Flexible battery and electronic device

Abstract

The present invention provides a highly secure or durable flexible battery. Provided is a flexible battery that has a negative electrode and a positive electrode. The negative electrode has a first carbon-containing material, a first current collector, and a negative-electrode active material formed on the first current collector. The first carbon-containing material encloses the first current collector and the negative-electrode active material. The positive electrode has a second carbon-containing material, a second current collector, and a positive-electrode active material formed on the second current collector. The second carbon-containing material encloses the second current collector and the positive-electrode active material.

Description

Flexible batteries and electronic devices

[0001] One aspect of the present invention relates to a battery and an electronic device, and more particularly to a flexible battery and an electronic device including the flexible battery.

[0002] One embodiment of the present invention is not limited to the above technical fields, but relates to a semiconductor device, a display device, a light-emitting device, a recording device, a driving method thereof, or a manufacturing method thereof. That is, the technical field of one embodiment of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method.

[0003] In recent years, there has been active development of wearable devices such as smart watches and head-mounted displays. To ensure comfortable wearing, the exterior of wearable devices often has a curved portion that fits comfortably to the human body, and a configuration with a curved portion has also been proposed for secondary batteries to be installed in wearable devices (see Patent Document 1).

[0004] Furthermore, in mobile devices such as smartphones or tablets, a flexible display sandwiched between housings is used, allowing the flexible display to follow the moving housing (see Patent Document 2).

[0005] Graphene has also attracted considerable attention due to its excellent electrical conductivity, and large-scale production methods are being explored. As shown in Non-Patent Document 1, a compound obtained by reducing graphene oxide (GO) is sometimes called reduced GO (rGO), and its physical properties have attracted attention.

[0006] JP 2016-110640 A JP 2016-075884 A

[0007] A. Bagri et al. , “Structural evolution during the reduction of chemically derived graphene oxide”, NATURE CHEMISTRY, vol. 2, 2010, pp. 581-587.

[0008] In the field of secondary batteries, where safety is a key issue, fixation has been considered important. Patent Document 1 above describes that it is preferable for the secondary battery to be flexible in the event that the smartwatch is deformed by external force, but the deformation is small when the smartwatch is worn, and the secondary battery is fixed to the smartwatch together with the plate. Patent Document 2 above also describes the incorporation of a lithium-ion battery, but it is fixed in a position overlapping the immovable housing.

[0009] In view of the above, an object of one embodiment of the present invention is to provide a flexible battery that can move with a movable housing.

[0010] 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 it is possible to extract problems other than these from the description in the specification, drawings, and claims (hereinafter referred to as the specification, etc.).

[0011] In view of the above description, one embodiment of the present invention is a flexible battery including a negative electrode and a positive electrode. The negative electrode includes a first carbon-containing material, a first current collector, and a negative electrode active material formed on the first current collector, and the first carbon-containing material envelops the first current collector and the negative electrode active material. The positive electrode includes a second carbon-containing material, a second current collector, and a positive electrode active material formed on the second current collector, and the second carbon-containing material envelops the second current collector and the positive electrode active material.

[0012] Another aspect of the present invention is a flexible battery including a negative electrode and a positive electrode. The negative electrode includes a first carbon-containing material, a first current collector, a second current collector positioned in an opening of the first current collector, and a negative electrode active material formed on the first current collector and the second current collector, and the first carbon-containing material envelops the first current collector, the second current collector, and the negative electrode active material. The positive electrode includes a second carbon-containing material, a third current collector, a fourth current collector positioned in an opening of the third current collector, and a positive electrode active material formed on the third current collector and the fourth current collector, and the second carbon-containing material envelops the third current collector, the fourth current collector, and the positive electrode active material.

[0013] In another aspect of the present invention, the second current collector and the fourth current collector are preferably provided so as to overlap with a bending region.

[0014] In another aspect of the present invention, it is preferable that the first carbon-containing material and the second carbon-containing material each have a bag-like or cylindrical shape.

[0015] In another aspect of the present invention, it is preferable that the first carbon-containing material and the second carbon-containing material each include a graphene compound.

[0016] In another embodiment of the present invention, the graphene compound is preferably graphene oxide.

[0017] In another embodiment of the present invention, the graphene compound is preferably reduced graphene oxide.

[0018] In another embodiment of the present invention, the first carbon-containing material and the second carbon-containing material each preferably include graphene.

[0019] In another aspect of the present invention, it is preferable that the first carbon-containing material and the second carbon-containing material each include carbon fibers.

[0020] In another embodiment of the present invention, it is preferable to have a separator between the negative electrode and the positive electrode.

[0021] In another aspect of the present invention, the separator preferably has a bag-like or cylindrical shape.

[0022] In another embodiment of the present invention, it is preferable that there is no separator located between the negative electrode and the positive electrode.

[0023] In another embodiment of the present invention, the area of ​​the positive electrode is preferably smaller than the area of ​​the negative electrode.

[0024] In another aspect of the present invention, the negative electrode active material or the positive electrode active material preferably has a median diameter (D50) of 10 nm or more and 30 μm or less.

[0025] In another aspect of the present invention, the positive electrode active material preferably has secondary particles, and the median diameter (D50) of primary particles constituting the secondary particles is preferably 10 nm or more and 1 μm or less.

[0026] Another embodiment of the present invention is an electronic device equipped with a flexible battery.

[0027] According to one embodiment of the present invention, a flexible battery that can move with a moving housing can be provided.

