the start of measurement, when performing Rietveld analysis, it is preferable that the O3'-type crystal structure is 35 wt% or more, more preferably 40 wt% or more, and even more preferably 43 wt% or more.

[0239] In addition, the crystallite size of the O3'-type crystal structure possessed by the particles of the positive electrode active material only decreases to about 1 / 10 of that of LiCoO2 (O3) in the discharged state. Therefore, even under the same XRD measurement conditions as the positive electrode before charge and discharge, a clear peak of the O3'-type crystal structure can be confirmed in the high-voltage charged state. On the other hand, in simple LiCoO2, even if a part has a structure similar to the O3'-type crystal structure, the crystallite size becomes small and the peak becomes broad and small. The crystallite size can be obtained from the half-width of the XRD peak.

[0240] In one embodiment of the present invention, the positive electrode active material preferably has a small effect of the Jahn-Teller effect, as described above. The positive electrode active material in one embodiment of the present invention preferably has a layered rock salt type crystal structure and mainly contains cobalt as a transition metal. In addition, the positive electrode active material in one embodiment of the present invention may contain the aforementioned additive element X in addition to cobalt, as long as the effect of the Jahn-Teller effect is small.

[0241] Upon considering a preferred range for the lattice constant, it was found that in a positive electrode active material according to one embodiment of the present invention, the layered rock salt type crystal structure of the particles of the positive electrode active material in a non-charged or discharged state, as estimated from the XRD pattern, has a lattice constant of 2.814 × 10⁻¹⁴ in the a-axis. -10 Larger than m, 2.817 × 10 -10 It is smaller than m, and the lattice constant of the c axis is greater than 14.05 × 10⁻¹⁰m, which is 14.07 × 10⁻¹⁰m. -10 It was found that a value smaller than m is preferable. The state without charging and discharging may, for example, be the powder state before the positive electrode of the secondary battery is manufactured.

[0242] Alternatively, in the layered rock salt-type crystal structure of the positive electrode active material particles in a non-charging or discharged state, it is preferable that the value obtained by dividing the lattice constant of the a-axis by the lattice constant of the c-axis (a-axis / c-axis) is greater than 0.20000 and less than 0.20049.

[0243] Alternatively, when XRD analysis is performed on the layered rock salt-type crystal structure of the positive electrode active material particles in a non-charging or discharged state, a first peak may be observed when 2θ is between 18.50° and 19.30°, and a second peak may be observed when 2θ is between 38.00° and 38.80°.

[0244] The peaks appearing in the powder XRD pattern reflect the crystal structure of the interior 100b of the positive electrode active material 100, which occupies most of the volume of the positive electrode active material 100. The crystal structure of the surface layer 100a and other parts can be analyzed by electron diffraction of the cross-section of the positive electrode active material 100.

[0245] <xps> X-ray photoelectron spectroscopy (XPS) allows for analysis of regions from the surface to a depth of approximately 2 to 8 nm (usually around 5 nm), enabling quantitative analysis of the concentration of each element in about half of the surface layer 100a. Furthermore, narrow-scan analysis allows for the analysis of elemental bonding states. The quantitative accuracy of XPS is generally around ±1 atomic percent, and the detection limit is approximately 1 atomic percent, although this varies depending on the element.

[0246] When XPS analysis is performed on the positive electrode active material 100 according to one embodiment of the present invention, the number of atoms of the additive element X is preferably 1.6 to 6.0 times the number of atoms of the transition metal, and more preferably 1.8 to less than 4.0 times. When the additive element X is magnesium and the transition metal M1 is cobalt, the number of magnesium atoms is preferably 1.6 to 6.0 times the number of cobalt atoms, and more preferably 1.8 to less than 4.0 times. Furthermore, the number of halogen atoms such as fluorine is preferably 0.2 to 6.0 times the number of atoms of the transition metal, and more preferably 1.2 to 4.0 times.

[0247] When performing XPS analysis, for example, monochromatic aluminum can be used as the X-ray source. The extraction angle can also be set to, for example, 45°.

[0248] Furthermore, when the positive electrode active material 100 according to one embodiment of the present invention is subjected to XPS analysis, the peak indicating the bond energy between fluorine and other elements is preferably 682 eV or more and less than 685 eV, and more preferably around 684.3 eV. This value is different from both the bond energy of lithium fluoride, which is 685 eV, and the bond energy of magnesium fluoride, which is 686 eV. In other words, when the positive electrode active material 100 according to one embodiment of the present invention contains fluorine, it is preferable that the bond is with something other than lithium fluoride and magnesium fluoride.

[0249] Furthermore, when the positive electrode active material 100 according to one embodiment of the present invention is subjected to XPS analysis, the peak indicating the bond energy between magnesium and other elements is preferably 1302 eV or more and less than 1304 eV, and more preferably around 1303 eV. This value is different from the bond energy of magnesium fluoride, which is 1305 eV, and is close to the bond energy of magnesium oxide. In other words, when the positive electrode active material 100 according to one embodiment of the present invention contains magnesium, it is preferable that the bond is with an element other than magnesium fluoride.

[0250] It is preferable that the additive element X, such as magnesium and aluminum, which is preferably present in large quantities in the surface layer 100a, has a higher concentration measured by XPS or the like than the concentration measured by ICP-MS (inductively coupled plasma mass spectrometry) or GD-MS (glow discharge mass spectrometry).

[0251] When magnesium and aluminum are processed to expose their cross-sections and analyzed using TEM-EDX, it is preferable that the concentration in the surface layer 100a is higher than the concentration in the interior 100b. Processing can be carried out, for example, by FIB.

[0252] In XPS (X-ray photoelectron spectroscopy) analysis, the number of magnesium atoms is preferably 0.4 to 1.5 times the number of cobalt atoms. On the other hand, the ratio of magnesium atoms (Mg / Co) determined by ICP-MS analysis is preferably 0.001 to 0.06.

[0253] On the other hand, it is preferable that the nickel contained in the transition metal is not concentrated in the surface layer 100a but is distributed throughout the entire positive electrode active material 100. However, this does not apply if there is a region where the aforementioned excess additive element X is concentrated.

[0254] <Surface roughness and specific surface area> The positive electrode active material 100 of one embodiment of the present invention preferably has a smooth surface with few irregularities. The fact that the surface is smooth and has few irregularities is one factor indicating that the distribution of the additive element X in the surface layer portion 100a is good. In the production process of the positive electrode active material 100, when initial heating is performed on lithium cobaltate or lithium nickel-cobalt-manganese oxide before adding the additive element X, it is particularly preferable as the positive electrode active material 100 because the charge-discharge cycle characteristics at high voltage are remarkably excellent.

[0255] In addition, due to the smooth surface and few irregularities of the positive electrode active material 100, the stability of the surface of the positive electrode active material 100 is improved, and the generation of pits may be suppressed.

[0256] The fact that the surface is smooth and has few irregularities can be determined from, for example, the cross-sectional SEM image or cross-sectional TEM image of the positive electrode active material 100, the specific surface area of the positive electrode active material 100, etc.

[0257] For example, as follows, the smoothness of the surface can be quantified from the cross-sectional SEM image of the positive electrode active material 100.

[0258] First, the positive electrode active material 100 is processed by FIB or the like to expose the cross-section. At this time, it is preferable to cover the positive electrode active material 100 with a protective film, a protective agent, etc. Next, an SEM image of the interface between the protective film or the like and the positive electrode active material 100 is taken. Noise processing is performed on the SEM image with image processing software. For example, after performing Gaussian blur (σ = 2), binarization is performed. Further, interface extraction is performed with image processing software. Further, the interface line between the protective film or the like and the positive electrode active material 100 is selected with a magic hand tool or the like, and the data is extracted into spreadsheet software or the like. Using the functions of spreadsheet software or the like, correction is performed from the regression curve (quadratic regression), a parameter for calculating roughness is obtained from the data after slope correction, and the root mean square (RMS) surface roughness with the standard deviation calculated is obtained. Also, this surface roughness is the surface roughness of the positive electrode active material at least at 400 nm on the outer periphery of the particles.

[0259] In this embodiment, the particle surface of the positive electrode active material 100 preferably has a root mean square (RMS) surface roughness of 10 nm or less, less than 3 nm, preferably less than 1 nm, and more preferably less than 0.5 nm.

[0260] The image processing software used for noise reduction, interface extraction, etc., is not particularly limited, but for example, "ImageJ" can be used. Similarly, the spreadsheet software is not particularly limited, but for example, Microsoft Office Excel can be used.

[0261] Furthermore, for example, the surface smoothness of the positive electrode active material 100 can also be quantified from the ratio of the actual specific surface area AR, measured by the gas adsorption method using the constant-volume method, to the ideal specific surface area Ai.

[0262] The ideal specific surface area Ai is calculated assuming that all particles have the same diameter D50, the same weight, and are ideally spherical in shape.

[0263] The median diameter D50 can be measured using a particle size analyzer that employs laser diffraction and scattering methods. The specific surface area can be measured using a specific surface area measuring device that employs a gas adsorption method based on constant volume, for example.

