Method for manufacturing electrode

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

Electrode fabrication method

[0001] The present invention relates to a secondary battery and a manufacturing method thereof, a method for manufacturing an electrode, and an apparatus for manufacturing an electrode, or a portable information terminal, a vehicle, or the like having a secondary battery.

[0002] One embodiment 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 manufacturing method thereof.

[0003] In this specification, the term "electronic device" refers to any device having a power storage device, and includes electro-optical devices having a power storage device, information terminal devices having a power storage device, and the like.

[0004] In this specification, the term "power storage device" refers to all elements and devices having a power storage function, including, for example, power storage devices such as lithium ion secondary batteries (also called secondary batteries), lithium ion capacitors, and electric double layer capacitors.

[0005] In recent years, various types of power storage devices have been actively developed, such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries. In particular, demand for high-power, high-energy-density lithium-ion secondary batteries has rapidly expanded in conjunction with the development of the semiconductor industry, and they are now indispensable in the modern information society as a rechargeable energy source, as they are used in portable information terminals such as mobile phones, smartphones, and notebook computers, portable music players, digital cameras, medical devices, and next-generation clean-energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs).

[0006] Lithium-ion secondary batteries are made of lithium cobalt oxide (LiCoO ２ ), lithium nickel-cobalt-manganese oxide (LiNi １−ｘ−ｙ Co ｘ Mn ｙ O ２ ) or lithium iron phosphate (LiFePO ４The battery is composed of a positive electrode containing a positive electrode active material such as ethylene carbonate (EC) or diethyl carbonate (DEC), a negative electrode containing a negative electrode active material such as graphite or other carbon material capable of absorbing and releasing 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 producing an electrode that can increase the capacity density of a secondary battery.

[0009] WO2020 / 128699 Brochure

[0010] It is an object of the present invention to realize a manufacturing method that enables a secondary battery to have a high capacity density, and to provide a manufacturing method of a secondary battery that is safe and highly reliable.

[0011] Electrodes (positive and negative electrodes) for lithium-ion secondary batteries are fabricated by applying a slurry containing particulate active material to a metal foil called a current collector and drying the slurry. Electrodes fabricated in this manner have an active material layer on the current collector. The active material layer contains active material and voids, and in order to increase the capacity density of secondary batteries, it is necessary to minimize the voids. By using an electrode with fewer voids, a secondary battery with the same volume can achieve a larger battery capacity and improve the capacity density per volume. Note that an electrode with a layer of active material with fewer voids is sometimes referred to as a high-density electrode, a densified electrode, or an electrode with high film density.

[0012] To produce high-density electrodes, a process of compressing an active material layer using a roll press or the like is often used. Conventional methods involve applying a constant load in one direction to an electrode having an active material layer to compress it, making it difficult to obtain a sufficiently densified electrode. Even when a sufficiently densified electrode is obtained, defects such as cracks and slippage are unavoidable in the active material. Defects in the active material can lead to the elution of transition metals from the active material, decomposition of the electrolyte, and reduced stability of the active material at high temperatures during high-voltage charging, which can potentially lead to problems in terms of safety or reliability.

[0013] Note that the description of these problems does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily solve all of these problems. Note that problems other than these can be extracted from the description in the specification, drawings, and claims.

[0014] One of the inventions disclosed in this specification is a pressing method used for either or both of a positive electrode and a negative electrode, which has a mechanism or pre-process for applying vibrations such as ultrasonic waves, which can reduce defects that occur in the active material in a sufficiently densified electrode.

[0015] Furthermore, one of the inventions disclosed in this specification is a method for manufacturing an electrode to be used for either or both of a positive electrode and a negative electrode, which uses a mechanism for applying vibrations such as ultrasonic waves or a pressing method having a pre-process, which can reduce defects that occur in the active material in a sufficiently densified electrode.

[0016] The present invention also provides a high-density electrode with fewer defects in the active material, a high-density electrode secondary battery with fewer defects in the active material, and a method for fabricating the same. High-density electrodes with fewer defects in the active material enable the realization of excellent secondary batteries that satisfy high capacity density, high performance, and safety requirements in various operating environments.

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

[0018] Another embodiment of the present invention is a method for manufacturing an electrode for a secondary battery, the method including a vibration treatment step of applying a first vibration to the electrode and a press step of applying pressure to the electrode to compress an active material layer of the electrode, in which a second vibration is applied to the electrode simultaneously with the pressurization, and the vibration treatment step is performed before the press step.

[0019] Another embodiment of the present invention is a method for manufacturing an electrode for a secondary battery, the method including a vibration treatment step of applying vibration to the electrode to adjust the temperature, and a press step of applying pressure to the electrode to compress an active material layer of the electrode, in which the vibration treatment step is performed before the press step.

[0020] Another embodiment of the present invention is a method for manufacturing an electrode for a secondary battery, the method including a vibration treatment step of applying a first vibration to the electrode to adjust the temperature, and a press step of applying pressure to the electrode to compress an active material layer of the electrode, in which a second vibration is applied to the electrode simultaneously with the pressurization, and the vibration treatment step is performed before the pressurization step.

[0021] In any one of the above methods for producing an electrode, the electrode may be either or both of a positive electrode and a negative electrode.

[0022] In any one of the above methods for producing an electrode, the temperature in the vibration treatment step and / or the pressing step is preferably adjusted so that the temperature of the electrode is 80°C or higher and 150°C or lower.

[0023] It is possible to realize a manufacturing method that enables a secondary battery to have a high capacity density. It is also possible to provide a manufacturing method for a secondary battery that is safe or highly reliable. Or, it is possible to realize a manufacturing method that can reduce defects that occur in the active material in a sufficiently densified electrode. A high-density electrode with few defects in the active material makes it possible to realize an excellent secondary battery that satisfies high capacity density, high performance, and safety in various operating environments.

[0024] FIG. 1 illustrates an example of an electrode manufacturing apparatus according to one embodiment of the present invention. FIGS. 2A and 2B are cross-sectional schematic views of an electrode illustrating an example of the effect of a method for manufacturing an electrode according to one embodiment of the present invention. FIG. 2C illustrates a cross-sectional example of an electrode according to one embodiment of the present invention. FIGS. 3A and 3B are an example of an electrode manufacturing apparatus according to one embodiment of the present invention. FIG. 4 illustrates an example of an electrode manufacturing apparatus according to one embodiment of the present invention. FIG. 5A is a top view of a positive electrode active material according to one embodiment of the present invention, and FIGS. 5B and 5C are cross-sectional views of the positive electrode active material according to one embodiment of the present invention. FIG. 6 illustrates a crystalline structure of a positive electrode active material according to one embodiment of the present invention. FIG. 7 illustrates an XRD pattern calculated from the crystalline structure. FIG. 8 illustrates a crystalline structure of a positive electrode active material according to a comparative example. FIG. 9 illustrates an XRD pattern calculated from the crystalline structure. FIG. 10 illustrates a cross-sectional schematic view of a positive electrode active material particle. FIG. 11A is an STEM photograph of the particle after pressing, and FIGS. 11B and 11C are cross-sectional schematic views. FIG. 12A is an exploded perspective view of a coin-type secondary battery, FIG. 12B is a perspective view of the coin-type secondary battery, and FIG. 12C is a cross-sectional perspective view thereof. FIG. 13A shows an example of a cylindrical secondary battery. FIG. 13B shows an example of a cylindrical secondary battery. FIG. 13C shows an example of a plurality of cylindrical secondary batteries. FIG. 13D shows an example of a power storage system having a plurality of cylindrical secondary batteries. FIGS. 14A and 14B are diagrams illustrating an example of a secondary battery, and FIG. 14C is a diagram illustrating the internal state of the secondary battery. FIGS. 15A to 15C are diagrams illustrating an example of a secondary battery. FIGS. 16A and 16B are diagrams illustrating the external appearance of a secondary battery. FIGS. 17A to 17C are diagrams illustrating a method for manufacturing a secondary battery. FIGS. 18A to 18C are diagrams illustrating an example of the configuration of a battery pack. FIGS. 19A and 19B are diagrams illustrating an example of a secondary battery. FIGS. 20A to 20C are diagrams illustrating an example of a secondary battery. FIGS. 21A and 21B are diagrams illustrating an example of a secondary battery. 22A is a perspective view of a battery pack illustrating one embodiment of the present invention, FIG. 22B is a block diagram of the battery pack, and FIG. 22C is a block diagram of a vehicle having a motor. 23A to 23D are diagrams illustrating an example of a transportation vehicle. 24A and 24B are diagrams illustrating a power storage device according to one embodiment of the present invention.Fig. 25A is a diagram showing an electric bicycle, Fig. 25B is a diagram showing a secondary battery for the electric bicycle, and Fig. 25C is a diagram explaining an electric motorcycle. Figs. 26A to 26D are diagrams explaining an example of an electronic device. Fig. 27A shows an example of a wearable device, Fig. 27B is a perspective view of a wristwatch-type device, and Fig. 27C is a diagram explaining a side view of the wristwatch-type device. Fig. 27D is a diagram explaining an example of a wireless earphone.

[0025] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be readily understood by those skilled in the art that various modifications can be made to the embodiments and details. Furthermore, the present invention should not be interpreted as being limited to the description of the embodiments shown below.

[0026] In this specification and the like, the term "composite oxide" refers to an oxide containing multiple types of metal atoms in its structure.

[0027] In addition, in this specification, crystal planes and directions are indicated by Miller indices. In crystallography, crystal planes and directions are indicated by a superscript bar. However, in this specification, due to limitations in application notation, instead of a bar above the number, a minus sign (-) may be placed before the number. Individual orientations indicating directions within a crystal are expressed with [ ], collective orientations indicating all equivalent directions with < >, individual planes indicating crystal faces with ( ), and collective planes with equivalent symmetry with {}. In addition, Miller indices for trigonal and hexagonal crystals, including R-3m, may use (hkil) instead of just (hkl). Here, i is -(h+k).

[0028] 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 ion arrangement in which cations and anions are alternately arranged, and in which the transition metal and lithium are regularly arranged to form a two-dimensional plane, allowing two-dimensional diffusion of lithium. Defects such as cation or anion deficiencies may also be present. Strictly speaking, the layered rock-salt type crystal structure may have a distorted rock-salt type crystal lattice.

[0029] In this specification and the like, the rock salt type crystal structure refers to a structure in which cations and anions are arranged alternately. Note that the crystal structure may have a deficiency of cations or anions in part.

[0030] In this specification, the theoretical capacity of a positive electrode active material refers to the amount of electricity when all of the intercalable and deintercalable lithium contained in the positive electrode active material is deintercalated. For example, LiFePO ４ The theoretical capacity of LiCoO is 170 mAh / g. ２ The theoretical capacity of LiNiO is 274 mAh / g. ２ The theoretical capacity of LiMn is 275mAh / g. ２ O ４ The theoretical capacity of the battery is 148 mAh / g.

[0031] The amount of lithium remaining in the positive electrode active material that can be inserted or removed can be determined by x in the composition formula, for example, Li ｘ CoO ２ x in, or Li ｘ M1O ２ In this specification, Li ｘ CoO ２ Li as appropriate ｘ M1O ２ x can be considered as an occupancy rate, and in the case of a positive electrode active material in a secondary battery, x may be expressed as x = (theoretical capacity - charging capacity) / theoretical capacity. For example, LiCoO ２ When a secondary battery using as a positive electrode active material is charged to 219.2 mAh / g, Li ０．２ CoO ２ Or we can say x = 0.2. ｘ CoO ２ The small value of x in the formula means, for example, 0.1<x≦0.24.

[0032] When the lithium cobalt oxide satisfies the stoichiometric ratio, LiCoO ２ The occupancy rate of Li on the lithium site is x = 1. The secondary battery after discharge also has a LiCoO ２In this case, x = 1. The end of discharge here refers to the state where the voltage is 2.5 V (lithium counter electrode) or less at a current of 100 mA / g, for example. In a lithium ion secondary battery, when the occupancy rate of lithium in the lithium site reaches x = 1 and no more lithium can enter, the voltage drops sharply. At this point, discharge can be said to be complete. Generally, LiCoO ２ In the case of a lithium ion secondary battery using the above method, the discharge voltage drops rapidly until it reaches 2.5 V, so it is assumed that the discharge is completed under the above conditions.

[0033] In addition, in this specification and the like, the depth of charge when all of the intercalable / deintercalable lithium in the positive electrode active material is intercalated may be referred to as 0, and the depth of charge when all of the intercalable / deintercalable lithium in the positive electrode active material is deintercalated may be referred to as 1.

[0034] Embodiment 1 In this embodiment, a method for manufacturing an electrode according to one embodiment of the present invention will be described.

[0035] An example of a method for manufacturing an electrode according to one embodiment of the present invention will be described with reference to FIGS.

[0036] [Fabrication Method 1] Electrodes (positive electrode, negative electrode) have an active material layer and a current collector. An electrode in which an active material layer is provided on one side of a current collector is called a single-sided coated electrode, and an electrode in which active material layers are provided on both sides of a current collector is called a double-sided coated electrode. The fabrication method of an electrode according to one embodiment of the present invention is applicable to both single-sided coated electrodes and double-sided coated electrodes. Note that the active material layer contains an active material and may also contain a conductive material and a binder. Materials such as the active material contained in the positive electrode and the active material contained in the negative electrode may be the materials described in the following embodiments.

[0037] The electrode manufacturing method preferably includes a slurry manufacturing step, a coating step, a vibration treatment step, and a pressing step. The vibration treatment step and the pressing step can be performed using the apparatus 10 shown in FIG.

[0038] <Slurry Preparation Step> In the slurry preparation step, the active material is dispersed in a dispersion medium to prepare a 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 Step> In the coating step, the slurry is coated onto a current collector. The slurry can be coated using a slot die method, a gravure method, a blade method, or a combination thereof. After coating, the dispersion medium is evaporated to obtain a coated electrode 1. The dispersion medium evaporation step (also referred to as a drying step) is preferably performed at 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 step is shown in FIG. 2A. The active material layer 3 having the active material 5 formed on the current collector 2 has many voids 4 within the active material layer 3 immediately after the coating step, as shown in the electrode 1a schematically shown in FIG. 2A. The contour lines representing the active material layer 3 in FIGS. 2A to 2C indicate the area that can be considered as the volume of the active material layer 3 when calculating the film density of the active material layer 3 (the mass per unit volume of the active material layer).

[0040] <Vibration Treatment Step> The vibration treatment step can use the vibration treatment unit 20 of the device 10 shown in FIG. 1 . The device 10 includes an electrode roll unwinding unit 41, a winding unit 42, a vibration treatment unit 20, and a press unit 30. The electrode 1 is in contact with the surface of the roll 21 of the vibration treatment unit 20 between the unwinding unit 41 and the press unit 30, and the electrode 1 is in contact with the surface of the roll 21, facilitating the transmission of vibrations and heat (described below) to the electrode 1. The vibration treatment unit 20 includes the roll 21 in contact with the electrode 1 and a support 22, and the support 22 includes 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 includes vertical vibration (Z direction in FIG. 1 ) and / or horizontal vibration (X and / or Y direction in FIG. 1 ). By applying the vibration to the electrode 1, the active material 5 in the active material layer 3 can move to a stable position, allowing for increased film density with a lower pressing pressure in the subsequent pressing step. Furthermore, the roll 21 preferably has an internal heating unit such as a sheathed heater, and the temperature of the roll 21 is adjusted so that the electrode 1 is heated to a temperature of 50°C or higher and 200°C or lower, preferably 80°C or higher and 150°C or lower, in the vibration treatment step. The roll 21 may have a structure similar to that shown in FIG. 3B (described later). Heating the electrode 1 to the above temperature and applying vibration to the electrode 1 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 step, making this highly preferable.

[0041] The vibrator may be, for example, a piezoelectric ceramic vibrator. The piezoelectric ceramic vibrator may have a Langevin structure, which has a cylindrical piezoelectric ceramic portion sandwiched between two annular electrode portions and polarized in the thickness direction. The piezoelectric ceramic may be, for example, a ceramic having piezoelectricity, such as PZT (lead zirconate titanate).

[0042] <Pressing Step> In the pressing step, the pressing unit 30 of the apparatus 10 shown in FIG. 1 can be used. The pressing unit 30 has an upper roll 31, an upper support 32, a lower roll 33, and a lower support 34. The upper roll 31 has an internal heating unit such as a sheathed heater, and the temperature of the upper roll 31 is preferably adjusted so that the temperature of the electrode 1 is 50°C or higher and 200°C or lower, preferably 80°C or higher and 150°C or lower, in the pressing step. The electrode 1 is pressed by the upper roll 31 and the lower roll 33, reducing the thickness of the active material layer 3 of the electrode 1. In other words, the voids 4 in the active material layer 3 are reduced, and the film density of the active material layer 3 (the mass per unit volume of the active material layer) is increased.

[0043] As described above, FIG. 2A schematically illustrates the state of electrode 1a immediately after the coating process, in which active material layer 3 has many voids 4. Because a high capacity per volume is desirable for a secondary battery, it is desirable for the voids 4 in active material layer 3 to be as small as possible (high film density). Therefore, in the past, electrode 1 was pressed with a very strong force to increase the film density of active material layer 3. However, when electrode 1 was pressed with a very strong force, the active material 5 could not withstand the pressure, as in electrode 1b schematically shown in FIG. 2B , resulting in defects such as cracks 6 and slips 7. On the other hand, in the electrode fabrication method of one embodiment of the present invention, by including a vibration treatment step, it is possible to obtain an active material layer 3 with high film density even when electrode 1 was pressed with a force smaller than conventional methods. In this case, an active material layer 3 with high film density and significantly reduced occurrence of defects such as cracks 6 and slips 7 could be obtained, as in electrode 1c schematically shown in FIG. 2C.

