Manufacturing method for secondary battery

Abstract

To provide a manufacturing method that can automate the manufacture of a secondary battery, a manufacturing method that can manufacture a secondary battery efficiently in a short time, a manufacturing method that can manufacture a secondary battery with a high yield, or a manufacturing method in a case of manufacturing a relatively large secondary battery.SOLUTION: An electrolyte is dropped on any one or a plurality of a positive electrode, a separator, and a negative electrode, and any one or a plurality of the positive electrode, the separator, and the negative electrode are impregnated with the electrolyte solution. After that, the pressure is reduced and a multilayer body of the positive electrode, the separator, and the negative electrode is sealed with an exterior film. On the exterior film, a plurality of the multilayer bodies may be arranged, the electrolyte may be dropped to the multilayer bodies, the sealing may be performed under the reduced pressure, and then secondary batteries may be separated from each other by dividing the exterior film.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a secondary battery and a method for manufacturing the same, or to a mobile information terminal, a vehicle, etc. that has a secondary battery.

[0002] One embodiment of the present invention relates to an object, a method, or a manufacturing method. Alternatively, the present invention relates to a process, a machine, a manufacture, or a composition of matter. 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 elements and devices in general that have 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. [Background technology]

[0005] In recent years, there has been active development of various types of electricity storage devices, such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries. Demand for high-power, high-energy-density lithium-ion secondary batteries, in particular, has rapidly expanded alongside the development of the semiconductor industry, 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), making them indispensable in today's information society as a rechargeable energy source.

[0006] A lithium-ion secondary battery consists of a positive electrode containing a positive electrode active material such as lithium cobalt oxide (LiCoO2) or lithium iron phosphate (LiFePO4), a negative electrode containing a negative electrode active material such as graphite or other carbon materials that can absorb and release 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, high performance, and safety in various operating environments.

[0008] Patent Document 1 discloses a manufacturing device for a stacked battery that can improve the efficiency of manufacturing. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2017-117729 Summary of the Invention [Problem to be solved by the invention]

[0010] It is an object of the present invention to realize a method for automating the production of secondary batteries. Another object is to realize a method for efficiently producing secondary batteries in a short time. Another object is to realize a method for producing secondary batteries with a high yield.

[0011] Another object of the present invention is to realize a method for manufacturing a secondary battery having a relatively large size.

[0012] Another object is to provide a method for manufacturing a secondary battery with reduced manufacturing costs.

[0013] Another object is to provide a method for manufacturing a safe or highly reliable secondary battery.

[0014] Note that the description of these problems does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily solve all of these problems. Note that problems other than these can be extracted from the description of the specification, drawings, and claims. [Means for solving the problem]

[0015] Conventionally, secondary batteries are often fabricated by placing a laminate of a positive electrode, a separator, and a negative electrode into a can or bag-shaped exterior, injecting an electrolyte solution, and then sealing the exterior. This conventional method can lead to the risk of lithium ions easily diffusing outward from the injection port. Furthermore, this conventional method tends to require a large number of steps, and it can be difficult to precisely control the amount of electrolyte solution injected. Accurately providing the required amount of electrolyte solution for secondary batteries can be said to lead to mass production of secondary batteries with uniform characteristics.

[0016] In one aspect of the invention disclosed herein, electrolyte is uniformly impregnated by dropping multiple electrolyte droplets onto one or more of the positive electrode, separator, and negative electrode. The laminate of the positive electrode, separator, and negative electrode is then sandwiched between exterior films, and the outer edges (four sides as viewed from the top, if the secondary battery has a thin rectangular parallelepiped shape) are sealed without gaps. Here, a thin battery (also called a laminated type) is mainly used as an example. Note that terminals for external connection (such as lead wiring or lead electrodes (also called lead terminals)) are assumed to protrude outside the exterior film. The lead terminals are provided to extend the positive or negative electrode of the secondary battery outside the exterior film. Note that sealing is preferably performed under reduced pressure, at least below atmospheric pressure, to prevent the incorporation of impurities.

[0017] When multiple drops of electrolyte are dispensed, they are dispensed at a uniform interval across the flat surface. The dispensing method can be any one of the following: dispensing, spraying, inkjet printing, etc. The dispensing method uses a constant-volume liquid dispenser, dispensing a constant amount from a nozzle. Using multiple constant-volume liquid dispensers can also shorten manufacturing time. Drops can also be dispensed at regular intervals by moving the nozzle or the object to be dispensed (one or more of the positive electrode, separator, and negative electrode) relative to one another. If the amount dispensed at one location with a given nozzle diameter is 0.01 cc, dispensing at n (n > 1) locations allows for the impregnation of 0.01 cc × n of electrolyte, thereby enabling precise control of the drop locations and total amount dispensed. For example, dispensing at n (n > 1) locations on a flat surface can shorten the time required to impregnate the entire positive electrode compared to dispensing at only one location on the positive electrode, thereby shortening manufacturing time.

[0018] It is also preferable to adjust the viscosity of the electrolyte dripped from a nozzle as appropriate. The electrolyte can be dripped from a nozzle as long as the viscosity of the entire electrolyte is within the range of 10 mPa·s to 95 mPa·s at room temperature (25°C). A rotary viscometer (Toki Sangyo TVE-35L) is used to measure the viscosity.

[0019] The electrolyte to be dropped can be an organic solvent or an ionic liquid.

[0020] Furthermore, after the electrolyte is dropped, it is preferable to seal the cell under reduced pressure. Therefore, when dropping and sealing are performed consecutively, it is preferable to use the same chamber or multiple connected chambers. For example, after dropping the electrolyte in the first chamber, the cell is transferred to the second chamber without being exposed to the atmosphere, the pressure in the second chamber is reduced, and then the laminate is sealed with an exterior film in the second chamber, which is preferable because it prevents the inclusion of impurities such as dust. Alternatively, dropping the electrolyte and sealing with an exterior film may be performed consecutively in the same chamber, allowing for efficient production of secondary batteries.

[0021] The chamber where the sealing is performed is connected to a vacuum pumping chamber, and can be evacuated to a vacuum, or after evacuating, an inert gas can be introduced to atmospheric pressure. The vacuum pumping chamber is equipped with a magnetic levitation turbomolecular pump, a cryopump, or a dry pump. This allows the ultimate vacuum of the sealing chamber to be 10 -5 Pa to 10 -6 It is possible to keep the pressure at around Pa, and it is also possible to control the back diffusion of impurities from the pump side and the exhaust system. To prevent impurities from being introduced into the device, an inert gas such as nitrogen or a rare gas is used as the gas to be introduced. These gases to be introduced into the device are highly purified using a gas purifier before being introduced into the device.

[0022] Ionic liquids are preferred because they hardly volatilize even under high vacuum conditions. Alternatively, an ionic liquid mixed with an organic solvent may be used as the electrolyte. When an organic solvent is used as the electrolyte, the vacuum level in the chamber should be 5×10 -1 The vacuum should be lower than about Pa.

[0023] In the configuration of the invention disclosed in this specification, an electrolyte is dropped onto one or more of the positive electrode, negative electrode, and separator, and one or more of the positive electrode, negative electrode, and separator are impregnated with the electrolyte, and then the pressure is reduced and the laminate of the positive electrode, separator, and negative electrode is sealed with an exterior film.

[0024] Furthermore, by using a large-area exterior film, it is possible to produce many secondary batteries at once. For example, a method can be provided for efficiently producing multiple secondary batteries from a single large-area exterior film, even for exterior film sizes such as 320 mm x 400 mm, 370 mm x 470 mm, 550 mm x 650 mm, 600 mm x 720 mm, 680 mm x 880 mm, 1000 mm x 1200 mm, 1100 mm x 1250 mm, and 1150 mm x 1300 mm. Furthermore, a method for producing secondary batteries suitable for mass production using large-area exterior film sizes such as 1500 mm x 1800 mm, 1800 mm x 2000 mm, 2000 mm x 2100 mm, 2200 mm x 2600 mm, and 2600 mm x 3100 mm is provided.

[0025] Another configuration of the manufacturing method disclosed in this specification is a method for manufacturing a secondary battery, in which a plurality of laminates are arranged on an exterior film, an electrolyte is dropped onto the laminates, the laminates are sealed under reduced pressure, and the exterior film is cut to separate the secondary batteries into individual units, where the laminates are stacked together with at least two of a positive electrode, a separator, and a negative electrode. The exterior film can be cut using a laser beam or the like.

[0026] Using a film (also called a laminate film) containing a laminate of metal foil (aluminum, stainless steel, etc.) and resin (thermally adhesive resin) as the exterior film allows for the production of a thinner secondary battery that is lighter than a secondary battery using a metal can. The metal foil has an adhesive layer on one or both sides. The first adhesive layer of the first laminate film and the second adhesive layer of the second laminate film are tightly attached with the first adhesive layer and the second adhesive layer facing inward, and then thermocompression-bonded to form a sealed region. Furthermore, the method is not limited to thermocompression bonding; a sealant may be applied to the sealed region using a thermosetting resin or ultraviolet-curing resin.

[0027] The sealed area is in the shape of a frame or a closed loop. The laminate of the positive electrode, separator, and negative electrode is disposed and sealed within the area surrounded by the sealed area. Therefore, the area surrounded by the sealed area is at least larger than the area of ​​the positive electrode of the secondary battery.

[0028] The film used for the exterior body of the secondary battery is a single layer film selected from metal films (metals or alloys that can be used as metal foil, such as aluminum, stainless steel, nickel steel, gold, silver, copper, titanium, nichrome, iron, tin, tantalum, niobium, molybdenum, zirconium, and zinc), plastic films made of organic materials, hybrid material films containing organic materials (organic resins or fibers, etc.) and inorganic materials (ceramics, etc.), and carbon-containing inorganic films (carbon films, graphite films, etc.), or a laminate film made of two or more of these.

[0029] The secondary battery's sealing structure is such that a single rectangular exterior film is folded in the center, two of the four corners that sandwich the bent portion are overlapped, and the four sides are fixed with an adhesive layer to seal the structure. With this configuration, the stack of the positive electrode, separator, and negative electrode is housed in a manner that it is wrapped in the exterior film. Alternatively, two exterior films are stacked, and the four sides of the exterior film are fixed with an adhesive layer to seal the structure. In this specification, the structure after sealing with the exterior film may be referred to as an exterior body rather than an exterior film.

[0030] The fabrication method using two exterior films also has its own unique features. This involves placing a positive electrode on a first exterior film, dripping a first electrolyte onto the positive electrode, placing a separator on the positive electrode, dripping a second electrolyte onto the separator, placing a negative electrode on the separator, dripping a third electrolyte onto the negative electrode, and then placing the positive electrode, separator, and negative electrode stack under reduced pressure. The stack is then sandwiched between the stack and sealed with the first and second exterior films. Sealing refers to isolating a sealed area from the outside air. In secondary batteries, the sealed area is the stack and its periphery, and the outside of the sealed area is surrounded by one or two exterior films to seal it from the outside air. After sealing, the edges of the exterior films are folded to increase sealing strength and prevent the intrusion of impurities from the outside or the release of gases from the inside.