[0028] Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of these effects. Note that effects other than these will become apparent from the description in the specification, drawings, claims, etc., and it is possible to extract other effects from the description in the specification, drawings, claims, etc.

[0029] FIGS. 1A and 1B are cross-sectional views of a flexible battery of one embodiment of the present invention. FIGS. 2A and 2B are cross-sectional views of a flexible battery of one embodiment of the present invention. FIGS. 3A and 3B are cross-sectional views of a flexible battery of one embodiment of the present invention. FIGS. 4A and 4B are cross-sectional views and top views of a negative electrode of one embodiment of the present invention. FIGS. 5A to 5C are cross-sectional views of an active material layer and the like of a negative electrode of one embodiment of the present invention. FIGS. 6A and 6B are diagrams of a graphene compound of one embodiment of the present invention. FIGS. 7A and 7B are diagrams of a spray drying apparatus. FIGS. 8A and 8B are cross-sectional views of an active material layer and the like of a negative electrode of one embodiment of the present invention. FIGS. 9A and 9B are cross-sectional views and top views of a positive electrode of one embodiment of the present invention. FIG. 10 is a cross-sectional view of a negative electrode of one embodiment of the present invention. FIG. 11 is a cross-sectional view of a negative electrode of one embodiment of the present invention. FIG. 12 is a cross-sectional view of a negative electrode of one embodiment of the present invention. FIG. 13 is a cross-sectional view of a flexible battery of one embodiment of the present invention. FIGS. 14A to 14C are cross-sectional views and top views of a flexible battery of one embodiment of the present invention. FIGS. 15A to 15D are cross-sectional views of a negative electrode of one embodiment of the present invention. FIGS. 16A to 16D are cross-sectional views of a negative electrode of one embodiment of the present invention. FIGS. 17A to 17D are cross-sectional views of a negative electrode of one embodiment of the present invention. FIGS. 18A and 18B are cross-sectional views of a flexible battery of one embodiment of the present invention. FIGS. 19A to 19E are cross-sectional views, etc., of an exterior body of one embodiment of the present invention. FIGS. 20A to 20C are cross-sectional views, etc., of an exterior body of one embodiment of the present invention. FIGS. 21A and 21B are cross-sectional views, etc., of an exterior body of one embodiment of the present invention. FIGS. 22A to 22E are cross-sectional views, etc., of an exterior body of one embodiment of the present invention. FIGS. 23A to 23E are cross-sectional views, etc., of an exterior body of one embodiment of the present invention. FIG. 24 is a cross-sectional view of an exterior body of one embodiment of the present invention. FIGS. 25A and 25B are top views of an exterior body of one embodiment of the present invention. FIGS. 26A to 26C are top views of an exterior body of one embodiment of the present invention. 27A to 27E are top views or cross-sectional views of a flexible battery of one embodiment of the present invention. 28A and 28B are cross-sectional views of an exterior body of one embodiment of the present invention. 29 is a flowchart illustrating a method for producing a positive electrode active material by coprecipitation according to one embodiment of the present invention.30A to 30C are a flowchart illustrating a method for manufacturing a positive electrode active material by a solid-phase method according to one embodiment of the present invention. FIGS. 31A and 31B are diagrams illustrating electronic devices of one embodiment of the present invention. FIGS. 32A and 32B are diagrams illustrating electronic devices of one embodiment of the present invention. FIGS. 33A to 33D are diagrams illustrating electronic devices of one embodiment of the present invention. FIGS. 34A to 34D are diagrams illustrating electronic devices of one embodiment of the present invention. FIGS. 35A to 35C are diagrams illustrating electronic devices of one embodiment of the present invention. FIGS. 36A to 36C are diagrams illustrating electronic devices of one embodiment of the present invention.

[0030] Hereinafter, examples of embodiments of the present invention will be described with reference to the drawings, etc. However, the present invention should not be construed as being limited to the following examples. The embodiments of the present invention can be modified within the scope of the spirit of the present invention.

[0031] In this specification, a flexible battery is a battery that has mobility, and specifically refers to a battery that can move with the moving housing when clamped in the housing.

[0032] Embodiment 1 In this embodiment, a flexible battery 100 according to one embodiment of the present invention will be described. The flexible battery 100 can move when a housing in which the battery is mounted is movable, and a lithium-ion battery (lithium-ion secondary battery) can be used as the battery. The flexible battery 100 according to one embodiment of the present invention can also be bent.

[0033] [Configuration Example 1] The cross-sectional view shown in FIG. 1A shows the flexible battery 100 in a straight state. The cross-sectional view shown in FIG. 1B shows the flexible battery 100 in a bent state. The flexible battery 100 of one embodiment of the present invention can alternate between the straight state shown in FIG. 1A and the bent state shown in FIG. 1B. When the flexible battery 100 is bent as shown in FIG. 1B, it has a curved portion, and therefore may be referred to as a battery having a curved portion, etc. Note that the bending position can be located in the center of the flexible battery 100, but the bending position can also be located elsewhere.

[0034] 1A and 1B , the flexible battery 100 has a negative electrode 101 and a positive electrode 131, and has a structure in which the negative electrode 101 and the positive electrode 131 are stacked (sometimes referred to as a stacked structure or an electrode with a stacked structure). In the flexible battery 100, the number of stacked negative electrodes 101 and the number of stacked positive electrodes 131 may be the same, or the number of stacked negative electrodes 101 may be different from the number of stacked positive electrodes 131. For example, the number of stacked negative electrodes 101 may be greater than the number of stacked positive electrodes 131.