[0264] In one embodiment of the present invention, the positive electrode active material 100 preferably has a ratio AR / Ai of 2 or less between the ideal specific surface area Ai, which is determined from the median diameter D50, and the actual specific surface area AR.

[0265] [Defects in positive electrode active material] Examples of defects that may occur in positive electrode active material particles are shown in Figures 10 and 11. A positive electrode active material according to one aspect of the present invention is expected to have the effect of suppressing the occurrence of the progressive defects shown below.

[0266] Charging and discharging under high voltage conditions of 4.5V or higher or high temperature (45°C or higher) may cause progressive defects (also called pits) to occur in the positive electrode active material particles. In addition, expansion and contraction of the positive electrode active material particles due to charging and discharging may cause new defects such as cracks to occur. Figure 10 shows a schematic cross-sectional view of the positive electrode active material particles 51. In the positive electrode active material particles 51, pits are shown as holes in 54 and 58, but the opening shape is not circular and has depth, and cracks are shown in 57. 55 is a crystal plane, 52 is a recess, and 53 and 56 are barrier films. Cracks may occur when the electrode is pressed, but cracks that occur during pressing do not have the surface layer containing the aforementioned additive element X, and therefore may induce progressive defects during charging and discharging. When an electrode is manufactured using the electrode manufacturing method according to one embodiment of the present invention, it is expected that the occurrence of cracks during electrode pressing will be suppressed, and therefore, it is expected that the occurrence of progressive defects due to charging and discharging under high voltage conditions of 4.5V or higher or high temperature (45°C or higher) will be suppressed.

[0267] The positive electrode active material of lithium-ion secondary batteries is typically LCO and NCM, which can be described as an alloy containing multiple metallic elements (such as cobalt and nickel). At least one of the multiple positive electrode active material particles has a defect, and this defect may change before and after charging and discharging. When used in secondary batteries, the positive electrode active material particles may be chemically or electrochemically eroded by the surrounding environmental substances (such as electrolyte), or the material may deteriorate. This deterioration does not occur uniformly on the particle surface, but rather concentrates locally, and repeated charging and discharging of the secondary battery can cause defects to develop deeply from the surface into the interior.

[0268] The phenomenon in which defects progress in positive electrode active material particles to form holes can also be called pitting corrosion, and the holes generated by this phenomenon are referred to as pits in this specification.

[0269] In this specification, cracks and pits are distinct. Cracks may exist immediately after the fabrication of positive electrode active material particles, but pits do not. A pit can be described as a hole where several layers of cobalt and oxygen have been removed due to charging and discharging under high voltage conditions of 4.5V or higher or high temperature (45°C or higher), and can also be described as a location where cobalt has leached out. A crack refers to a new surface created by the application of physical pressure, or a fissure caused by a grain boundary. Cracks may also occur due to the expansion and contraction of particles due to charging and discharging. Furthermore, pits may occur from cracks or cavities within particles.

[0270] <Slip> Figure 11A is a cross-sectional STEM image of a defect in the positive electrode active material after a positive electrode active material layer has been formed on the current collector and then pressed using a general method. Pressing has resulted in a step on the particle surface perpendicular to the grid lines (c-axis direction), and evidence of deformation along the grid line direction (ab-plane direction) can be observed.

[0271] Figure 11B is a schematic cross-sectional view of a particle before pressing. In the particle before pressing, a barrier layer 56 containing Mg, Al, etc., is present relatively uniformly on the particle surface perpendicular to the lattice pattern. Figure 11B also shows a crystal plane 55 that does not have slip.

[0272] Figure 11C is a schematic cross-sectional view of the particles after pressing. The pressing process causes displacement in the lattice pattern direction (ab-plane direction). The Mg and Al layers also have multiple steps and become non-uniform. Regarding the displacement in the ab-plane direction, the same shape of irregularities is observed on the particle surface opposite to the surface where irregularities were observed, indicating that some particles are displaced in the ab-plane direction.

[0273] The multiple steps shown in Figure 11C are observed as striped patterns on the particle surface. These striped patterns on the particle surface, observed due to steps caused by shifting during pressing, are called slip (stack faults). Such particle slip can lead to unevenness in the barrier film, potentially causing degradation. When electrodes are manufactured using the electrode manufacturing method according to one embodiment of the present invention, it is expected that the occurrence of slip during electrode pressing can be suppressed, thus enabling the production of secondary batteries with less degradation.

[0274] [Cathode active material composite] Alternatively, the positive electrode active material 100 in one embodiment of the present invention may be a positive electrode active material composite having a coating layer covering at least a portion of the positive electrode active material 100. For example, one or more of glass, oxide, and LiM2PO4 (where M2 is one or more selected from Fe, Ni, Co, and Mn) can be used as the coating layer.

[0275] As the glass coating layer of the positive electrode active material composite, a material having an amorphous portion can be used. Examples of materials having an amorphous portion include materials having one or more selected from SiO2, SiO, Al2O3, TiO2, Li4SiO4, Li3PO4, Li2S, SiS2, B2S3, GeS4, AgI, Ag2O, Li2O, P2O5, B2O3, and V2O5, and Li7P3S. 11 , or Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 < x < 2, 0 < y < 3, etc.) can be used. The material having an amorphous portion can be used in an entirely amorphous state or in a state of crystallized glass (also referred to as glass ceramics) in which a part is crystallized. It is desirable for the glass to have lithium ion conductivity. Lithium ion conductivity can also be said to have lithium ion diffusivity and lithium ion penetrability. Further, the glass preferably has a melting point of 800 °C or lower, more preferably 500 °C or lower. Further, it is preferable for the glass to have electronic conductivity. Further, the glass preferably has a softening point of 800 °C or lower, and for example, a Li2O-B2O3-SiO2-based glass can be used.

[0276] Examples of the oxide included in the coating layer of the positive electrode active material composite include aluminum oxide, zirconium oxide, hafnium oxide, niobium oxide, etc. Further, examples of LiM2PO4 (M2 is one or more selected from Fe, Ni, Co, Mn) included in the coating layer of the positive electrode active material composite include LiFePO4, LiNiPO4, LiCoPO4, LiMnPO4, LiFe a Ni b PO4, LiFe a Co b PO4, LiFe a Mn b PO4, LiNi a Co b PO4, LiNi a Mn b PO4 (a + b is 1 or less, 0 < a < 1, 0 < b < 1), LiFe c Ni d Co e PO4, LiFe c Ni d Mn e PO4, LiNi c Co d Mn e PO4 (c + d + e is 1 or less, 0 < c < 1, 0 < d < 1, 0 < e < 1), LiFe f Ni g Co h Mn i PO4 (f + g + h + i is 1 or less, 0 < f < 1, 0 < g < 1, 0 < h < 1, 0 < i < 1), etc.

[0277] A composite treatment can be used to fabricate the coating layer of the positive electrode active material composite. Examples of composite treatments include mechanical energy composite treatments such as mechanochemical methods, mechanofusion methods, and ball milling methods; liquid phase reaction composite treatments such as coprecipitation, hydrothermal methods, and sol-gel methods; and gas phase reaction composite treatments such as barrel sputtering, ALD (Atomic Layer Deposition), vapor deposition, and CVD (Chemical Vapor Deposition). For example, Picobond manufactured by Hosokawa Micron can be used as a mechanical energy composite treatment. Furthermore, it is preferable to perform one or more heat treatments during the composite treatment.

[0278] Because the positive electrode active material composite reduces contact between the positive electrode active material and the electrolyte, the degradation of the secondary battery can be suppressed.

[0279] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0280] (Embodiment 3) This embodiment describes examples of multiple shapes of secondary batteries having a positive or negative electrode, manufactured by the manufacturing method described in the previous embodiment.

[0281] [Coin-type rechargeable battery] An example of a coin-type rechargeable battery is described below. Figure 12A is an exploded perspective view of a coin-type (single-layer flat type) rechargeable battery, Figure 12B is an external view, and Figure 12C is a cross-sectional view thereof. Coin-type rechargeable batteries are mainly used in small electronic devices. In this specification, the term "coin-type battery" includes button-type batteries.

[0282] Figure 12A is a schematic diagram to show the overlapping (upper and lower relationships and positional relationships) of the components for clarity. Therefore, Figures 12A and 12B are not perfectly identical corresponding diagrams.

[0283] In Figure 12A, the positive electrode 304, separator 310, negative electrode 307, spacer 322, and washer 312 are stacked. These are sealed with the negative electrode can 302 and the positive electrode can 301. Note that the gasket for sealing is not shown in Figure 12A. The spacer 322 and washer 312 are used to protect the inside or to fix their position within the can when the positive electrode can 301 and the negative electrode can 302 are crimped together. The spacer 322 and washer 312 are made of stainless steel or insulating material.

[0284] The positive electrode 304 is a laminated structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305.

[0285] To prevent a short circuit between the positive and negative electrodes, a separator 310 and a ring-shaped insulator 313 are arranged to cover the sides and top surfaces of the positive electrode 304, respectively. The separator 310 has a larger planar area than the positive electrode 304.

[0286] Figure 12B is a perspective view of the completed coin-type rechargeable battery.