[0031] In the above configurations, the first electrolyte, the second electrolyte, and the third electrolyte may be made of the same material or different materials. Furthermore, in each of the above configurations, the laminate may be formed by stacking the positive electrode, the separator, and the negative electrode in this order, or the negative electrode, the separator, and the positive electrode in this order. Furthermore, the separator is used to prevent short-circuiting between the positive electrode and the negative electrode. When stacking the laminates to increase capacity, a single common separator may be folded to reduce the number of components.

[0032] The adhesive layer (also called the heat seal layer) can be made of a thermoplastic film material, a heat-curing adhesive, an anaerobic adhesive, a photo-curing adhesive such as an ultraviolet-curing adhesive, or a reaction-curing adhesive. The adhesive material can be epoxy resin, acrylic resin, silicone resin, or phenolic resin.

[0033] Current collectors, such as positive and negative electrode current collectors, can be made of metals such as stainless steel, gold, platinum, zinc, iron, nickel, copper, aluminum, titanium, and tantalum, as well as alloys thereof, which are highly conductive and do not alloy with carrier ions such as lithium ions. Aluminum alloys containing elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, and molybdenum, can also be used. They may also be made of metal elements that react with silicon to form silicides. Examples of metal elements that react with silicon to form silicides include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. Current collectors can be in various shapes, such as foil, plate (sheet), mesh, cylinder, coil, punched metal, and expanded metal. It is preferable to use a current collector with a thickness of 10 μm to 30 μm.

[0034] Although the above mainly describes an example of a thin battery (laminated type), it is not particularly limited and can also be applied to a wound type. In the case of a wound type, the electrolyte can be dripped onto the wound body, or dripped before forming the wound body, i.e., before winding. A wound body refers to a body in which a strip-shaped positive electrode, a strip-shaped separator, and a strip-shaped negative electrode are stacked in this order and wound while still stacked. [Effects of the Invention]

[0035] Since the number of sealing steps for the secondary battery is small, the manufacturing process for the secondary battery can be significantly shortened. Therefore, a manufacturing method for a secondary battery with reduced manufacturing costs can be provided. Alternatively, a manufacturing method that can efficiently manufacture a secondary battery in a short time can be realized. Alternatively, a manufacturing method that can automate the manufacturing of a secondary battery can be realized. Alternatively, a manufacturing method that can manufacture a secondary battery with a high yield can be realized.

[0036] Alternatively, a manufacturing method for manufacturing a relatively large secondary battery can be realized. When a large-capacity secondary battery is installed, the number of large secondary batteries to be installed can be reduced compared to the number of small secondary batteries to be installed. Reducing the number of large secondary batteries to be installed makes it easier to control each battery individually, and reduces the burden on the charge control circuit.

[0037] Furthermore, the secondary battery obtained by the manufacturing method disclosed in this specification can be tightly sealed in a single sealing step, and therefore can be a safe or highly reliable secondary battery. [Brief explanation of the drawings]

[0038] [Figure 1] FIG. 1A is a schematic cross-sectional view of a secondary battery showing one embodiment of the present invention, FIG. 1B is a top view after dropping of an electrolyte, and FIG. 1C is an example of a top view in the case where multiple panels are taken. [Figure 2] FIG. 2 is a flow chart illustrating an example of a method for manufacturing a secondary battery of one embodiment of the present invention. [Figure 3] 3A, 3B, 3C, 3D, and 3E are cross-sectional views illustrating an example of a method for manufacturing a secondary battery of one embodiment of the present invention. [Figure 4] FIG. 4 is a diagram illustrating the crystal structure of the positive electrode active material. [Figure 5] FIG. 5 is a diagram illustrating the crystal structure of the positive electrode active material. [Figure 6] 6A, 6B, and 6C are diagrams showing the external appearance of the secondary battery. [Figure 7] 7A and 7B are diagrams showing the external appearance of the secondary battery. [Figure 8] 8A, 8B, and 8C are diagrams illustrating a method for producing a secondary battery. [Figure 9] FIG. 9A is a perspective view showing a battery pack, FIG. 9B is a block diagram of the battery pack, and FIG. 9C is a block diagram of a vehicle having a motor. [Figure 10] 10A to 10D are diagrams illustrating an example of a transportation vehicle. [Figure 11]11A and 11B are diagrams illustrating a power storage device. [Figure 12] 12A, 12B, 12C, 12D, and 12E are perspective views of electronic devices illustrating embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0039] 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.

[0040] (Embodiment 1) In this embodiment, a secondary battery of one embodiment of the present invention and a manufacturing method thereof will be described.

[0041] An example of a secondary battery of one embodiment of the present invention will be described with reference to FIG. 1A.

[0042] 1A includes an exterior body 509 and a laminate 512 disposed within the exterior body 509. The laminate 512 includes a positive electrode 503, a negative electrode 506, and a separator 507. In the laminate 512, the positive electrode 503 and the negative electrode 506 are stacked, with the separator 507 disposed therebetween.

[0043] The positive electrode 503 has a positive electrode current collector 501 and a positive electrode active material layer 502 provided on both sides of the positive electrode current collector 501. The positive electrode active material layer 502 may be provided on only one side of the positive electrode current collector 501.

[0044] The negative electrode 506 includes a negative electrode current collector 504 and a negative electrode active material layer 505 provided on both sides of the negative electrode current collector 504. The negative electrode active material layer 505 may be provided on only one side of the negative electrode current collector 504.

[0045] The positive electrode active material layer 502 and the negative electrode active material layer 505 are preferably disposed so as to face each other with a separator 507 sandwiched therebetween. Fig. 1A shows an example of a secondary battery having four pairs of positive electrode active material layers 502 and negative electrode active material layers 505 facing each other with a separator 507 sandwiched therebetween.

[0046] Positive electrode 503 has a region (hereinafter referred to as tab region) where positive electrode current collector 501 is partially exposed. Negative electrode 506 has a region where negative electrode current collector 504 is partially exposed, that is, a tab region.

[0047] For example, in the case of a plurality of positive electrode current collectors 501, the tab regions are arranged so as to overlap each other. The overlapping tab regions and the positive electrode lead electrode may be overlapped and joined using ultrasonic welding or the like. Furthermore, in the case of a plurality of negative electrode current collectors 504, the tab regions are arranged so as to overlap each other. The overlapping tab regions and the negative electrode lead electrode may be overlapped and joined using ultrasonic welding or the like. The timing of joining using ultrasonic welding or the like can be appropriately selected by the practitioner, and may be before or after sealing.

[0048] In a secondary battery according to one embodiment of the present invention, electrolyte can be uniformly impregnated by dropping multiple electrolyte droplets onto one or more of the positive electrode, negative electrode, and separator. Figure 1B illustrates an example of dropping multiple electrolyte droplets onto a negative electrode. The negative electrode has a negative electrode active material layer on a negative electrode current collector. The negative electrode active material layer contains a negative electrode active material, a conductive material, a binder, or the like, with gaps between the layers. The dropped electrolyte moves from the drop position into the gaps in the negative electrode active material layer, resulting in a uniform impregnation of the electrolyte, ideally without any voids. Figure 1B illustrates 140 evenly spaced electrolyte droplets 515c (7 columns x 20 rows) on the negative electrode, but this is not particularly limited and can be determined appropriately by the practitioner. When using a single nozzle, the drop positions can be scanned sequentially while being monitored by a CCD or the like. Dropping droplets simultaneously from multiple nozzles is preferable because it shortens the drop processing time.

[0049] A secondary battery according to one embodiment of the present invention can be manufactured by dropping a plurality of drops of electrolyte into one or more of the positive electrode, negative electrode, and separator to uniformly impregnate the electrodes, and then sandwiching a stack 512 of the positive electrode, separator, and negative electrode between exterior films that serve as exterior bodies, and sealing the outer periphery (four sides as viewed from above in the case of a thin rectangular parallelepiped secondary battery) without gaps. For example, the outer periphery may be sealed in the sealing region 513 shown in FIG. 1B. Sealing can be performed under atmospheric pressure, and in this case, it is performed in an inert atmosphere such as argon gas or nitrogen gas. Sealing under reduced pressure is preferable because impurities or air are less likely to enter the sealed region surrounded by the exterior film. In this embodiment, sealing is performed at a pressure of approximately 4×10 4 The experiment was carried out in a chamber with a pressure of 100 Pa.

[0050] 1C, multiple laminates 512 can be arranged on an exterior film to form multiple panels. Multiple panels refers to a method of fabricating multiple secondary batteries by arranging multiple laminates on a single large exterior film, fabricating secondary batteries, and then dividing the laminates into multiple panels. By using multiple panels, the fabrication time per secondary battery can be shortened.

[0051] Fig. 2 is a flow chart illustrating a method for manufacturing a secondary battery according to one embodiment of the present invention, and Fig. 3 is a cross-sectional view illustrating the method for manufacturing a secondary battery according to one embodiment of the present invention, corresponding to the two-dot chain line AB in Fig. 1C.

[0052] An example of a method for manufacturing a secondary battery of one embodiment of the present invention will be described along the flow shown in FIG.

[0053] In step S000, the process starts.

[0054] In step S001, a positive electrode is placed. The positive electrode is placed on exterior film 509b, which becomes exterior body 509. Exterior film 509b is placed on stage 516. The positive electrode, exterior film, and stage are all placed in a chamber, but for simplicity, the inner walls of the chamber and the like are not shown here.

[0055] Next, in step S002, the electrolyte is dropped. Fig. 3A shows a state in which the positive electrode 503 is placed on the exterior film 509b and the electrolyte 515a is dropped from the nozzle 514. By moving the nozzle 514, the electrolyte 515a can be dropped over the entire surface of the positive electrode 503, as shown in Fig. 3B. Alternatively, the electrolyte 515a may be dropped over the entire surface of the positive electrode 503 by moving the stage 516.

[0056] Next, in step S003, separator 507 is placed on positive electrode 503. Next, in step S004, electrolyte 515b is dropped onto separator 507. Fig. 3C shows the state in which electrolyte 515b has been dropped onto separator 507.

[0057] Next, in step S005, a negative electrode is placed on top of positive electrode 503 and separator 507. Next, in step S006, electrolyte 515c is dripped onto the negative electrode. Fig. 3D shows the state in which electrolyte 515c has been dripped onto the negative electrode.

[0058] After step S006, a laminate of a positive electrode, a separator, and a negative electrode may be further laminated. For example, after step S006, a separator, a positive electrode, a separator, a negative electrode, a separator, and a positive electrode may be laminated in this order to produce laminate 512 shown in FIG. 1A. After the positive electrode, the negative electrode, and the separator are each arranged, it is preferable to drop an electrolyte.

[0059] In some cases, the electrolyte does not need to be dropped in the steps of disposing the positive electrode, negative electrode, and separator. For example, the electrolyte may be dropped only in the step of disposing the positive electrode and negative electrode. Alternatively, for example, the electrolyte may be dropped only in the step of disposing the separator.

[0060] Next, in step S007, exterior film 509b is sealed under reduced pressure. Fig. 3E shows the state after exterior film 509b is sealed.

[0061] After the above steps, the process ends in step S008.

[0062] (Embodiment 2) In this embodiment, an example of a secondary battery of one embodiment of the present invention will be described.