[0044] [Fabrication Method 2] In another embodiment of the present invention, the vibration treatment step and the pressing step shown in Fabrication Method 1 may be performed integrally using the apparatus 11 shown in FIG. 3A. A method of performing the vibration treatment step and the pressing step integrally can be called a vibration press treatment. Similar to the upper roll 31 shown in FIG. 1, the upper roll 31 shown in FIG. 3A has an internal heating unit 37 such as a sheathed heater. Preferably, 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 step. An example of the heating unit 37 of the roll is shown in FIG. 3B. FIG. 3B is a schematic diagram of the upper portion of the vibration press unit of FIG. 3A as viewed from the X direction (the direction of movement of the electrode 1) in the figure. The upper support 32 shown in FIG. 3B holds the shaft of the upper roll 31 with two holding units 32b, and has vibrators 35 (35a, 35b) between the main body 32a and the holding unit 32b of the upper support 32. The vibrator 35 is connected to an 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. Note that the vibrators 35a and 35b may be connected to different oscillators, but it is desirable that the vibrations emitted by the vibrators 35a and 35b have the same amplitude, frequency, and phase.

[0045] [Production Method 3] In another embodiment of the present invention, an apparatus 12 shown in Fig. 4 can be used that combines the vibration treatment step shown in Production Method 1 and the vibration press treatment shown in Production Method 2. The roll 21 and upper roll 31 shown in Fig. 4 may have the same structure as that shown in Fig. 3B described above.

[0046] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0047] Embodiment 2 In this embodiment, an example of a secondary battery according to one embodiment of the present invention will be described. Either one or both of a positive electrode and a negative electrode are preferably manufactured by the manufacturing method described in Embodiment 1.

[0048] <Configuration Example of Secondary Battery> Hereinafter, a secondary battery in which a positive electrode, a negative electrode, and an electrolyte are enclosed in an exterior body will be described as an example.

[0049] [Positive Electrode] The positive electrode has a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer has a positive electrode active material, and may also have a conductive material and a binder, which will be described later.

[0050] [Negative Electrode] The negative electrode has a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer has a negative electrode active material, and may also have a conductive material described below and the binder described above.

[0051] [Current Collector] The positive electrode current collector and the negative electrode current collector can be made of a material that has high conductivity and does not alloy with carrier ions such as lithium, such as metals such as stainless steel, gold, platinum, zinc, iron, copper, aluminum, and titanium, and alloys thereof. The current collector can be appropriately shaped, such as a sheet, mesh, punched metal, or expanded metal. The current collector should preferably have a thickness of 10 μm or more and 30 μm or less.

[0052] The negative electrode current collector is preferably made of a material that does not alloy with carrier ions such as lithium.

[0053] A titanium compound may be provided as a current collector by being laminated on the metals listed above. Examples of titanium compounds include titanium nitride, titanium oxide, titanium nitride in which part of the nitrogen is substituted with oxygen, titanium oxide in which part of the oxygen is substituted with nitrogen, and titanium oxynitride (TiO ｘ N ｙ , 0 < x < 2, 0 < y < 1), or a mixture or stack of two or more of these can be used. Among these, titanium nitride is particularly preferred because of its high conductivity and excellent oxidation suppression function. By providing a titanium compound on the surface of the current collector, for example, reaction between the metal and the material contained in the active material layer formed on the current collector can be suppressed. When the active material layer contains an oxygen-containing compound, 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), oxidation reaction between oxygen contained in graphene oxide and aluminum is a concern. In such a case, providing a titanium compound on aluminum can suppress oxidation reaction between the current collector and graphene oxide.

[0054] [Conductive Material] The conductive material, also called a conductivity imparting agent or a conductivity aid, is made of a carbon material. By attaching the conductive material between multiple active materials, the multiple active materials are electrically connected to each other, thereby increasing the conductivity. Note that the term "attachment" does not only refer to physical adhesion between the active material and the conductive material, but also includes cases where a covalent bond is formed, bonding due to van der Waals forces, where the conductive material covers part of the surface of the active material, where the conductive material is embedded in the surface irregularities of the active material, and where the materials are electrically connected even when not in contact with each other.

[0055] The active material layers such as the positive electrode active material layer and the negative electrode active material layer preferably contain a conductive material.

[0056] As the conductive material, for example, one 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] Examples of carbon fibers that can be used include mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers. Carbon nanofibers and carbon nanotubes can also be used as carbon fibers. Carbon nanotubes can be produced by vapor phase growth, for example.

[0058] The active material layer may also contain, as a conductive material, metal powder or metal fiber such as copper, nickel, aluminum, silver, or gold, or a conductive ceramic material.

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

[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, and therefore can improve the electrical conductivity between the granular active material and the graphene compound with a smaller amount than that of ordinary conductive materials. This allows the ratio of the active material in the active material layer to be increased, thereby increasing 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, tend to fill microscopic spaces. Microscopic spaces refer to, for example, the spaces between multiple active materials. By combining a carbon-containing compound that easily fills microscopic spaces with a sheet-like carbon-containing compound such as graphene, which can impart conductivity across multiple particles, the density of the electrode can be increased, resulting in the formation of an excellent conductive path. A secondary battery obtained by the manufacturing method of one embodiment of the present invention has high capacity density and stability, making it effective as an in-vehicle secondary battery.

[0062] [Binder] The active material layer preferably contains 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 another carbon-based material, multiple active materials together, multiple carbon-based materials, etc.

[0063] As the binder, it is preferable to use a material such as polystyrene, polymethyl acrylate, 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, or nitrocellulose.

[0064] Polyimide has excellent thermal, mechanical and chemical stability.

[0065] A fluorine-containing polymer material, such as a fluoropolymer, 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] As the binder, it is preferable to use a rubber material such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, etc. As the binder, fluororubber can also be used.

[0067] Furthermore, it is preferable to use, for example, a water-soluble polymer as the binder. Examples of the water-soluble polymer that can be used include polysaccharides. Examples of the polysaccharide that can be used include cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, as well as starch. It is even more preferable to use these water-soluble polymers in combination with the above-mentioned rubber material.

[0068] The binder may be used in combination with two or more of the above.

[0069] <Graphene Compound> In this specification and the like, graphene compounds include graphene, multilayer graphene, multigraphene, graphene oxide, multilayer graphene oxide, multi-graphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multi-graphene oxide, graphene quantum dots, and the like. Graphene compounds contain carbon, have a shape such as a plate or sheet, and have a two-dimensional structure formed by six-membered carbon rings. The two-dimensional structure formed by six-membered carbon rings may also be referred to as a carbon sheet. Graphene compounds may have functional groups. Furthermore, graphene compounds preferably have a curved shape. Furthermore, graphene compounds may be rolled up to resemble carbon nanofibers.

[0070] In this specification and the like, graphene oxide refers to, for example, a material that contains carbon and oxygen, has a sheet-like shape, and has a functional group, in particular, an epoxy group, a carboxy group, or a hydroxy group.

[0071] In this specification, reduced graphene oxide refers to, for example, a material containing carbon and oxygen, having a sheet-like shape, and having a two-dimensional structure formed by six-membered carbon rings. It may also be called a carbon sheet. A single reduced graphene oxide can function, but multiple sheets may be stacked. Reduced graphene oxide preferably has a portion where the carbon concentration is greater than 80 atomic % and the oxygen concentration is 2 atomic % or more and 15 atomic % or less. By achieving these carbon and oxygen concentrations, reduced graphene oxide can function as a highly conductive material even in small amounts. Furthermore, reduced graphene oxide preferably has an intensity ratio G / D of the G band to the D band in a Raman spectrum of 1 or more. Reduced graphene oxide with such an intensity ratio can function as a highly conductive material even in small amounts.

[0072] By reducing graphene oxide, it may be possible to provide holes in the graphene compound.

[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, the sheet-like graphene compound is dispersed substantially uniformly in the inner region of the active material layer. The plurality of graphene compounds are formed so as to partially cover the plurality of granular active material particles or to be attached to the surfaces of the plurality of granular active material particles, and are in surface contact with each other.

[0075] Here, a mesh-like graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net) can be formed by bonding multiple graphene compounds together. When an active material is covered with a graphene net, the graphene net can also function as a binder that bonds the active materials together. Therefore, the amount of binder can be reduced or no binder can be used, thereby improving the ratio of the active material to the electrode volume or weight. In other words, the charge / discharge capacity of a secondary battery can be increased.

[0076] Here, it is preferable to use graphene oxide as the graphene compound, mix it with an active material to form a layer that will become an active material layer, and then reduce it. That is, the completed active material layer preferably contains reduced graphene oxide. By using graphene oxide, which has extremely high dispersibility in a polar solvent, to form the graphene compound, it is possible to substantially uniformly disperse the graphene compound in the internal region of the active material layer. Since the solvent is volatilized and removed from the dispersion medium containing the uniformly dispersed graphene oxide and the graphene oxide is reduced, the graphene compound remaining in the active material layer partially overlaps and is dispersed to such an extent that it is in surface contact with each other, thereby forming a three-dimensional conductive path. Note that the reduction of graphene oxide may be performed, for example, by heat treatment or using a reducing agent.

[0077] Furthermore, by using a spray dryer in advance, a graphene compound, which is a conductive material, can be formed as a coating that covers the entire surface of the active material, and further, the active material can be electrically connected to each other by the graphene compound to form a conductive path.

[0078] Furthermore, a material used in forming the graphene compound may be mixed with the graphene compound and used in the active material layer. For example, particles used as a catalyst in forming the graphene compound may be mixed with the graphene compound. Examples of catalysts used in forming the graphene compound include silicon oxide (SiO ２ , SiO ｘ(x<2)), aluminum oxide, iron, nickel, ruthenium, iridium, platinum, copper, germanium, etc. The particles preferably have an average particle diameter (D50: also referred to as median diameter) of 1 μm or less, more preferably 100 nm or less.

[0079] [Separator] A separator is disposed between the positive electrode and the negative electrode. Examples of separators that can be used include those made of cellulose-containing fibers such as paper, nonwoven fabrics, glass fibers, ceramics, or synthetic fibers such as nylon (polyamide), vinylon (polyvinyl alcohol-based fibers), polyester, acrylic, polyolefin, and polyurethane. The separator is preferably processed into a bag shape and disposed so as to encase either the positive electrode or the 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 film such as polypropylene or polyethylene may be coated with a ceramic material, a fluorine-based material, a polyamide material, or a mixture thereof. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine-based 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 improving the reliability of secondary batteries. Coating with fluorine-based materials also improves adhesion between the separator and electrodes, improving output characteristics. Coating with polyamide materials, especially aramid, improves heat resistance, improving the safety of secondary batteries.

[0083] For example, both sides of a polypropylene film may be coated with a mixed material of aluminum oxide and aramid, or the surface of the polypropylene film that contacts the positive electrode may be coated with a mixed material of aluminum oxide and aramid, and the surface that contacts the negative electrode may be coated with a fluorine-based material.

[0084] When a separator with a multilayer structure is used, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, and therefore the capacity per volume of the secondary battery can be increased.

[0085] [Electrolyte] When a liquid electrolyte is used in a secondary battery, for example, the electrolyte may be one of 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, and the like, or two or more of these may 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 electrolyte solvent, it is possible to prevent the secondary battery from exploding or catching fire even if the temperature of the internal region of the secondary battery rises due to a short circuit in the internal region or overcharging. The ionic liquid is composed of a cation and an anion, and includes an organic cation and an anion. Examples of the organic cation 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 the anion include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.

[0087] In particular, in the case where silicon is used as the second active material in the negative electrode of the secondary battery of one embodiment of the present invention, a liquid electrolyte containing an ionic liquid is preferably used.

[0088] The secondary battery of one embodiment of the present invention has, for example, an alkali metal ion such as a sodium ion or a potassium ion, or an alkaline earth metal ion such as a calcium ion, a strontium ion, a barium ion, a beryllium ion, or a magnesium ion as a carrier ion.

[0089] When lithium ions are used as carrier ions, the electrolyte contains a lithium salt, for example, LiPF ６ , LiClO ４ , LiAsF ６ , LiBF ４ , LiAlCl ４ , LiSCN, LiBr, LiI, Li ２ SO ４ , Li ２ B １０ Cl １０ , Li ２ B １２ Cl １２ , LiCF ３ SO３ , LiC ４ F ９ SO ３ , LiC(CF ３ SO ２ ) ３ , LiC(C ２ F ５ SO ２ ) ３ , LiN(CF ３ SO ２ ) ２ , LiN(C ４ F ９ SO ２ ) (CF ３ SO ２ ), LiN(C ２ F ５ SO ２ ) ２ etc. can be used.

[0090] The electrolyte preferably contains fluorine. For example, an electrolyte containing one or more fluorinated cyclic carbonates and lithium ions can be used as the fluorine-containing electrolyte. The fluorinated cyclic carbonate improves non-flammability and can enhance the safety of the lithium ion secondary battery.

[0091] Examples of fluorinated cyclic carbonates that can be used include fluorinated ethylene carbonate, such as monofluoroethylene carbonate (fluoroethylene carbonate, FEC, F1EC), difluoroethylene carbonate (DFEC, F2EC), trifluoroethylene carbonate (F3EC), and tetrafluoroethylene carbonate (F4EC). DFEC includes isomers such as cis-4,5 and trans-4,5. For low-temperature operation, it is important to use one or more fluorinated cyclic carbonates as an electrolyte to solvate lithium ions and transport them within the electrolyte contained in the electrode during charging and discharging. Using a fluorinated cyclic carbonate not as a small amount of additive but contributing to the transport of lithium ions during charging and discharging enables low-temperature operation. Within a secondary battery, lithium ions move in clusters of several to several tens of ions.

[0092] The use of a fluorinated cyclic carbonate in the electrolyte reduces the desolvation energy required for lithium ions solvated in the electrolyte contained in the electrode to enter active material particles. Reducing this desolvation energy facilitates insertion and desorption of lithium ions into active material particles, even at low temperatures. While lithium ions may migrate in a solvated state, a hopping phenomenon, in which the coordinated solvent molecules switch positions, may also occur. When lithium ions are more easily desolvated, they may be more susceptible to migration via the hopping phenomenon, which may facilitate lithium ion migration. There is a concern that electrolyte decomposition products cling to the surface of the active material during charging and discharging of secondary batteries, causing deterioration of the secondary battery. However, when the electrolyte contains fluorine, the electrolyte is smooth, making it difficult for electrolyte decomposition products to adhere to the surface of the active material. This reduces secondary battery degradation.

[0093] A plurality of solvated lithium ions may form clusters in the electrolyte and move within the negative electrode, between the positive electrode and the negative electrode, within the positive electrode, etc.

[0094] In this specification, the term "electrolyte" is a general term that includes solid, liquid, or semi-solid materials.

[0095] Deterioration is likely to occur at interfaces present in secondary batteries, such as the interface between the active material and the electrolyte. In a secondary battery according to one embodiment of the present invention, the presence of a fluorine-containing electrolyte can prevent deterioration that may occur at the interface between the active material and the electrolyte, typically, electrolyte alteration or increased viscosity. Furthermore, a binder, graphene compound, or the like may be attached to or retained by the fluorine-containing electrolyte. This configuration can maintain a reduced viscosity of the electrolyte, in other words, a smooth electrolyte, thereby improving the reliability of the secondary battery. DFEC, which has two fluorine atoms, and F4EC, which has four fluorine atoms, have lower viscosity and smoother texture than FEC, which has one fluorine atom, and their coordination bond with lithium is weaker. Therefore, adhesion of viscous decomposition products to active material particles can be reduced. Adhesion or adhesion of viscous decomposition products to active material particles hinders lithium ion migration at the interface between the active material particles. A fluorine-containing electrolyte reduces the formation of decomposition products on the surface of the active material (positive electrode active material or negative electrode active material) by solvation. Furthermore, by using an electrolyte containing fluorine, it is possible to prevent the adhesion of decomposition products, thereby preventing the generation and growth of dendrites.

[0096] Another feature is that a fluorine-containing electrolyte is used as the main component, and the fluorine-containing electrolyte is 5% by volume or more, 10% by volume or more, preferably 30% by volume or more and 100% by volume or less.

[0097] In this specification, the term "main component of the electrolyte" refers to 5% by volume or more of the total electrolyte of the secondary battery. Furthermore, "5% by volume or more of the total electrolyte of the secondary battery" refers to the percentage of the total electrolyte measured during the manufacture of the secondary battery. Furthermore, when disassembling a secondary battery after fabrication, it is difficult to quantify the percentage of each of multiple types of electrolytes, but it is possible to determine whether a certain type of organic compound accounts for 5% by volume or more of the total electrolyte.

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

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

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

[0101] Furthermore, the use of a gelling polymer material in the electrolyte increases safety against leakage, etc. Typical examples of gelling polymer materials include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, and fluorine-based polymer gel.

[0102] Examples of polymeric materials that can be used include polymers having a polyalkylene oxide structure, such as polyethylene oxide (PEO), PVDF, and polyacrylonitrile, as well as copolymers containing these. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. The polymers formed may also have a porous shape.

[0103] Although the above configuration shows an example of a secondary battery using a liquid electrolyte, it is not particularly limited. For example, semi-solid batteries and all-solid batteries can also be produced.

[0104] In this specification, the layer disposed between the positive electrode and the negative electrode is referred to as the electrolyte layer in both the case of a secondary battery using a liquid electrolyte and the case of a semi-solid battery. The electrolyte layer of a semi-solid battery can be said to be a layer formed by film formation, and can be distinguished from a liquid electrolyte layer.

[0105] In addition, in this specification, a semi-solid battery refers to a battery having a semi-solid material in at least one of the electrolyte layer, positive electrode, and negative electrode. Here, semi-solid does not mean that the ratio of solid material is 50%. Semi-solid means that while having solid properties such as small volume change, it also has some liquid-like properties such as flexibility. As long as these properties are met, the battery may be made of a single material or multiple materials. For example, a porous solid material may be impregnated with a liquid material.