[0287] The coin-type secondary battery 300 has a positive electrode casing 301, which also serves as the positive electrode terminal, and a negative electrode casing 302, which also serves as the negative electrode terminal, insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with it. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with it. Furthermore, the negative electrode 307 is not limited to a laminated structure, and lithium metal foil or a lithium-aluminum alloy foil may be used.

[0288] Furthermore, for the positive electrode 304 and negative electrode 307 used in the coin-type secondary battery 300, the active material layer only needs to be formed on one side.

[0289] The positive electrode can 301 and the negative electrode can 302 can be made of metals such as nickel, aluminum, or titanium, or alloys thereof, or alloys of these with other metals (e.g., stainless steel), which are corrosion-resistant to the electrolyte. Furthermore, it is preferable to coat them with nickel and aluminum, etc., to prevent corrosion caused by the electrolyte. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307.

[0290] The negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte solution, and as shown in Figure 12C, the positive electrode 304, separator 310, negative electrode 307, and negative electrode 302 are stacked in this order with the positive electrode 301 at the bottom, and the positive electrode 301 and negative electrode 302 are crimped together via a gasket 303 to manufacture a coin-type secondary battery 300.

[0291] The above configuration makes it possible to create a coin-type secondary battery 300 with high capacity, high charge / discharge capacity, and excellent cycle characteristics. Furthermore, if a solid electrolyte layer is present between the negative electrode 307 and the positive electrode 304, the separator 310 may be unnecessary.

[0292] [Cylindrical rechargeable battery] An example of a cylindrical secondary battery will be explained with reference to Figure 13A. As shown in Figure 13A, the cylindrical secondary battery 616 has a positive electrode cap (battery cover) 601 on the top surface and a battery casing (outer casing) 602 on the sides and bottom. The positive electrode cap 601 and the battery casing (outer casing) 602 are insulated from each other by a gasket (insulating packing) 610.

[0293] Figure 13B is a schematic diagram showing a cross-section of a cylindrical secondary battery. The cylindrical secondary battery shown in Figure 13B has a positive electrode cap (battery cover) 601 on the top surface and a battery casing (outer casing) 602 on the sides and bottom. The positive electrode cap and the battery casing (outer casing) 602 are insulated from each other by a gasket (insulating packing) 610.

[0294] Inside the hollow cylindrical battery casing 602, a battery element is provided, in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 in between. Although not shown, the battery element is wound around a central axis. The battery casing 602 is closed at one end and open at the other. The battery casing 602 can be made of metals such as nickel, aluminum, and titanium, or alloys thereof, or alloys of these with other metals (e.g., stainless steel), which are corrosion-resistant to the electrolyte. Furthermore, it is preferable to coat the battery casing 602 with nickel and aluminum to prevent corrosion by the electrolyte. Inside the battery casing 602, the battery element, in which the positive electrode, negative electrode, and separator are wound, is sandwiched between a pair of opposing insulating plates 608 and 609. In addition, a non-aqueous electrolyte (not shown) is injected into the inside of the battery casing 602 in which the battery element is provided. The non-aqueous electrolyte can be the same as that used in coin-type secondary batteries.

[0295] Since the positive and negative electrodes used in cylindrical storage batteries are wound, it is preferable to form the active material on both sides of the current collector. Figures 13A to 13D illustrate a secondary battery 616 in which the height of the cylinder is greater than the diameter of the cylinder, but the battery is not limited to this configuration. A secondary battery in which the diameter of the cylinder is greater than the height of the cylinder is also possible. Such a configuration allows for, for example, miniaturization of the secondary battery.

[0296] By using the positive electrode active material 100 obtained in the above-described embodiment as the positive electrode 604, a cylindrical secondary battery 616 with high capacity, high charge / discharge capacity, and excellent cycle characteristics can be obtained.

[0297] A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be made of metal materials such as aluminum. The positive electrode terminal 603 is resistance-welded to the safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC element (Positive Temperature Coefficient) 611. The safety valve mechanism 613 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery rises above a predetermined threshold. The PTC element 611 is a thermal resistance element whose resistance increases when the temperature rises, and it prevents abnormal heat generation by limiting the amount of current through the increase in resistance. Barium titanate (BaTiO3) based semiconductor ceramics can be used for the PTC element.

[0298] Figure 13C shows an example of an energy storage system 615. The energy storage system 615 has multiple secondary batteries 616. The positive electrode of each secondary battery is in contact with a conductor 624 separated by an insulator 625 and is electrically connected. The conductor 624 is electrically connected to a control circuit 620 via wiring 623. The negative electrode of each secondary battery is also electrically connected to the control circuit 620 via wiring 626. The control circuit 620 can be a protective circuit to prevent overcharging or over-discharging, etc.

[0299] Figure 13D shows an example of an energy storage system 615. The energy storage system 615 has multiple secondary batteries 616, which are sandwiched between conductive plates 628 and 614. The multiple secondary batteries 616 are electrically connected to conductive plates 628 and 614 by wiring 627. The multiple secondary batteries 616 may be connected in parallel or in series. By configuring an energy storage system 615 with multiple secondary batteries 616, a large amount of power can be extracted.

[0300] Multiple secondary batteries 616 may be connected in parallel and then further connected in series.

[0301] A temperature control device may be provided between the multiple secondary batteries 616. When a secondary battery 616 overheats, it can be cooled by the temperature control device, and when a secondary battery 616 becomes too cold, it can be heated by the temperature control device. This makes the performance of the energy storage system 615 less susceptible to the influence of ambient temperature.

[0302] Furthermore, in Figure 13D, the energy storage system 615 is electrically connected to the control circuit 620 via wiring 621 and wiring 622. Wiring 621 is electrically connected to the positive terminals of the multiple secondary batteries 616 via conductive plate 628, and wiring 622 is electrically connected to the negative terminals of the multiple secondary batteries 616 via conductive plate 614.

[0303] [Other structural examples of secondary batteries] Examples of secondary battery structures will be explained using Figures 14 and 15.

[0304] The secondary battery 913 shown in Figure 14A has a wound body 950 with terminals 951 and 952 inside a housing 930. The wound body 950 is immersed in an electrolyte inside the housing 930. Terminal 952 is in contact with the housing 930, while terminal 951 is not in contact with the housing 930 due to the use of an insulating material or the like. In Figure 14A, the housing 930 is shown separated for convenience, but in reality, the wound body 950 is covered by the housing 930, and terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (e.g., aluminum) or a resin material.

[0305] Furthermore, as shown in Figure 14B, the housing 930 shown in Figure 14A may be formed from multiple materials. For example, in the secondary battery 913 shown in Figure 14B, housing 930a and housing 930b are bonded together, and the winding body 950 is provided in the area surrounded by housing 930a and housing 930b.

[0306] For the housing 930a, an insulating material such as organic resin can be used. In particular, by using a material such as organic resin on the surface where the antenna is formed, shielding of the electric field by the secondary battery 913 can be suppressed. If the shielding of the electric field by housing 930a is small, the antenna may be placed inside housing 930a. For housing 930b, for example, a metal material can be used.

[0307] Furthermore, the structure of the wound body 950 is shown in Figure 14C. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the separator 933 in between, and the stacked sheets are wound up. Note that multiple stacks of the negative electrode 931, positive electrode 932, and separator 933 may be stacked.

[0308] Alternatively, the secondary battery 913 may have a wound body 950a as shown in Figures 15A to 15C. The wound body 950a shown in Figure 15A 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.

[0309] By using the positive electrode active material 100 obtained in the above-described embodiment as the positive electrode 932, a secondary battery 913 with high capacity, high charge / discharge capacity, and excellent cycle characteristics can be obtained.

[0310] The separator 933 has a wider width than the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap with the negative electrode active material layer 931a and the positive electrode active material layer 932a. Furthermore, it is preferable from a safety standpoint that the negative electrode active material layer 931a is wider than the positive electrode active material layer 932a. A wound body 950a of this shape is also preferable due to its good safety and productivity.

[0311] As shown in Figure 15B, the negative electrode 931 is electrically connected to terminal 951. Terminal 951 is electrically connected to terminal 911a. The positive electrode 932 is electrically connected to terminal 952. Terminal 952 is electrically connected to terminal 911b.

[0312] As shown in Figure 15C, the coiled body 950a and electrolyte are covered by the housing 930, forming a secondary battery 913. It is preferable to provide a safety valve, an overcurrent protection element, etc., in the housing 930. The safety valve is a valve that opens the inside of the housing 930 at a predetermined internal pressure to prevent the battery from rupturing.

[0313] As shown in Figure 15B, the secondary battery 913 may have multiple windings 950a. By using multiple windings 950a, a secondary battery 913 with a larger charge / discharge capacity can be made. Other elements of the secondary battery 913 shown in Figures 15A and 15B can be referenced from the description of the secondary battery 913 shown in Figures 14A to 14C.

[0314] <Laminated rechargeable battery> Next, an example of a laminate-type secondary battery is shown in Figures 16A and 16B, which show an example of its external appearance. Figures 16A and 16B show a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0315] Figure 17A shows the external views of the positive electrode 503 and the negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and the positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. The positive electrode 503 also has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as the tab region). The negative electrode 506 has a negative electrode current collector 504, and the negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. The negative electrode 506 also has a region where the negative electrode current collector 504 is partially exposed, i.e., the tab region. The area and shape of the tab regions of the positive and negative electrodes are not limited to the example shown in Figure 17A.