[0035] 1A shows a case where the area of ​​the negative electrode 101 is equal to the area of ​​the positive electrode 131. In the flexible battery 100, the area of ​​the negative electrode 101 and the area of ​​the positive electrode 131 may be equal to each other, or the area of ​​the negative electrode 101 may be different from the area of ​​the positive electrode 131.

[0036] FIG. 2A shows a configuration in which the area of ​​the negative electrode 101 is larger than the area of ​​the positive electrode 131. FIG. 2B shows a configuration in which the area of ​​the negative electrode 101 is larger than the area of ​​the positive electrode 131, and one end of the negative electrode 101 and one end of the positive electrode 131 are aligned. That is, in the flexible battery 100 of one embodiment of the present invention, one end of the negative electrode 101 and one end of the positive electrode 131 may or may not be aligned. However, the current collectors protruding from the one end are welded to the negative electrodes 101 and further to the positive electrodes 131. When the area of ​​the negative electrode 101 is larger than the area of ​​the positive electrode 131 as shown in FIGS. 2A and 2B , it is possible to reduce the area of ​​the positive electrode 131 that does not face the negative electrode 101 when the flexible battery 100 is bent.

[0037] 1B, when the flexible battery 100 is bent while one end thereof is fixed, the laminated structure of the negative electrode 101 and the positive electrode 131 is maintained, but the position of the end of the negative electrode 101 at the other end of the flexible battery 100 is misaligned with the position of the end of the positive electrode 131. In Figures 2A and 2B as well, when the flexible battery 100 is bent while one end thereof is fixed, the position of the end of the negative electrode 101 at the other end of the flexible battery 100 is misaligned with the position of the end of the positive electrode 131, but the laminated structure of the negative electrode 101 and the positive electrode 131 is maintained.

[0038] 1A and the bent state shown in FIG. 1B alternately, the negative electrode 101 and the positive electrode 131 move in accordance with the above-described positional deviation. The same applies to the case where the straight state shown in FIG. 2A and the bent state shown in FIG. 2B alternately alternately. When the negative electrode 101 and the positive electrode 131 move in accordance with the above-described positional deviation, the adjacent negative electrode 101 and the positive electrode 131 may rub against each other, resulting in friction.

[0039] The flexible battery 100 of one embodiment of the present invention includes a carbon-containing material 105 located at least between adjacent negative electrodes 101 and positive electrodes 131 to reduce friction between the adjacent negative electrodes 101 and positive electrodes 131. Specifically, the flexible battery 100 of one embodiment of the present invention has a structure in which the carbon-containing material 105 encases the active material layer in the negative electrode 101 or the active material layer in the positive electrode 131. By encasing either of the active material layers with the carbon-containing material 105, friction between the negative electrode 101 and the positive electrode 131 can be reduced. Furthermore, the flexible battery 100 of one embodiment of the present invention preferably has a structure in which the carbon-containing material 105 encases the active material layers in the negative electrode 101 and the positive electrode 131. Furthermore, the flexible battery 100 including the carbon-containing material 105 can form a good electron conduction path even with a small amount of conductive material.

[0040] A graphene compound, graphene, or carbon fiber can be used as the carbon-containing material 105. The friction during movement can be suppressed by simply attaching a graphene compound, graphene, or carbon fiber to the active material layer. Graphene compounds and the like will be described later. The carbon-containing material 105 can exhibit electrical conductivity if it is, for example, a carbon material, and can also exhibit insulating properties depending on the proportion of oxygen and the like it contains.

[0041] The negative electrode 101 includes a current collector 102 (sometimes referred to as a negative electrode current collector) and an active material layer 103 (sometimes referred to as a negative electrode active material layer). The positive electrode 131 includes a current collector 132 (sometimes referred to as a positive electrode current collector) and an active material layer 133 (sometimes referred to as a positive electrode active material layer). Ordinal numbers may be assigned to distinguish the current collectors from each other.

[0042] If the carbon-containing material 105 exhibits conductivity, it is preferable to provide a separator in the flexible battery 100. Figure 3A shows a flexible battery 100 that has a separator 134, unlike Figures 1A to 2B. The separator 134 is preferably bag-shaped or cylindrical, and Figure 3A shows a positive electrode 131 in which an active material layer 133 is housed within the separator 134. When the separator 134 is bag-shaped or cylindrical, the positive electrode 131 does not protrude from the separator 134, making it possible to provide a flexible battery that is highly safe and durable.

[0043] 3A shows a case where the positive electrode 131 has a smaller area than the negative electrode 101 as in FIG. 2A or 2B , so the positive electrode 131 is housed in the separator 134. Of course, the negative electrode 101 may also be housed in the separator 134.

[0044] 3A, Fig. 3B shows a flexible battery 100 having a sheet-like separator 109. By providing the sheet-like separator 109, a flexible battery with high safety and reliability can be provided.

[0045] Depending on the conductivity of the carbon-containing material 105, it may be preferable to provide the flexible battery 100 with a separator.

[0046] Furthermore, when the carbon-containing material 105 exhibits insulating properties, the carbon-containing material 105 can function as a separator, which is preferable as it makes the flexible battery 100 unnecessary to use a separator.

[0047] <Negative Electrode> The structure of the negative electrode 101 will be described. Fig. 4A shows a cross-sectional view of the negative electrode 101, and Fig. 4B shows a top view of the negative electrode 101. The cross-sectional view in Fig. 4A corresponds to the cross section at the position indicated by the dotted line in Fig. 4B.