[0106] In this specification, a polymer electrolyte secondary battery refers to a secondary battery having a polymer in the electrolyte layer between a positive electrode and a 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, the lithium ion conductive polymer is a polymer that has conductivity for cations such as lithium. More specifically, it is a polymer compound having a polar group to which a cation can be coordinated. The polar group preferably has an ether group, an ester group, a nitrile group, a carbonyl group, a siloxane group, or the like.

[0109] Examples of the lithium ion conductive polymer that can be used include polyethylene oxide (PEO), derivatives having polyethylene oxide as the main chain, polypropylene oxide, polyacrylic acid ester, polymethacrylic acid ester, polysiloxane, and polyphosphazene.

[0110] The lithium ion conductive polymer may be branched or crosslinked, or may be a copolymer. The molecular weight is preferably 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 due to the partial motion (also called segmental motion) of the polymer chain. For example, in the case of PEO, lithium ions move while changing the oxygen they interact with due to the segmental motion of the ether chain. When the temperature is close to or higher than the melting point or softening point of the lithium ion conductive polymer, the crystalline regions dissolve, the amorphous regions increase, 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 charge and discharge at 60°C or higher.

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

[0113] As the lithium salt, for example, a compound containing lithium and at least one of phosphorus, fluorine, nitrogen, sulfur, oxygen, chlorine, arsenic, boron, aluminum, bromine, and iodine can be used. For example, LiPF ６ , LiN(FSO ２ ) ２(lithium bis(fluorosulfonyl)imide, LiFSI), LiClO ４ , LiAsF ６ , LiBF ４ , LiAlCl ４ , LiSCN, LiBr, LiI, Li ２ SO ４ , Li ２ B １０ Cl １０ , Li ２ B １２ Cl １２ , LiCF ３ SO ３ , LiC ４ F ９ SO ３ , LiC(CF ３ SO ２ ) ３ , LiC(C ２ F ５ SO ２ ) ３ , LiN(CF ３ SO ２ ) ２ , LiN(C ４ F ９ SO ２ ) (CF ３ SO ２ ), LiN(C ２ F ５ SO ２ ) ２ , lithium bis(oxalato)borate (LiBOB), or the like, can be used alone or in any combination and ratio of two or more of these.

[0114] In particular, the use of LiFSI is preferable because it provides good low-temperature properties. Furthermore, LiFSI and LiTFSA are less reactive with water than LiPF6 and other compounds. This facilitates dew point control when fabricating electrodes and electrolyte layers using LiFSI. For example, LiFSI can be used in an inert atmosphere such as argon, where moisture is minimized, or in a dry room with a controlled dew point, as well as in normal air. This improves productivity and is therefore preferable. Furthermore, the use of highly dissociable and plasticizing Li salts such as LiFSI and LiTFSA is particularly preferable when using lithium conduction utilizing the segmental motion of ether chains, because they can be used over a wide temperature range.

[0115] The absence or very small amount of organic solvents makes it possible to produce a secondary battery that is less likely to catch fire or ignite, which is preferable because it improves safety. Furthermore, if the electrolyte contains no or very little organic solvent, the electrolyte layer has sufficient strength even without a separator, and it is possible to electrically insulate the positive electrode and the negative electrode. Since a separator is not required, a secondary battery with high productivity can be produced. If the electrolyte layer contains an electrolyte and an inorganic filler, the strength is further increased, and a secondary battery with higher safety can be produced.

[0116] [Exterior Body] Exterior bodies of secondary batteries can be made of metal materials such as aluminum and resin materials. Film-like exterior bodies can also be used. Examples of films that can be used include a three-layer structure in which a thin, flexible metal film such as aluminum, stainless steel, copper, or nickel is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide resin or polyester resin is further provided on the thin metal film as the outer surface of the exterior body. It is also preferable to use a fluororesin film as the film. Fluororesin films have high stability against acids, alkalis, organic solvents, etc., and can suppress side reactions, corrosion, etc. associated with secondary battery reactions, thereby achieving excellent secondary batteries. Examples of fluororesin films include PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxyalkane: a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether), FEP (perfluoroethylene propene copolymer: a copolymer of tetrafluoroethylene and hexafluoropropylene), and ETFE (ethylene tetrafluoroethylene copolymer: a copolymer of tetrafluoroethylene and ethylene).

[0117] <Example of Negative Electrode Active Material> As the negative electrode active material, it is preferable to use a material capable of reacting with carrier ions of a secondary battery, a material capable of inserting and desorbing carrier ions, a material capable of alloying with a metal that becomes a carrier ion, a material capable of dissolving and precipitating a metal that becomes a carrier ion, or the like.

[0118] An example of the negative electrode active material will be described below.

[0119] As the negative electrode active material, a metal or a compound containing 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 Mg ２ Si, Mg ２ Ge, Mg ２ Sn, SnS ２ , V２ Sn ３ , FeSn ２ , CoSn ２ , Ni ３ Sn ２ , Cu ６ Sn ５ , Ag ３ Sn, Ag ３ Sb, Ni ２ MnSb, CeSb ３ , LaSn ３ , La ３ Co ２ Sn ７ , CoSb ３ , InSb, SbSn, etc.

[0120] Furthermore, materials with low resistance obtained by adding impurity elements such as phosphorus, arsenic, boron, aluminum, and gallium to silicon may also be used. Silicon materials pre-doped with lithium may also be used. Pre-doping methods include mixing silicon with lithium fluoride, lithium carbonate, and the like and annealing the mixture, or mechanical alloying of lithium metal and silicon. Furthermore, after forming an electrode containing silicon (silicon electrode), it can be combined with an electrode such as lithium metal to dope (pre-dope) lithium through a charge-discharge reaction. The doped silicon electrode may then be combined with a counter electrode (e.g., a positive electrode for the pre-doped negative electrode) to produce a secondary battery.

[0121] For example, silicon nanoparticles can be used as the negative electrode active material. The silicon nanoparticles preferably have an average particle diameter D50 of 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] The silicon nanoparticles may be crystalline, or may have a crystalline region and an amorphous region.

[0123] Examples of silicon-containing materials include SiO ｘ (x is preferably smaller than 2, more preferably 0.5 or more and 1.6 or less) can be used.

[0124] As the negative electrode active material, for example, carbon-based materials such as graphite, graphitizable carbon, non-graphitizable carbon, carbon nanotubes, carbon black, and graphene compounds can be used.

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

[0126] As the negative electrode active material, a combination of the above-mentioned metals, materials, compounds, etc. can be used.

[0127] Examples of the negative electrode active material include SnO, SnO ２ , titanium dioxide (TiO ２ ), lithium titanium oxide (Li ４ Ti ５ O １２ ), lithium-graphite intercalation compound (Li ｘ C ６ ), niobium pentoxide (Nb ２ O ５ ), tungsten oxide (WO ２ ), molybdenum oxide (MoO ２ ) and other oxides can be used.

[0128] In addition, as the negative electrode active material, a composite nitride of lithium and a transition metal, Li ３ Li with N-type structure ３−ｘ M ｘ N (M=Co, Ni, Cu) can be used. For example, Li ２．６ Co ０．４ N ３ exhibits a large charge / discharge capacity (900 mAh / g) and is therefore preferred.

[0129] When a composite nitride of lithium and transition metals is used as the negative electrode material, V containing no lithium ions can be used as the positive electrode material. ２ O ５ , Cr ３ O ８It is preferable that the composite nitride of lithium and a transition metal be used as the negative electrode material, even when a material containing lithium ions is used as the positive electrode material, by first removing the lithium ions contained in the positive electrode material.

[0130] Furthermore, a material that undergoes a conversion reaction can also be used as the negative electrode active material. For example, a transition metal oxide that does not undergo an alloying reaction with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), or iron oxide (FeO), can be used as the negative electrode active material. Further examples of materials that undergo a conversion reaction include Fe ２ O ３ ,CuO,Cu ２ O, RuO ２ , Cr ２ O ３ oxides such as CoS ０．８９ , sulfides such as NiS and CuS, Zn ３ N ２ , Cu ３ N, Ge ３ N ４ Nitrides such as NiP ２ , FeP ２ , CoP ３ Phosphides such as FeF ３ , BiF ３ This phenomenon also occurs with fluorides such as those listed above. Since the potential of the fluorides is high, they may also be used as positive electrode materials.

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

[0132] As the positive electrode active material of one embodiment of the present invention, a positive electrode active material having a layered crystal structure is preferably used.

[0133] An example of a layered crystal structure is a layered rock salt type crystal structure. An example of a composite oxide having a layered rock salt type crystal structure is LiM ｘ O ｙ(x>0 and y>0, more specifically, for example, y=2 and 0.8<x<1.2) can be used. Here, M is a metal element, and is 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 As an example of a composite oxide represented by the formula: LiCoO ２ , LiNiO ２ , LiMnO ２ Also, LiNi ｘ Co １−ｘ O ２ NiCo-based compounds represented by (0<x<1), LiM ｘ O ｙ As a composite oxide represented by the formula, for example, LiNi ｘ Mn １−ｘ O ２ NiMn-based alloys represented by (0<x<1), etc.

[0135] Also, LiMO ２ As a composite oxide represented by the formula, for example, LiNi ｘ Co ｙ Mn ｚ O ２ Examples include NiCoMn-based alloys (also referred to as NCM) represented by the formula (x > 0, y > 0, 0.8 < x + y + z < 1.2). Specifically, for example, it is preferable to satisfy 0.1x < y < 8x and 0.1x < z < 8x. As an example, it is preferable that x, y, and z satisfy x:y:z = 1:1:1 or a value thereabout. As another example, it is preferable that x, y, and z satisfy x:y:z = 5:2:3 or a value thereabout. As another example, it is preferable that x, y, and z satisfy x:y:z = 8:1:1 or a value thereabout. As another example, it is preferable that x, y, and z satisfy x:y:z = 6:2:2 or a value thereabout. As another example, it is preferable that x, y, and z satisfy x:y:z = 1:4:1 or a value thereabout.

[0136] Furthermore, examples of composite oxides having a layered rock salt type crystal structure include Li ２ MnO ３ , Li ２ MnO ３ -LiMeO ２ (Me is Co, Ni, Mn), etc.

[0137] The use of a cathode active material having a layered crystalline structure, such as the composite oxides described above, can sometimes realize a secondary battery with a high lithium content per volume and a high capacity per volume. Such cathode active materials also exhibit a large amount of lithium elimination per volume during charging, and stable charging and discharging requires stabilization of the crystalline structure after elimination. Furthermore, the collapse of the crystalline structure during charging and discharging can sometimes impede high-speed charging or discharging.

[0138] LiMn as the positive electrode active material ２ O ４ Lithium-containing materials having a spinel-type crystal structure containing manganese, such as lithium nickel oxide (LiNiO ２ or LiNi １−ｘ M ｘ O ２ It is preferable to mix (0<x<1) (M=Co, Al, etc.) This configuration can improve the characteristics of the secondary battery.

[0139] In addition, as the positive electrode active material, ａ Mn ｂ M ｃ O ｄA lithium-manganese composite oxide that can be expressed by the formula (1) can be used. Here, element M is preferably a metal element selected from among lithium and manganese, or silicon or phosphorus, and more preferably nickel. Furthermore, when measuring the entire lithium-manganese composite oxide particle, it is preferable that 0<a / (b+c)<2, c>0, and 0.26≦(b+c) / d<0.5 are satisfied during discharge. The composition of metals, silicon, phosphorus, etc. in the entire lithium-manganese composite oxide particle can be measured, for example, using an inductively coupled plasma mass spectrometer (ICP-MS). The oxygen composition in the entire lithium-manganese composite oxide particle can be measured, for example, using energy dispersive X-ray spectroscopy (EDX). Furthermore, the composition can be determined by using valence evaluation of fused 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, phosphorus, and the like.

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

[0141] 5A is a schematic top view of a positive electrode active material 100 according to one embodiment of the present invention. FIG. 5B is a schematic cross-sectional view taken along line A-B in FIG. 5A.

[0142] <Contained Elements and Distribution> The positive electrode active material 100 contains lithium, a transition metal M1, oxygen, and an additional element X. The positive electrode active material 100 is LiM1O ２ It can be said that the additive element X is added to a composite oxide represented by the formula (M1 is one or more selected from Fe, Ni, Co, and Mn).

[0143] The transition metal contained in the positive electrode active material 100 is preferably a metal capable of forming a layered rock-salt composite oxide belonging to the space group R-3m with lithium. For example, at least one of manganese, cobalt, and nickel can be used. That is, the transition metal contained in the positive electrode active material 100 may be cobalt alone, nickel alone, a combination of cobalt and manganese, or a combination of cobalt and nickel, or three of cobalt, manganese, and nickel. That is, the positive electrode active material 100 may contain a composite oxide containing lithium and a transition metal, such as lithium cobalt oxide, lithium nickel oxide, lithium cobalt oxide in which some of the cobalt is replaced with manganese, lithium cobalt oxide in which some of the cobalt is replaced with nickel, or nickel-manganese-lithium cobalt oxide. Including nickel in addition to cobalt as a transition metal may result in a more stable crystal structure in a charged state at a high voltage, which is preferable.

[0144] The additive element X contained 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 crystalline structure of the positive electrode active material 100. That is, the positive electrode active material 100 may contain lithium cobalt oxide containing magnesium and fluorine, lithium cobalt oxide containing magnesium, fluorine, and titanium, lithium nickel-cobalt oxide containing magnesium and fluorine, lithium cobalt-aluminate containing magnesium and fluorine, nickel-cobalt-aluminate, lithium nickel-cobalt-aluminate, lithium nickel-cobalt-aluminate containing magnesium and fluorine, or lithium nickel-manganese-cobalt oxide containing magnesium and fluorine. In this specification and the like, the additive element X may be referred to as a mixture, a part of a raw material, or the like.

[0145] As shown in FIG. 5B , the positive electrode active material 100 has a surface layer portion 100a and an interior portion 100b. The surface layer portion 100a preferably has a higher concentration of the additive element X than the interior portion 100b. Furthermore, as shown by the gradation in FIG. 5B , the additive element X preferably has a concentration gradient that increases from the interior toward the surface. In this specification, the surface layer portion 100a refers to the region extending from the surface of the positive electrode active material 100 to a depth of approximately 10 nm. Surfaces formed by cracks and / or fissures may also be referred to as the surface, and as shown in FIG. 5C , the region extending from the surface to a depth of approximately 10 nm is referred to as the surface layer portion 100c. Furthermore, the region deeper than the surface layer portion 100a and the surface layer portion 100c of the positive electrode active material 100 is referred to as the interior portion 100b.

[0146] In the positive electrode active material 100 according to one embodiment of the present invention, even when lithium is released from the positive electrode active material 100 due to charging, the surface layer portion 100 a having a high concentration of the additive element X, i.e., the outer periphery of the particle, is reinforced so as not to destroy the layered structure formed of octahedra of cobalt and oxygen.

[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. Even if a portion of the surface layer 100a is reinforced, if there is a portion without reinforcement, stress may be concentrated in the unreinforced portion, which is undesirable. If stress is concentrated in a portion of the particle, defects such as cracks may occur there, which may lead to breakage of the positive electrode active material and a decrease in charge / discharge capacity.

[0148] Magnesium is divalent and is more stable at the lithium site than at the transition metal site in the layered rock-salt crystal structure, and therefore more likely to enter the lithium site. The presence of magnesium at an appropriate concentration at the lithium site in the surface layer 100a facilitates the maintenance of the layered rock-salt crystal structure. Furthermore, magnesium has a strong bond with oxygen, which can suppress the desorption of oxygen around the magnesium. At an appropriate concentration, magnesium is preferable because it does not adversely affect the intercalation and deintercalation of lithium during charge and discharge. However, excessive magnesium may adversely affect the intercalation and deintercalation of lithium.

[0149] Aluminum is trivalent and can exist at the transition metal site in the layered rock salt crystal structure. Aluminum can suppress the elution of surrounding cobalt. Furthermore, aluminum has a strong bond with oxygen, so it can suppress the desorption of oxygen from around the aluminum. Therefore, if aluminum is included as the additive element X, it is possible to obtain a positive electrode active material 100 whose crystal structure is resistant to collapse even after repeated charge and discharge.

[0150] Fluorine is a monovalent anion, and when a portion of the oxygen in the surface layer portion 100a is substituted with fluorine, the lithium desorption energy is reduced. This is because the change in valence of cobalt ions accompanying lithium desorption differs depending on whether or not fluorine is present. For example, the oxidation-reduction potential of cobalt ions differs, from trivalent to tetravalent in the absence of fluorine, and from divalent to trivalent in the presence of fluorine. Therefore, when a portion of the oxygen in the surface layer portion 100a of the positive electrode active material 100 is substituted with fluorine, it can be said that desorption and insertion of lithium ions near the fluorine is more likely to occur smoothly. Therefore, when used in a secondary battery, charge / discharge characteristics, rate characteristics, etc. are improved, which is preferable.

[0151] Titanium oxide is known to have superhydrophilic properties. Therefore, by forming the cathode active material 100 with titanium oxide in the surface layer portion 100a, it is possible that the cathode active material 100 has good wettability with highly polar solvents. When formed into a secondary battery, it is possible that the interface between the cathode active material 100 and a highly polar electrolyte solution will have good contact, thereby suppressing an increase in resistance. In this specification and the like, the electrolyte solution corresponds to a liquid electrolyte.

[0152] As the charging voltage of a secondary battery increases, the voltage of the positive electrode generally increases. The positive electrode active material of one embodiment of the present invention has a stable crystal structure even at high voltages. The stable crystal structure of the positive electrode active material in a charged state can suppress a decrease in capacity due to repeated charge and discharge.