[0063] <Configuration example 1 of secondary battery> The following description will be given taking as an example a secondary battery in which a positive electrode, a negative electrode, and an electrolyte are enclosed in an exterior body.

[0064] [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 the above-described conductive material and binder.

[0065] [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 the above-described conductive material and the above-described binder.

[0066] [Current collector] The positive electrode current collector and the negative electrode current collector can be made of a highly conductive material that 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 collectors can be in any suitable shape, such as sheet, mesh, punched metal, or expanded metal. The current collectors should preferably have a thickness of 10 μm to 30 μm.

[0067] It is preferable to use a material that does not alloy with carrier ions such as lithium for the negative electrode current collector.

[0068] A titanium compound may be provided by laminating it on the metal shown above as the current collector. As the titanium compound, for example, titanium nitride, titanium oxide, titanium nitride in which a part of nitrogen is substituted by oxygen, titanium oxide in which a part of oxygen is substituted by nitrogen, and titanium oxynitride (TiO x N y , where 0 < x < 2 and 0 < y < 1), one selected therefrom, or two or more may be mixed or laminated and used. Among them, titanium nitride is particularly preferable because it has high conductivity and a high function of suppressing oxidation. By providing a titanium compound on the surface of the current collector, for example, the reaction between the material of the active material layer formed on the current collector and the metal is suppressed. When the active material layer contains a compound having oxygen, the oxidation reaction between the metal element and oxygen can be suppressed. For example, when aluminum is used as the current collector and the active material layer is formed using graphene oxide described later, there may be a concern about the oxidation reaction between the oxygen of graphene oxide and aluminum. In such a case, by providing a titanium compound on aluminum, the oxidation reaction between the current collector and graphene oxide can be suppressed.

[0069] Active material layers such as the positive electrode active material layer and the negative electrode active material layer preferably have a conductive material. As the conductive material, it is preferable to have a carbon-based material such as a graphene compound, carbon black, graphite, carbon fiber, fullerene, etc., and particularly preferably have a graphene compound. As carbon black, for example, acetylene black (AB) etc. can be used. As graphite, for example, natural graphite, artificial graphite such as mesocarbon microbeads, etc. can be used. In addition, these carbon-based materials may function as active materials.

[0070] 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.

[0071] 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.

[0072] The content of the conductive material 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.

[0073] 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.

[0074] Particulate carbon-containing compounds such as carbon black and graphite, or fibrous carbon-containing compounds such as carbon nanotubes, easily enter microscopic spaces. Microscopic spaces refer to, for example, the regions between multiple active materials. By combining a carbon-containing compound that easily enters 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 and an excellent conductive path can be formed. A secondary battery obtained by a manufacturing method according to one embodiment of the present invention can be stable and is effective as an in-vehicle secondary battery. Increasing the number of secondary batteries complicates control. Using large secondary batteries reduces the number of secondary batteries and the burden on the charge control circuit.

[0075] 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.

[0076] As the binder, it is preferable to use materials 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, and nitrocellulose.

[0077] Polyimide has excellent thermal, mechanical and chemical stability.

[0078] Fluorine-containing polymer materials, specifically polyvinylidene fluoride (PVDF), can be used. PVDF is a resin with a melting point between 134°C and 169°C, and is a material with excellent thermal stability.

[0079] 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.

[0080] 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 aforementioned rubber material.

[0081] The binder may be used in combination with two or more of the above.

[0082] <Graphene compounds> 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, etc. 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 called 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.

[0083] 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.

[0084] 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. Although a single sheet of reduced graphene oxide can function, multiple sheets may also be stacked. Reduced graphene oxide preferably has a portion where the carbon concentration is greater than 80 atomic % and the oxygen concentration is between 2 atomic % and 15 atomic %. By achieving these carbon and oxygen concentrations, it can function as a highly conductive material even in small amounts. Furthermore, reduced graphene oxide preferably has an intensity ratio G / D between the G band and 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.

[0085] By reducing graphene oxide, it may be possible to provide holes in the graphene compound.

[0086] Alternatively, a material in which the ends of graphene are terminated with fluorine may be used.

[0087] 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.

[0088] Here, a plurality of graphene compounds are bonded together to form a mesh-like graphene compound sheet (hereinafter referred to as a graphene compound net or graphene net). When an active material is covered with a graphene net, the graphene net can also function as a binder that binds the active materials together. Therefore, the amount of binder can be reduced or 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.

[0089] 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.

[0090] 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 graphene compound can be used to electrically connect the active materials together, thereby forming a conductive path.

[0091] 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 (SiO2, SiO x (x<2)), aluminum oxide, iron, nickel, ruthenium, iridium, platinum, copper, germanium, etc. The particles preferably have a D50 of 1 μm or less, more preferably 100 nm or less.

[0092] <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 the 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.

[0093] An example of the negative electrode active material will be described below.

[0094] The negative electrode active material may be a metal or compound containing one or more elements selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium. Examples of alloy compounds using such elements include Mg2Si, Mg2Ge, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, and SbSn.

[0095] Alternatively, a material with low resistance may be used by adding impurity elements such as phosphorus, arsenic, boron, aluminum, or gallium to silicon. A silicon material pre-doped with lithium may also be used. Pre-doping methods include mixing silicon with lithium fluoride, lithium carbonate, or the like and annealing the mixture, or mechanically alloying lithium metal with silicon. After forming the electrode, the material may be combined with an electrode such as lithium metal to dope lithium through a charge-discharge reaction. The doped electrode may then be combined with a counter electrode (e.g., a positive electrode for a pre-doped negative electrode) to produce a secondary battery.

[0096] For example, silicon nanoparticles can be used as the negative electrode active material. The average diameter of the silicon nanoparticles is preferably 5 nm or more and less than 1 μm, more preferably 10 nm or more and 300 nm or less, and even more preferably 10 nm or more and 100 nm or less.

[0097] The silicon nanoparticles may be crystalline, or may have a crystalline region and an amorphous region.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] As the negative electrode active material, a combination of the above-mentioned metals, materials, compounds, etc. can be used.

[0102] Examples of negative electrode active materials include SnO, SnO2, titanium dioxide (TiO2), and lithium titanium oxide (Li4Ti5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), molybdenum oxide (MoO2), and other oxides can be used.

[0103] In addition, the negative electrode active material is a composite nitride of lithium and transition metals, Li3N-type 3-x M x N (M=Co, Ni, Cu) can be used. For example, Li 2.6 Co 0.4 N3 is preferable because it exhibits a large charge / discharge capacity (900 mAh / g).

[0104] The use of a lithium-transition metal complex nitride as the negative electrode material is preferable because it can be combined with a lithium-ion-free positive electrode material such as V2O5 or Cr3O8. Even when a material containing lithium ions is used as the positive electrode material, the lithium-transition metal complex nitride can be used as the negative electrode material by first removing the lithium ions contained in the positive electrode material.

[0105] In addition, materials in which a conversion reaction occurs can also be used as the negative electrode active material. For example, transition metal oxides that do not undergo an alloying reaction with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), iron oxide (FeO), etc., may be used as the negative electrode active material. The conversion reaction further occurs in oxides such as Fe2O3, CuO, Cu2O, RuO2, Cr2O3, etc., CoS 0.89 sulfides such as NiS, CuS, nitrides such as Zn3N2, Cu3N, Ge3N4, phosphides such as NiP2, FeP2, CoP3, and fluorides such as FeF3, BiF3. Since the potential of the above fluorides is high, they may be used as the positive electrode material.

[0106] <An example of the positive electrode active material> Examples of the positive electrode active material include lithium-containing materials having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure.

[0107] It is preferable to use a positive electrode active material having a layered crystal structure as the positive electrode active material of one aspect of the present invention.

[0108] Examples of the layered crystal structure include a layered rock salt-type crystal structure. Examples of the lithium-containing material having a layered rock salt-type crystal structure include 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, 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.

[0109] LiM x O y Examples of the lithium-containing material represented by include LiCoO2, LiNiO2, LiMnO2, etc. Also, examples of the lithium-containing material represented by LiM x O y include, for example, LiNi x Co 1-xNiCo-based represented by O2(0 < x < 1), LiNi x Mn 1-x NiMn-based represented by O2(0 < x < 1), etc. can be mentioned.

[0110] Also, as the lithium-containing material represented by LiMO2, for example, LiNi x Co y Mn z NiCoMn-based (also referred to as NCM) represented by O2(x > 0, y > 0, 0.8 < x + y + z < 1.2) can be mentioned. Specifically, for example, it is preferable to satisfy 0.1x < y < 8x and 0.1x < z < 8x. As an example, x, y, and z preferably satisfy x:y:z = 1:1:1 or values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 5:2:3 or values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 8:1:1 or values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 6:2:2 or values in the vicinity thereof. Or as an example, x, y, and z preferably satisfy x:y:z = 1:4:1 or values in the vicinity thereof.

[0111] Also, as the lithium-containing material having a layered rock salt-type crystal structure, for example, Li2MnO3, Li2MnO3-LiMeO2 (Me is Co, Ni, Mn), etc. can be mentioned.

[0112] In the positive electrode active material having a layered crystal structure represented by the above lithium-containing material, there may be cases where a secondary battery with a large lithium content per volume and a high capacity per volume can be realized. In such a positive electrode active material, the amount of lithium desorbed per volume during charging is also large, and in order to perform stable charge and discharge, stabilization of the crystal structure after desorption is required. Also, when the crystal structure collapses during charge and discharge, high-speed charging or high-speed discharging may be inhibited.

[0113] A lithium-containing material having a spinel-type crystal structure containing manganese such as LiMn2O4 as a positive electrode active material is preferably mixed with lithium nickelate (LiNiO2 or LiNi 1-x M x O2 (0 < x < 1) (M = Co, Al, etc.)). By adopting such a configuration, the characteristics of the secondary battery can be improved.

[0114] Also, as the positive electrode active material, a lithium manganese composite oxide represented by the composition formula Li a Mn b M c O d can be used. Here, the element M is preferably a metal element selected from those other than lithium and manganese, or silicon or phosphorus, and more preferably nickel. Further, when measuring the entire particles of the lithium manganese composite oxide, it is preferable to satisfy 0 < a / (b + c) < 2, c > 0, and 0.26 ≦ (b + c) / d < 0.5 during discharge. The composition of metals, silicon, phosphorus, etc. in the entire particles of the lithium manganese composite oxide can be measured using, for example, ICP-MS (inductively coupled plasma mass spectrometer). Also, the oxygen composition of the entire particles of the lithium manganese composite oxide can be measured using, for example, EDX (energy dispersive X-ray analysis method). Further, it can be determined by using valence evaluation of melting gas analysis and XAFS (X-ray absorption fine structure) analysis in combination with ICP-MS analysis. The lithium manganese composite oxide refers to an oxide containing at least lithium and manganese, and may contain at least one element selected from the group consisting of chromium, cobalt, aluminum, nickel, iron, magnesium, molybdenum, zinc, indium, gallium, copper, titanium, niobium, silicon, and phosphorus.