[0048] The negative electrode 101 has a current collector 102 and an active material layer 103. As shown in FIG. 4A , the active material layer 103 may be formed on two surfaces (one surface and the other surface) of the current collector 102. Forming the active material layer 103 on two surfaces is referred to as a double-sided formed structure or a double-sided coated structure. Although not shown in FIG. 4A , the active material layer 103 may be formed on either one surface or the other surface of the current collector 102. Forming the active material layer 103 on one surface is referred to as a single-sided formed structure or a single-sided coated structure.

[0049] As shown in FIGS. 1A to 4B , in the negative electrode 101, the current collector 102 and the active material layer 103 are wrapped with the carbon-containing material 105. In other words, the carbon-containing material 105 wraps the current collector 102 and the active material layer 103. With such a structure including the carbon-containing material 105, the flexible battery 100 of one embodiment of the present invention is easily movable when the battery 100 alternates between a straight state such as that shown in FIGS. 1A , 2A to 3B , and a bent state such as that shown in FIG. 1B . The carbon-containing material 105 serves as a buffer material that reduces friction, making the battery 100 more safe and durable. The carbon-containing material 105 may also be referred to as a buffer layer or a buffer film.

[0050] The carbon-containing material 105 is preferably flexible and easily deformable, and is expected to have increased mechanical strength in electrodes and the like in which the carbon-containing material 105 is disposed.

[0051] To reiterate, a graphene compound, graphene, or carbon fiber can be used as the carbon-containing material 105, and even if the graphene compound, graphene, or carbon fiber is merely attached to the active material layer, the friction during the movement described above can be suppressed.

[0052] The carbon-containing material 105 may simply be attached to the active material layer, but may also be disposed in the form of a layer or film on the negative electrode 101 in order to further reduce friction between adjacent negative and positive electrodes. A layer-like carbon-containing material may be referred to as a carbon-containing material layer, and a film-like carbon-containing material may be referred to as a carbon-containing material film. The thinner the carbon-containing material layer or carbon-containing material film, the more active material can be contained per volume, which is preferable, and the upper limit of the thickness is 100 μm or less, preferably 10 μm or less. If a distinction is made between a carbon-containing material layer and a carbon-containing material film, a carbon-containing material film may be one having an upper limit of thickness of 1 μm or less.

[0053] 5A shows the details of the negative electrode 101, specifically, the active material layer 103. The active material layer 103 includes an active material 104 (sometimes referred to as a negative electrode active material), a first conductive material 107a, and a second conductive material 107b. Although an example using two conductive materials is shown in this embodiment, one conductive material or three or more conductive materials may be used. The negative electrode 101 includes a current collector 102, and the current collector 102 also includes a region in which the active material 104 is embedded.

[0054] 5B shows an enlarged view of the active material layer 103. The active material layer 103 contains an active material 104. The material of the active material 104 will be described later, but it may be either a primary particle or a secondary particle. By pressing the negative electrode 101, the multiple active material particles 104 come into close contact with each other. The proportion of the active material per volume can be increased by pressing or the like.

[0055] 5B , the first conductive material 107a and the second conductive material 107b are preferably dispersed, and more preferably dispersed uniformly, inside the active material layer 103. However, the second conductive material 107b is a fine particle, and may have lower dispersibility than the first conductive material 107a.

[0056] 5B, the first conductive material 107a is schematically represented by a thick line, but the first conductive material 107a in a film form can be positioned so as to wrap around, cover, or stick to the surfaces of the active materials 104, which is preferable. The first conductive materials 107a can also be in surface contact with each other. The first conductive materials 107a in surface contact with each other may be positioned so as to wrap around, cover, or stick to the surfaces of the active materials 104.

[0057] The first conductive material 107a can be a graphene compound, graphene, or carbon fiber. A graphene compound will be described later; since it is used as a conductive material, it is a material that exhibits electrical conductivity. Furthermore, since a graphene compound has the thickness of a single layer or multiple layers of carbon molecules, it often takes the form of a very thin film and can be positioned so as to adhere to the surface of the active material 104. Since graphene has the thickness of multiple layers of carbon molecules, it is thin, but it can also have a rectangular shape. Carbon fiber can have a shape in which the fibers are entangled with each other. It should be noted that even graphene and carbon fiber can be positioned so as to come into contact with the surface of the active material 104 by pressing them.

[0058] The graphene compound used for the first conductive material 107a is in a state in which graphene compounds are bonded to each other, and this may be referred to as a graphene compound sheet or a graphene compound net. Depending on how the graphene compounds are bonded to each other, they may be arranged in a mesh-like shape, and this may be referred to as a mesh-like graphene compound sheet or a mesh-like graphene compound net. Such a graphene compound sheet may be used for the first conductive material 107a.

[0059] When a graphene compound sheet is used as the first conductive material 107a, the graphene compound sheet can cover the active material 104 and can also function as a binder. When the graphene compound sheet functions as a binder, the amount of binder in the negative electrode 101 can be reduced or the binder can be eliminated, thereby increasing the proportion of the active material per volume in the negative electrode 101.

[0060] 5C shows an enlarged view of the carbon-containing material 105, illustrating a case where a graphene compound sheet is used as the carbon-containing material 105. The graphene compound sheet is as described for the first conductive material 107a, and may have a plurality of planar graphene compounds 120 as shown in the enlarged view of FIG. 5C. Although the graphene compounds 120 are shown, the graphene compound sheet may also have graphene.