[0153] Furthermore, a short circuit in a secondary battery not only causes problems in the charging and / or discharging operations of the secondary battery, but may also lead to heat generation and fire. To achieve a safe secondary battery, it is preferable that a short circuit current be suppressed even at a high charging voltage. The positive electrode active material 100 of one embodiment of the present invention suppresses a short circuit current even at a high charging voltage. Therefore, a secondary battery that achieves both high capacity and safety can be obtained.

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

[0155] The concentration gradient of the added element X can be evaluated, for example, by using energy dispersive X-ray spectroscopy (EDX). Among EDX measurements, measuring while scanning an area and evaluating the area two-dimensionally is sometimes called EDX area analysis. Extracting data of a linear area from EDX area analysis and evaluating the distribution of atomic concentration within the positive electrode active material particles is sometimes called line analysis.

[0156] EDX area analysis (e.g., element mapping) can quantitatively analyze the concentration of the additive element X in the surface layer portion 100a, the interior 100b, and the vicinity of the grain boundaries of the positive electrode active material 100. Furthermore, EDX ray analysis can analyze the distribution of the concentration of the additive element X.

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

[0158] Furthermore, the fluorine distribution in the positive electrode active material 100 preferably overlaps with the magnesium distribution, and therefore, when EDX-ray analysis is performed, the peak of the fluorine concentration (the position where the concentration is maximum) in the surface layer portion 100 a is preferably present at a depth of up to 3 nm from the surface of the positive electrode active material 100 toward the center, more preferably at a depth of up to 1 nm, and even more preferably at a depth of up to 0.5 nm.

[0159] It should be noted that not all of the additive elements X need have the same concentration distribution. For example, when the positive electrode active material 100 contains aluminum as the additive element X, it is preferable that the distribution is slightly different from that of magnesium and fluorine. For example, when EDX-ray analysis is performed, it is preferable that the magnesium concentration peak is closer to the surface than the aluminum concentration peak in the surface layer portion 100a. For example, the aluminum concentration peak is preferably present 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 ray analysis or EDX area analysis is performed on the positive electrode active material 100, the ratio of the number of atoms of the additive element X to the number of atoms of the transition metal M1 (X / M1) in the vicinity of the grain boundaries is preferably 0.020 or more and 0.50 or less. More preferably, it is 0.025 or more and 0.30 or less. Even more preferably, it is 0.030 or more and 0.20 or less. For example, when the additive element X is magnesium and the transition metal M1 is cobalt, the ratio of the number of magnesium atoms to the number of cobalt atoms in the vicinity of the grain boundaries (Mg / Co) is preferably 0.020 or more and 0.50 or less. Even more preferably, it is 0.025 or more and 0.30 or less. Even more preferably, it is 0.030 or more and 0.20 or less.

[0161] As described above, an excess of the additive element contained in the positive electrode active material 100 may adversely affect the insertion and desorption of lithium. Furthermore, when used in a secondary battery, this may result in an increase in resistance and a decrease in capacity. On the other hand, an insufficient amount of the additive element may not be distributed throughout the entire surface layer portion 100a, resulting in an insufficient effect of maintaining the crystalline structure. In this way, the additive element X is adjusted to an appropriate concentration in the positive electrode active material 100.

[0162] Therefore, for example, the positive electrode active material 100 may have a region where excess additive element X is unevenly distributed. The presence of such a region allows excess additive element X to be removed from other regions, and an appropriate concentration of additive element X can be achieved in the interior and most of the surface layer portion of the positive electrode active material 100. By achieving an appropriate concentration of additive element X in the interior and most of the surface layer portion of the positive electrode active material 100, an increase in resistance and a decrease in capacity when the positive electrode active material 100 is used as a secondary battery can be suppressed. The ability to suppress an increase in resistance of a secondary battery is an extremely desirable characteristic, particularly in high-rate charge / discharge.

[0163] Furthermore, in the positive electrode active material 100 having a region where the excess additive element X is unevenly distributed, it is permissible to mix a certain amount of excess additive element X in the manufacturing process, which is preferable because it widens the margin in production.

[0164] In this specification and the like, uneven distribution refers to the difference in concentration of a certain element between a certain region A and a certain region B. It may also be referred to as segregation, precipitation, non-uniformity, deviation, high concentration or low concentration, etc.

[0165] <Crystal structure> Lithium cobalt oxide (LiCoO ２ Materials having a layered rock salt type crystal structure, such as LiM1O2, have a high discharge capacity and are known to be excellent as positive electrode active materials for secondary batteries. ２ (M1 is one or more selected from Fe, Ni, Co, and Mn).

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

[0167] In compounds containing nickel, distortion may easily occur due to the Jahn-Teller effect. ２ When LiCoO is charged and discharged at a high voltage, there is a concern that the crystal structure may be destroyed due to distortion. ２ It is suggested that the influence of the Jahn-Teller effect is small in this case, and the durability of charge and discharge at high voltages may be superior, which is preferable.

[0168] The positive electrode active material will be described with reference to Fig. 6 to Fig. 9. Fig. 6 to Fig. 9 describe the case where cobalt is used as the transition metal contained in the positive electrode active material.

[0169] <Conventional Positive Electrode Active Material> The positive electrode active material shown in FIG. 8 is lithium cobalt oxide (LiCoO ２ , LCO). The crystal structure of the lithium cobalt oxide shown in FIG. 8 changes depending on the charge depth. In other words, LixCoO ２ In this case, the crystal structure changes depending on the occupancy rate x of lithium at the lithium site.

[0170] As shown in FIG. 8, lithium cobalt oxide in the state where x=1 (discharged state) has a region having a crystal structure of the space group R-3m, and CoO ２ There are three layers. Therefore, this crystal structure is sometimes called an O3 type crystal structure. ２ The layer refers to a structure in which octahedral structures in which cobalt is six-coordinated with oxygen atoms are continuous in the plane direction with edge sharing.

[0171] When x = 0, the crystal structure has a space group P-3m1, and CoO ２ There is one layer, and therefore this crystal structure is sometimes called an O1-type crystal structure.

[0172] When x is about 0.12, lithium cobalt oxide has a crystal structure of the space group R-3m. This structure is similar to CoO such as P-3m1(O1). ２ and LiCoO such as R-3m(O3). ２ It can also be said that the structure of and are stacked alternately. Therefore, this crystal structure is sometimes called an H1-3 crystal structure. Since actual lithium insertion and desorption can be uneven, the H1-3 crystal structure is experimentally observed from about x = 0.25. In reality, the number of cobalt atoms per unit cell in the H1-3 crystal structure is twice that of other structures. However, in Figure 8 and other parts of this specification, the c-axis of the H1-3 crystal structure is shown as half the unit cell to make it easier to compare with other structures.

[0173] As an example, the coordinates of cobalt and oxygen in the unit cell of the H1-3 crystal structure can be expressed as 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 each an oxygen atom. In this way, the H1-3 crystal structure is expressed by a unit cell using one cobalt and two oxygen atoms. On the other hand, as described below, the O3' crystal structure of one embodiment of the present invention is preferably expressed by a unit cell using one cobalt and one oxygen atom. This indicates that the symmetry between cobalt and oxygen differs between the O3' crystal structure and the H1-3 structure, and that the O3' crystal structure changes less from the O3 structure than the H1-3 structure. The unit cell that is more preferably used to represent the crystal structure of the positive electrode active material may be selected, for example, so that the GOF (goodness of fit) value becomes smaller in Rietveld analysis of the XRD pattern.

[0174] When lithium cobalt oxide is repeatedly charged at a high voltage of 4.6 V or higher based on the redox potential of lithium metal, or when it is deeply charged to a depth of x of 0.24 or lower, and then discharged, the crystal structure of the lithium cobalt oxide repeatedly changes (i.e., undergoes a non-equilibrium phase change) between the H1-3 crystal structure and the R-3m(O3) structure in the discharged state.

[0175] However, these two crystal structures are different from CoO ２ As shown by the dotted lines and arrows in FIG. 8, in the H1-3 type crystal structure, CoO ２ The layers deviate significantly from R-3m(O3). Such dynamic structural changes can adversely affect the stability of the crystal structure.

[0176] Furthermore, the difference in volume is large: when compared per the same number of cobalt atoms, the difference in volume between the H1-3 type crystal structure and the O3 type crystal structure in a discharged state is 3.0% or more.

[0177] In addition, the H1-3 type crystal structure has CoO such as P-3m1(O1). ２A structure with continuous layers is likely to be unstable.

[0178] Therefore, repeated high-voltage charging and discharging causes the crystalline structure of lithium cobalt oxide to collapse, which leads to a deterioration in cycle characteristics. This is thought to be because the collapse of the crystalline structure reduces the number of sites where lithium can exist stably and makes it difficult for lithium to be inserted and extracted.

[0179] <Positive Electrode Active Material of One Embodiment of the Present Invention> <Interior> The positive electrode active material 100 of one embodiment of the present invention is a material that, when repeatedly charged and discharged at a high voltage, ２ The layer misalignment can be reduced. Furthermore, the volume change can be reduced. Therefore, the positive electrode active material of one embodiment of the present invention can achieve excellent cycle characteristics. Furthermore, the positive electrode active material of one embodiment of the present invention can have a stable crystal structure in a charged state at a high voltage. Therefore, the positive electrode active material of one embodiment of the present invention may be less likely to cause a short circuit when maintained in a charged state at a high voltage. In such a case, safety is further improved, which is preferable.

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

[0181] The crystal structure of the positive electrode active material 100 before and after charge and discharge is shown in Figure 6. 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 that the positive electrode active material 100 contains magnesium as the additional element X. It is also preferable that the additional element X further contains a halogen such as fluorine or chlorine.

[0182] The crystal structure of Figure 6 when x = 1 (discharged state) is the same as that of Figure 8, which is R-3m(O3). 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 fully charged. This structure belongs to the space group R-3m, and ions such as cobalt and magnesium ions occupy the oxygen hexacoordination positions. In addition, CoO in this structure ２The symmetry of the layers is the same as that of the O3 type. Therefore, this structure is referred to as an O3' type crystal structure in this specification. In the diagram of the O3' type crystal structure shown in FIG. 6, lithium is omitted in order to explain the symmetry of the cobalt atom and the symmetry of the oxygen atom. However, in reality, CoO ２ Between the layers, for example, 20 atomic % or less of lithium is present relative to cobalt. In both the O3 type crystal structure and the O3' type crystal structure, CoO ２ It is preferable that magnesium is present in a dilute form between the layers, i.e., at the lithium sites, and it is also preferable that halogen such as fluorine is present randomly and dilutely at the oxygen sites.

[0183] In the O3' type crystal structure, a light element such as lithium may occupy the oxygen tetracoordination position.

[0184] The O3' type crystal structure has random lithium between layers, but it can also be said to be a crystal structure similar to the CdCl2 type crystal structure. ２ A crystal structure similar to the type was formed when lithium nickel oxide was charged to x = 0.06 (Li ０．０６ NiO ２ ), but it is known that pure lithium cobaltate or layered rock salt-type positive electrode active materials containing a large amount of cobalt do not usually adopt this crystal structure.

[0185] In the positive electrode active material 100 of one embodiment of the present invention, when a large amount of lithium is released by charging at a high voltage, the change in the crystal structure is suppressed more than in conventional positive electrode active materials. For example, as shown by the dotted line in FIG. 6, in these crystal structures, CoO ２ There is almost no layer misalignment.

[0186] More specifically, the cathode active material 100 of one embodiment of the present invention has high structural stability even at high charge voltages. For example, in conventional cathode active materials, there exists a charge voltage region where the R-3m(O3) crystal structure can be maintained even at a charge voltage where the H1-3 crystal structure is formed, for example, at a voltage of about 4.6 V relative to the potential of lithium metal. Furthermore, there exists a region where the O3' crystal structure can be formed even at a higher charge voltage, for example, at a voltage of about 4.65 V to 4.7 V relative to the potential of lithium metal. Furthermore, there exists a region where the H1-3 crystal structure can be formed even at a higher charge voltage, for example, at a voltage of about 4.65 V to 4.7 V relative to the potential of lithium metal. Furthermore, there exists a region where the H1-3 crystal can be formed even at a higher charge voltage, for example, at a voltage of 4.3 V or higher and 4.5 V or lower relative to the potential of lithium metal.

[0187] Therefore, in the positive electrode active material 100 of one embodiment of the present invention, the crystal structure is not easily broken even when charge and discharge are repeated at a high voltage.

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

[0189] In the O3' type crystal structure, the coordinates of cobalt and oxygen in the unit cell can be expressed within the range of Co(0,0,0.5), O(0,0,x), 0.20≦x≦0.25.

[0190] The additive element X, for example, magnesium, which is randomly and dilutely present between the CoO2 layers, i.e., at the lithium site, has the effect of suppressing the displacement of the CoO2 layers. ２When magnesium is present between layers, the O3'-type crystal structure is likely to be formed. Therefore, magnesium is preferably distributed in at least a part of the surface layer portion of the positive electrode active material 100 of one embodiment of the present invention, and more preferably distributed throughout the entire surface layer portion of the positive electrode active material 100. In order to distribute magnesium throughout the entire surface layer portion of the positive electrode active material 100, heat treatment is preferably performed in the process of manufacturing the positive electrode active material 100 of one embodiment of the present invention.

[0191] However, if the heat treatment temperature is too high, cation mixing occurs, increasing the possibility that the additive element X, such as magnesium, will enter the cobalt site. Magnesium present at the cobalt site is ineffective in maintaining the R-3m structure under high-voltage charging. Furthermore, if the heat treatment temperature is too high, there are concerns about adverse effects such as cobalt being reduced to divalent and lithium evaporating.

[0192] Therefore, it is preferable to add a halogen compound such as a fluorine compound to the lithium cobalt oxide before the heat treatment for distributing magnesium over the entire surface layer of the positive electrode active material 100. The addition of the halogen compound lowers the melting point of the lithium cobalt oxide. Lowering the melting point makes it easier to distribute magnesium over the entire surface layer of the positive electrode active material 100 at a temperature where cation mixing is unlikely to occur. Furthermore, the presence of a fluorine compound is expected to improve corrosion resistance to hydrofluoric acid produced by decomposition of the electrolyte.

[0193] Note that if the magnesium concentration is increased above a desired value, the effect on stabilizing the crystal structure may be reduced. This is thought to be because magnesium enters the cobalt site in addition to the lithium site. The number of magnesium atoms in the positive electrode active material of one embodiment of the present invention is preferably 0.001 to 0.1 times the number of atoms of the transition metal, such as cobalt, more preferably more than 0.01 to 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 performing elemental analysis of the entire positive electrode active material using ICP-MS or the like, or may be based on the value of the raw material composition in the process of producing the positive electrode active material 100.

[0194] Lithium cobalt oxide may contain one or more metals selected from nickel, aluminum, manganese, titanium, vanadium, and chromium as a metal other than cobalt (hereinafter, "additive element X"). Addition of one or more of nickel and aluminum is particularly preferred. Manganese, titanium, vanadium, and chromium may be stable due to their tetravalent nature, and may contribute significantly to structural stability. Addition of the additive element X may further stabilize the crystal structure in a charged state at a high voltage. In the positive electrode active material of one embodiment of the present invention, the additive element X is preferably added at a concentration that does not significantly change the crystallinity of the lithium cobalt oxide. For example, the amount is preferably such that the aforementioned Jahn-Teller effect or the like is not exhibited.

[0195] The transition metals, such as nickel and manganese, and aluminum are preferably present at the cobalt site, but may be partially present at the lithium site. Magnesium is preferably present at the lithium site. Oxygen may be partially substituted with fluorine.

[0196] As the magnesium concentration in the positive electrode active material of one embodiment of the present invention increases, the capacity of the positive electrode active material may decrease. One possible cause of this is the incorporation of magnesium into the lithium site, which may reduce the amount of lithium contributing to charge and discharge. When the positive electrode active material of one embodiment of the present invention contains nickel in addition to magnesium as the additive element X, the charge and discharge cycle characteristics may be improved. Furthermore, when the positive electrode active material of one embodiment of the present invention contains aluminum in addition to magnesium as the additive element X, the charge and discharge cycle characteristics may be improved. Furthermore, when the positive electrode active material of one embodiment of the present invention contains magnesium, nickel, and aluminum as the additive element X, the charge and discharge cycle characteristics may be improved.

[0197] The element concentrations of a positive electrode active material according to one embodiment of the present invention, which contains magnesium, nickel, and aluminum as the additional element X, will be discussed below.

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

[0199] If the battery is charged at a high voltage for a long period of time, the constituent elements of the positive electrode active material may leach into the electrolyte, causing the crystal structure to collapse. However, by containing nickel in the above proportions, it may be possible to suppress the leach-out of the constituent elements from the positive electrode active material 100.

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

[0201] In addition, the positive electrode active material of one embodiment of the present invention including an additional element X preferably uses phosphorus as the additional element X. In addition, the positive electrode active material of one embodiment of the present invention more preferably includes a compound containing phosphorus and oxygen.

[0202] When the positive electrode active material of one embodiment of the present invention includes a compound containing phosphorus as the additional element X, a short circuit may be less likely to occur when a charged state at high temperature and high voltage is maintained for a long period of time.

[0203] When the positive electrode active material of one embodiment of the present invention contains phosphorus as the additional element X, hydrogen fluoride generated by decomposition of the electrolyte solution may react with phosphorus, resulting in a decrease in the hydrogen fluoride concentration in the electrolyte solution.

[0204] The electrolyte is LiPF as a lithium salt. ６In the case where the electrolyte contains PVDF, hydrogen fluoride may be generated by hydrolysis. Hydrogen fluoride may also be generated by the reaction of PVDF, which is used as a component of the positive electrode, with an alkali. By reducing the hydrogen fluoride concentration in the electrolyte, corrosion of the current collector and / or peeling of the coating may be suppressed. Furthermore, gelation and / or insolubilization of PVDF may be suppressed, which may result in a decrease in adhesion.