[0316] <Method for manufacturing laminated rechargeable batteries> Here, an example of a method for manufacturing a laminate-type secondary battery, whose external view is shown in Figure 16A, will be explained using Figures 17B and 17C.

[0317] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. Figure 17B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example using 5 sets of negative electrodes and 4 sets of positive electrodes is shown. This can also be called a laminate consisting of negative electrodes, separators, and positive electrodes. Next, the tab regions of the positive electrode 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For joining, ultrasonic welding, for example, can be used. Similarly, the tab regions of the negative electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0318] Next, the negative electrode 506, separator 507, and positive electrode 503 are placed on the outer casing 509.

[0319] Next, as shown in Figure 17C, the outer casing 509 is bent at the portion indicated by the dashed line. Then, the outer periphery of the outer casing 509 is joined. For joining, for example, heat compression bonding may be used. At this time, a region that is not joined (hereinafter referred to as the inlet) is provided on a part (or one side) of the outer casing 509 so that the electrolyte can be added later.

[0320] Next, the electrolyte is introduced into the inside of the outer casing 509 through an inlet provided in the outer casing 509. It is preferable to introduce the electrolyte under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is sealed. In this way, a laminate-type secondary battery 500 can be manufactured.

[0321] By using the positive electrode active material 100 obtained in the above-described embodiment as the positive electrode 503, a secondary battery 500 can be made that has high capacity, high charge / discharge capacity, and excellent cycle characteristics.

[0322] [Example of a battery pack] An example of a secondary battery pack according to one embodiment of the present invention, which is capable of wireless charging using an antenna, will be explained with reference to Figures 18A to 18C.

[0323] Figure 18A shows the external appearance of the secondary battery pack 531, which has a thin rectangular parallelepiped shape (it can also be called a thick flat plate shape). Figure 18B is a diagram illustrating the configuration of the secondary battery pack 531. The secondary battery pack 531 has a circuit board 540 and a secondary battery 513. A label 529 is attached to the secondary battery 513. The circuit board 540 is fixed by a seal 515. The secondary battery pack 531 also has an antenna 517.

[0324] The internal structure of the secondary battery 513 may have a wound structure or a laminated structure.

[0325] In the secondary battery pack 531, for example, as shown in Figure 18B, a control circuit 590 is located on the circuit board 540. The circuit board 540 is electrically connected to terminal 514. The circuit board 540 is also electrically connected to the antenna 517, one of the positive and negative leads 551 of the secondary battery 513, and the other of the positive and negative leads 552.

[0326] Alternatively, as shown in Figure 18C, the system 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 terminals 514.

[0327] The antenna 517 is not limited to a coil shape; for example, it may be linear or plate-shaped. Alternatively, antennas such as planar antennas, aperture antennas, traveling wave antennas, EH antennas, magnetic field antennas, and dielectric antennas 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 the capacitor. This allows for power exchange not only through electromagnetic and magnetic fields, but also through electric fields.

[0328] The secondary battery pack 531 has a layer 519 between the antenna 517 and the secondary battery 513. The layer 519 has the function of shielding, for example, the electromagnetic field from the secondary battery 513. For the layer 519, a magnetic material can be used, for example.

[0329] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0330] (Embodiment 4) This embodiment shows an example of fabricating an all-solid-state battery using the positive electrode active material 100 obtained in the above-described embodiment.

[0331] As shown in Figure 19A, a secondary battery 400 according to one embodiment of the present invention has a positive electrode 410, a solid electrolyte layer 420, and a negative electrode 430.

[0332] The positive electrode 410 has a positive electrode current collector 413 and a positive electrode active material layer 414. The positive electrode active material layer 414 has a positive electrode active material 411 and a solid electrolyte 421. The positive electrode active material 411 is the positive electrode active material 100 obtained in the above embodiment. The positive electrode active material layer 414 may also have a conductive material and a binder.

[0333] The solid electrolyte layer 420 has a solid electrolyte 421. The solid electrolyte layer 420 is located between the positive electrode 410 and the negative electrode 430 and is a region that does not contain either the positive electrode active material 411 or the negative electrode active material 431.

[0334] The negative electrode 430 has a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 has a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also have a conductive material and a binder. When metallic lithium is used as the negative electrode active material 431, it is not necessary to form it into particles, so the negative electrode 430 can be made without the solid electrolyte 421, as shown in Figure 19B. Using metallic lithium in the negative electrode 430 is preferable because it can improve the energy density of the secondary battery 400.

[0335] As the solid electrolyte 421 included in the solid electrolyte layer 420, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, or the like can be used.

[0336] Among the sulfide-based solid electrolytes, there are thiolischicon-based (Li 10 GeP2S 12 , Li 3.25 Ge 0.25 P 0.75 S4, etc.), sulfide glasses (70Li2S·30P2S5, 30Li2S·26B2S3·44LiI, 63Li2S·36SiS2·1Li3PO4, 57Li2S·38SiS2·5Li4SiO4, 50Li2S·50GeS2, etc.), and sulfide crystallized glasses (Li7P3S 11 , Li 3.25 P 0.95 S4, etc.). Sulfide-based solid electrolytes have advantages such as having materials with high conductivity, being synthesizable at low temperatures, and being relatively soft, so the conductive path is likely to be maintained even after charge and discharge.

[0337] Among the oxide-based solid electrolytes, there are materials having a perovskite-type crystal structure (La 2 / 3-x Li 3x TiO3, etc.), materials having a NASICON-type crystal structure (Li 1-Y Al Y Ti 2-Y (PO4)3, etc.), materials having a garnet-type crystal structure (Li7La3Zr2O 12 , etc.), materials having a LISICON-type crystal structure (Li 14 ZnGe4O 16 , etc.), LLZO (Li7La3Zr2O 12 ), oxide glasses (Li3PO4-Li4SiO, 50Li4SiO4·50Li3BO3, etc.), and oxide crystallized glasses (Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, etc.). Oxide-based solid electrolytes have the advantage of being stable in the atmosphere.

[0338] Halide-based solid electrolytes include LiAlCl4, Li3InBr6, LiF, LiCl, LiBr, LiI, etc. In addition, composite materials in which these halide-based solid electrolytes are filled in the pores of porous alumina or porous silica can also be used as solid electrolytes.

[0339] Also, different solid electrolytes may be mixed and used.

[0340] Among them, Li 1+x Al x Ti 2-x (PO4)3 (0 < x < 1) (hereinafter referred to as LATP) contains aluminum and titanium, which are elements that the positive electrode active material used in the secondary battery 400 of one aspect of the present invention may have. Therefore, a synergistic effect can be expected for improving the cycle characteristics, which is preferable. In addition, an improvement in productivity due to reduction of processes can also be expected. In this specification, etc., the NASICON-type crystal structure refers to a compound represented by M2(XO4)3 (M: transition metal, X: S, P, As, Mo, W, etc.), and has a structure in which MO6 octahedrons and XO4 tetrahedrons share vertices and are three-dimensionally arranged.

[0341] 〔Shape of the exterior body and the secondary battery〕 For the exterior body of the secondary battery 400 of one aspect of the present invention, those of various materials and shapes can be used, but it is preferable to have a function of pressing the positive electrode, the solid electrolyte layer, and the negative electrode.

[0342] For example, FIG. 20 is an example of a cell for evaluating the materials of an all-solid-state battery.

[0343] Figure 20A is a schematic cross-sectional view of the evaluation cell, which has a lower member 761, an upper member 762, and fixing screws or wing nuts 764 that secure them together. The evaluation material is fixed by pressing the electrode plate 753 by rotating the retaining screw 763. An insulator 766 is provided between the lower member 761 and the upper member 762, which are made of stainless steel. An O-ring 765 for sealing is provided between the upper member 762 and the retaining screw 763.

[0344] The evaluation material is placed on an electrode plate 751, surrounded by an insulating tube 752, and pressed from above by an electrode plate 753. Figure 20B is a magnified perspective view of the area around this evaluation material.

[0345] As an example of the evaluated material, an example of a stacked structure consisting of a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c is shown, and a cross-sectional view is shown in Figure 20C. Note that the same parts are referred to in Figures 20A to 20C.

[0346] The electrode plate 751 and lower member 761, which are electrically connected to the positive electrode 750a, can be considered to correspond to the positive electrode terminal. The electrode plate 753 and upper member 762, which are electrically connected to the negative electrode 750c, can be considered to correspond to the negative electrode terminal. Electrical resistance and other parameters can be measured while applying pressure to the evaluation material via the electrode plates 751 and 753.

[0347] Furthermore, it is preferable to use a package with excellent airtightness for the outer casing of a secondary battery according to one embodiment of the present invention. For example, a ceramic package or a resin package can be used. Also, when sealing the outer casing, it is preferable to block out the outside air and perform the sealing in a sealed atmosphere, for example, inside a glove box.

[0348] Figure 21A shows a perspective view of a secondary battery according to one embodiment of the present invention, having a different exterior and shape from that shown in Figure 20. The secondary battery in Figure 21A has external electrodes 771 and 772 and is sealed with an exterior having a plurality of package members.