[0061] The length of one side of the graphene compound (also referred to as flake size) is 50 nm or more and 100 μm or less, preferably 800 nm or more and 20 μm or less. Therefore, a region 121 through which ions can pass exists between adjacent graphene compound sheets. Such a graphene compound sheet has excellent ion conductivity and is preferable as the carbon-containing material 105. Such a graphene compound sheet also allows an electrolyte, specifically an electrolyte solution, to penetrate into the graphene compound sheet via the region 121 through which ions can pass.

[0062] 5A , the graphene compound sheet can be provided as the carbon-containing material 105 so as to extend along the surface of the active material layer 103. Specifically, the graphene compound sheet can be provided as the carbon-containing material 105 so as to extend continuously along part of the surface of a plurality of active materials 104. This state may be referred to as the carbon-containing material 105 enveloping the active material layer or the active materials.

[0063] 5C illustrates the case of a graphene compound sheet, but a graphene sheet or graphene net in which graphene molecules are bonded together may also be used. The length of one side of the graphene (also referred to as flake size) is 50 nm to 100 μm, preferably 800 nm to 20 μm, so that a region through which ions can pass may exist between adjacent graphene molecules. Such a graphene sheet has excellent ion conductivity and is preferable as the carbon-containing material 105. A graphene sheet or graphene net may also be referred to as multilayer graphene based on its cross-sectional view.

[0064] The active material 104 is a material capable of undergoing charge-discharge reactions by inserting and extracting carrier ions. Lithium ions are preferably used as the carrier ions. Other than lithium ions, sodium ions, potassium ions, calcium ions, strontium ions, barium ions, beryllium ions, magnesium ions, or the like may also be used. Specific examples of active materials using lithium ions will be described later.

[0065] A granular material can be used as the active material 104. The term "granular" refers to an external shape having any surface area, including, for example, spherical (powder-like), plate-like, angular, columnar, needle-like, or scale-like shapes. In other words, a granular active material does not necessarily refer to a spherical shape, but includes the various external shapes described above. Furthermore, the active material layer 103 includes multiple active materials 104, but the shapes of the active materials 104 may be different from each other.

[0066] The active material 104 has a particle size distribution, and the median diameter (D50) is often used, and the median diameter (D50) of the active material 104 is, for example, 10 nm to 30 μm, preferably 100 nm to 20 μm, and more preferably 1 μm to 10 μm. A small median diameter (D50) is preferable because the negative electrode 101 can be easily bent as shown in FIG. 1B .

[0067] When the active material 104 is a secondary particle, the median diameter (D50) of the primary particles constituting the secondary particle is, for example, 10 nm to 1 μm, preferably 100 nm to 500 μm. A small median diameter (D50) is preferable because it makes it easier to bend the negative electrode 101 as shown in FIG. 1B .

[0068] 5A , in order for the carbon-containing material 105 to enclose the active material layer 103, the carbon-containing material 105 may be provided so as to conform to the shape of the active material 104 located on the surface of the active material layer 103. The carbon-containing material 105 has high flexibility, and therefore can be provided so as to conform to the shape of the active material 104.

[0069] If the expansion and contraction of the active material 104 due to charging and discharging of the battery is large, the active material 104 may fall off the current collector 102 with repeated charging and discharging. Furthermore, the active material 104 may fall off the current collector 102 when the battery is in operation. In the flexible battery 100 of one embodiment of the present invention, the carbon-containing material 105 is positioned so as to enclose the current collector 102 and the active material layer 103, and thus exerts a force to hold down the active material 104, thereby preventing the active material 104 from falling off the current collector 102. When the carbon-containing material 105 has a region in contact with the current collector 102, the force to hold down the active material 104 may be strengthened.

[0070] In order to efficiently encase the current collector 102 and the active material layer 103, a bag-shaped carbon-containing material 105 may be prepared. When the negative electrode 101 or the like is bent as shown in FIG. 1B , the current collector 102 and the active material layer 103 are unlikely to protrude from the side or bottom of the bag-shaped carbon-containing material 105, thereby improving safety or durability. Alternatively, a cylindrical carbon-containing material 105 may be prepared instead of the bag-shaped carbon-containing material 105. When the negative electrode 101 or the like is bent as shown in FIG. 1B , the current collector 102 and the active material layer 103 are unlikely to protrude from the side or bottom of the cylindrical carbon-containing material 105, thereby improving safety or durability.

[0071] Although not shown in FIG. 5A and other drawings, the active material layer 103 may contain an electrolyte. An electrolyte that is liquid at room temperature (25° C.) is also referred to as an electrolyte solution. The carbon-containing material 105 can be impregnated with the electrolyte solution. When a graphene compound sheet as shown in FIG. 5C is used for the carbon-containing material 105, the electrolyte solution can also penetrate between the graphene compounds 120.

[0072] 5, the active material layer 103 may contain a binder. In addition, since the active material layer can be wrapped with the carbon-containing material 105, the binder may not be necessary.

[0073] <Graphene Compound> Here, graphene compounds will be explained again. First, graphene will be explained. Graphene is a single atomic layer of carbon arranged, with π bonds between the carbon atoms. In other words, graphene refers to a substance that contains carbon, has a shape such as a sheet (also referred to as a plate), and has a two-dimensional structure formed by six-membered carbon rings. The two-dimensional structure formed by the six-membered carbon rings may be called a carbon sheet.