[0205] When the cathode active material 100 of one embodiment of the present invention contains phosphorus and magnesium as the additive element X, the stability in a high-voltage charged state is extremely high. When the additive element X contains phosphorus and magnesium, 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%, more preferably 0.5% to 5%, and even more preferably 0.7% to 4% of the number of cobalt atoms. The concentrations of phosphorus and magnesium shown here may be values ​​obtained by performing elemental analysis of the entire cathode active material 100 using, for example, ICP-MS or the like, or may be based on values ​​of the composition of raw materials in the process of producing the cathode active material 100.

[0206] When the positive electrode active material 100 has cracks, the presence of phosphorus, more specifically, a compound containing phosphorus and oxygen, inside the cracks may inhibit the progression of the cracks.

[0207] As shown in Figure 6, the symmetry of oxygen atoms is slightly different between the O3 type crystal structure and the O3' type crystal structure. 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 aligned strictly. This is because in the O3' type crystal structure, as lithium decreases, tetravalent cobalt increases, causing Jahn-Teller distortion to increase, resulting in CoO ６ This is because the octahedral structure of CoO is distorted. ２ Another factor is the increased repulsion between oxygen atoms in the layers.

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

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

[0210] The surface layer 100a of the positive electrode active material 100 is, so to speak, entirely composed of crystal defects. Furthermore, because lithium is removed from the surface during charging, this portion is prone to have a lower lithium concentration than the interior. This makes the surface unstable and prone to collapse of the crystal structure. A high magnesium concentration in the surface layer 100a can more effectively suppress changes in the crystal structure. Furthermore, a high magnesium concentration in the surface layer 100a can be expected to improve corrosion resistance to hydrofluoric acid produced by decomposition of the electrolyte.

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

[0212] As described above, the surface layer portion 100a of the positive electrode active material 100 of one embodiment of the present invention preferably has a different composition from the inner portion 100b, i.e., a higher concentration of additive elements, such as magnesium and fluorine, than the inner portion 100b. Furthermore, the composition preferably has a stable crystal structure at room temperature. Therefore, the surface layer portion 100a may have a different crystal structure from the inner portion 100b. For example, at least a portion of the surface layer portion 100a of the positive electrode active material 100 of one embodiment of the present invention may have a rock salt crystal structure. Furthermore, when the surface layer portion 100a and the inner portion 100b have different crystal structures, it is preferable that the crystal orientations of the surface layer portion 100a and the inner portion 100b approximately match.

[0213] Layered rock salt crystals and the anions in rock salt crystals have a cubic close-packed structure (face-centered cubic lattice structure). It is presumed that the anions in O3'-type crystals also have a cubic close-packed structure. In this specification, if the anions have a structure in which three layers are stacked with a skewed relationship, such as ABCABC, it is referred to as a cubic close-packed structure. Therefore, the anions do not necessarily have to be strictly cubic lattices. At the same time, because real crystals always have defects, the analysis results do not necessarily conform to theory. For example, in electron diffraction or FFT (fast Fourier transform) of TEM images, etc., spots may appear at positions slightly different from the theoretical positions. For example, if the orientation from the theoretical positions is 5 degrees or less, or 2.5 degrees or less, it can be said to have a cubic close-packed structure.

[0214] When layered rock salt crystals come into contact with each other, there are crystal faces where the cubic close-packed structures formed by anions are oriented in the same direction.

[0215] Alternatively, it can be explained as follows: Anions on the (111) plane of the cubic crystal structure have a triangular arrangement. The layered rock salt type has a space group R-3m and a rhombohedral structure, but to make the structure easier to understand, it is generally expressed as a compound hexagonal lattice, and the (0001) plane of the layered rock salt type has a hexagonal lattice. The triangular lattice of the cubic (111) has the same atomic arrangement as the hexagonal lattice of the (0001) plane of the layered rock salt type. The compatibility of the two lattices can be said to be the alignment of the cubic close-packed structure.

[0216] However, the space group of the layered rock salt type crystal and the O3' type crystal is R-3m, which is different from the space group of the rock salt type crystal, Fm-3m (the space group of a general rock salt type crystal) and Fd-3m (the space group of a rock salt type crystal having the simplest symmetry), and therefore the Miller indices of the crystal planes that satisfy the above conditions are different between the layered rock salt type crystal and the O3' type crystal and the rock salt type crystal. In this specification, when the orientations of the cubic close-packed structures formed by anions are aligned in the layered rock salt type crystal, the O3' type crystal, and the rock salt type crystal, it may be said that the crystal orientations are approximately the same.

[0217] The fact that the crystal orientations of the two regions roughly coincide can be determined from TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle 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), neutron diffraction, etc. can also be used as materials for determination.

[0218] <Grain Boundary> The additional element X contained in the positive electrode active material 100 of one embodiment of the present invention may be present randomly and dilutely inside the positive electrode active material 100, but it is more preferable that a portion of the additional element X segregates at the grain boundary.

[0219] In other words, the concentration of the additional element X in and near the grain boundaries of the positive electrode active material 100 of one embodiment of the present invention is preferably higher than that in other regions inside the grain boundaries.

[0220] The grain boundaries can be considered as planar defects. Therefore, like the particle surfaces, they are easily unstable and tend to initiate changes in the crystal structure. Therefore, if the concentration of the added element X at and near the grain boundaries is high, the change in the crystal structure can be more effectively suppressed.

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

[0222] In this specification and the like, the vicinity of the grain boundary refers to the region up to about 10 nm from the grain boundary.

[0223] <Particle size> If the particle size of the positive electrode active material 100 of one embodiment of the present invention is too large, problems such as difficulty in diffusing lithium or excessive roughness of the surface of the active material layer when applied to a current collector occur. On the other hand, if the particle size is too small, problems such as difficulty in supporting the active material layer when applied to a current collector or excessive reaction with the electrolyte solution occur. Therefore, 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 or not a certain positive electrode active material is the positive electrode active material 100 of one embodiment of the present invention that exhibits an O3′-type crystal structure when charged at a high voltage can be determined by analyzing the positive electrode charged at a high voltage using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc. XRD is particularly preferred in that it can analyze the symmetry of transition metals such as cobalt contained in the positive electrode active material with high resolution, it can compare the level of crystallinity and the orientation of the crystals, it can analyze the periodic distortion of the lattice and the crystallite size, and it can obtain sufficient accuracy even when measuring a positive electrode obtained by disassembling a secondary battery as is.

[0225] As described above, the positive electrode active material 100 of one embodiment of the present invention is characterized by minimal change in crystal structure between a high-voltage charged state and a discharged state. Materials in which a crystal structure that exhibits a significant change between a high-voltage charged state and a discharged state accounts for 50 wt % or more are undesirable because they cannot withstand high-voltage charging and discharging. It should be noted that the desired crystal structure may not be achieved simply by adding an additive element. For example, even if both materials share the common feature of being lithium cobalt oxide containing magnesium and fluorine, there are cases in which the O3′-type crystal structure accounts for 60 wt % or more and cases in which the H1-3-type crystal structure accounts for 50 wt % or more when charged at a high voltage. Furthermore, at a predetermined voltage, the O3′-type crystal structure may be nearly 100 wt %, and further increasing the predetermined voltage may result in the H1-3-type crystal structure. Therefore, to determine whether a material is the positive electrode active material 100 of one embodiment of the present invention, analysis of the crystal structure, such as XRD, is required.

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

[0227] <Charging Method> High-voltage charging for determining whether a certain composite oxide is the positive electrode active material 100 of one embodiment of the present invention can be performed by preparing a coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) using a lithium counter electrode, for example, and charging the coin cell.

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

[0229] Lithium metal can be used for the counter electrode. When a material other than lithium metal is used for the counter electrode, the potential of the secondary battery differs from the potential of the positive electrode. Unless otherwise specified, voltages and potentials in this specification refer to the potential of the positive electrode.

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

[0231] The separator can be made of polypropylene having a thickness of 25 μm.

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

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

[0234] <XRD> Ideal powder XRD patterns calculated from the O3'-type crystal structure and H1-3-type crystal structure models using CuKα1 radiation are shown in Figures 7 and 9. For comparison, LiCoO ２ (O3) and CoO with x = 0 ２ The ideal XRD pattern calculated from the crystal structure of LiCoO (O1) is also shown. ２ (O3) and CoO ２The (O1) pattern was created using Reflex Powder Diffraction, a module of Materials Studio (BIOVIA), from crystal structure information obtained from ICSD (Inorganic Crystal Structure Database). The 2θ range was set to 15° to 75°, with a step size of 0.01, a wavelength of λ1 = 1.540562 × 10 m, no λ2 setting, and a single monochromator. The O3'-type crystal structure pattern was estimated from the XRD pattern of the positive electrode active material of one embodiment of the present invention, and fitted using TOPAS ver. 3 (crystal structure analysis software manufactured by Bruker). Similarly to the other patterns, an XRD pattern was created.

[0235] As shown in Figure 7, in the O3' type crystal structure, diffraction peaks appear at 2θ = 19.30 ± 0.20° (19.10° to 19.50°) and 2θ = 45.55 ± 0.10° (45.45° to 45.65°). More specifically, sharp diffraction peaks appear at 2θ = 19.30 ± 0.10° (19.20° to 19.40°) and 2θ = 45.55 ± 0.05° (45.50° to 45.60°). However, as shown in Figure 9, in the H1-3 type crystal structure and CoO ２ In the case of (P-3m1, O1), no peaks appear at these positions. Therefore, the appearance of peaks at 2θ = 19.30 ± 0.20° and 2θ = 45.55 ± 0.10° in a state charged at a high voltage can be said to be a characteristic of the positive electrode active material 100 of one embodiment of the present invention.

[0236] This means that the positions at which the XRD diffraction peaks appear are close between the crystal structure with x = 1 and the crystal structure in the high-voltage charging state. More specifically, the difference in the positions at which two or more, preferably three or more, of the main diffraction peaks of both structures 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 embodiment of the present invention has an O3'-type crystal structure when charged at a high voltage. However, the entire positive electrode active material 100 does not necessarily have an O3'-type crystal structure. It may contain other crystal structures, or may be partially amorphous. However, when Rietveld analysis is performed on the XRD pattern, the O3'-type crystal structure is preferably 50 wt % or more, more preferably 60 wt % or more, and even more preferably 66 wt % or more. When the O3'-type crystal structure is 50 wt % or more, more preferably 60 wt % or more, and even more preferably 66 wt % or more, the positive electrode active material can have sufficiently excellent cycle characteristics.

[0238] Furthermore, even after 100 or more charge / discharge cycles from the start of measurement, when Rietveld analysis is performed, the O3' type crystal structure is preferably 35 wt% or more, more preferably 40 wt% or more, and even more preferably 43 wt% or more.

[0239] The crystallite size of the O3'-type crystal structure of the positive electrode active material particles is ２ Therefore, even under the same XRD measurement conditions as the positive electrode before charging and discharging, a clear peak of the O3' type crystal structure can be confirmed in the high voltage charging state. ２ In this case, even if a part of the crystal structure resembles the O3'-type crystal structure, the crystallite size will be small and the peak will be broad and small. The crystallite size can be determined from the half-width of the XRD peak.

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

[0241] A preferable range of the lattice constant was considered, and it was found that in the positive electrode active material of one embodiment of the present invention, the layered rock-salt crystal structure of the particles of the positive electrode active material in a state where no charge / discharge is performed or in a discharged state, which can be estimated from the XRD pattern, has an a-axis lattice constant of 2.814 × 10 −１０ m is greater than 2.817 x 10 −１０ m, and the lattice constant of the c-axis is greater than 14.05 × 10 m and is 14.07 × 10 −１０ It has been found that the value is preferably smaller than m. The state in which no charge and discharge are performed may be, for example, the state of powder before the positive electrode of the secondary battery is produced.

[0242] Alternatively, in the layered rock-salt crystal structure of the particles of the positive electrode active material in a state where no charge or discharge is performed or in a 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 smaller than 0.20049.

[0243] Alternatively, when XRD analysis is performed on a layered rock salt type crystal structure possessed by particles of a positive electrode active material in a state where no charge / discharge is performed or in a discharged state, a first peak may be observed at 2θ of not less than 18.50° and not more than 19.30°, and a second peak may be observed at 2θ of not less than 38.00° and not more than 38.80°.

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

[0245] <XPS> X-ray photoelectron spectroscopy (XPS) can analyze a region from the surface to a depth of about 2 to 8 nm (usually about 5 nm), so the concentration of each element can be quantitatively analyzed for about half of the surface layer 100a. Furthermore, narrow scan analysis can be used to analyze the bonding state of elements. The quantitative accuracy of XPS is often about ±1 atomic %, and the lower detection limit is about 1 atomic %, depending on the element.

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

[0247] When XPS analysis is performed, for example, monochromated aluminum can be used as the X-ray source, and the take-off angle can be set to, for example, 45°.

[0248] Furthermore, when the positive electrode active material 100 of one embodiment of the present invention is subjected to XPS analysis, the peak representing the bond energy between fluorine and another element is preferably equal to or greater than 682 eV and less than 685 eV, and more preferably about 684.3 eV. This value is different from both the bond energy of lithium fluoride (685 eV) and the bond energy of magnesium fluoride (686 eV). In other words, when the positive electrode active material 100 of one embodiment of the present invention contains fluorine, the bond is preferably other than that of lithium fluoride or magnesium fluoride.

[0249] Furthermore, when the positive electrode active material 100 of one embodiment of the present invention is subjected to XPS analysis, the peak representing the bond energy between magnesium and another element is preferably equal to or greater than 1302 eV and less than 1304 eV, and more preferably about 1303 eV. This value is different from the bond energy of magnesium fluoride, 1305 eV, and is close to the bond energy of magnesium oxide. In other words, when the positive electrode active material 100 of one embodiment of the present invention contains magnesium, the bond is preferably other than that of magnesium fluoride.

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

[0251] When a cross section of magnesium and aluminum is exposed by processing and analyzed using TEM-EDX, the concentration of the surface layer 100 a is preferably higher than the concentration of the inner portion 100 b. The processing can be performed using, for example, FIB.

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

[0253] On the other hand, it is preferable that nickel contained in the transition metal is not unevenly distributed in the surface layer portion 100a but is distributed throughout the positive electrode active material 100. However, this does not apply when there is a region where the excess additional element X described above is unevenly distributed.

[0254] <Surface Roughness and Specific Surface Area> The cathode active material 100 of one embodiment of the present invention preferably has a smooth surface with little unevenness. A smooth surface with little unevenness is one factor indicating that the distribution of the additive element X in the surface layer portion 100a is good. Note that, in the process of producing the cathode active material 100, if the lithium cobalt oxide or the lithium nickel-cobalt-manganese oxide before the addition of the additive element X is initially heated, the cathode active material 100 is particularly preferred because it has significantly excellent high-voltage charge / discharge cycle characteristics.

[0255] Furthermore, since the surface of the positive electrode active material 100 is smooth and has few irregularities, the stability of the surface of the positive electrode active material 100 is improved, and it is possible to suppress the occurrence of pits.

[0256] Whether the surface is smooth and has few irregularities can be determined from, for example, a 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, or the like.

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

[0258] First, the cathode active material 100 is processed using an FIB or the like to expose a cross section. At this time, it is preferable to cover the cathode active material 100 with a protective film, protective agent, or the like. Next, an SEM image of the interface between the protective film or the like and the cathode active material 100 is taken. The SEM image is subjected to noise processing using image processing software. For example, Gaussian blurring (σ = 2) is performed, followed by binarization. Interface extraction is then performed using image processing software. The interface line between the protective film or the like and the cathode active material 100 is then selected using a magic hand tool or the like, and the data is extracted into a spreadsheet software or the like. Using the functions of the spreadsheet software or the like, correction is performed from the regression curve (quadratic regression), and parameters for calculating roughness are obtained from the data after slope correction, and the root mean square (RMS) surface roughness is calculated from the standard deviation. Furthermore, this surface roughness is the surface roughness at least within 400 nm of the outer periphery of the particle of the cathode active material.

[0259] On the particle surfaces of the positive electrode active material 100 of the present embodiment, the root mean square (RMS) surface roughness, which is an index of roughness, is preferably 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 processing, boundary extraction, etc. is not particularly limited, but for example, "ImageJ" can be used. The spreadsheet software is also 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 between the actual specific surface area AR measured by a constant volume gas adsorption method and the ideal specific surface area Ai.

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

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

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

[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. The positive electrode active material of one embodiment of the present invention is expected to have the effect of suppressing the occurrence of progressive defects as described below.

[0266] Charging and discharging under high voltage conditions of 4.5 V or higher or at high temperatures (45°C or higher) can cause progressive defects (also called pits) in the positive electrode active material particles. Furthermore, expansion and contraction of the positive electrode active material particles due to charging and discharging can also cause new defects such as fissures (also called cracks). Figure 10 shows a schematic cross-sectional view of a positive electrode active material particle 51. In the positive electrode active material particle 51, pits are shown as holes at 54 and 58, but the openings are not circular but have depth, and cracks are shown at 57. 55 indicates a crystal plane, 52 indicates a recess, and 53 and 56 indicate a barrier film. Cracks can occur during electrode pressing. However, because the cracks that occur during pressing do not have a surface layer containing the aforementioned additive element X, they may induce progressive defects during charging and discharging. When an electrode is fabricated using the method for fabricating an electrode according to one embodiment of the present invention, it is expected that the occurrence of cracks during pressing of the electrode can be suppressed, and therefore it is expected that the occurrence of progressive defects due to charge and discharge under high voltage conditions of 4.5 V or more or at high temperatures (45° C. or more) can be suppressed.