[0349] Figure 21B shows an example of a cross-section cut by the dashed line in Figure 21A. The laminate having a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c is enclosed and sealed by a package member 770a having an electrode layer 773a on a flat plate, a frame-shaped package member 770b, and a package member 770c having an electrode layer 773b on a flat plate. Insulating materials such as resin materials and ceramics can be used for the package members 770a, 770b, and 770c.

[0350] The external electrode 771 is electrically connected to the positive electrode 750a via the electrode layer 773a and functions as a positive electrode terminal. The external electrode 772 is electrically connected to the negative electrode 750c via the electrode layer 773b and functions as a negative electrode terminal.

[0351] By using the positive electrode active material 100 obtained in the above-described embodiment, an all-solid-state secondary battery with high energy density and good output characteristics can be realized.

[0352] The contents of this embodiment can be appropriately combined with the contents of other embodiments.

[0353] (Embodiment 5) In this embodiment, Figure 22C shows an example of applying a secondary battery different from the cylindrical secondary battery shown in Figure 13D to an electric vehicle (EV).

[0354] Electric vehicles are equipped with a first battery 1301a and 1301b as the main secondary battery for propulsion, and a second battery 1311 that supplies power to the inverter 1312 that starts the motor 1304. The second battery 1311 is also called the cranking battery (or starter battery). The second battery 1311 only needs to be able to output power, and does not require a large capacity, so its capacity is smaller than that of the first batteries 1301a and 1301b.

[0355] The internal structure of the first battery 1301a may be a wound type as shown in Figure 14A or Figure 15C, or a stacked type as shown in Figure 16A or Figure 16B. Alternatively, the first battery 1301a may use the all-solid-state battery of Embodiment 4. Using the all-solid-state battery of Embodiment 4 for the first battery 1301a allows for higher capacity, improved safety, and miniaturization and weight reduction.

[0356] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more may be connected in parallel. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack with multiple secondary batteries, a large amount of power can be extracted. Multiple secondary batteries may be connected in parallel, in series, or connected in parallel and then in series. Multiple secondary batteries are also called a battery pack.

[0357] Furthermore, in the vehicle-mounted secondary battery, a service plug or circuit breaker that can cut off high voltage without using tools is provided in order to interrupt the power from multiple secondary batteries, and this is installed in the first battery 1301a.

[0358] Furthermore, the power from the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V onboard components (electric power steering 1307, heater 1308, defogger 1309, etc.) via the DC-DC circuit 1306. If a rear motor 1317 is located on the rear wheels, the first battery 1301a is also used to rotate the rear motor 1317.

[0359] Furthermore, the second battery 1311 supplies power to 14V automotive components (such as audio equipment 1313, power windows 1314, and lights 1315) via the DC-DC circuit 1310.

[0360] Furthermore, the first battery 1301a will be explained using Figure 22A.

[0361] Figure 22A shows an example where nine rectangular secondary batteries 1300 are arranged in a single battery pack 1415. In this example, nine rectangular secondary batteries 1300 are connected in series, with one electrode fixed by an insulating fixing part 1413 and the other electrode fixed by an insulating fixing part 1414. While this embodiment shows an example of fixing with fixing parts 1413 and 1414, the batteries may also be housed in a battery housing box (also called a casing). Since vehicles are expected to be subjected to vibrations or shaking from external sources (such as the road surface), it is preferable to fix multiple secondary batteries using fixing parts 1413, 1414 and a battery housing box. Furthermore, one electrode is electrically connected to the control circuit unit 1320 by wiring 1421, and the other electrode is electrically connected to the control circuit unit 1320 by wiring 1422.

[0362] Furthermore, the control circuit unit 1320 may also use a memory circuit that includes a transistor made of an oxide semiconductor. A charging control circuit or battery control system having a memory circuit that includes a transistor made of an oxide semiconductor may be referred to as a BTOS (Battery operating system or Battery oxide semiconductor).

[0363] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, as the oxide, a metal oxide such as In-M-Zn oxide (where element M is one or more selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, or magnesium) is preferable. In particular, the In-M-Zn oxide that can be applied as the oxide is preferably CAAC-OS (C-Axis Aligned Crystal Oxide Semiconductor) or CAC-OS (Cloud-Aligned Composite Oxide Semiconductor). Alternatively, In-Ga oxide or In-Zn oxide may be used as the oxide. CAAC-OS is an oxide semiconductor having multiple crystalline regions, the c-axis of which is oriented in a specific direction. The specific direction is the thickness direction of the CAAC-OS film, the normal direction to the surface on which the CAAC-OS film is formed, or the normal direction to the surface of the CAAC-OS film. Furthermore, a crystalline region is a region in which the atomic arrangement has periodicity. If the atomic arrangement is considered as a lattice arrangement, then a crystalline region is also a region in which the lattice arrangement is aligned. In addition, CAAC-OS has regions in which multiple crystalline regions are connected in the ab-plane direction, and these regions may have distortion. Distortion refers to a point in a region in which multiple crystalline regions are connected where the orientation of the lattice arrangement changes between a region in which the lattice arrangement is aligned and another region in which the lattice arrangement is aligned. In other words, CAAC-OS is an oxide semiconductor that is c-axis oriented and does not have a clear orientation in the ab-plane direction. Furthermore, CAC-OS is a material composition in which, for example, elements constituting a metal oxide are unevenly distributed in sizes of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or close to that size. In the following, in a metal oxide, a state in which one or more metal elements are unevenly distributed, and regions containing these metal elements are mixed in sizes of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or close to that size, is also referred to as a mosaic or patchy state.

[0364] Furthermore, CAC-OS is a composite metal oxide having a mosaic-like structure formed by the separation of the material into a first region and a second region, with the first region distributed within the film (hereinafter also referred to as a cloud-like structure). In other words, CAC-OS is a composite metal oxide having a structure in which the first region and the second region are mixed.

[0365] Here, the atomic ratios of In, Ga, and Zn to the metal elements constituting the CAC-OS in In-Ga-Zn oxide are denoted as [In], [Ga], and [Zn], respectively. For example, in the CAC-OS of In-Ga-Zn oxide, the first region is the region where [In] is greater than the [In] in the composition of the CAC-OS film. The second region is the region where [Ga] is greater than the [Ga] in the composition of the CAC-OS film. Alternatively, for example, the first region is the region where [In] is greater than the [In] in the second region, and [Ga] is smaller than the [Ga] in the second region. The second region is the region where [Ga] is greater than the [Ga] in the first region, and [In] is smaller than the [In] in the first region.

[0366] Specifically, the first region described above is a region whose main components are indium oxide, indium zinc oxide, etc. The second region described above is a region whose main components are gallium oxide, gallium zinc oxide, etc. In other words, the first region can be rephrased as a region whose main component is In. Similarly, the second region can be rephrased as a region whose main component is Ga.

[0367] Furthermore, a clear boundary may not be observed between the first region and the second region described above.

[0368] For example, in the case of CAC-OS in In-Ga-Zn oxide, EDX mapping obtained using energy dispersive X-ray spectroscopy (EDX) confirms that it has a structure in which regions mainly composed of In (first region) and regions mainly composed of Ga (second region) are unevenly distributed and mixed.

[0369] When CAC-OS is used in a transistor, the conductivity due to the first region and the insulation due to the second region work complementaryly to give CAC-OS a switching function (on / off function). In other words, CAC-OS has conductive function in some parts of the material, insulating function in other parts of the material, and semiconductor function as a whole. By separating the conductive and insulating functions, both functions can be maximized. Therefore, by using CAC-OS in a transistor, high on-current (Ion), high field-effect mobility (μ), and good switching operation can be achieved.

[0370] Oxide semiconductors can take on diverse structures, each possessing different properties. One embodiment of the present invention may include two or more of the following: amorphous oxide semiconductors, polycrystalline oxide semiconductors, a-like OS, CAC-OS, nc-OS, and CAAC-OS.

[0371] Furthermore, since it can be used in high-temperature environments, it is preferable that the control circuit section 1320 uses a transistor made of an oxide semiconductor. To simplify the process, the control circuit section 1320 may be formed using a unipolar transistor. Transistors using an oxide semiconductor in the semiconductor layer have a wider operating ambient temperature range of -40°C to 150°C than single-crystal Si transistors, and even if the secondary battery overheats, the change in characteristics is smaller compared to single-crystal Si transistors. The off-current of a transistor using an oxide semiconductor is below the lower limit of measurement even at 150°C, but the off-current characteristics of a single-crystal Si transistor are highly temperature-dependent. For example, at 150°C, the off-current of a single-crystal Si transistor increases, and the current on / off ratio does not become sufficiently large. The control circuit section 1320 can improve safety. In addition, a synergistic effect on safety can be obtained by combining it with a secondary battery that uses the positive electrode active material 100 obtained in the above embodiment as the positive electrode.