[0074] Furthermore, a stack of 2 to 100 graphene layers may be referred to as multilayer graphene. Graphene and multilayer graphene have, for example, a length of the longitudinal direction or major axis on a plane of 50 nm to 100 μm, or 800 nm to 50 μm.

[0075] Next, graphene compounds will be described. A compound having graphene or multilayer graphene as a basic skeleton is called a "graphene compound (also called a "graphene compound")." Other graphene compounds include graphene oxide, multilayer graphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, graphene quantum dots, and the like, which will be described later.

[0076] A graphene compound is, for example, a compound in which graphene or multilayer graphene is modified with an atom other than carbon or an atomic group having an atom other than carbon. Alternatively, the graphene or multilayer graphene may be a compound in which graphene or multilayer graphene is modified with an atomic group mainly composed of carbon, such as an alkyl group or an alkylene group. The atomic group modifying graphene or multilayer graphene may be referred to as a substituent, a functional group, a characteristic group, or the like. In this specification and the like, "modification" refers to the introduction of an atomic group having an atom other than carbon or an atomic group having an atom other than carbon into graphene, multilayer graphene, a graphene compound, or graphene oxide (described later) by a substitution reaction, an addition reaction, or other reaction. The front and back surfaces of graphene may be modified with different atoms or atomic groups. In multilayer graphene, each layer may be modified with different atoms or atomic groups.

[0077] A graphene compound refers to, for example, a compound that contains carbon, has a shape such as a sheet, and has a two-dimensional structure formed by six-membered carbon rings. The two-dimensional structure formed by six-membered carbon rings may be called a carbon sheet.

[0078] <Graphene oxide> An example of graphene modified with the above-mentioned atoms or atomic groups is graphene or multilayer graphene modified with oxygen or a functional group containing oxygen. Examples of the oxygen-containing functional group include an epoxy group, a carbonyl group such as a carboxyl group, a hydroxyl group, or a lactol group. A graphene compound modified with oxygen or a functional group containing oxygen may be referred to as graphene oxide. In this specification, graphene oxide also includes multilayer graphene oxide. Graphene oxide can exhibit insulating properties.

[0079] <Fluorine Termination> Furthermore, as the graphene compound, a material in which the edges of graphene are terminated with fluorine may be used.

[0080] <Method for Producing Graphene Oxide> Next, an example of a method for producing graphene oxide will be described. Graphene oxide can be obtained by oxidizing the above-mentioned graphene or multilayer graphene. Alternatively, graphene oxide can be obtained by separating the layers of graphite oxide. Graphite oxide can be obtained by oxidizing graphite. Here, graphene oxide may be further modified with the above-mentioned atoms or atomic groups.

[0081] Graphene oxide can be produced by various synthesis methods, such as the Hummers method, the modified Hummers method, or oxidation of graphite.

[0082] For example, the Hummers method and the modified Hummers method are techniques for forming graphite oxide by oxidizing graphite such as flake graphite. The graphite oxide thus formed is formed by oxidizing the graphite in places, resulting in the bonding of functional groups such as carbonyl groups, carboxyl groups, hydroxyl groups, and lactol groups. This impairs the crystallinity of the graphite and increases the distance between layers. Therefore, the layers can be easily separated by ultrasonic treatment or the like to obtain graphene oxide.

[0083] Here, an example of a method for producing graphene oxide using the modified Hummers method will be described. A sulfuric acid solution of potassium permanganate or the like is added to graphite powder to cause an oxidation reaction, forming a mixed solution containing graphite oxide. Graphite oxide contains functional groups such as epoxy groups, carbonyl groups, carboxyl groups, and hydroxyl groups due to the oxidation of carbon in graphite. Therefore, the interlayer distance of graphene oxide is longer than that of graphite. Next, ultrasonic vibration is applied to the mixed solution containing graphite oxide to cleave the graphite oxide with a long interlayer distance, allowing graphene oxide to be separated and forming a dispersion containing graphene oxide.

[0084] When graphene oxide is produced by the modified Hummers method, the obtained graphene oxide may contain elements such as sulfur and nitrogen.

[0085] The sulfur concentration in the graphene compound of one embodiment of the present invention is, for example, preferably 5% or less, more preferably 3% or less.

[0086] The graphene compound of one embodiment of the present invention may contain, for example, 10 ppm or more and 5% or less, or 100 ppm or more and 3% or less, or 0.1% or more and 3% or less of sulfur.

[0087] Here, the concentration of sulfur contained in the graphene compound can be evaluated using elemental analysis such as XPS, for example.

[0088] The graphene compound of one embodiment of the present invention may contain, for example, 0.1% to 3% nitrogen.

[0089] <Reduced Graphene Oxide> A compound obtained by reducing graphene oxide is sometimes called "RGO (Reduced Graphene Oxide)." Here, RGO may also be written as "rGO" as shown in Non-Patent Document 1. Note that in RGO, not all of the oxygen contained in graphene oxide is released, and some oxygen or atomic groups containing oxygen may remain bonded to carbon. For example, RGO may have a functional group such as an epoxy group, a carbonyl group such as a carboxyl group, or a hydroxyl group.

[0090] The reduced graphene oxide preferably has a portion having a carbon concentration of more than 80 atomic % and an oxygen concentration of 2 atomic % to 15 atomic %. By setting the carbon concentration and oxygen concentration in this range, the electrical conductivity of the reduced graphene oxide can be increased.

[0091] Furthermore, the reduced graphene oxide preferably has an intensity ratio G / D of the G band to the D band in the Raman spectrum of at least 1. Reduced graphene oxide having such an intensity ratio can have high electrical conductivity.