[0267] The positive electrode active material of a lithium-ion secondary battery is typically LCO or NCM, which can also be considered an alloy containing multiple metal elements (e.g., cobalt, nickel, etc.). At least one of the multiple positive electrode active material particles may have defects, and the defects may change before and after charge and discharge. When used in a secondary battery, the positive electrode active material particles may be chemically or electrochemically eroded by the environmental substances (e.g., electrolyte) surrounding the positive electrode active material particles, or the material may deteriorate. This deterioration does not occur uniformly on the particle surface, but occurs in a locally concentrated manner, and repeated charge and discharge of the secondary battery can cause defects to form deep from the surface to the interior, for example.

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

[0269] In this specification, cracks and pits are different. Immediately after the production of positive electrode active material particles, cracks may be present but pits do not. Pits can be said to be holes formed by the loss of several layers of cobalt and oxygen due to charging and discharging under high voltage conditions of 4.5 V or higher or at high temperatures (45°C or higher), and can also be said to be locations where cobalt has dissolved. Cracks refer to new surfaces formed by the application of physical pressure or cracks caused by grain boundaries. Cracks can also occur due to particle expansion and contraction caused by charging and discharging. Pits can also occur from cracks or cavities within particles.

[0270] 11A is a cross-sectional STEM image of a defect in a positive electrode active material obtained by forming a positive electrode active material layer on a current collector and then pressing the current collector using a conventional method. Due to pressing, steps are observed on the particle surface in the direction perpendicular to the lattice fringes (c-axis direction), and evidence of deformation along the lattice fringe direction (the ab-plane direction) is observed.

[0271] 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 in the direction perpendicular to the lattice fringes. Also shown in FIG. 11B is a crystal face 55 that does not have slip.

[0272] 11C is a cross-sectional schematic diagram of a particle after pressing. The pressing process causes misalignment in the lattice fringe direction (the ab plane direction). The Mg and Al layers also have multiple steps and are non-uniform. Regarding the misalignment in the ab plane direction, the particle surface opposite to the surface where the irregularities were observed also has irregularities of a similar shape, and some of the particles have misalignment in the ab plane direction.

[0273] The multiple steps shown in FIG. 11C are observed as striped patterns on the particle surface. Such striped patterns on the particle surface due to the steps caused by displacement due to pressing are called slips (stacking faults). Such particle slippage can also cause the barrier film to become non-uniform, which can lead to deterioration. When an electrode is fabricated using the method for fabricating an electrode according to one embodiment of the present invention, it is expected that slippage during pressing of the electrode can be suppressed, and therefore a secondary battery with little deterioration can be obtained.

[0274] [Cathode Active Material Composite] Alternatively, the cathode active material 100 of one embodiment of the present invention may be a cathode active material composite having a coating layer that covers at least a part of the cathode active material 100. Examples of the coating layer include glass, oxide, and LiM2PO4. ４ (M2 is one or more selected from Fe, Ni, Co, and Mn).

[0275] The glass contained in the coating layer of the positive electrode active material composite can be a material having an amorphous portion. Examples of the material having an amorphous portion include SiO ２ , SiO, Al ２ O ３ , TiO ２ , Li ４ SiO ４ , Li ３ P.O. ４ , Li ２ S, SiS ２ , B ２ S ３ , GeS ４ , AgI, Ag ２ O, Li ２ O, P ２ O ５ , B ２ O３ , and V ２ O ５ A material having one or more selected from the group consisting of Li, ７ P ３ S 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. A material having an amorphous portion can be used in an amorphous state as a whole, or in a partially crystallized state as crystallized glass (also called glass ceramics). The glass desirably has lithium ion conductivity. Lithium ion conductivity can also be said to have lithium ion diffusibility and lithium ion penetration. The glass preferably has a melting point of 800°C or less, more preferably 500°C or less. The glass preferably has electronic conductivity. The glass preferably has a softening point of 800°C or less, for example, Li ２ O-B ２ O ３ -SiO ２ Glasses containing fluorine can be used.

[0276] Examples of oxides contained in the coating layer of the positive electrode active material composite include aluminum oxide, zirconium oxide, hafnium oxide, and niobium oxide. ４ (M2 is one or more selected from Fe, Ni, Co, and Mn) ４ , LiNiPO ４ , LiCoPO ４ , LiMnPO ４ , LiFe ａ Ni ｂ P.O. ４ , LiFe ａ Co ｂ P.O. ４ , LiFe ａ Mn ｂ P.O. ４ , LiNi ａ Co ｂ P.O. ４ , LiNi ａ Mnｂ P.O. ４ (a+b is 1 or less, 0<a<1, 0<b<1), LiFe ｃ Ni ｄ Co ｅ P.O. ４ , LiFe ｃ Ni ｄ Mn ｅ P.O. ４ , LiNi ｃ Co ｄ Mn ｅ P.O. ４ (c+d+e is 1 or less, 0<c<1, 0<d<1, 0<e<1), LiFe ｆ Ni ｇ Co ｈ Mn ｉ P.O. ４ (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 prepare the coating layer of the positive electrode active material composite. Examples of the composite treatment include one or more of the following: composite treatments using mechanical energy, such as mechanochemical, mechanofusion, and ball milling; composite treatments using liquid-phase reactions, such as coprecipitation, hydrothermal, and sol-gel; and composite treatments using gas-phase reactions, such as barrel sputtering, atomic layer deposition (ALD), vapor deposition, and chemical vapor deposition (CVD). For example, Picobond, manufactured by Hosokawa Micron, can be used as a composite treatment using mechanical energy. Furthermore, it is preferable to perform a heat treatment once or multiple times during the composite treatment.

[0278] The positive electrode active material composite reduces contact of the positive electrode active material with the electrolyte solution and the like, thereby suppressing deterioration of the secondary battery.

[0279] The content of this embodiment mode can be freely combined with the content of other embodiment modes.

[0280] Embodiment Mode 3 In this embodiment mode, examples of various shapes of secondary batteries each having a positive electrode or a negative electrode manufactured by the manufacturing method described in the previous embodiment will be described.

[0281] [Coin-Type Secondary Battery] An example of a coin-type secondary battery will be described. Fig. 12A is an exploded perspective view of a coin-type (single-layer flat) secondary battery, Fig. 12B is an external view, and Fig. 12C is a cross-sectional view thereof. Coin-type secondary batteries are mainly used in small electronic devices. In this specification, coin-type batteries include button-type batteries.

[0282] 12A is a schematic diagram that shows the overlapping of components (upper and lower relationships and positional relationships) for ease of understanding, and therefore, FIGS. 12A and 12B are not completely identical corresponding views.

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

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

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

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

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

[0288] It is to be noted that the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 each only need to have an active material layer formed on one side.

[0289] The positive electrode can 301 and the negative electrode can 302 can be made of a metal such as nickel, aluminum, or titanium that is corrosion-resistant to the electrolyte, or an alloy of these metals, or an alloy of these metals with other metals (e.g., stainless steel). Furthermore, to prevent corrosion by the electrolyte, etc., it is preferable to coat them with nickel, aluminum, etc. 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] These negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte solution, and as shown in FIG. 12C , the positive electrode 304, separator 310, negative electrode 307, and negative electrode can 302 are stacked in this order with the positive electrode can 301 facing downwards, and the positive electrode can 301 and the negative electrode can 302 are crimped together via a gasket 303, thereby producing a coin-shaped secondary battery 300.

[0291] The above-described configuration allows the coin-type secondary battery 300 to have a high capacity, a high charge / discharge capacity, and excellent cycle characteristics. Note that, when a solid electrolyte layer is provided between the negative electrode 307 and the positive electrode 304, the separator 310 may be unnecessary.

[0292] [Cylindrical Secondary Battery] An example of a cylindrical secondary battery will be described with reference to Fig. 13A. As shown in Fig. 13A, a cylindrical secondary battery 616 has a positive electrode cap (battery lid) 601 on the top surface and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap 601 and the battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

[0293] 13B is a schematic diagram showing a cross section of a cylindrical secondary battery. The cylindrical secondary battery shown in FIG. 13B has a positive electrode cap (battery lid) 601 on the top surface and a battery can (external can) 602 on the side and bottom surfaces. The positive electrode cap and battery can (external can) 602 are insulated by a gasket (insulating packing) 610.

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

[0295] Since the positive and negative electrodes used in a cylindrical storage battery are wound, it is preferable to form active materials on both sides of the current collector. While the secondary battery 616 shown in Figures 13A to 13D has a cylinder whose height is greater than its diameter, this is not limiting. A secondary battery whose diameter is greater than its height may also be used. This configuration, for example, can reduce the size of the secondary battery.

[0296] By using the positive electrode active material 100 obtained in the above embodiment for the positive electrode 604, a cylindrical secondary battery 616 having a high capacity, a 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 a metal material such as aluminum. The positive electrode terminal 603 is resistance-welded to a safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC (Positive Temperature Coefficient) element 611. The safety valve mechanism 613 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the increase in internal pressure of the battery exceeds a predetermined threshold. The PTC element 611 is a thermosensitive resistor whose resistance increases as the temperature increases, and the increased resistance limits the amount of current to prevent abnormal heat generation. The PTC element can be made of barium titanate (BaTiO3) based semiconductor ceramics or the like.

[0298] 13C shows an example of a power storage system 615. The power storage system 615 has a plurality of secondary batteries 616. The positive electrodes of each secondary battery are in contact with and electrically connected to conductors 624 separated by insulators 625. The conductors 624 are electrically connected to a control circuit 620 via wiring 623. The negative electrodes of each secondary battery are electrically connected to the control circuit 620 via wiring 626. A protection circuit or the like that prevents overcharging or overdischarging can be used as the control circuit 620.

[0299] 13D shows an example of a power storage system 615. The power storage system 615 has a plurality of secondary batteries 616, which are sandwiched between a conductive plate 628 and a conductive plate 614. The plurality of secondary batteries 616 are electrically connected to the conductive plate 628 and the conductive plate 614 by wiring 627. The plurality of secondary batteries 616 may be connected in parallel or in series. By configuring the power storage system 615 to have a plurality of secondary batteries 616, it is possible to extract a large amount of power.

[0300] A plurality of 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 the secondary batteries 616 are overheated, they can be cooled by the temperature control device, and when the secondary batteries 616 are too cold, they can be heated by the temperature control device. This makes it difficult for the performance of the power storage system 615 to be affected by the outside air temperature.

[0302] 13D , the power storage system 615 is electrically connected to a control circuit 620 via wiring 621 and wiring 622. The wiring 621 is electrically connected to the positive electrodes of the plurality of secondary batteries 616 via a conductive plate 628, and the wiring 622 is electrically connected to the negative electrodes of the plurality of secondary batteries 616 via a conductive plate 614.

[0303] [Another Example of Secondary Battery Structure] An example of the structure of a secondary battery will be described with reference to FIGS. 14 and 15. FIG.

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

[0305] 14B, the housing 930 shown in Fig. 14A may be formed from a plurality of materials. For example, the secondary battery 913 shown in Fig. 14B has a housing 930a and a housing 930b bonded together, and a wound body 950 is provided in the area surrounded by the housing 930a and the housing 930b.

[0306] The housing 930a can be made of an insulating material such as organic resin. In particular, by using a material such as organic resin on the surface on which the antenna is formed, it is possible to suppress shielding of the electric field by the secondary battery 913. Note that if the shielding of the electric field by the housing 930a is small, the antenna may be provided inside the housing 930a. The housing 930b can be made of, for example, a metal material.

[0307] 14C shows the structure of the wound body 950. 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 sandwiched therebetween, and the laminated sheet is wound. Note that multiple stacks of the negative electrode 931, the positive electrode 932, and the separator 933 may be stacked.

[0308] 15A to 15C may be used as a secondary battery 913 having a wound body 950a. The wound body 950a shown in Fig. 15A includes a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 includes a negative electrode active material layer 931a. The positive electrode 932 includes a positive electrode active material layer 932a.

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

[0310] The separator 933 has a width wider than the negative electrode active material layer 931 a and the positive electrode active material layer 932 a, and is wound so as to overlap the negative electrode active material layer 931 a and the positive electrode active material layer 932 a. From the standpoint of safety, it is preferable that the negative electrode active material layer 931 a be wider than the positive electrode active material layer 932 a. A wound body 950 a having such a shape is preferable due to its high safety and productivity.

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

[0312] 15C , the wound body 950 a and the electrolyte are covered by the housing 930 to form the secondary battery 913. It is preferable to provide the housing 930 with a safety valve, an overcurrent protection element, etc. The safety valve is a valve that opens when the inside of the housing 930 reaches a predetermined internal pressure to prevent the battery from exploding.

[0313] As shown in Fig. 15B, the secondary battery 913 may have multiple wound bodies 950a. Using multiple wound bodies 950a can result in a secondary battery 913 with a larger charge / discharge capacity. For other elements of the secondary battery 913 shown in Figs. 15A and 15B, the descriptions of the secondary battery 913 shown in Figs. 14A to 14C can be referred to.

[0314] 16A and 16B show examples of external views of a laminated secondary battery, which includes a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

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

[0316] <Method of Manufacturing Laminated Secondary Battery> Here, an example of a method of manufacturing the laminated secondary battery whose external view is shown in FIG. 16A will be described with reference to FIGS. 17B and 17C.

[0317] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. FIG. 17B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example is shown in which five pairs of negative electrodes and four pairs of positive electrodes are used. This can also be called a laminate consisting of a negative electrode, a separator, and a positive electrode. Next, the tab regions of the positive electrode 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For example, ultrasonic welding or the like may be used for joining. Similarly, the tab regions of the negative 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 , the separator 507 and the positive electrode 503 are arranged on the outer casing 509 .

[0319] Next, as shown in Fig. 17C, the exterior body 509 is folded at the portion indicated by the dashed line. Thereafter, the outer periphery of the exterior body 509 is joined. For example, thermocompression bonding may be used for joining. At this time, an area (hereinafter referred to as an inlet) that is not joined is provided in a part (or one side) of the exterior body 509 so that an electrolyte can be introduced later.

[0320] Next, the electrolyte solution is introduced into the inside of the exterior body 509 through an inlet provided in the exterior body 509. The introduction of the electrolyte solution is preferably carried out under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is joined. In this manner, the laminated secondary battery 500 can be produced.

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

[0322] [Example of Battery Pack] An example of a secondary battery pack according to one embodiment of the present invention that can be wirelessly charged using an antenna will be described with reference to FIGS. 18A to 18C.

[0323] Fig. 18A is a diagram showing the appearance of secondary battery pack 531, which has a thin rectangular parallelepiped shape (also called a thick flat plate shape). Fig. 18B is a diagram illustrating the configuration of secondary battery pack 531. Secondary battery pack 531 has circuit board 540 and secondary battery 513. Label 529 is affixed to secondary battery 513. Circuit board 540 is fixed with sticker 515. Secondary battery pack 531 also has antenna 517.

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

[0325] 18B , the secondary battery pack 531 has a control circuit 590 on a circuit board 540. The circuit board 540 is electrically connected to the terminals 514. The circuit board 540 is also electrically connected to the antenna 517, one 551 of the positive and negative leads of the secondary battery 513, and the other 552 of the positive and negative leads.

[0326] Alternatively, as shown in FIG. 18C, the device may have a circuit system 590 a provided on a circuit board 540 and a circuit system 590 b electrically connected to the circuit board 540 via a terminal 514 .

[0327] The antenna 517 is not limited to a coil shape and may be, for example, a wire shape or a plate shape. Furthermore, antennas such as a planar antenna, an aperture antenna, a traveling wave antenna, an EH antenna, a magnetic field antenna, and a dielectric antenna may also be used. Alternatively, the antenna 517 may be a flat conductor. This flat conductor can function as one of the conductors for electric field coupling. In other words, the antenna 517 may function as one of the two conductors of a capacitor. This allows power to be exchanged not only by electromagnetic fields and magnetic fields but also by electric fields.

[0328] The secondary battery pack 531 includes a layer 519 between the antenna 517 and the secondary battery 513. The layer 519 has a function of, for example, shielding an electromagnetic field generated by the secondary battery 513. The layer 519 can be formed using, for example, a magnetic material.

[0329] The content of this embodiment mode can be freely combined with the content of other embodiment modes.

[0330] Embodiment 4 In this embodiment, an example of fabricating an all-solid-state battery using the positive electrode active material 100 obtained in the above-described embodiment will be described.

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

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

[0333] Solid electrolyte layer 420 has solid electrolyte 421. Solid electrolyte layer 420 is located between positive electrode 410 and negative electrode 430, and is a region that has neither positive electrode active material 411 nor negative electrode active material 431.

[0334] The negative electrode 430 includes a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 includes a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also include a conductive material and a binder. When metallic lithium is used as the negative electrode active material 431, it is not necessary to form the material into particles, and therefore, as shown in FIG. 19B , the negative electrode 430 can be free of the solid electrolyte 421. Using metallic lithium for the negative electrode 430 is preferable because it can improve the energy density of the secondary battery 400.

[0335] The solid electrolyte 421 of the solid electrolyte layer 420 may be, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a halide-based solid electrolyte.

[0336] The sulfide-based solid electrolytes include thiolithium-based (Li １０ GeP ２ S １２ , Li ３．２５ Ge ０．２５ P ０．７５ S４ etc.), sulfide glass (70Li ２ S・30P ２ S ５ , 30Li ２ S・26B ２ S ３ ・44LiI, 63Li ２ S・36SiS ２ ・1Li ３ P.O. ４ , 57Li ２ S・38SiS ２ ・5Li ４ SiO ４ , 50Li ２ S・50GeS ２ etc.), sulfide crystallized glass (Li ７ P ３ S １１ , Li ３．２５ P ０．９５ S ４ Sulfide-based solid electrolytes have the advantages of being highly conductive, being able to be synthesized at low temperatures, and being relatively soft, which makes it easy to maintain conductive paths even after charging and discharging.