[0115] [Structure of Positive Electrode Active Material] Materials with a layered rock-salt crystal structure, such as lithium cobalt oxide (LiCoO2), are known to have high discharge capacity and are excellent as positive electrode active materials for secondary batteries. An example of a material with a layered rock-salt crystal structure is a composite oxide represented by LiMO2. Metal M includes metal Me1. Metal Me1 is one or more metals including cobalt. Metal M can also include metal X in addition to metal Me1. Metal X is one or more metals selected from magnesium, calcium, zirconium, lanthanum, barium, copper, potassium, sodium, and zinc.

[0116] The amount of lithium remaining in the positive electrode active material that can be inserted or removed can be determined by the x in the composition formula, for example, Li x x in CoO2, or Li x In this specification, Li x CoO2 is appropriately Li x In the case of the positive electrode active material in a secondary battery, x can be expressed as charge capacity / theoretical capacity. For example, when a secondary battery using LiCoO2 as the positive electrode active material is charged at 219.2mAh / g, Li 0.8 CoO2 or x=0.8. x A small value of x in CoO2 is, for example, 0.1 <x≦0.24をいう。

[0117] 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.

[0118] In compounds containing nickel, distortion may occur due to the Jahn-Teller effect. Therefore, when LiNiO2 is charged and discharged at high voltages, there is a concern that the crystal structure may collapse due to distortion. In LiCoO2, the influence of the Jahn-Teller effect is suggested to be small, and LiCoO2 may have better durability against charge and discharge at high voltages, which is preferable.

[0119] The positive electrode active material will be described with reference to FIGS.

[0120] <Crystal structure> <Li x When x in CoO2 is 1≫ The positive electrode active material according to one embodiment of the present invention is in a discharged state, i.e., Li x When x = 1 in CoO2, it is preferable for the layered rock-salt complex oxide to have a layered rock-salt crystal structure belonging to the space group R-3m. Layered rock-salt complex oxides have high discharge capacity, two-dimensional lithium ion diffusion paths, and are suitable for lithium ion insertion / extraction reactions, making them excellent cathode active materials for secondary batteries. Therefore, it is particularly preferable for the interior, which accounts for most of the volume of the cathode active material, to have a layered rock-salt crystal structure. Figure 4 shows the layered rock-salt complex oxide crystal structure, labeled R-3m O3.

[0121] The surface layer is the area where lithium ions are first released during charging, and is prone to have a lower lithium concentration than the interior. In addition, the atoms on the surface of the positive electrode active material in the surface layer can be said to have some of their bonds broken. Therefore, the surface layer is prone to becoming unstable, and is a region where deterioration of the crystal structure is likely to begin. On the other hand, if the surface layer can be made sufficiently stable, Li x Even when x in CoO2 is small, for example, 0.24 or less, the layered structure consisting of the internal transition metal M and oxygen octahedra can be made less likely to break. Furthermore, it is possible to suppress the displacement of the internal transition metal M and oxygen octahedra.

[0122] In order to give the surface layer a stable composition and crystal structure, the surface layer preferably contains an additive element A, and more preferably contains a plurality of additive elements A. Furthermore, it is preferable that the concentration of one or more selected from the additive elements A is higher in the surface layer than in the interior. Furthermore, it is preferable that the one or more selected from the additive elements A contained in the positive electrode active material have a concentration gradient. Furthermore, it is more preferable that the distribution of the additive element A in the positive electrode active material differs depending on the additive element A. For example, it is more preferable that the depth from the surface of the concentration peak differs depending on the additive element A. Here, the concentration peak refers to the maximum value of the concentration in the surface layer or within 50 nm from the surface.

[0123] For example, some of the additive elements A, such as magnesium, fluorine, titanium, silicon, phosphorus, boron, and calcium, preferably have a concentration gradient that increases from the inside toward the surface. Elements having such a concentration gradient will be referred to as additive elements X.

[0124] For example, magnesium, one of the added elements X, is divalent, and magnesium ions are more stable at the lithium site than at the transition metal M site in the layered rock salt crystal structure, so they tend to enter the lithium site. The presence of magnesium at an appropriate concentration at the lithium site in the surface layer makes it easier to maintain the layered rock salt crystal structure. This is presumably because the magnesium present at the lithium site functions as a pillar supporting the CoO2 layers. The presence of magnesium also makes it easier to maintain the Li x When x in CoO2 is, for example, 0.24 or less, the release of oxygen from the surrounding magnesium can be suppressed. The presence of magnesium is also expected to increase the density of the positive electrode active material. Furthermore, a high magnesium concentration in the surface layer is expected to improve corrosion resistance to hydrofluoric acid produced by the decomposition of the electrolyte.

[0125] At an appropriate concentration, magnesium does not adversely affect the intercalation and deintercalation of lithium during charging and discharging, providing the above benefits. However, excessive magnesium may adversely affect the intercalation and deintercalation of lithium. Furthermore, it may be less effective at stabilizing the crystal structure. This is thought to be because magnesium occupies both the lithium site and the transition metal M site. In addition, unnecessary magnesium compounds (oxides, fluorides, etc.) that do not substitute for either the lithium site or the transition metal M site may segregate on the surface of the positive electrode active material and become resistance components in the secondary battery. Furthermore, as the magnesium concentration in the positive electrode active material increases, the discharge capacity of the positive electrode active material may decrease. This is thought to be due to excessive magnesium occupancy in the lithium site, reducing the amount of lithium contributing to charging and discharging.

[0126] Therefore, it is preferable that the amount of magnesium contained in the entire positive electrode active material is appropriate. For example, the number of magnesium atoms is preferably 0.001 to 0.1 times the number of cobalt atoms, more preferably more than 0.01 to less than 0.04 times, and even more preferably about 0.02 times. The amount of magnesium contained in the entire positive electrode active material referred to here may be a value obtained by performing elemental analysis of the entire positive electrode active material using, for example, GD-MS, ICP-MS, etc., or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material.

[0127] Furthermore, aluminum, one of the additive elements Y, can exist at the transition metal M site in the layered rock salt crystal structure. Because aluminum is a trivalent typical element and its valence does not change, lithium around the aluminum is less likely to move during charging and discharging. Therefore, the aluminum and its surrounding lithium function as pillars, suppressing changes in the crystal structure. Aluminum also suppresses the elution of the surrounding transition metal M, improving continuous charging durability. Furthermore, because the Al-O bond is stronger than the Co-O bond, it can suppress the release of oxygen around the aluminum. These effects improve thermal stability. Therefore, the presence of aluminum as the additive element Y can improve safety when used in secondary batteries. Furthermore, it can produce a positive electrode active material whose crystal structure is less likely to collapse even after repeated charging and discharging.

[0128] On the other hand, an excess of aluminum may adversely affect the intercalation and deintercalation of lithium.

[0129] Therefore, it is preferable that the total amount of aluminum contained in the positive electrode active material is appropriate. For example, the number of aluminum atoms contained in the total amount of aluminum contained in the positive electrode active material is preferably 0.05% to 4% of the number of cobalt atoms, preferably 0.1% to 2% and more preferably 0.3% to 1.5%. Alternatively, 0.05% to 2% is preferable. Alternatively, 0.1% to 4% is preferable. The amount contained in the total amount of aluminum contained in the positive electrode active material may be, for example, a value obtained by performing elemental analysis of the entire positive electrode active material using GD-MS, ICP-MS, or the like, or may be based on the value of the composition of raw materials in the process of producing the positive electrode active material.

[0130] For example, it is preferable that the crystal structure continuously changes from the inside of the layered rock salt type toward the surface and surface layer portion having characteristics of the rock salt type or both the rock salt type and the layered rock salt type.Alternatively, it is preferable that the orientation of the rock salt type or the surface layer portion having characteristics of both the rock salt type and the layered rock salt type is approximately the same as that of the inside of the layered rock salt type.

[0131] In this specification, the layered rock-salt crystal structure belonging to the space group R-3m, which is possessed by a composite oxide containing lithium and a transition metal M such as cobalt, refers to a crystal structure having a rock-salt ion arrangement in which cations and anions are alternately arranged, and in which the transition metal M and lithium are regularly arranged to form a two-dimensional plane, allowing two-dimensional diffusion of lithium. Defects such as vacancies of cations or anions may also be present. Furthermore, strictly speaking, the layered rock-salt crystal structure may have a structure in which the lattice of the rock-salt crystal is distorted.

[0132] The rock salt crystal structure refers to a cubic crystal structure, such as that of the space group Fm-3m, in which cations and anions are arranged alternately. Note that cation or anion deficiencies are also acceptable.

[0133] Furthermore, the fact that it has both the characteristics of the layered rock salt type and the rock salt type crystal structure can be determined by electron diffraction, TEM images, cross-sectional STEM images, etc.

[0134] Layered rock salt crystals and the anions in rock salt crystals have a cubic close-packed structure (face-centered cubic lattice structure). It is estimated that the anions in the O3' crystals (also called pseudospinel crystals), which will be described later, also have a cubic close-packed structure. Therefore, when layered rock salt crystals and rock salt crystals come into contact, there are crystal faces where the cubic close-packed structure composed of anions is aligned.

[0135] Alternatively, it can be explained as follows: Anions on the {111} plane of the cubic crystal structure have a triangular lattice. Layered rocksalt has a space group of 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 (000l) plane of the layered rocksalt has a hexagonal lattice. The triangular lattice of the cubic {111} plane has the same atomic arrangement as the hexagonal lattice of the (000l) plane of the layered rocksalt. The compatibility of the two lattices can be said to be the alignment of the cubic close-packed structure.

[0136] 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 Fm-3m of the rock salt type crystal (the space group of a general rock salt type crystal), 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 in the layered rock salt type crystal, the O3' type, and the rock salt type crystal are aligned, it may be said that the crystal orientations are approximately the same.

[0137] The general agreement of the crystal orientations of the two regions can be determined from TEM (Transmission Electron Microscope) images, STEM (Scanning Transmission Electron Microscope) images, HAADF-STEM (High-Angle Annular Dark Field Scanning TEM) images, ABF-STEM (Annular Bright-Field Scanning Transmission Electron Microscopy) images, electron diffraction, FFT of TEM and STEM images, etc. XRD (X-ray Diffraction), neutron diffraction, etc. can also be used as materials for determination.

[0138] Figure 5 shows R-3m O3 and Li xThis shows the crystal structure of lithium cobalt oxide with x=1 in CoO2. In this crystal structure, lithium occupies octahedral sites, and there are three CoO2 layers in the unit cell. For this reason, this crystal structure is sometimes called an O3-type crystal structure. Note that a CoO2 layer is an octahedral structure in which cobalt is coordinated with six oxygen atoms, and these structures are connected in a plane with edge sharing. This is sometimes called a layer consisting of octahedra of cobalt and oxygen.

[0139] Conventional lithium cobalt oxide is known to have a crystal structure that belongs to the monoclinic space group P2 / m when the symmetry of lithium increases when x is around 0.5. This structure has one CoO2 layer in the unit cell. For this reason, it is sometimes called the O1 type or monoclinic O1 type.

[0140] When x = 0, the positive electrode active material has a trigonal space group P-3m1 crystal structure, with one CoO2 layer in each unit cell. This crystal structure is sometimes called the O1 type or trigonal O1 type. The trigonal structure may also be converted to a composite hexagonal lattice, which is sometimes called the hexagonal O1 type.