[0092] Note that the reduction of graphene oxide may be performed by, for example, heat treatment or by using a reducing agent.

[0093] Reduced graphene oxide refers to, for example, a material that contains carbon and oxygen, has a sheet-like shape, or the like, and has a two-dimensional structure formed of six-membered carbon rings.

[0094] <Pores> By reducing graphene oxide, pores can be formed in the graphene compound in some cases. The pores in the graphene compound can correspond to regions through which carrier ions, specifically lithium ions, can pass. The presence of such pores facilitates the insertion and desorption of carrier ions, thereby improving the rate characteristics of the battery. Holes formed in a part of the carbon sheet are sometimes called voids, defects, or gaps. In addition to carrier ions, it is also preferable that ions of alkali metals other than lithium, anions and cations used in the electrolyte, anions and cations contained in the electrolyte solution, etc., can pass through.

[0095] The graphene compound may have holes formed by a plurality of carbon atoms and one or more fluorine atoms. The plurality of carbon atoms are preferably bonded in a ring, and one or more of the ring-bonded carbon atoms are preferably terminated with the fluorine. Fluorine has a high electronegativity and is easily negatively charged. Positively charged lithium ions approaching each other cause an interaction, stabilizing energy and lowering the barrier energy for carrier ions, specifically lithium ions, to pass through the holes. Therefore, the presence of fluorine in the holes of the graphene compound allows carrier ions to pass easily through even small holes, and the graphene compound can have excellent conductivity.

[0096] <Multi-membered ring> In addition to the six-membered ring composed of carbon, the graphene compound may have a five-membered ring composed of carbon or a seven- or more-membered ring composed of carbon. Here, a region through which ions can pass may be generated near the seven- or more-membered ring. The region through which ions can pass can be regarded as the hole. One example of the ion is a carrier ion, specifically a lithium ion. Other examples of the above-mentioned ion include ions of alkali metals other than lithium, anions contained in the electrolyte, and cations.

[0097] 6A and 6B show an example of the structure of a graphene compound having holes.

[0098] 6A has a 22-membered ring, and each of the eight carbon atoms constituting the 22-membered ring is terminated with hydrogen. It can also be said that the graphene compound has a structure in which two connected six-membered rings are removed and the carbon atoms bonded to the removed six-membered rings are terminated with hydrogen.

[0099] 6B has a 22-membered ring, and of the carbon atoms constituting the 22-membered ring, 8 carbon atoms, 6 carbon atoms, and 2 carbon atoms are terminated with hydrogen and fluorine, respectively. It can also be said that the graphene compound has a structure in which two connected 6-membered rings are removed and the carbon atoms bonded to the removed 6-membered rings are terminated with hydrogen or fluorine.

[0100] When a graphene compound has holes, for example, it may be possible to observe a spectrum based on characteristics attributable to the holes by Raman spectroscopy mapping measurement. Furthermore, it may be possible to observe bonds and functional groups that constitute the holes by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Furthermore, it may be possible to analyze the vicinity of the holes, the periphery of the holes, etc. by TEM (transmission electron microscope) observation.

[0101] <Sheet-like graphene compound> The graphene compound may be in the form of a single sheet with a plurality of graphene compounds partially overlapping each other. Alternatively, a plurality of graphene compounds may be gathered together to form a sheet. The graphene compound has a planar shape, allowing for surface contact. Such a graphene compound may be referred to as a graphene compound sheet or a graphene compound net, as described above. The graphene compound sheet has, for example, a region having a thickness of 0.33 nm or more and 100 μm or less, more preferably 0.34 nm or more and 10 μm or less.

[0102] In a graphene compound sheet, for example, a region through which ions can pass may be generated between adjacent graphene compounds. Therefore, the graphene compound sheet may have excellent ion conductivity. Alternatively, the graphene compound sheet may easily adsorb ions. Again, one example of the ions is a carrier ion, specifically, a lithium ion. Further, other examples of the above-mentioned ions include ions of alkali metals other than lithium, anions contained in an electrolyte solution, and cations.

[0103] Furthermore, it is thought that the graphene compound sheet can be deformed when an external force is applied due to sliding between graphene compounds stacked on top of each other in a plane, and may be less susceptible to cracks or the like.

[0104] Such a graphene compound sheet may be modified with an atom other than carbon, an atomic group having an atom other than carbon, or an atomic group mainly containing carbon such as an alkyl group, etc. Furthermore, each of a plurality of layers of the graphene compound sheet may be modified with a different atom or atomic group.

[0105] <Conductivity> Graphene compounds can have high conductivity even when they are thin, and the surface contact can increase the contact area between graphene compounds or between a graphene compound and an active material, thereby efficiently forming a conductive path even when the amount per volume is small.

[0106] <Insulating Properties> A graphene compound can also be used as an insulator. For example, a graphene compound sheet can be used as a sheet-like insulator. Here, for example, graphene oxide may have higher insulating properties than a non-oxidized graphene compound. Furthermore, a graphene compound modified with an atomic group may have improved insulating properties depending on the type of the modified atomic group.

[0107] <Method for Producing Graphene Compound> A graphene compound can be produced by a spray-drying method, a coating method, or the like. In this embodiment, as an example, a case where a graphene compound sheet is produced by a spray-drying method using a graphene oxide dispersion as a raw material will be described. Note that the graphene oxide contained in the graphene oxide dispersion may be multilayer graphene oxide, and the graphene oxide dispersion may contain graphene oxide, or graphene oxide and multilayer graphene oxide.