[0337] The oxide-based solid electrolyte includes a material having a perovskite crystal structure (La ２／３−ｘ Li ３ｘ TiO ３ etc.), materials having a NASICON type crystal structure (Li １−Ｙ Al Ｙ Ti ２−Ｙ (P.O. ４ ) ３ etc.), materials having a garnet-type crystal structure (Li ７ La ３ Zr ２ O １２ etc.), materials having a LISICON type crystal structure (Li １４ ZnGe ４ O １６ etc.), LLZO (Li ７ La ３ Zr ２ O １２ ), oxide glass (Li ３ P.O. ４ -Li ４ SiO ４ , 50Li ４ SiO４ ・50Li ３ BO ３ etc.), oxide crystallized glass (Li １．０７ Al ０．６９ Ti １．４６ (P.O. ４ ) ３ , Li １．５ Al ０．５ Ge １．５ (P.O. ４ ) ３ Oxide-based solid electrolytes have the advantage of being stable in the atmosphere.

[0338] Halide-based solid electrolytes include LiAlCl ４ , Li ３ InBr ６ , LiF, LiCl, LiBr, LiI, etc. Composite materials in which these halide-based solid electrolytes are filled into the pores of porous aluminum oxide or porous silica can also be used as the solid electrolyte.

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

[0340] Among them, Li having a NASICON type crystal structure １＋ｘ Al ｘ Ti ２−ｘ (P.O. ４ ) ３ (0<x<1) (hereinafter, LATP) is preferable because it contains aluminum and titanium, elements that may be contained in the positive electrode active material used in the secondary battery 400 of one embodiment of the present invention, and therefore a synergistic effect can be expected in improving cycle characteristics. In addition, productivity can be expected to be improved by reducing the number of steps. Note that in this specification and the like, the NASICON-type crystal structure refers to a structure having a NASICON-type crystal structure, which is a structure having a NASICON-type crystal structure, and which is ... ２ (XO ４ ) ３ (M: transition metal, X: S, P, As, Mo, W, etc.), ６ Octahedron and XO ４ It refers to a structure in which tetrahedrons are arranged three-dimensionally with their vertices shared.

[0341] [Exterior Body and Shape of Secondary Battery] Various materials and shapes can be used for the exterior body of the secondary battery 400 of one embodiment of the present invention, but it is preferable that the exterior body has a function of applying pressure to the positive electrode, the solid electrolyte layer, and the negative electrode.

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

[0343] 20A is a schematic cross-sectional view of the evaluation cell, which has a lower member 761, an upper member 762, and a fixing screw or wing nut 764 that fixes them together, and electrode plate 753 is pressed to fix the evaluation material by rotating a holding screw 763. An insulator 766 is provided between lower member 761 and upper member 762, both made of stainless steel. An O-ring 765 is also provided between upper member 762 and holding screw 763 to provide a tight seal.

[0344] The evaluation material is placed on electrode plate 751, surrounded by insulating tube 752, and pressed from above by electrode plate 753. An enlarged perspective view of the evaluation material and its surroundings is shown in Figure 20B.

[0345] The evaluation material is an example of a laminate of a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c, and its cross-sectional view is shown in Fig. 20C. Note that the same reference numerals are used for the same parts in Figs. 20A to 20C.

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

[0347] The secondary battery of one embodiment of the present invention preferably uses an airtight package for its exterior. For example, a ceramic package or a resin package can be used. Furthermore, the exterior is preferably sealed in a sealed atmosphere, such as in a glove box, while blocking external air.

[0348] Fig. 21A is a perspective view of a secondary battery of one embodiment of the present invention, which has an exterior body and a shape different from those in Fig. 20. The secondary battery in Fig. 21A has external electrodes 771 and 772 and is sealed in an exterior body having a plurality of package members.

[0349] 21B shows an example of a cross section taken along the dashed line in FIG. 21A. A stack including a positive electrode 750a, a solid electrolyte layer 750b, and a negative electrode 750c is enclosed and sealed by a package member 770a having a flat plate with an electrode layer 773a, a frame-shaped package member 770b, and a package member 770c having a flat plate with an electrode layer 773b. The package members 770a, 770b, and 770c can be made of insulating materials, such as resin materials and ceramics.

[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, while 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 having high energy density and good output characteristics can be realized.

[0352] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0353] Embodiment Mode 5 In this embodiment mode, an example in which a secondary battery different from the cylindrical secondary battery shown in FIG. 13D is applied to an electric vehicle (EV) will be described with reference to FIG. 22C.

[0354] The electric vehicle is equipped with first batteries 1301a and 1301b as main driving secondary batteries, and a second battery 1311 that supplies power to an inverter 1312 that starts a motor 1304. The second battery 1311 is also called a cranking battery (also called a starter battery). The second battery 1311 only needs to have high output, and does not need to have a large capacity, and the capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0355] The internal structure of the first battery 1301a may be a wound type shown in Fig. 14A or 15C or a stacked type shown in Fig. 16A or 16B. The first battery 1301a may use the all-solid-state battery of Embodiment 4. By using the all-solid-state battery of Embodiment 4 for the first battery 1301a, a high capacity can be achieved, safety can be improved, and the battery can be made smaller and lighter.

[0356] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more batteries may be connected in parallel. Furthermore, if the first battery 1301a can store sufficient power, the first battery 1301b may be omitted. By configuring a battery pack having multiple secondary batteries, it is possible to extract large amounts of power. The multiple secondary batteries may be connected in parallel, in series, or in series after being connected in parallel. A plurality of secondary batteries is also called a battery pack.

[0357] In addition, in a secondary battery for vehicle use, a service plug or circuit breaker that can cut off high voltage without using tools is provided in the first battery 1301a in order to cut off power from multiple secondary batteries.

[0358] The power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V in-vehicle components (such as an electric power steering (power steering) 1307, a heater 1308, and a defogger 1309) via a DCDC circuit 1306. When a rear motor 1317 is provided on the rear wheels, the first battery 1301a is also used to rotate the rear motor 1317.

[0359] In addition, the second battery 1311 supplies power to 14V in-vehicle components (audio 1313, power windows 1314, lamps 1315, etc.) via the DCDC circuit 1310.

[0360] The first battery 1301a will be described with reference to FIG. 22A.

[0361] FIG. 22A shows an example in which nine prismatic secondary batteries 1300 are combined into one battery pack 1415. Furthermore, nine prismatic secondary batteries 1300 are connected in series, with one electrode fixed by a fixing portion 1413 made of an insulator and the other electrode fixed by a fixing portion 1414 made of an insulator. While this embodiment shows an example in which the batteries are fixed by fixing portions 1413 and 1414, they may also be housed in a battery housing box (also called a casing). Because it is expected that a vehicle will be subjected to external vibrations or shaking (such as from the road surface), it is preferable to fix multiple secondary batteries using fixing portions 1413 and 1414 and a battery housing box. Furthermore, one electrode is electrically connected to a control circuit unit 1320 by wiring 1421. The other electrode is electrically connected to the control circuit unit 1320 by wiring 1422.

[0362] A memory circuit including a transistor using an oxide semiconductor may be used for the control circuit portion 1320. A charge control circuit or a battery control system including a memory circuit including a transistor using an oxide semiconductor may be referred to as a battery operating system (BTOS) or a battery oxide semiconductor (BTOS).

[0363] It is preferable to use a metal oxide that functions as an oxide semiconductor. For example, a metal oxide such as In-M-Zn oxide (wherein element M is one or more selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, and magnesium) may be used as the oxide. In particular, the In-M-Zn oxide that can be used as the oxide is preferably a C-Axis Aligned Crystal Oxide Semiconductor (CAAC-OS) or a Cloud-Aligned Composite Oxide Semiconductor (CAC-OS). Alternatively, an In—Ga oxide or an In—Zn oxide may be used as the oxide. A CAAC-OS is an oxide semiconductor having multiple crystalline regions, each with its c-axis aligned in a specific direction. The specific direction refers to the thickness direction of the CAAC-OS film, the normal direction to the surface where the CAAC-OS film is formed, or the normal direction to the surface of the CAAC-OS film. A crystalline region is a region with periodic atomic arrangement. If the atomic arrangement is considered as a lattice arrangement, a crystalline region is also a region with a uniform lattice arrangement. Furthermore, a CAAC-OS has a region where multiple crystalline regions are connected in the a-b plane direction, and the region may have distortion. Note that distortion refers to a portion where the lattice arrangement changes between a region with a uniform lattice arrangement and a region with another uniform lattice arrangement in a region where multiple crystalline regions are connected. In other words, a CAAC-OS is an oxide semiconductor with a c-axis aligned and no clear orientation in the a-b plane direction. CAC-OS is a material in which elements constituting a metal oxide are unevenly distributed in a size range of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or in the vicinity thereof. Note that hereinafter, a state in which one or more metal elements are unevenly distributed in a metal oxide and regions containing the metal elements are mixed in a size range of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or in the vicinity thereof, is also referred to as a mosaic or patch state.

[0364] Furthermore, the CAC-OS has a mosaic structure in which a material is separated into a first region and a second region, and the first region is distributed throughout the film (hereinafter also referred to as a cloud structure). That is, the 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 the In—Ga—Zn oxide are denoted as [In], [Ga], and [Zn], respectively. For example, in the CAC-OS in the In—Ga—Zn oxide, the first region is a region where [In] is larger than [In] in the composition of the CAC-OS film. The second region is a region where [Ga] is larger than [Ga] in the composition of the CAC-OS film. Alternatively, for example, the first region is a region where [In] is larger than [In] in the second region and [Ga] is smaller than [Ga] in the second region. The second region is a region where [Ga] is larger than [Ga] in the first region and [In] is smaller than [In] in the first region.

[0366] Specifically, the first region is a region whose main component is indium oxide, indium zinc oxide, or the like. The second region is a region whose main component is gallium oxide, gallium zinc oxide, or the like. In other words, the first region can be referred to as a region whose main component is In. The second region can be referred to as a region whose main component is Ga.

[0367] It should be noted that there are cases where a clear boundary between the first region and the second region cannot be observed.

[0368] For example, in the case of CAC-OS in an In—Ga—Zn oxide, EDX mapping obtained using energy dispersive X-ray spectroscopy (EDX) can confirm that the CAC-OS has a structure in which a region containing In as a main component (first region) and a region containing Ga as a main component (second region) are unevenly distributed and mixed.

[0369] When a CAC-OS is used in a transistor, the conductivity due to the first region and the insulating property due to the second region act complementarily, thereby imparting a switching function (on / off function) to the CAC-OS. That is, a CAC-OS has a conductive function in a part of the material and an insulating function in a part of the material, and the entire material functions as a semiconductor. By separating the conductive function and the insulating function, both functions can be maximized. Therefore, by using a CAC-OS in a transistor, a high on-state current (Ion), a high field-effect mobility (μ), and good switching operation can be achieved.

[0370] Oxide semiconductors have a variety of structures, each of which has different characteristics. The oxide semiconductor of one embodiment of the present invention may include two or more of an amorphous oxide semiconductor, a polycrystalline oxide semiconductor, an a-like OS, a CAC-OS, an nc-OS, and a CAAC-OS.

[0371] Furthermore, because the control circuit unit 1320 can be used in high-temperature environments, it is preferable to use a transistor using an oxide semiconductor. To simplify the process, the control circuit unit 1320 may be formed using a unipolar transistor. Transistors using an oxide semiconductor in the semiconductor layer have a wider operating ambient temperature range than single-crystal Si transistors, from −40° C. to 150° C., and their characteristics change less even when the secondary battery overheats than 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., whereas the off-current characteristics of single-crystal Si transistors 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 is not sufficiently large. The control circuit unit 1320 can improve safety. Furthermore, combining the cathode active material 100 obtained in the above-described embodiment with a secondary battery using the cathode as the cathode can provide a synergistic effect in terms of safety.

[0372] The control circuit unit 1320, which uses a memory circuit including transistors using oxide semiconductors, can also function as an automatic control device for the secondary battery to address causes of instability such as micro-short circuits. Functions for eliminating causes of secondary battery instability include overcharging prevention, overcurrent prevention, overheating control during charging, cell balancing in the battery pack, over-discharging prevention, a fuel gauge, automatic control of charging voltage and current according to temperature, control of charging current according to the degree of deterioration, detection of abnormal behavior of micro-short circuits, and prediction of abnormalities related to micro-short circuits, and the control circuit unit 1320 has at least one of these functions. Furthermore, the automatic control device for the secondary battery can be made ultra-miniaturized.

[0373] A micro-short circuit refers to a tiny short circuit inside a secondary battery, which is not so small that the positive and negative electrodes of the secondary battery are short-circuited and the battery is unable to be charged or discharged, but rather a small short-circuit current flows through the tiny short circuit.Even if the short circuit occurs in a relatively short period of time and in a small location, a large voltage change occurs, and this abnormal voltage value may affect subsequent estimations.

[0374] One of the causes of micro-short circuits is said to be that multiple charge and discharge cycles cause uneven distribution of the positive electrode active material, resulting in localized current concentration in parts of the positive electrode and negative electrode, causing parts of the separator to stop functioning, or the generation of by-products due to side reactions, resulting in micro-short circuits.

[0375] In addition to detecting micro-shorts, the control circuit 1320 can also be said to detect the terminal voltage of the secondary battery and manage the charge / discharge state of the secondary battery. For example, to prevent overcharging, it can turn off both the output transistor and the cutoff switch of the charging circuit almost simultaneously.

[0376] FIG. 22B shows an example of a block diagram of the battery pack 1415 shown in FIG. 22A.

[0377] The control circuit 1320 includes a switch unit 1324 including at least a switch for preventing overcharging and a switch for preventing overdischarging, a control circuit 1322 for controlling the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit 1320 sets upper and lower voltage limits for the secondary battery used and limits the upper limit of the external current and the upper limit of the output current. The range between the lower and upper voltage limits of the secondary battery is within the recommended voltage range, and when the secondary battery falls outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent overcharging and overdischarging. For example, if the control circuit 1322 detects a voltage that could cause overcharging, it turns off the switch unit 1324 to cut off the current. Furthermore, a PTC element may be provided in the charge / discharge path to provide a function for cutting off the current in response to an increase in temperature. The control circuit section 1320 also has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0378] The switch portion 1324 can be configured by combining n-channel transistors and p-channel transistors. The switch portion 1324 is not limited to a switch having a Si transistor using single crystal silicon. For example, the switch portion 1324 may be formed using a power transistor having Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), or GaOx (gallium oxide; x is a real number greater than 0). Furthermore, memory elements using OS transistors can be freely arranged by stacking them on circuits using Si transistors, for example, and thus can be easily integrated. Furthermore, OS transistors can be manufactured using the same manufacturing equipment as Si transistors, and therefore can be manufactured at low cost. That is, the control circuit portion 1320 using OS transistors can be stacked on the switch portion 1324 and integrated into a single chip. The volume occupied by the control circuit section 1320 can be reduced, which allows for miniaturization.

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

[0380] In this embodiment, an example in which lithium ion secondary batteries are used for both the first battery 1301a and the second battery 1311 is shown. A lead-acid battery, an all-solid-state battery, or an electric double layer capacitor may be used for the second battery 1311. 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 reductions in size and weight can be achieved.

[0381] Furthermore, regenerative energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305, and is then charged into the second battery 1311 from the motor controller 1303 and the battery controller 1302 via the control circuit unit 1321. Alternatively, the first battery 1301a is charged from the battery controller 1302 via the control circuit unit 1320. Alternatively, the first battery 1301b is charged from the battery controller 1302 via the control circuit unit 1320. In order to efficiently charge the regenerative energy, it is desirable that the first batteries 1301a and 1301b be 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 charging conditions in accordance with the charging characteristics of the secondary battery used, and can perform rapid charging.

[0383] Although not shown, when an external charger is connected, the charger's outlet or charger connection cable is electrically connected to the battery controller 1302. Power supplied from the external charger is charged to the first batteries 1301a and 1301b via the battery controller 1302. Some chargers are provided with a control circuit, and although the functions of the battery controller 1302 may not be used, it is preferable to charge the first batteries 1301a and 1301b via the control circuit unit 1320 to prevent overcharging. The charger's outlet or charger connection cable may also be provided with 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) provided in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU includes a microcomputer. The ECU uses a CPU or a GPU.

[0384] External chargers installed at charging stations and the like come in a variety of types, including 100V outlets, 200V outlets, and three-phase 200V and 50kW outlets. Charging can also be performed by receiving power from external charging equipment using a wireless power supply system or the like.

[0385] When rapid charging is performed, a secondary battery that can withstand high voltage charging is desired in order to charge in a short time.

[0386] The secondary battery of the present embodiment described above uses the positive electrode active material 100 obtained in the above-described embodiment. Furthermore, by using graphene as a conductive material, a secondary battery with significantly improved electrical characteristics can be realized, as a synergistic effect of suppressing capacity reduction and maintaining high capacity even when the electrode layer is thickened and the loading amount is increased. This is particularly effective for secondary batteries used in vehicles, and a vehicle with a long cruising range, specifically a cruising range of 500 km or more per charge, can be provided 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 the present embodiment described above can increase the operating voltage of the secondary battery by using the cathode active material 100 described in the above embodiment, and can increase the usable capacity as the charging voltage increases. Furthermore, by using the cathode active material 100 described in the above embodiment for the cathode, a secondary battery for vehicles with excellent cycle characteristics can be provided.

[0388] Next, an example in which a secondary battery according to one embodiment of the present invention is mounted on a vehicle, typically a transportation vehicle, will be described.