[0141] Furthermore, conventional lithium cobalt oxides with x = approximately 0.24 have a crystal structure of the space group R-3m. This structure can be described as a structure in which a trigonal O1-type CoO2 structure and an R-3m O3-type LiCoO2 structure are alternately stacked. For this reason, this crystal structure is sometimes referred to as the H1-3-type crystal structure. In reality, the H1-3-type crystal structure has twice the number of cobalt atoms per unit cell as other structures. However, in Figure 5 and other parts of this specification, the c-axis of the H1-3-type crystal structure is shown as half the unit cell to facilitate comparison with other crystal structures.

[0142] As shown by the dotted line in Figure 4, there is almost no deviation in the CoO2 layer between the R-3m(O3) in the discharged state and the O3'-type crystal structure.

[0143] The difference in volume per the same number of cobalt atoms between R-3m(O3) in a discharged state and the O3'-type crystal structure is 2.5% or less, more specifically 2.2% or less, and typically 1.8%.

[0144] As described above, in the positive electrode active material according to one embodiment of the present invention, Li x When x in CoO2 is small, i.e., when a large amount of lithium is released, the change in crystal structure is suppressed compared to conventional positive electrode active materials. Furthermore, the change in volume is also suppressed when compared per the same number of cobalt atoms. Therefore, the positive electrode active material's crystal structure is less likely to collapse even when repeatedly charged and discharged so that x is 0.24 or less. This suppresses the decrease in charge / discharge capacity during charge / discharge cycles. Furthermore, because it can stably utilize more lithium than conventional positive electrode active materials, the positive electrode active material has a higher discharge capacity per weight and per volume. Therefore, using this positive electrode active material makes it possible to fabricate secondary batteries with high discharge capacity per weight and per volume.

[0145] The positive electrode active material is Li x It has been confirmed that when x in CoO2 is between 0.15 and 0.24, it may have an O3' type crystal structure, and it is also presumed that when x is between 0.24 and 0.27, it also has an O3' type crystal structure. However, the crystal structure is Li x Since it is affected not only by x in CoO2 but also by the number of charge / discharge cycles, charge / discharge current, temperature, electrolyte, etc., it is not necessarily limited to the above range of x.

[0146] Therefore, the positive electrode active material is Li x When x in CoO2 is more than 0.1 and not more than 0.24, the entire interior of the positive electrode active material does not have to have an O3'-type crystal structure, but may contain other crystal structures, or may be partially amorphous.

[0147] Also Li x To make the x in CoO2 small, it is generally necessary to charge at a high charging voltage. xA state in which x in CoO2 is small can be rephrased as a state in which the battery is charged at a high charging voltage. For example, when conventional positive electrode active materials are charged at a voltage of 4.6 V or higher relative to the potential of lithium metal in a 25°C environment under CC / CV charging, an H1-3 crystal structure appears. Therefore, a charging voltage of 4.6 V or higher relative to the potential of lithium metal can be considered a high charging voltage. Unless otherwise specified, charging voltages in this specification and elsewhere are expressed relative to the potential of lithium metal.

[0148] Therefore, in other words, the positive electrode active material of one embodiment of the present invention is preferable because it can maintain a crystal structure with R-3m O3 symmetry even when charged at a high charging voltage, for example, a voltage of 4.6 V or higher at 25° C. In other words, it is preferable because it can adopt an O3'-type crystal structure when charged at a higher charging voltage, for example, a voltage of 4.65 V or higher and 4.7 V or lower at 25° C.

[0149] Even in the case of a positive electrode active material, the H1-3 type crystal may be observed only when the charge voltage is further increased. Furthermore, as described above, since the crystal structure is affected by the number of charge / discharge cycles, the charge / discharge current, the electrolyte, etc., the positive electrode active material of one embodiment of the present invention may be able to adopt the O3' type crystal structure even when the charge voltage is lower, for example, even when the charge voltage is 4.5 V or higher but lower than 4.6 V at 25°C.

[0150] In addition, when graphite is used as the negative electrode active material in a secondary battery, the voltage of the secondary battery is lower than the above by the amount of the potential of the graphite. The potential of graphite is about 0.05 V to 0.2 V relative to the potential of lithium metal. Therefore, in the case of a secondary battery using graphite as the negative electrode active material, the same crystalline structure is maintained at a voltage obtained by subtracting the potential of graphite from the above voltage.

[0151] <Particle size> If the particle size of the positive electrode active material of one embodiment of the present invention is too large, problems such as difficulty in diffusing lithium and excessive roughness of the surface of the active material layer when applied to a current collector may occur. On the other hand, if the particle size is too small, problems such as difficulty in supporting the active material layer when applied to a current collector and excessive reaction with the electrolyte may occur. Therefore, the median diameter (D50) is preferably 1 μm to 100 μm, more preferably 2 μm to 40 μm, and even more preferably 5 μm to 30 μm. Alternatively, 1 μm to 40 μm is preferred. Alternatively, 1 μm to 30 μm is preferred. Alternatively, 2 μm to 100 μm is preferred. Alternatively, 2 μm to 30 μm is preferred. Alternatively, 5 μm to 100 μm is preferred. Alternatively, 5 μm to 40 μm is preferred.

[0152] <Analysis method> A certain positive electrode active material is Li x When x in CoO2 is small, whether or not the positive electrode active material of one embodiment of the present invention has an O3'-type crystal structure can be determined by Li x This can be determined by analyzing a positive electrode having a positive electrode active material with a small x in CoO2 using XRD, electron beam diffraction, neutron diffraction, electron spin resonance (ESR), nuclear magnetic resonance (NMR), etc.

[0153] XRD is particularly preferred for its ability to analyze with high resolution the symmetry of the transition metal M, such as cobalt, contained in the positive electrode active material, to compare the level of crystallinity and the orientation of the crystals, to analyze the periodic distortion of the lattice and the crystallite size, and to obtain sufficient accuracy even when measuring the positive electrode obtained by disassembling the secondary battery. Among XRD methods, powder XRD can obtain diffraction peaks that reflect the internal crystalline structure of the positive electrode active material, which accounts for most of the volume of the positive electrode active material.

[0154] As described above, the positive electrode active material according to one embodiment of the present invention is Li x A characteristic of CoO2 is that there is little change in the crystal structure when x in CoO2 is 1 and when it is 0.24 or less. When charged at high voltage, materials in which the crystal structure that undergoes large changes when charged at high voltage accounts for 50% or more are not desirable because they cannot withstand high-voltage charging and discharging.

[0155] It should also be noted that simply adding an additional element A may not result in an O3'-type crystal structure. For example, even if lithium cobalt oxide with magnesium and fluorine or lithium cobalt oxide with magnesium and aluminum has something in common, depending on the concentration and distribution of the additional element A, the structure may be different from Li x When x in CoO2 is 0.24 or less, the O3' type crystal structure accounts for 60% or more, and when the H1-3 type crystal structure accounts for 50% or more.

[0156] Furthermore, even in a positive electrode active material of one embodiment of the present invention, an H1-3 type or trigonal O1 type crystal structure may be formed if x is too small, such as 0.1 or less, or under conditions where the charge voltage exceeds 4.9 V. Therefore, to determine whether or not a positive electrode active material is one embodiment of the present invention, analysis of the crystal structure, such as XRD, and information such as the charge capacity or the charge voltage are required.

[0157] However, positive electrode active materials with a small x value may undergo a change in crystal structure when exposed to air. For example, the crystal structure may change from an O3'-type to an H1-3-type. Therefore, it is recommended that all samples used for crystal structure analysis be handled in an inert atmosphere such as an argon atmosphere.

[0158] Furthermore, whether the distribution of the additive element A in a certain positive electrode active material is in the state described above can be determined by analyzing it using, for example, XPS, energy dispersive X-ray spectroscopy (EDX), electron probe microanalysis (EPMA), or the like.

[0159] The crystalline structure of the surface layer, grain boundaries, etc. can be analyzed by electron beam diffraction of a cross section of the positive electrode active material.

[0160] As an example of an H1-3 type crystal structure, the coordinates of cobalt and oxygen in the unit cell 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 oxygen atoms. The unit cell that should be used to represent the crystal structure of the positive electrode active material can be determined, for example, by Rietveld analysis of XRD. In this case, the unit cell that results in the smallest GOF (goodness of fit) value should be used.

[0161] Li x When conventional lithium cobalt oxide is repeatedly charged and discharged so that x in CoO2 becomes 0.24 or less, the crystal structure changes repeatedly (i.e., a non-equilibrium phase change) between the H1-3 type crystal structure and the R-3m O3 structure in the discharged state.

[0162] However, these two crystal structures have a large misalignment of the CoO2 layers. As shown by the dotted lines and arrows in Figure 5, in the H1-3 crystal structure, the CoO2 layers are significantly misaligned from those in the R-3m O3 discharged state. Such dynamic structural changes can adversely affect the stability of the crystal structure.

[0163] Furthermore, the difference in volume between these two crystal structures is large: when compared per the same number of cobalt atoms, the difference in volume between the H1-3 crystal structure and the discharged R-3m O3 crystal structure exceeds 3.5%, typically 3.9% or more.

[0164] In addition, the H1-3 type crystal structure, which has continuous CoO2 layers like the trigonal O1 type, is likely to be unstable.

[0165] Therefore, when charging and discharging is repeated so that x becomes 0.24 or less, the crystal structure of conventional lithium cobalt oxide collapses. This collapse of the crystal structure causes a deterioration in cycle characteristics. This is because the collapse of the crystal structure reduces the number of sites where lithium can exist stably and makes it difficult for lithium to be inserted and extracted.

[0166] <Electrolytes> When a liquid electrolyte layer is used in a secondary battery, for example, the electrolyte layer can be made of 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 can be used in any combination and ratio.

[0167] 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.

[0168] Fluorinated cyclic carbonates include fluorinated ethylene carbonates, 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 electrodes during charging and discharging. Using fluorinated cyclic carbonates not as a small additive but as a catalyst for lithium ion transport during charging and discharging enables low-temperature operation. Lithium ions move in clusters of several to several tens of ions within a secondary battery.

[0169] 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.

[0170] 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.

[0171] Examples of fluorinated cyclic carbonates are shown below.

[0172] Monofluoroethylene carbonate (FEC) is represented by the following formula (1).

[0173] [ka]

[0174] Tetrafluoroethylene carbonate (F4EC) is represented by the following formula (2).

[0175] [ka]

[0176] Difluoroethylene carbonate (DFEC) is represented by the following formula (3).

[0177] [ka]

[0178] 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 short-circuiting or overcharging. Ionic liquids are composed of cations and anions, including organic cations and anions. Examples of organic cations include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions include monovalent amide anions, monovalent methide anions, fluorosulfonate anions, perfluoroalkylsulfonate anions, tetrafluoroborate anions, perfluoroalkylborate anions, hexafluorophosphate anions, and perfluoroalkylphosphate anions.

[0179] As an ionic liquid having an imidazolium cation, for example, an ionic liquid represented by the following general formula (G1) can be used. In general formula (G1), R 1 represents an alkyl group having 1 to 10 carbon atoms, and R 2 ~R 4 each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R 5 represents an alkyl group having 1 to 6 carbon atoms, or a main chain composed of two or more atoms selected from C, O, Si, N, S, and P. 5 A substituent may be introduced into the main chain of the polymer. Examples of the substituent to be introduced include an alkyl group and an alkoxy group.