[0372] The control circuit unit 1320, which uses a memory circuit including an oxide semiconductor transistor, can also function as an automatic control device for secondary batteries to address causes of instability such as micro-shorts. Functions to eliminate causes of secondary battery instability include overcharging prevention, overcurrent prevention, overheating control during charging, cell balancing in the battery pack, over-discharge prevention, remaining charge indicator, automatic control of charging voltage and current according to temperature, charging current control according to the degree of degradation, detection of abnormal behavior of micro-shorts, and prediction of abnormalities related to micro-shorts. The control circuit unit 1320 has at least one of these functions. Furthermore, it is possible to miniaturize the automatic control device for secondary batteries.

[0373] Furthermore, a micro-short refers to a tiny short circuit inside a secondary battery. It does not mean that the positive and negative electrodes of the secondary battery are short-circuited, making charging and discharging impossible. Rather, it refers to a phenomenon where a small short-circuit current flows through a tiny short circuit. Because even a relatively short-circuit in a small area can cause a large voltage change, the abnormal voltage value may affect subsequent estimations.

[0374] One of the causes of micro-short circuits is said to be that multiple charge-discharge cycles result in an uneven distribution of the positive electrode active material, causing localized current concentration in parts of the positive and negative electrodes, leading to areas where the separator malfunctions, or causing micro-short circuits due to the generation of by-reactants from side reactions.

[0375] Furthermore, in addition to detecting micro-shorts, the control circuit unit 1320 also detects the terminal voltage of the secondary battery and manages the charging and discharging state of the secondary battery. For example, to prevent overcharging, both the output transistor and the cutoff switch of the charging circuit can be turned off almost simultaneously.

[0376] Furthermore, an example of a block diagram of the battery pack 1415 shown in Figure 22A is shown in Figure 22B.

[0377] The control circuit unit 1320 includes at least a switch to prevent overcharging, a switch unit 1324 including a switch to prevent over-discharging, a control circuit 1322 that controls the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 has upper and lower voltage limits set for the secondary battery used, and limits the upper limit of external current and the upper limit of output current to the outside. Within the range between the lower voltage limit and the upper voltage limit of the secondary battery, it is within the voltage range for which use is recommended, and if it goes outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit unit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent over-discharge and overcharge. For example, if the control circuit 1322 detects a voltage that is likely to cause overcharging, it cuts off the current by turning off the switch in the switch unit 1324. Furthermore, a PTC element may be provided in the charge / discharge path to provide a function to cut off the current in response to the rise in temperature. Furthermore, the control circuit unit 1320 has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0378] The switch section 1324 can be constructed by combining n-channel and p-channel transistors. The switch section 1324 is not limited to switches using Si transistors made of single-crystal silicon, but may also be formed using power transistors made of, for example, Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), GaOx (gallium oxide; x is a real number greater than 0), etc. Furthermore, since memory elements using OS transistors can be freely arranged by stacking them on circuits using Si transistors, integration can be easily achieved. Also, since OS transistors can be manufactured using the same manufacturing equipment as Si transistors, they can be manufactured at low cost. That is, by stacking a control circuit section 1320 using OS transistors on the switch section 1324 and integrating them, it is possible to create a single chip. This allows for miniaturization as the occupied volume of the control circuit section 1320 can be reduced.

[0379] The first batteries 1301a and 1301b primarily supply power to 42V (high-voltage) in-vehicle equipment, while the second battery 1311 supplies power to 14V (low-voltage) in-vehicle equipment.

[0380] This embodiment shows an example in which lithium-ion secondary batteries are used for both the first battery 1301a and the second battery 1311. The second battery 1311 may be a lead-acid battery, an all-solid-state battery, or an electric double-layer capacitor. For example, the all-solid-state battery of Embodiment 4 may be used. By using the all-solid-state battery of Embodiment 4 for the second battery 1311, high capacity can be achieved, and the device can be made smaller and lighter.

[0381] Furthermore, the regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305 and charged the second battery 1311 via the control circuit unit 1321 from the motor controller 1303 and battery controller 1302. Alternatively, it is charged the first battery 1301a via the control circuit unit 1320 from the battery controller 1302. Alternatively, it is charged the first battery 1301b via the control circuit unit 1320 from the battery controller 1302. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b are capable of rapid charging.

[0382] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set the charging conditions according to the charging characteristics of the secondary battery being used and enable rapid charging.

[0383] Although not shown in the diagram, when connected to an external charger, the charger's outlet or connection cable is electrically connected to the battery controller 1302. Power supplied from the external charger charges the first batteries 1301a and 1301b via the battery controller 1302. In some chargers, a control circuit is provided, and the functions of the battery controller 1302 may not be used, but it is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320 to prevent overcharging. In some cases, the charger's outlet or connection cable may also have a control circuit. The control circuit unit 1320 is sometimes called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) installed in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU also includes a microcomputer. The ECU also uses a CPU or GPU.

[0384] External chargers installed at charging stations and other locations include 100V outlets, 200V outlets, and 3-phase 200V with 50kW output. Additionally, it is possible to charge by receiving power from external charging equipment using contactless power supply methods.

[0385] For rapid charging, a rechargeable battery capable of withstanding high-voltage charging is desired to achieve short charging times.

[0386] Furthermore, the secondary battery of this embodiment described above uses the positive electrode active material 100 obtained in the previously described embodiment. In addition, by using graphene as a conductive material, even if the electrode layer is thickened and the load is increased, the decrease in capacity is suppressed and high capacity is maintained, resulting in a secondary battery with significantly improved electrical characteristics as a synergistic effect. This is particularly effective for secondary batteries used in vehicles, and it is possible to provide a vehicle with a long driving range, specifically a driving range of 500 km or more on a single charge, without increasing the ratio of the weight of the secondary battery to the total weight of the vehicle.

[0387] In particular, the secondary battery of this embodiment described above can achieve a higher operating voltage by using the positive electrode active material 100 described in the previous embodiment, and the usable capacity can be increased with increasing charging voltage. Furthermore, by using the positive electrode active material 100 described in the previous embodiment as the positive electrode, a secondary battery for vehicles with excellent cycle characteristics can be provided.

[0388] Next, we will describe an example in which a secondary battery, which is one aspect of the present invention, is implemented in a vehicle, typically a transport vehicle.

[0389] Furthermore, by mounting a secondary battery shown in any one of Figures 13D, 15C, or 22A onto a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV) can be realized. Secondary batteries can also be mounted on agricultural machinery, motorized bicycles including electric-assist bicycles, motorcycles, electric wheelchairs, electric carts, small or large vessels, submarines, aircraft such as fixed-wing and rotary-wing aircraft, rockets, satellites, space probes, planetary probes, and spacecraft. A secondary battery according to one embodiment of the present invention can be a high-capacity secondary battery. Therefore, a secondary battery according to one embodiment of the present invention is suitable for miniaturization and weight reduction, and can be suitably used in transport vehicles.

[0390] In Figures 23A to 23D, a transport vehicle is shown as an example of a mobile body using one aspect of the present invention. The automobile 2001 shown in Figure 23A is an electric vehicle that uses an electric motor as a power source for driving. Alternatively, it is a hybrid vehicle that can appropriately select and use an electric motor and an engine as power sources for driving. When a secondary battery is mounted on the vehicle, one or more examples of the secondary battery shown in Embodiment 3 are installed in one location. The automobile 2001 shown in Figure 23A has a battery pack 2200, and the battery pack has a secondary battery module in which multiple secondary batteries are connected. Furthermore, it is preferable to have a charging control device electrically connected to the secondary battery module.

[0391] Furthermore, the automobile 2001 can be charged by receiving power from an external charging facility via a plug-in method or a contactless power supply method to the secondary battery of the automobile 2001. When charging, the charging method and connector specifications may be carried out as appropriate using a prescribed method such as CHAdeMO (registered trademark) or Combo. The secondary battery may be a charging station installed in a commercial facility or a household power supply. For example, the energy storage device mounted on the automobile 2001 can be charged by supplying power from an external source using plug-in technology. Charging can be performed by converting AC power to DC power via a conversion device such as an AC / DC converter.

[0392] Although not shown in the diagram, the vehicle can also be charged by mounting a power receiving device on the vehicle and receiving power wirelessly from a ground-based power transmission device. In this wireless power supply method, charging can be performed not only when the vehicle is stopped but also while it is in motion by incorporating the power transmission device into the road or exterior wall. Furthermore, this wireless power supply method can be used to transmit and receive power between two vehicles. In addition, solar panels can be installed on the exterior of the vehicle to charge the secondary battery when the vehicle is stopped and when it is in motion. For such wireless power supply, electromagnetic induction or magnetic resonance methods can be used.

[0393] Figure 23B shows a large transport vehicle 2002 equipped with an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 has a maximum voltage of 170V, achieved by connecting 48 cells in series, each consisting of four secondary batteries with a nominal voltage of 3.0V to 5.0V. The secondary battery module of the battery pack 2201 has the same functions as Figure 23A, except for differences in the number of secondary batteries that make up the module, so the explanation is omitted.