[0389] 13D , 15C , and 22A can be installed in a vehicle to realize next-generation clean energy automobiles, such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs). Furthermore, the secondary battery can also be installed in transportation vehicles, such as agricultural machinery, mopeds including electrically assisted bicycles, motorcycles, electric wheelchairs, electric carts, small or large ships, submarines, aircraft such as fixed-wing aircraft and rotary-wing aircraft, rockets, artificial satellites, space probes, planetary probes, and spacecraft. The secondary battery of one embodiment of the present invention can be a high-capacity secondary battery. Therefore, the secondary battery of one embodiment of the present invention is suitable for miniaturization and weight reduction and can be suitably used in transportation vehicles.

[0390] 23A to 23D illustrate a transportation vehicle as an example of a moving object using one embodiment of the present invention. The automobile 2001 illustrated in FIG. 23A is an electric automobile using an electric motor as a power source for traveling. Alternatively, it is a hybrid automobile that can appropriately select and use an electric motor or an engine as a power source for traveling. When a secondary battery is installed in a vehicle, an example of the secondary battery described in Embodiment 3 is installed in one or more locations. The automobile 2001 illustrated in FIG. 23A includes a battery pack 2200, which includes a secondary battery module to which multiple secondary batteries are connected. It is preferable that the automobile further include a charge control device electrically connected to the secondary battery module.

[0391] Furthermore, the automobile 2001 can charge its secondary battery by receiving power from an external charging facility using a plug-in system, a contactless power supply system, or the like. Charging can be performed using a predetermined charging method and connector standards, such as CHAdeMO (registered trademark) or Combo, as appropriate. The secondary battery may be charged at a charging station installed in a commercial facility or from a household power source. For example, plug-in technology can be used to charge an electric storage device installed in the automobile 2001 using an external power supply. Charging can be performed by converting AC power to DC power via a conversion device, such as an AC-DC converter.

[0392] Although not shown, a power receiving device can be mounted on a vehicle and power can be supplied contactlessly from a ground-based power transmitting device to charge the vehicle. In the case of this contactless power supply method, by incorporating a power transmitting device into a road or an exterior wall, charging can be performed not only while the vehicle is stopped but also while the vehicle is moving. This contactless power supply method can also be used to transmit and receive power between two vehicles. Furthermore, solar cells can be installed on the exterior of the vehicle to charge the secondary battery while the vehicle is stopped and while moving. For such contactless power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0393] 23B shows a large transport vehicle 2002 having an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 is, for example, a four-cell unit of secondary batteries with a nominal voltage of 3.0 V to 5.0 V, with 48 cells connected in series for a maximum voltage of 170 V. Apart from the number of secondary batteries constituting the secondary battery module of the battery pack 2201, the transport vehicle 2002 has the same functions as those shown in FIG. 23A, and therefore a description thereof will be omitted.

[0394] FIG. 23C shows, as an example, a large transport vehicle 2003 having an electrically controlled motor. The secondary battery module of the transport vehicle 2003 has, for example, a maximum voltage of 600 V, with one hundred or more secondary batteries connected in series, each having a nominal voltage of 3.0 V or more and 5.0 V or less. By using a secondary battery whose positive electrode is the positive electrode active material 100 described in the above embodiment, a secondary battery with excellent rate characteristics and charge / discharge cycle characteristics can be manufactured, contributing to improved performance and a longer life of the transport vehicle 2003. Furthermore, except for the number of secondary batteries constituting the secondary battery module of the battery pack 2202, the battery pack 2202 has the same functions as those shown in FIG. 23A , and therefore a description thereof will be omitted.

[0395] Fig. 23D shows, as an example, an aircraft 2004 having an engine that burns fuel. Since the aircraft 2004 shown in Fig. 23D has wheels for takeoff and landing, it can also be considered a type of transport vehicle, and has a battery pack 2203 that includes a secondary battery module formed by connecting multiple secondary batteries and the secondary battery module and a charge control device.

[0396] The secondary battery module of the aircraft 2004 is, for example, eight 4 V secondary batteries connected in series to produce a maximum voltage of 32 V. Other than the number of secondary batteries constituting the secondary battery module of the battery pack 2203, the secondary battery module has the same functions as those shown in Fig. 23A, and therefore a description thereof will be omitted.

[0397] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0398] Embodiment 6 In this embodiment, an example in which a secondary battery which is one embodiment of the present invention is mounted in a building will be described with reference to FIGS. 24A and 24B.

[0399] The house illustrated in FIG. 24A includes a power storage device 2612 including a secondary battery of one embodiment of the present invention, and a solar panel 2610. The power storage device 2612 is electrically connected to the solar panel 2610 via a wiring 2611 or the like. The power storage device 2612 may also be electrically connected to a ground-mounted charging device 2604. The power obtained by the solar panel 2610 can be charged to the power storage device 2612. The power stored in the power storage device 2612 can be charged to a secondary battery included in the vehicle 2603 via the charging device 2604. The power storage device 2612 is preferably installed in an underfloor space. By installing the power storage device 2612 in the underfloor space, the space above the floor can be effectively utilized. Alternatively, the power storage device 2612 may be installed on the floor.

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

[0401] 24B illustrates an example of a power storage device according to one embodiment of the present invention. As illustrated in FIG. 24B , a power storage device 791 according to one embodiment of the present invention is installed in an underfloor space 796 of a building 799. The control circuit described in Embodiment 5 may be provided in the power storage device 791. The power storage device 791 can have a long lifetime by using a secondary battery in which the positive electrode active material 100 obtained in the above embodiment is used for its positive electrode.

[0402] A control device 790 is installed in the power storage device 791, and the control device 790 is electrically connected to the distribution board 703, the power storage controller 705 (also called the control device), the display 706, and the router 709 by wiring.

[0403] Electric power is sent from commercial power source 701 to distribution board 703 via service line attachment portion 710. Electric power is also sent to distribution board 703 from power storage device 791 and commercial power source 701, and distribution board 703 supplies the sent electric power to general load 707 and power storage load 708 via outlets (not shown).

[0404] The general load 707 is, for example, an electrical appliance such as a television or a personal computer, and the power storage load 708 is, for example, an electrical appliance such as a microwave oven, a refrigerator, or an air conditioner.

[0405] The power storage controller 705 includes a measurement unit 711, a prediction unit 712, and a planning unit 713. The measurement unit 711 has a function of measuring the amount of power consumed by the general load 707 and the power storage load 708 during a day (e.g., from midnight to midnight). The measurement unit 711 may also have a function of measuring the amount of power of the power storage device 791 and the amount of power supplied from the commercial power source 701. The prediction unit 712 has a function of predicting the amount of power demand to be consumed by the general load 707 and the power storage load 708 during the next day based on the amount of power consumed by the general load 707 and the power storage load 708 during the previous day. The planning unit 713 has a function of creating a plan for charging and discharging the power storage device 791 based on the amount of power demand predicted by the prediction unit 712.

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

[0407] The content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0408] Embodiment 7 In this embodiment, an example in which a power storage device according to one embodiment of the present invention is mounted on a motorcycle or a bicycle will be described.

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

[0410] The electric bicycle 8700 includes a power storage device 8702. The power storage device 8702 can supply electricity to a motor that assists a rider. The power storage device 8702 is portable and is shown in a state detached from the bicycle in FIG. 25B . The power storage device 8702 includes a plurality of built-in storage batteries 8701, which are included in the power storage device of one embodiment of the present invention, and the remaining battery charge and the like can be displayed on a display unit 8703. The power storage device 8702 also includes a control circuit 8704 that can control charging or detect an abnormality of the secondary battery, an example of which is shown in Embodiment 5. The control circuit 8704 is electrically connected to the positive and negative electrodes of the storage battery 8701. The control circuit 8704 may be provided with the small-sized solid-state secondary battery shown in FIGS. 21A and 21B. By providing the small-sized solid-state secondary battery shown in FIGS. 21A and 21B in the control circuit 8704, power can be supplied to retain data in a memory circuit included in the control circuit 8704 for a long period of time. Furthermore, a synergistic effect in terms of safety can be obtained by combining the positive electrode active material 100 obtained in the above-described embodiment with a secondary battery using the positive electrode active material 100 obtained in the above-described embodiment. The secondary battery using the positive electrode active material 100 obtained in the above-described embodiment and the control circuit 8704 can greatly contribute to eliminating accidents such as fires caused by secondary batteries.

[0411] 25C is an example of a two-wheeled vehicle using the power storage device of one embodiment of the present invention. A scooter 8600 shown in FIG. 25C includes a power storage device 8602, a side mirror 8601, and a turn signal light 8603. The power storage device 8602 can supply electricity to the turn signal light 8603. The power storage device 8602, which includes a plurality of secondary batteries each using the positive electrode active material 100 obtained in the above embodiment for its positive electrode, can have a high capacity and contribute to miniaturization.

[0412] 25C can store a power storage device 8602 in an 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 content of this embodiment mode can be combined with the content of other embodiment modes as appropriate.

[0414] Embodiment 8 In this embodiment, an example of mounting a secondary battery according to one embodiment of the present invention in an electronic device will be described. Examples of electronic devices mounting a secondary battery include television sets (also referred to as televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also referred to as mobile phones or mobile phone devices), portable game consoles, personal digital assistants, sound players, and large game consoles such as pachinko machines. Examples of personal digital assistants include notebook personal computers, tablet devices, e-book readers, and mobile phones.

[0415] 26A shows an example of a mobile phone. The mobile phone 2100 includes a display unit 2102 built into a housing 2101, operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. The mobile phone 2100 also includes a secondary battery 2107. By including the secondary battery 2107 using the positive electrode active material 100 described in the above embodiment as a 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 execute various applications such as mobile phone calls, e-mail, document browsing and creation, music playback, internet communication, and computer games.

[0417] The operation button 2103 can be provided with various functions such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, power saving mode activation / deactivation, etc. For example, the functions of the operation button 2103 can be freely set by an operating system incorporated in the mobile phone 2100.

[0418] The mobile phone 2100 is also capable of performing standardized short-range wireless communication, and can also make hands-free calls by communicating with a wirelessly enabled headset, for example.

[0419] The mobile phone 2100 also includes an external connection port 2104, which allows direct data exchange with other information terminals via a connector. Charging can also be performed via the external connection port 2104. Note that charging may be performed by wireless power supply without using the external connection port 2104.

[0420] The mobile phone 2100 preferably has a sensor, such as a fingerprint sensor, a pulse sensor, a body temperature sensor, a touch sensor, a pressure sensor, an acceleration sensor, or the like.

[0421] FIG. 26B illustrates an unmanned aerial vehicle 2300 having a plurality of rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 includes a secondary battery 2301 according to one embodiment of the present invention, a camera 2303, and an antenna (not shown). The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. A secondary battery using the positive electrode active material 100 obtained in the above embodiment for its positive electrode has high energy density and high safety, and therefore can be used safely for a long period of time. Therefore, the secondary battery is suitable as a secondary battery to be mounted on the unmanned aerial vehicle 2300.

[0422] Fig. 26C shows an example of a robot. A robot 6400 shown in Fig. 26C includes a secondary battery 6409, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a movement mechanism 6408, a computing device, etc.

[0423] The microphone 6402 has a function of detecting the user's speaking voice, environmental sounds, etc. The speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.

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

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

[0426] The robot 6400 includes a secondary battery 6409 according to one embodiment of the present invention and a semiconductor device or an electronic component in its internal region. A secondary battery using the positive electrode active material 100 obtained in the above embodiment for its positive electrode has high energy density and high safety, and therefore can be used safely for a long period of time. Therefore, the secondary battery is suitable as the secondary battery 6409 to be mounted on the robot 6400.

[0427] 26D shows an example of a cleaning robot. The cleaning robot 6300 includes a display unit 6302 arranged on the top surface of a housing 6301, a plurality of cameras 6303 arranged on the side surfaces, a brush 6304, operation buttons 6305, a secondary battery 6306, various sensors, and the like. Although not shown, the cleaning robot 6300 is provided with tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck up the dust from a suction port arranged on the bottom surface.

[0428] For example, the cleaning robot 6300 can analyze an image captured by the camera 6303 and determine whether or not there is an obstacle such as a wall, furniture, or a step. Furthermore, if an object that may become entangled in the brush 6304, such as a wire, is detected through image analysis, the cleaning robot 6300 can stop the rotation of the brush 6304. The cleaning robot 6300 includes a secondary battery 6306 according to one embodiment of the present invention and a semiconductor device or an electronic component in its internal region. A secondary battery using the positive electrode active material 100 obtained in the above embodiment for its positive electrode has high energy density and high safety, and therefore can be used safely for a long period of time. Therefore, the secondary battery 6306 is suitable for use in the cleaning robot 6300.

[0429] 27A shows an example of a wearable device. The wearable device uses a secondary battery as a power source. Furthermore, in order to improve splash-proof, water-resistant, or dust-proof performance when used at home or outdoors, there is a demand for a wearable device that can be charged wirelessly as well as via a wired connection with an exposed connector.

[0430] For example, a secondary battery according to one embodiment of the present invention can be mounted on an eyeglasses-type device 4000 as shown in FIG. 27A . The eyeglasses-type device 4000 includes a frame 4000 a and a display unit 4000 b. Mounting a secondary battery on temples of the curved frame 4000 a makes it possible to provide the eyeglasses-type device 4000 with a lightweight design, a good weight balance, and a long continuous use time. A secondary battery using the positive electrode active material 100 obtained in the above embodiment as its positive electrode has a high energy density and can realize a configuration that can accommodate space saving associated with a smaller housing.

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

[0432] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a device 4002 that can be directly attached to the body. A secondary battery 4002b can be provided in a thin housing 4002a of the device 4002. A secondary battery using the positive electrode active material 100 obtained in the above embodiment for its positive electrode has high energy density, and a configuration that can accommodate space saving associated with a miniaturized housing can be realized.

[0433] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on a device 4003 that can be attached to clothing. A secondary battery 4003b can be provided in a thin housing 4003a of the device 4003. A secondary battery using the positive electrode active material 100 obtained in the above embodiment for its positive electrode has high energy density, and a configuration that can accommodate space saving associated with a miniaturized housing can be realized.

[0434] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 includes a belt portion 4006a and a wireless power receiving portion 4006b, and the secondary battery can be mounted in an internal region of the belt portion 4006a. A secondary battery using the positive electrode active material 100 obtained in the above embodiment as a positive electrode has a high energy density and can realize a configuration that can accommodate space saving associated with a miniaturized housing.

[0435] Furthermore, the secondary battery according to one embodiment of the present invention can be mounted on the wristwatch device 4005. The wristwatch device 4005 includes a display portion 4005a and a belt portion 4005b, and the secondary battery can be provided in the display portion 4005a or the belt portion 4005b. A secondary battery using the positive electrode active material 100 obtained in the above embodiment as a positive electrode has high energy density, and a configuration that can accommodate space saving associated with miniaturization of the housing can be realized.

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

[0438] FIG. 27B shows a perspective view of the wristwatch-type device 4005 removed from the wrist.

[0439] 27C shows a side view of the display portion 4005a. Fig. 27C shows a state in which a secondary battery 913 is built in the internal region. The secondary battery 913 is the secondary battery described in Embodiment 3. The secondary battery 913 is provided in a position overlapping with the display portion 4005a, and can have high density and high capacity, and is small and lightweight.

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

[0441] 27D shows an example of a wireless earphone. Here, the wireless earphone is shown as having a pair of main bodies 4100a and 4100b, but this does not necessarily have to be a pair.

[0442] The main bodies 4100a and 4100b each have a driver unit 4101, an antenna 4102, and a secondary battery 4103. They may also have a display unit 4104. They also preferably have a substrate on which a circuit such as a wireless IC is mounted, a charging terminal, and the like. They may also have a microphone.

[0443] The case 4110 has a secondary battery 4111. It is preferable that the case 4110 also has a board on which circuits such as a wireless IC and a charge control IC are mounted, and a charging terminal. It may also have a display unit, buttons, and the like.

[0444] The main units 4100a and 4100b can wirelessly communicate with other electronic devices such as smartphones. This allows sound data and the like sent from other electronic devices to be played back on the main units 4100a and 4100b. If the main units 4100a and 4100b have microphones, the sound picked up by the microphones can be sent to the other electronic device, and the sound data after processing by the electronic device can be sent back to the main units 4100a and 4100b for playback. This allows the devices to be used as, for example, translation devices.

[0445] Furthermore, the secondary battery 4103 included in the main body 4100a can be charged from the secondary battery 4111 included in the case 4110. The coin-type secondary battery, the cylindrical secondary battery, or the like described in the above embodiment can be used as the secondary battery 4111 and the secondary battery 4103. A secondary battery using the positive electrode active material 100 obtained in the above embodiment as a positive electrode has high energy density, and by using the secondary battery 4103 and the secondary battery 4111 as the positive electrode, a configuration that can accommodate space saving associated with miniaturization of wireless earphones can be realized.

[0446] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0447] 1: Electrode, 2: Current collector, 3: Active material layer, 4: Gap, 5: Active material, 6: Crack, 7: Slip, 10: Device, 20: Vibration processing 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

Claims

1. A method for producing an electrode for a secondary battery, comprising the steps of: a vibration treatment step of applying vibration to the electrode; a pressing step of applying pressure to the electrode to compress an active material layer of the electrode, The apparatus used in the vibration treatment step has a vibration treatment section, The apparatus used in the pressing step has a pressing unit, The press section has an upper roll, an upper support, a lower roll, and a lower support, The upper support has a holding portion that holds a shaft of the upper roll, and a main body portion, the vibration processing section has a vibrator disposed between the holding section and the main body section, The vibration treatment step is performed integrally with the pressing step. A method for making electrodes for secondary batteries.

2. In claim 1, The upper roll further has a heating section, In the vibration treatment step, the temperature of the electrode is adjusted. A method for making 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. A method for making electrodes for secondary batteries.

4. According to any one of claims 1 to 3, the electrode is either one or both of a positive electrode and a negative electrode. A method for making electrodes for secondary batteries.