[0180] [ka]

[0181] Examples of the cation represented by general formula (G1) include 1-ethyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-methyl-3-(propoxyethyl)imidazolium cation, and 1-hexyl-3-methylimidazolium cation.

[0182] As the ionic liquid having a pyridinium cation, for example, an ionic liquid represented by the following general formula (G2) may be used. In general formula (G2), R 6 represents an alkyl group having 1 to 6 carbon atoms, or a main chain composed of two or more atoms selected from C, O, Si, N, S, and P, and R 7 ~R 11 each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. 6 A substituent may be introduced into the main chain of the polymer. Examples of the substituent to be introduced include an alkyl group and an alkoxy group.

[0183] [ka]

[0184] As the ionic liquid having a quaternary ammonium cation, for example, ionic liquids represented by the following general formulae (G3), (G4), (G5) and (G6) can be used.

[0185] [ka]

[0186] In general formula (G3), R 28 ~R 31 each independently represents an alkyl group having 1 to 20 carbon atoms, a methoxy group, a methoxymethyl group, a methoxyethyl group, or a hydrogen atom.

[0187] [ka]

[0188] In general formula (G4), R 12 and R 17 R each independently represents an alkyl group having 1 to 3 carbon atoms. 13 ~R 16 each independently represents a hydrogen atom or an alkyl group having a carbon number of 1 to 3. An example of a cation represented by general formula (G4) is a 1-methyl-1-propylpyrrolidinium cation.

[0189] [ka]

[0190] In general formula (G5), R 18 and R 24 R each independently represents an alkyl group having 1 to 3 carbon atoms. 19 ~R 23 each independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. Examples of the cation represented by general formula (G5) include an N-methyl-N-propylpiperidinium cation and a 1,3-dimethyl-1-propylpiperidinium cation.

[0191] [ka]

[0192] In general formula (G6), n and m are 1 or more and 3 or less. α is 0 or more and 6 or less; when n is 1, α is 0 or more and 4 or less; when n is 2, α is 0 or more and 5 or less; and when n is 3, α is 0 or more and 6 or less. β is 0 or more and 6 or less; when m is 1, β is 0 or more and 4 or less; when m is 2, β is 0 or more and 5 or less; and when m is 3, β is 0 or more and 6 or less. When α or β is 0, this indicates unsubstituted. This does not include cases where both α and β are 0. X or Y represents, as a substituent, a linear or side-chain alkyl group having 1 to 4 carbon atoms, a linear or side-chain alkoxy group having 1 to 4 carbon atoms, or a linear or side-chain alkoxyalkyl group having 1 to 4 carbon atoms.

[0193] As an ionic liquid having a tertiary sulfonium cation, for example, an ionic liquid represented by the following general formula (G7) can be used. In general formula (G7), R 25 ~R 27 each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group. 25 ~R 27 A main chain composed of two or more atoms selected from C, O, Si, N, S and P atoms may be used as the main chain.

[0194] [ka]

[0195] As an ionic liquid having a quaternary phosphonium cation, for example, an ionic liquid represented by the following general formula (G8) can be used. In general formula (G8), R 32 ~R 35 each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group. 32 ~R 35 A main chain composed of two or more atoms selected from C, O, Si, N, S and P atoms may be used as the main chain.

[0196] [ka]

[0197] A represented by general formulas (G1) to (G8) - As the anion, one or more of a monovalent amide anion, a monovalent methide anion, a fluorosulfonate anion, a perfluoroalkylsulfonate anion, a tetrafluoroborate anion, a perfluoroalkylborate anion, a hexafluorophosphate anion, and a perfluoroalkylphosphate anion can be used.

[0198] Monovalent amide anions include (C n F 2n+1 SO2)2N - (n = 0 to 3), and the monovalent cyclic amide anion is (CF2SO2)2N - The monovalent methide anions include (C n F 2n+1 SO2)3C - (n = 0 to 3), monovalent cyclic methide anions include (CF2SO2)2C - (CF3SO2) and the like can be used. As the fluoroalkylsulfonate anion, (C m F 2m+1 SO3) - (m=0 or more and 4 or less). Fluoroalkylborate anions include {BF n (C m H k F 2m+1-k ) 4-n} - (n = 0 or more and 3 or less, m = 1 or more and 4 or less, k = 0 or more and 2m or less). Fluoroalkyl phosphate anions include {PF n (C m H k F 2m+1-k ) 6-n} - (n = 0 to 5, m = 1 to 4, k = 0 to 2m)

[0199] Furthermore, as the monovalent amide anion, for example, one or more of a bis(fluorosulfonyl)amide anion and a bis(trifluoromethanesulfonyl)amide anion can be used.

[0200] The ionic liquid may also have one or more of a hexafluorophosphate anion and a tetrafluoroborate anion.

[0201] Hereafter, (FSO2)2N - The anion represented by the formula is the FSA anion, (CF3SO2)2N - The anion represented by the formula is sometimes referred to as the TFSA anion.

[0202] The secondary battery of one embodiment of the present invention includes, as carrier ions, alkali metal ions such as sodium ions and potassium ions, and alkaline earth metal ions such as calcium ions, strontium ions, barium ions, beryllium ions, and magnesium ions.

[0203] When lithium ions are used as carrier ions, the electrolyte contains a lithium salt, such as LiPF, LiClO, LiAsF, LiBF, LiAlCl, LiSCN, LiBr, LiI, LiSO, and LiB. 10 Cl 10 , Li2B 12 Cl 12 , LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, etc. can be used.

[0204] In this specification, the term "electrolyte" is a general term that includes solid, liquid, or semi-solid materials.

[0205] 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, typically electrolyte alteration or increased viscosity, that can occur at the interface between the active material and the electrolyte. Furthermore, a binder, a graphene compound, or the like may be attached to or retained by the fluorine-containing electrolyte. This configuration can maintain the 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.

[0206] 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.

[0207] 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 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.

[0208] By using an electrolyte containing fluorine, it is possible to realize 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.

[0209] The electrolyte may also contain additives such as vinylene carbonate, propane sultone (PS), tert-butylbenzene (TBB), lithium bis(oxalato)borate (LiBOB), or dinitrile compounds such as succinonitrile and adiponitrile. The concentration of the additive may be, for example, 0.1% by volume or more and less than 5% by volume of the entire electrolyte.

[0210] In addition to the above, the electrolyte may contain one or more aprotic organic solvents such as γ-butyrolactone, acetonitrile, dimethoxyethane, and tetrahydrofuran.

[0211] 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.

[0212] Examples of polymeric materials that can be used include polymers having a polyalkylene oxide structure, such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and 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.

[0213] [Separator] A separator is placed 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 made of nylon resin (polyamide), vinylon resin (polyvinyl alcohol-based fibers), polyester resin, acrylic resin, polyolefin resin, and polyurethane resin. The separator is preferably processed into a bag shape and placed so as to encase either the positive electrode or the negative electrode.

[0214] The separator is a porous material having pores of about 20 nm in size, preferably pores of 6.5 nm or larger in size, and more preferably pores of at least 2 nm in diameter.

[0215] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine-based material, a polyamide material, or a mixture of these. Examples of ceramic materials that can be used include aluminum oxide particles and silicon oxide particles. Examples of fluorine-based materials that can be used include PVDF and polytetrafluoroethylene. Examples of polyamide materials that can be used include nylon and aramid (meta-aramid, para-aramid).

[0216] 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.

[0217] 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.

[0218] 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.

[0219] [Exterior body] The exterior body of the secondary battery can be, for example, a can-type body made of a metal material such as aluminum, or a case-type body made of a resin material. A film-like exterior body can also be used. Examples of the film include a three-layer structure in which a flexible metal thin film made of aluminum, stainless steel, copper, nickel, or the like is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film made of polyamide resin, polyester resin, or the like is further provided on the metal thin film as the exterior body surface. 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 an excellent secondary battery. Examples of fluororesin films include PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxyalkane: a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether), FEP (perfluoroethylenepropene copolymer: a copolymer of tetrafluoroethylene and hexafluoropropylene), and ETFE (ethylenetetrafluoroethylene copolymer: a copolymer of tetrafluoroethylene and ethylene).

[0220] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0221] (Embodiment 3) In this embodiment, a specific configuration example of the secondary battery described in the previous embodiment will be described.

[0222] 6 and 7 show examples of external views of a secondary battery according to one embodiment of the present invention.

[0223] 6A has a positive electrode 503, a negative electrode 506, a separator 507, and an exterior body 509. The exterior body 509 is sealed by a seal area 513. The positive electrode 503, the negative electrode 506, and the separator 507 are stacked and placed inside the exterior body 509.

[0224] 6A, a positive electrode lead electrode 510 is joined to a positive electrode 503. The positive electrode lead electrode 510 is exposed to the outside of an outer casing 509. A negative electrode lead electrode 511 is joined to a negative electrode 506, and the negative electrode lead electrode 511 is exposed to the outside of the outer casing 509.

[0225] The joining of the lead electrodes will be described with reference to FIGS. 8A, 8B and 8C.

[0226] 8A shows an external view of positive electrode 503. Positive electrode 503 has positive electrode current collector 501, and positive electrode active material layer 502 is formed on the surface of positive electrode current collector 501. Positive electrode 503 also has a region where positive electrode current collector 501 is partially exposed (hereinafter referred to as a tab region).

[0227] 8B shows an external view of negative electrode 506. Negative electrode 506 has negative electrode current collector 504, and negative electrode active material layer 505 is formed on the surface of negative electrode current collector 504. Negative electrode 506 also has a region where negative electrode current collector 504 is partially exposed, i.e., a tab region. The area or shape of the tab regions of the positive electrode and negative electrode are not limited to the examples shown in FIGS. 8A and 8B.

[0228] FIG. 8C is a diagram illustrating the joining of lead electrodes. First, a negative electrode 506, a separator 507, and a positive electrode 503 are laminated. FIG. 8C shows the laminated negative electrode 506, separator 507, and positive electrode 503. Here, the laminate consisting of a negative electrode, a separator, and a positive electrode has five pairs of negative electrodes and four pairs of positive electrodes. The tab regions of the positive electrodes 503 are joined together, and a positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For example, ultrasonic welding or the like may be used for joining. Similarly, the tab regions of the negative electrode 506 are joined together, and a negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0229] The external view shown in Fig. 6B shows an example in which the ends of two sides of the exterior body 509 are folded. By folding the ends of the exterior body 509, the strength of the exterior body 509 can be increased. For example, when an external force is applied to the secondary battery 500, or when gas or the like is generated inside the exterior body 509 and the secondary battery 500 expands, defects such as loosening of the seal can be suppressed. Also, Fig. 6C shows an example in which three sides are folded.

[0230] 6A, 6B, and 6C show an example in which the positive electrode lead electrode 510 and the negative electrode lead electrode 511 are arranged on the same side, but the positive electrode lead electrode 510 and the negative electrode lead electrode 511 may be arranged on different sides, for example, on the upper and lower sides as shown in Fig. 7A. Fig. 7B shows an example in which the left and right sides of the exterior body 509 in Fig. 7A are folded.