[0394] Figure 23C shows, as an example, a large transport vehicle 2003 equipped with an electrically controlled motor. The secondary battery module of the transport vehicle 2003 has a maximum voltage of 600V, for example, by connecting 100 or more secondary batteries with a nominal voltage of 3.0V to 5.0V in series. By using secondary batteries with the positive electrode active material 100 described in the above embodiment as the positive electrode, it is possible to manufacture secondary batteries with good rate characteristics and charge / discharge cycle characteristics, which can contribute to the high performance and long lifespan of the transport vehicle 2003. Furthermore, the battery pack 2202 has the same functions as Figure 23A except for differences in the number of secondary batteries constituting the secondary battery module, so the explanation is omitted.

[0395] Figure 23D shows an example of an aircraft 2004 having a fuel-burning engine. The aircraft 2004 shown in Figure 23D can be considered a type of transport vehicle because it has wheels for takeoff and landing, and has a battery pack 2203 which includes a secondary battery module formed by connecting multiple secondary batteries and a charging control device.

[0396] The secondary battery module of aircraft 2004 has a maximum voltage of 32V, for example, by connecting eight 4V secondary batteries in series. The secondary battery module of battery pack 2203 has the same functionality as Figure 23A, except for differences in the number of secondary batteries that make up the module, so the explanation is omitted.

[0397] The contents of this embodiment can be appropriately combined with the contents of other embodiments.

[0398] (Embodiment 6) In this embodiment, an example of mounting a secondary battery, which is one aspect of the present invention, in a building will be explained using Figures 24A and 24B.

[0399] The house shown in Figure 24A has a power storage device 2612 having a secondary battery, which is one embodiment of the present invention, and a solar panel 2610. The power storage device 2612 is electrically connected to the solar panel 2610 via wiring 2611, etc. The power storage device 2612 may also be electrically connected to a ground-mounted charging device 2604. The electricity obtained from the solar panel 2610 can be used to charge the power storage device 2612. The electricity stored in the power storage device 2612 can be used to charge the secondary battery of the vehicle 2603 via the charging device 2604. The power storage device 2612 is preferably installed in the underfloor space. By installing it in the underfloor space, the space above the floor can be used effectively. Alternatively, the power storage device 2612 may be installed on the floor.

[0400] The electricity stored in the energy storage device 2612 can also supply power to other electronic devices in the house. Therefore, even when power cannot be supplied from the commercial power source due to a power outage or the like, electronic devices can be used by using the energy storage device 2612 according to one aspect of the present invention as an uninterruptible power supply.

[0401] Figure 24B shows an example of an energy storage device according to one aspect of the present invention. As shown in Figure 24B, an energy storage device 791 according to one aspect of the present invention is installed in the underfloor space 796 of the building 799. Furthermore, the energy storage device 791 may be equipped with the control circuit described in Embodiment 5, and by using a secondary battery with the positive electrode active material 100 obtained in the above embodiment as the positive electrode in the energy storage device 791, a long-life energy storage device 791 can be made.

[0402] The energy storage device 791 is equipped with a control device 790, which is electrically connected by wiring to the distribution board 703, the energy storage controller 705 (also called the control device), the display unit 706, and the router 709.

[0403] Power is supplied from the commercial power supply 701 to the distribution panel 703 via the service drop connection section 710. Power is also supplied to the distribution panel 703 from the energy storage device 791 and the commercial power supply 701, and the distribution panel 703 supplies the supplied power to the general load 707 and the energy storage system load 708 via outlets (not shown).

[0404] General loads 707 are electrical equipment such as televisions and personal computers, while energy storage loads 708 are electrical equipment such as microwave ovens, refrigerators, and air conditioners.

[0405] The energy storage controller 705 includes a measurement unit 711, a prediction unit 712, and a planning unit 713. The measurement unit 711 has the function of measuring the amount of electricity consumed by the general load 707 and the energy storage system load 708 during a day (for example, from 0:00 to 24:00). The measurement unit 711 may also have the function of measuring the amount of electricity consumed by the energy storage device 791 and the amount of electricity supplied from the commercial power supply 701. The prediction unit 712 has the function of predicting the amount of electricity demanded by the general load 707 and the energy storage system load 708 during the next day, based on the amount of electricity consumed by the general load 707 and the energy storage system load 708 during the day. The planning unit 713 has the function of planning the charging and discharging of the energy storage device 791 based on the amount of electricity demand predicted by the prediction unit 712.

[0406] The amount of electricity consumed by the general load 707 and the energy storage system load 708, as measured by the measurement unit 711, can be checked on the display unit 706. It can also be checked on electrical equipment such as televisions and personal computers via the router 709. Furthermore, it can be checked on portable electronic devices such as smartphones and tablets via the router 709. Additionally, the amount of electricity demand for each time period (or hourly) predicted by the prediction unit 712 can be checked on the display unit 706, electrical equipment, and portable electronic devices.

[0407] The contents of this embodiment can be appropriately combined with the contents of other embodiments.

[0408] (Embodiment 7) This embodiment shows an example of mounting an energy storage device according to one aspect of the present invention on a motorcycle or bicycle.

[0409] Furthermore, Figure 25A shows an example of an electric bicycle using a power storage device according to one embodiment of the present invention. The power storage device according to one embodiment of the present invention can be applied to the electric bicycle 8700 shown in Figure 25A. The power storage device according to one embodiment of the present invention includes, for example, a plurality of storage batteries and a protection circuit.

[0410] The electric bicycle 8700 is equipped with a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists the rider. The power storage device 8702 is also portable, and Figure 25B shows it detached from the bicycle. The power storage device 8702 also has multiple built-in batteries 8701, which are part of a power storage device according to one embodiment of the present invention, and the remaining battery level can be displayed on a display unit 8703. The power storage device 8702 also has a control circuit 8704 capable of controlling the charging of a secondary battery or detecting abnormalities, as exemplified in Embodiment 5. The control circuit 8704 is electrically connected to the positive and negative electrodes of the batteries 8701. A small solid-state secondary battery, as shown in Figures 21A and 21B, may also be provided in the control circuit 8704. By providing the small solid-state secondary battery shown in Figures 21A and 21B in the control circuit 8704, power can also be supplied to hold data in the memory circuit of the control circuit 8704 for extended periods. Furthermore, a synergistic effect on safety can be obtained by combining the positive electrode active material 100 obtained in the above-described embodiment with a secondary battery that uses it as the positive electrode. The secondary battery and control circuit 8704 that use the positive electrode active material 100 obtained in the above-described embodiment as the positive electrode can greatly contribute to eliminating accidents such as fires caused by secondary batteries.

[0411] Furthermore, Figure 25C shows an example of a two-wheeled vehicle using a power storage device according to one embodiment of the present invention. The scooter 8600 shown in Figure 25C is equipped with a power storage device 8602, side mirrors 8601, and turn signals 8603. The power storage device 8602 can supply electricity to the turn signals 8603. In addition, the power storage device 8602, which houses multiple secondary batteries using the positive electrode active material 100 obtained in the above embodiment as the positive electrode, can have a high capacity and contribute to miniaturization.

[0412] Furthermore, the scooter 8600 shown in Figure 25C can accommodate the power storage device 8602 in the under-seat storage compartment 8604. The power storage device 8602 can be stored in the under-seat storage compartment 8604 even if the under-seat storage compartment 8604 is small.

[0413] The contents of this embodiment can be appropriately combined with the contents of other embodiments.

[0414] (Embodiment 8) This embodiment describes an example of mounting a secondary battery, which is one aspect of the present invention, in an electronic device. Examples of electronic devices on which a secondary battery is mounted include television equipment (also called televisions or television receivers), monitors for computers, digital cameras, digital video cameras, digital photo frames, mobile phones (also called mobile phones or mobile phone devices), portable game consoles, personal information terminals, sound playback devices, and large game machines such as pachinko machines. Personal information terminals include notebook personal computers, tablet terminals, e-book readers, and mobile phones.

[0415] Figure 26A shows an example of a mobile phone. The mobile phone 2100 includes a display unit 2102 built into the housing 2101, as well as operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. The mobile phone 2100 also has a secondary battery 2107. By providing a secondary battery 2107 that uses the positive electrode active material 100 described in the above embodiment as the positive electrode, a high capacity can be achieved, and a configuration that can accommodate space saving due to the miniaturization of the housing can be realized.

[0416] The mobile phone 2100 can run various applications such as making phone calls, sending emails, reading and creating documents, playing music, communicating on the internet, and playing computer games.

[0417] The operation button 2103 can be assigned various functions, including time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, and power saving mode activation / deactivation. For example, the function of the operation button 2103 can be freely configured by the operating system built into the mobile phone 2100.

[0418] Furthermore, the 2100 mobile phone is capable of performing standardized short-range wireless communication. For example, it can communicate with a wireless headset to enable hands-free calling.

[0419] Furthermore, the mobile phone 2100 is equipped with an external connection port 2104, which allows for direct data exchange with other information terminals via a connector. It can also be charged via the external connection port 2104. Note that charging may also be performed wirelessly without using the external connection port 2104.

[0420] The mobile phone 2100 preferably has sensors. For example, it is preferable that the sensor includes a human body sensor such as a fingerprint sensor, pulse sensor, or body temperature sensor, as well as a touch sensor, pressure sensor, acceleration sensor, etc.