[0231] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0232] (Fourth embodiment) In this embodiment, an example in which the secondary battery is applied to an electric vehicle (EV) will be shown.

[0233] As shown in Fig. 9C, an electric vehicle is equipped with first batteries 1301a and 1301b as main driving secondary batteries, and a second battery 1311 that supplies power to an inverter 1312 that starts a motor 1304. The second battery 1311 is also called a cranking battery (starter battery). The second battery 1311 only needs to have high output, and does not need to have a large capacity, and the capacity of the second battery 1311 is smaller than that of the first batteries 1301a and 1301b.

[0234] The first battery 1301a can be a secondary battery manufactured using the method for manufacturing a secondary battery described in Embodiment 1.

[0235] In this embodiment, an example is shown in which two first batteries 1301a and 1301b are connected in parallel, but three or more may be connected in parallel. Also, if the first battery 1301a can store sufficient power, the first battery 1301b may not be necessary. By configuring a battery pack having multiple secondary batteries, it is possible to extract large amounts of power. The multiple secondary batteries may be connected in parallel, in series, or in series after being connected in parallel. A plurality of secondary batteries is also called a battery pack.

[0236] 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 first battery 1301a in order to cut off power from multiple secondary batteries.

[0237] The power of the first batteries 1301a and 1301b is mainly used to rotate the motor 1304, but also supplies power to 42V in-vehicle components (such as an electric power steering 1307, a heater 1308, and a defogger 1309) via a DC-DC circuit 1306. When a rear motor 1317 is provided on the rear wheels, the first battery 1301a is also used to rotate the rear motor 1317.

[0238] Furthermore, the second battery 1311 supplies power to 14V in-vehicle components (audio 1313, power windows 1314, lamps 1315, etc.) via the DCDC circuit 1310.

[0239] The first battery 1301a will be described with reference to FIG. 9A.

[0240] FIG. 9A shows an example in which nine prismatic secondary batteries 1300 are used as one battery pack 1415. Furthermore, nine prismatic secondary batteries 1300 are connected in series, with one electrode fixed by fixing portion 1413 made of an insulator and the other electrode fixed by fixing portion 1414 made of an insulator. While this embodiment shows an example in which the batteries are fixed by fixing portions 1413 and 1414, they may also be housed in a battery housing box (also called a casing). Because it is expected that a vehicle will be subjected to external vibrations or shaking (such as from the road surface), it is preferable to fix multiple secondary batteries in a battery housing box or the like by fixing portions 1413 and 1414. Furthermore, one electrode is electrically connected to control circuit unit 1320 by wiring 1421. Furthermore, the other electrode is electrically connected to control circuit unit 1320 by wiring 1422.

[0241] A memory circuit including a transistor using an oxide semiconductor may be used for the control circuit unit 1320. A charge control circuit or a battery control system having a memory circuit including a transistor using an oxide semiconductor may be referred to as a battery operating system (BTOS) or a battery oxide semiconductor.

[0242] The control circuit 1320 detects the terminal voltage of the secondary battery and manages the charge / discharge state of the secondary battery. For example, to prevent overcharging, it can turn off both the output transistor and the cutoff switch of the charging circuit almost simultaneously.

[0243] FIG. 9B shows an example of a block diagram of the battery pack 1415 shown in FIG. 9A.

[0244] The control circuit unit 1320 includes a switch unit 1324 including at least a switch for preventing overcharging and a switch for preventing overdischarging, a control circuit 1322 for controlling the switch unit 1324, and a voltage measurement unit for the first battery 1301a. The control circuit unit 1320 sets upper and lower voltage limits for the secondary battery used and limits the upper limit of the current from the outside or the upper limit of the output current to the outside. The range between the lower limit and the upper limit of the secondary battery's voltage is within the recommended voltage range. If the voltage falls outside this range, the switch unit 1324 activates and functions as a protection circuit. The control circuit unit 1320 can also be called a protection circuit because it controls the switch unit 1324 to prevent overcharging or overdischarging. For example, if the control circuit 1322 detects a voltage that could cause overcharging, it turns off the switch unit 1324 to cut off the current. A PTC element may also be provided in the charge / discharge path to provide a function for cutting off the current in response to a rise in temperature. The control circuit section 1320 also has an external terminal 1325 (+IN) and an external terminal 1326 (-IN).

[0245] The switch unit 1324 can be configured by combining n-channel transistors or p-channel transistors. The switch unit 1324 is not limited to a switch having a Si transistor using single crystal silicon. For example, the switch unit 1324 may be formed of a power transistor having Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), InP (indium phosphide), SiC (silicon carbide), ZnSe (zinc selenide), GaN (gallium nitride), or GaOx (gallium oxide; x is a real number greater than 0). Furthermore, memory elements using OS transistors can be freely arranged by stacking them on circuits using Si transistors, facilitating integration. Furthermore, OS transistors can be fabricated using the same manufacturing equipment as Si transistors, allowing for low-cost fabrication. Specifically, a control circuit unit 1320 using OS transistors can be stacked on the switch unit 1324 and integrated into a single chip. The control circuit unit 1320 occupies a smaller volume, enabling miniaturization.

[0246] The first batteries 1301a and 1301b mainly supply power to 42V (high voltage) in-vehicle devices, and the second battery 1311 supplies power to 14V (low voltage) in-vehicle devices. A lead-acid battery is often used as the second battery 1311 because of its cost advantage.

[0247] In this embodiment, an example is shown in which lithium ion secondary batteries are used as both the first battery 1301a and the second battery 1311. The second battery 1311 may be a lead storage battery, an all-solid-state battery, or an electric double layer capacitor.

[0248] Furthermore, regenerated energy generated by the rotation of the tire 1316 is sent to the motor 1304 via the gear 1305, and is then charged into the second battery 1311 via the control circuit unit 1321 from the motor controller 1303 or the battery controller 1302. Alternatively, the first battery 1301a is charged from the battery controller 1302 via the control circuit unit 1320. Alternatively, the first battery 1301b is charged from the battery controller 1302 via the control circuit unit 1320. In order to efficiently charge the regenerated energy, it is desirable that the first batteries 1301a and 1301b be capable of being rapidly charged.

[0249] The battery controller 1302 can set the charging voltage and charging current of the first batteries 1301a and 1301b. The battery controller 1302 can set charging conditions according to the charging characteristics of the secondary battery used, and can perform rapid charging.

[0250] Although not shown, when an external charger is connected, the charger's outlet or the charger's connection cable is electrically connected to the battery controller 1302. The power supplied from the external charger is charged to the first batteries 1301a, 1301b via the battery controller 1302. Some chargers are provided with a control circuit, and although the function of the battery controller 1302 may not be used, it is preferable to charge the first batteries 1301a, 1301b via a control circuit unit 1320 to prevent overcharging. In some cases, the connection cable or the charger's connection cable is provided with a control circuit. The control circuit unit 1320 is also called an ECU (Electronic Control Unit). The ECU is connected to a CAN (Controller Area Network) provided in the electric vehicle. CAN is one of the serial communication standards used as an in-vehicle LAN. The ECU includes a microcomputer. The ECU uses a CPU or a GPU.

[0251] 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.

[0252] Furthermore, when the secondary battery of one embodiment of the present invention is installed in a vehicle, next-generation clean energy vehicles such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs) can be realized. Furthermore, the secondary battery can also be installed in transportation vehicles such as agricultural machinery, mopeds including electrically assisted bicycles, motorcycles, electric wheelchairs, electric carts, small or large ships, submarines, aircraft such as fixed-wing aircraft or rotary-wing aircraft, rockets, artificial satellites, space probes or planetary probes, and spaceships. A large secondary battery can be obtained by using the manufacturing method of the secondary battery described in Embodiment 1. Therefore, the secondary battery of one embodiment of the present invention can be suitably used in transportation vehicles.

[0253] 10A to 10D illustrate examples of transportation vehicles using one embodiment of the present invention. The automobile 2001 shown in FIG. 10A is an electric automobile that uses an electric motor as a power source for traveling. Alternatively, it is a hybrid automobile that can appropriately select and use an electric motor or an engine as a power source for traveling. When a secondary battery is installed in a vehicle, the secondary battery is installed in one location or multiple locations. The automobile 2001 shown in FIG. 10A includes a battery pack 2200, which includes a secondary battery module to which multiple secondary batteries are connected. It is preferable that the automobile further includes a charge control device electrically connected to the secondary battery module.

[0254] Furthermore, automobile 2001 can charge its secondary battery by receiving power supply from an external charging facility using a plug-in system, a contactless power supply system, or the like. Charging can be performed using a predetermined charging method or connector standard, such as CHAdeMO (registered trademark) or Combo, as appropriate. The secondary battery may be charged at a charging station provided in a commercial facility or from a household power source. For example, plug-in technology can be used to charge an electricity storage device mounted on automobile 2001 using an external power supply. Charging can be performed by converting AC power to DC power via a conversion device such as an AC-DC converter.

[0255] Although not shown, a power receiving device can be mounted on a vehicle and power can be supplied contactlessly from a ground-based power transmitting device for charging. In the case of this contactless power supply method, by incorporating a power transmitting device into the road or an exterior wall, charging can be performed not only while the vehicle is stopped but also while the vehicle is moving. This contactless power supply method can also be used to transmit and receive power between two vehicles. Furthermore, a solar cell can be installed on the exterior of the vehicle, and the secondary battery can be charged while the vehicle is stopped or moving. For such contactless power supply, an electromagnetic induction method or a magnetic field resonance method can be used.

[0256] 10B shows a large transport vehicle 2002 having an electrically controlled motor as an example of a transport vehicle. The secondary battery module of the transport vehicle 2002 is, for example, a four-cell unit of secondary batteries of 3.5V to 4.7V, with 48 cells connected in series for a maximum voltage of 170V. Apart from the number of secondary batteries constituting the secondary battery module of the battery pack 2201, the transport vehicle 2002 has the same functions as those shown in FIG. 10A, and therefore a description thereof will be omitted.

[0257] FIG. 10C shows, as an example, a large transport vehicle 2003 having an electrically controlled motor. The secondary battery module of the transport vehicle 2003 has a maximum voltage of 600 V, for example, with more than 100 secondary batteries connected in series with a voltage of 3.5 V to 4.7 V. Therefore, a secondary battery with little variation in characteristics is required. By using the method for manufacturing a secondary battery shown in embodiment 1, secondary batteries with stable battery characteristics can be manufactured, and mass production at low cost is possible from the viewpoint of yield. Furthermore, except for the number of secondary batteries constituting the secondary battery module of the battery pack 2202, the same functions as those shown in FIG. 10A are provided, and therefore description thereof will be omitted.

[0258] Fig. 10D shows, as an example, an aircraft 2004 having an engine that burns fuel. Since the aircraft 2004 shown in Fig. 10D has wheels for takeoff and landing, it can also be said to be part of a transportation vehicle, and has a battery pack 2203 that includes a secondary battery module formed by connecting multiple secondary batteries and includes the secondary battery module and a charge control device.

[0259] The secondary battery module of the aircraft 2004 has, for example, eight 4V secondary batteries connected in series to produce a maximum voltage of 32V. Other than the number of secondary batteries constituting the secondary battery module of the battery pack 2203, it has the same functions as those in FIG. 10A, and therefore a description thereof will be omitted.

[0260] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0261] (Embodiment 5) In this embodiment, an example in which a secondary battery according to one embodiment of the present invention is mounted in a building will be described with reference to FIGS. 11A and 11B.

[0262] The house shown in FIG. 11A includes a power storage device 2612 including a secondary battery with stable battery characteristics obtained by using the manufacturing method of the secondary battery described in Embodiment 1, and a solar panel 2610. The power storage device 2612 is electrically connected to the solar panel 2610 via 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.

[0263] 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 the commercial power source due to a power outage or the like, the power storage device 2612 can be used as an uninterruptible power supply, allowing the use of electronic devices.

[0264] 11B illustrates an example of a power storage device 700 of one embodiment of the present invention. As illustrated in FIG. 11B, a large-sized power storage device 791 obtained by the method for manufacturing a secondary battery described in Embodiment 1 is installed in an underfloor space 796 of a building 799.

[0265] A control device 790 is installed in the power storage device 791, and the control device 790 is electrically connected to a distribution board 703, a power storage controller 705 (also called a control device), a display 706, and a router 709 by wiring.

[0266] Electric power is sent from commercial power source 701 to distribution board 703 via service line attachment section 710. Electric power is also sent to distribution board 703 from power storage device 791 and commercial power source 701, and distribution board 703 supplies the sent electric power to general load 707 and power storage load 708 via an outlet (not shown).

[0267] 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.

[0268] The power storage controller 705 has a measurement unit 711, a prediction unit 712, and a planning unit 713. The measurement unit 711 has a function of measuring the amount of power consumed by the general load 707 and the power storage load 708 during one day (for example, from midnight to midnight). The measurement unit 711 may also have a function of measuring the amount of power of the power storage device 791 and the amount of power supplied from the commercial power source 701. The prediction unit 712 has a function of predicting the amount of power demand to be consumed by the general load 707 and the power storage load 708 during the next day, based on the amount of power consumed by the general load 707 and the power storage load 708 during the previous day. The planning unit 713 has a function of creating a plan for charging and discharging the power storage device 791, based on the amount of power demand predicted by the prediction unit 712.

[0269] The amount of power consumed by the general load 707 and the power storage load 708 measured by the measurement unit 711 can be confirmed on the display 706. It can also be confirmed on an electrical device such as a television or a personal computer via the router 709. It can also be confirmed on a mobile electronic device such as a smartphone or a tablet via the router 709. The amount of power demand for each time period (or each hour) predicted by the prediction unit 712 can also be confirmed on the display 706, the electrical device, or the mobile electronic device.

[0270] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0271] (Sixth embodiment) 12A includes a housing 2801, a housing 2802, a display unit 2803, a keyboard 2804, a pointing device 2805, and the like. A secondary battery 2806 is provided inside the housing 2801, and a secondary battery 2807 is provided inside the housing 2802. A touch panel is also applied to the display unit 2803. As shown in FIG. 12B, the housings 2801 and 2802 can be removed from the personal computer 2800, and the personal computer 2800 can be used as a tablet terminal using only the housing 2802.

[0272] A large secondary battery obtained by the method for manufacturing a secondary battery described in Embodiment 1 can be applied to the secondary battery 2807. The secondary battery obtained by the method for manufacturing a secondary battery described in Embodiment 1 can increase the capacity of the secondary battery and extend the usage time of the personal computer 2800. In addition, the weight of the personal computer 2800 can be reduced.

[0273] A flexible display is applied to the display portion 2803 of the casing 2802. A large-sized secondary battery obtained by the manufacturing method of a secondary battery described in Embodiment 1 is used as the secondary battery 2807. A large-sized secondary battery obtained by the manufacturing method of a secondary battery described in Embodiment 1 can be made into a bendable secondary battery by using a flexible film for the exterior body of the large-sized secondary battery. Thus, the casing 2802 can be folded for use as shown in FIG. 12C. In this case, part of the display portion 2803 can also be used as a keyboard as shown in FIG. 12C.

[0274] The housing 2802 can be folded so that the display portion 2803 faces inward as shown in FIG. 12D, or so that the display portion 2803 faces outward as shown in FIG. 12E.

[0275] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0276] (Notes regarding the present specification) Furthermore, in this specification and the like, crystal planes and directions are indicated by Miller indices. In crystallography, crystal planes and directions are indicated by a superscript bar after the number, but in this specification and the like, due to restrictions on application notation, numbers may be expressed by a minus sign (-) before them instead of a bar above them. Furthermore, individual directions indicating directions within a crystal are expressed with [ ], collective directions indicating all equivalent directions are expressed with < >, individual planes indicating crystal planes are expressed with ( ), and collective planes with equivalent symmetry are expressed with {}.

[0277] In this specification and the like, segregation refers to a phenomenon in which a certain element (for example, B) is spatially distributed non-uniformly in a solid composed of multiple elements (for example, A, B, and C).

[0278] In this specification, the surface layer of particles of active material or the like is preferably, for example, a region within 50 nm from the surface, more preferably within 35 nm, and even more preferably within 20 nm. Surfaces formed by cracks or fissures may also be referred to as the surface. The region deeper than the surface layer is referred to as the interior.

[0279] 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. Furthermore, strictly speaking, the layered rock-salt type crystal structure may have a distorted rock-salt type crystal lattice structure.

[0280] In this specification and the like, the rock salt type crystal structure refers to a structure in which cations and anions are arranged alternately, and it is also possible for there to be a deficiency of cations or anions.

[0281] The general alignment of the crystal orientations of the two regions can be determined from TEM (transmission electron microscope), STEM (scanning transmission electron microscope), HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope), and ABF-STEM (annular bright-field scanning transmission electron microscope) images. X-ray diffraction (XRD), electron diffraction, and neutron diffraction can also be used. In TEM images, the arrangement of cations and anions can be observed as repeated bright and dark lines. When the orientation of the cubic close-packed structure of the layered rock salt crystal and the rock salt crystal is aligned, the angle between the repeated bright and dark lines between the crystals can be observed to be less than 5 degrees, and more preferably less than 2.5 degrees. Light elements such as oxygen and fluorine may not be clearly visible in TEM images, but in such cases, the alignment of the orientations can be determined from the arrangement of metal elements.

[0282] In this specification, the theoretical capacity of a positive electrode active material refers to the amount of electricity when all of the intercalable lithium contained in the positive electrode active material is deintercalated. For example, the theoretical capacity of LiCoO2 is 274 mAh / g, the theoretical capacity of LiNiO2 is 274 mAh / g, and the theoretical capacity of LiMn2O4 is 148 mAh / g.

[0283] In this specification and the like, the depth of charge when all intercalable and deintercalable lithium is intercalated is defined as 0, and the depth of charge when all intercalable and deintercalable lithium contained in the positive electrode active material is deintercalated is defined as 1.

[0284] In this specification, charging refers to the transfer of lithium ions from the positive electrode to the negative electrode within a battery and the transfer of electrons from the positive electrode to the negative electrode in an external circuit. Regarding a positive electrode active material, charging refers to the removal of lithium ions. A positive electrode active material with a charge depth of 0.7 to 0.9 is sometimes referred to as a positive electrode active material charged at a high voltage.

[0285] Similarly, discharging refers to the transfer of lithium ions from the negative electrode to the positive electrode within the battery and the transfer of electrons from the negative electrode to the positive electrode in an external circuit. For positive electrode active materials, discharging refers to the insertion of lithium ions. A fully discharged positive electrode active material is defined as a positive electrode active material with a charge depth of 0.06 or less, or a positive electrode active material that has been discharged to 90% or more of its charge capacity from a high-voltage charged state.

[0286] In this specification, a non-equilibrium phase change refers to a phenomenon that causes a non-linear change in a physical quantity. For example, a non-equilibrium phase change occurs around the peak in the dQ / dV curve obtained by differentiating capacitance (Q) with voltage (V), and it is believed that the crystal structure changes significantly.

[0287] A secondary battery has, for example, a positive electrode and a negative electrode. A material constituting the positive electrode is a positive electrode active material. The positive electrode active material is, for example, a substance that undergoes a reaction that contributes to the charge / discharge capacity. Note that the positive electrode active material may partially contain a substance that does not contribute to the charge / discharge capacity. [Explanation of symbols]

[0288] 500: secondary battery, 501: positive electrode current collector, 502: positive electrode active material layer, 503: positive electrode, 504: negative electrode current collector, 505: negative electrode active material layer, 506: negative electrode, 507: separator, 509: exterior body, 510: positive electrode lead electrode, 511: negative electrode lead electrode, 513: seal area, 514: nozzle, 515a, 515b, 515c: electrolyte, 700: power storage device, 701: commercial power source, 703: distribution board, 705: power storage controller, 706: display, 707: general load, 708: power storage system Load, 709: router, 710: service line attachment section, 711: measurement section, 712: prediction section, 713: planning section, 790: control device, 791: power storage device, 796: underfloor space section, 799: building, 1300: prismatic secondary battery, 1301a: battery, 1301b: battery, 1302: battery controller, 1303: motor controller, 1304: motor, 1305: gear, 1306: DCDC circuit, 1307: electric power steering, 1308: heater, 1309: defogger ,1310: DCDC circuit, 1311: battery, 1312: inverter, 1313: audio, 1314: power window, 1315: lamps, 1316: tires, 1317: rear motor, 1320: control circuit section, 1321: control circuit section, 1322: control circuit, 1324: switch section, 1325: external terminal, 1326: external terminal, 1413: fixed section, 1414: fixed section, 1415: battery pack, 1421: wiring, 1422: wiring, 2001: automobile, 20 02: Transport vehicle, 2003: Transport vehicle, 2004: Aircraft, 2200: Battery pack, 2201: Battery pack, 2202: Battery pack, 2203: Battery pack, 2603: Vehicle, 2604: Charging device, 2610: Solar panel, 2611: Wiring, 2612: Power storage device, 2800: Personal computer, 2801: Housing, 2802: Housing, 2803: Display unit, 2804: Keyboard, 2805: Pointing device, 2806: Secondary battery, 2807: Secondary battery

Claims

1. In the first chamber, a first exterior body is placed on a stage; A positive electrode is disposed on the first exterior body; After dropping a plurality of drops of the first electrolyte onto the entire surface of the positive electrode, A separator is disposed on the positive electrode in an overlapping manner; After dropping a plurality of drops of the second electrolyte onto the separator, a negative electrode is disposed on the positive electrode and the separator in an overlapping manner; a first step of dropping a third electrolyte onto the negative electrode; a second step of transporting the laminate of the positive electrode, the separator, and the negative electrode formed in the first step to a second chamber without exposing it to the atmosphere, reducing the pressure inside the second chamber, and then sealing the laminate in the second chamber using the first outer casing and the second outer casing.

2. In claim 1, the positive electrode has a positive electrode current collector, the negative electrode has a negative electrode current collector, The positive electrode current collector and the negative electrode current collector each have a partially exposed region.

Images