[0421] Figure 26B shows an unmanned aerial vehicle 2300 having multiple rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 has a secondary battery 2301, a camera 2303, and an antenna (not shown), which are embodiments of the present invention. The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. The secondary battery using the positive electrode active material 100 obtained in the above embodiment as the positive electrode has a high energy density and high safety, so it can be used safely for a long period of time over a long period of time and is suitable as a secondary battery to be mounted on an unmanned aerial vehicle 2300.

[0422] Figure 26C shows an example of a robot. The robot 6400 shown in Figure 26C is equipped with a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406 and an obstacle sensor 6407, a movement mechanism 6408, a computing device, and the like.

[0423] Microphone 6402 has the function of detecting the user's voice and ambient sounds. Speaker 6404 has the function of emitting sound. Robot 6400 can communicate with the user using microphone 6402 and speaker 6404.

[0424] The display unit 6405 has the function of displaying various types of information. The robot 6400 can display the information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a detachable information terminal, and by installing it in a fixed position on the robot 6400, charging and data transfer can be made possible.

[0425] The upper camera 6403 and lower camera 6406 have the function of imaging the area around the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize its surrounding environment and move safely using the upper camera 6403, lower camera 6406 and obstacle sensor 6407.

[0426] The robot 6400 is equipped with a secondary battery 6409 according to one aspect of the present invention and a semiconductor device or electronic components in its internal region. The secondary battery using the positive electrode active material 100 obtained in the above-described embodiment as the positive electrode has a high energy density and high safety, so it can be used safely for a long period of time over a long period of time and is suitable as a secondary battery 6409 to be mounted on the robot 6400.

[0427] Figure 26D shows an example of a cleaning robot. The cleaning robot 6300 has a display unit 6302 located on the top surface of the housing 6301, multiple cameras 6303 located on the sides, a brush 6304, operation buttons 6305, a secondary battery 6306, and various sensors. Although not shown, the cleaning robot 6300 is equipped with wheels, a suction port, etc. The cleaning robot 6300 is self-propelled, can detect dirt 6310, and can suck up the dirt from a suction port located on the bottom surface.

[0428] For example, the cleaning robot 6300 can analyze images captured by the camera 6303 to determine the presence or absence of obstacles such as walls, furniture, or steps. Furthermore, if the image analysis detects an object that might become entangled in the brush 6304, such as wiring, the rotation of the brush 6304 can be stopped. The cleaning robot 6300 is equipped with a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or electronic component within its internal region. The secondary battery using the positive electrode active material 100 obtained in the above-described embodiment as the positive electrode has high energy density and high safety, allowing for safe use over long periods, making it suitable as a secondary battery 6306 for the cleaning robot 6300.

[0429] Figure 27A shows an example of a wearable device. Wearable devices use rechargeable batteries as a power source. Furthermore, in order to enhance splash resistance, water resistance, or dust resistance when used by users in daily life or outdoors, there is a demand for wearable devices that can be charged wirelessly in addition to wired charging with exposed connectors.

[0430] For example, a secondary battery according to one embodiment of the present invention can be mounted in a spectacle-type device 4000 as shown in Figure 27A. The spectacle-type device 4000 has a frame 4000a and a display unit 4000b. By mounting the secondary battery in the temple portion of the curved frame 4000a, a lightweight spectacle-type device 4000 with good weight balance and a long continuous usage time can be made. The secondary battery using the positive electrode active material 100 obtained in the above embodiment as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0431] Furthermore, a secondary battery according to one aspect of the present invention can be mounted in the headset-type device 4001. The headset-type device 4001 has at least a microphone section 4001a, a flexible pipe 4001b, and an earphone section 4001c. The secondary battery can be provided in the flexible pipe 4001b or in the earphone section 4001c. The secondary battery using the positive electrode active material 100 obtained in the above embodiment as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0432] Furthermore, a 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. The secondary battery 4002b can be provided inside the thin housing 4002a of the device 4002. The secondary battery using the positive electrode active material 100 obtained in the above embodiment as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0433] Furthermore, a secondary battery according to one embodiment of the present invention can be mounted on a device 4003 that can be attached to clothing. The secondary battery 4003b can be provided inside the thin housing 4003a of the device 4003. The secondary battery using the positive electrode active material 100 obtained in the above embodiment as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0434] Furthermore, a secondary battery according to 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 supply and receiving portion 4006b, and a secondary battery can be mounted in the internal region of the belt portion 4006a. A secondary battery using the positive electrode active material 100 obtained in the above embodiment as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0435] Furthermore, a secondary battery according to one aspect of the present invention can be mounted in the wristwatch-type device 4005. The wristwatch-type device 4005 has a display unit 4005a and a belt unit 4005b, and the secondary battery can be provided in either the display unit 4005a or the belt unit 4005b. The secondary battery using the positive electrode active material 100 obtained in the above embodiment as the positive electrode has a high energy density and can realize a configuration that can accommodate space saving due to the miniaturization of the housing.

[0436] The display unit 4005a can display not only the time, but also various other information such as incoming emails and phone calls.

[0437] Furthermore, since the wristwatch-type device 4005 is a wearable device that is worn directly on the wrist, it may be equipped with sensors to measure the user's pulse, blood pressure, etc. It can accumulate data on the user's exercise level and health, allowing for health management.

[0438] Figure 27B shows a perspective view of the wristwatch-type device 4005 after it has been removed from the arm.

[0439] A side view is also shown in Figure 27C. Figure 27C shows how the secondary battery 913 is built into the internal region. The secondary battery 913 is the secondary battery shown in Embodiment 3. The secondary battery 913 is located in a position that overlaps with the display unit 4005a, allowing for high density and high capacity, as well as being small and lightweight.

[0440] Since the wristwatch-type device 4005 is required to be small and lightweight, using the positive electrode active material 100 obtained in the above embodiment as the positive electrode of the secondary battery 913 makes it possible to create a secondary battery 913 that is both high in energy density and compact.

[0441] Figure 27D shows an example of wireless earphones. Here, wireless earphones with a pair of main units 4100a and 4100b are illustrated, but they do not necessarily have to be a pair.

[0442] The main units 4100a and 4100b include a driver unit 4101, an antenna 4102, and a secondary battery 4103. They may also have a display unit 4104. Preferably, they also have a circuit board with a wireless IC or the like, charging terminals, etc. They may also have a microphone.

[0443] The case 4110 contains a secondary battery 4111. Preferably, it also has a circuit board on which circuits such as a wireless IC and a charging control IC are mounted, and charging terminals. It may also have a display unit, buttons, etc.

[0444] The main units 4100a and 4100b can communicate wirelessly with other electronic devices such as smartphones. This allows them to play audio data sent from other electronic devices. Furthermore, if the main units 4100a and 4100b have microphones, they can send sound acquired by the microphones to other electronic devices, process the audio data, and then send it back to the main units 4100a and 4100b for playback. This allows them to be used, for example, as translation devices.

[0445] Furthermore, the secondary battery 4103 in the main unit 4100a can be charged from the secondary battery 4111 in the case 4110. As the secondary battery 4111 and the secondary battery 4103, coin-type secondary batteries, cylindrical secondary batteries, etc., as in the previous embodiment can be used. The secondary battery using the positive electrode active material 100 obtained in the above embodiment as the positive electrode has a high energy density, and by using it in the secondary battery 4103 and the secondary battery 4111, a configuration that can accommodate space saving due to the miniaturization of wireless earphones can be realized.

[0446] This embodiment can be implemented in appropriate combination with other embodiments. [Explanation of symbols]

[0447] 1: Electrode, 2: Current collector, 3: Active material layer, 4: Gap, 5: Active material, 6: Crack, 7: Slip, 10: Device, 20: Vibration section, 21: Roll, 22: Support, 23: Vibrator, 30: Press section, 31: Upper roll, 32: Upper support, 33: Lower roll, 34: Lower support, 35: Vibrator, 35a Vibrator, 35b Vibrator, 36: Oscillator, 37: Heating section, 38: Gear< / xps> < / xrd>

Claims

1. A method for manufacturing electrodes for a secondary battery, A vibration treatment step in which vibration is applied to the electrode, The process includes a pressing step of applying pressure to the electrode and compressing the active material layer of the electrode, The apparatus used in the vibration processing step has a vibration processing unit, The apparatus used in the aforementioned pressing process has a pressing section, The pressing section comprises an upper roll, an upper support, a lower roll, and a lower support. The upper support comprises a first holding portion and a second holding portion for holding the shaft of the upper roll, and a main body portion. The vibration processing unit has a first vibrator disposed between the first holding portion and the main body portion, and a second vibrator disposed between the second holding portion and the main body portion. The first oscillator and the second oscillator are each connected to a separate oscillator. The vibration treatment process is performed integrally with the pressing process. Method for fabricating electrodes for secondary batteries.

2. In claim 1, The upper roll further has a heating section, In the vibration treatment process, the temperature of the electrode is adjusted. Method for fabricating electrodes for secondary batteries.

3. In claim 2, the temperature adjustment is performed at a temperature of 80°C or more and 150°C or less. Method for fabricating electrodes for secondary batteries.

4. In any one of claims 1 to 3, the electrode is either a positive electrode or a negative electrode, or both. Method for fabricating electrodes for secondary batteries.

Images