[0108] The solvent used for the graphene oxide dispersion is preferably a polar solvent, such as one or a mixture of two or more selected from water, methanol, ethanol, acetone, tetrahydrofuran (THF), dimethylformamide (DMF), 1-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), ethylene glycol, diethylene glycol, and glycerin.

[0109] A graphene compound having graphene oxides can be obtained by forming a film of multiple graphene oxides on a substrate or plate using a spray-drying method. When multiple graphene compounds are stacked on top of each other during film formation, a graphene compound sheet can also be produced. The spray-drying method can control the film thickness of the graphene compound or graphene compound sheet by adjusting the film formation time, the concentration of the dispersion, or the like, and is therefore suitable for producing the graphene compound or graphene compound sheet of one embodiment of the present invention.

[0110] The graphene compound or graphene compound sheet can be peeled off from the substrate or plate. The substrate or plate can also be interpreted as the active material layer in Figures 1 to 5, etc., and the graphene compound or graphene compound sheet can also be formed on the active material layer. In this case, the graphene compound or graphene compound sheet does not need to be peeled off.

[0111] 7A shows a schematic diagram of a spray dryer 280. The spray dryer 280 has a chamber 281 and a nozzle 282. A dispersion liquid 284 is pumped up by a pump (not shown), and the dispersion liquid 284 is supplied to the nozzle 282 via a tube 283. The atomized dispersion liquid 284 is supplied to the chamber 281, and the dispersion liquid 284 is dried within the chamber 281.

[0112] The spray-drying apparatus 280 may have a heater 285 for heating the nozzle 282. The heater 285 may also heat a region of the chamber 281 that is close to the nozzle 282, such as a region 290 surrounded by a dashed line in FIG. 7A.

[0113] When a graphene oxide dispersion is used as the dispersion 284, the graphene oxide supplied from the graphene oxide dispersion becomes a graphene compound or a graphene compound sheet 222, and is formed into a film on the wall surface of the chamber 281. Furthermore, a portion of the graphene oxide supplied from the graphene oxide dispersion dries into a powder state in the chamber 281 and is collected from the chamber 281 into a collection container 286. Furthermore, a nozzle (not shown) may be connected to the collection container 286, and the graphene oxide may be collected through the nozzle. The collected graphene oxide can be reused as a graphene oxide dispersion.

[0114] The atmosphere inside the chamber 281 may be adjusted, and for example, the inside of the chamber 281 may be suctioned using an aspirator or the like through a path indicated by an arrow 288 in Fig. 7A . Furthermore, a nozzle (not shown) may be connected to the collection container 286, and graphene oxide may be collected through the nozzle.

[0115] A substrate or plate may be placed in the chamber 281, and a graphene compound or a graphene compound sheet may be formed thereon. The substrate or plate may be flat or curved. The substrate or plate may be interpreted as the active material layer in FIGS. 1 to 5 , etc., and the graphene compound or a graphene compound sheet may be formed thereon.

[0116] The substrate or plate may be placed parallel to the nozzle 282 or at a certain angle. A spray may be used instead of the nozzle 282. For example, it may be placed perpendicular to the nozzle 282. FIG. 7B shows an example in which a substrate 287 is placed perpendicular to the nozzle 282 and a graphene compound or graphene compound sheet is deposited on the substrate. For example, the nozzle 282 may be moved left and right as shown by the arrows during deposition, which can improve the in-plane thickness uniformity of the graphene compound or graphene compound sheet. To improve the in-plane thickness uniformity of the graphene compound or graphene compound sheet, the substrate 287 may be moved left and right as shown by the arrows. To further improve the in-plane thickness uniformity of the graphene compound or graphene compound sheet, both the nozzle 282 and the substrate 287 may be moved left and right as shown by the arrows.

[0117] The following shows an example of the interlayer distance of a graphene compound or a graphene compound sheet. The interlayer distance of the graphene compound or the graphene compound sheet may be, for example, 0.335 nm or more and 0.7 nm or less, or 0.34 nm or more and 0.6 nm or less, or 0.34 nm or more and 0.5 nm or less, or 0.34 nm or more and less than 0.44 nm. With this interlayer distance, carrier ions can move between the layers.

[0118] Methods for calculating the interlayer distance include TEM observation and evaluation using X-ray diffraction (XRD). TEM observation involves observation of a small area, for example, an area of ​​several nanometers to several micrometers square. In comparison, evaluation using XRD can sometimes evaluate average information over a wider area.

[0119] The graphene compound or graphene compound sheet thus prepared can exhibit insulating properties.

[0120] When preparing a graphene compound or a graphene compound sheet exhibiting electrical conductivity, it is preferable to perform a reduction treatment. By reducing the graphene compound or the graphene compound sheet, graphene oxide is reduced, and the electrical conductivity of the graphene compound or the graphene compound sheet can be increased.

[0121] Again, reduction treatment techniques include reduction by heat treatment, reduction using a reducing agent (sometimes referred to as chemical reduction), etc. The reduction temperature for chemical reduction is, for example, from room temperature to 100°C, preferably from 40°C to 70°C. The treatment time for chemical reduction is from 3 minutes to 10 hours, preferably from 30 minutes to 3 hours.

[0122] Reducing agents include ascorbic acid, hydrazine, dimethylhydrazine, hydroquinone, and sodium borohydride (NaBH ４ ), lithium aluminum hydride (LiAlH ４ For example, ascorbic acid and hydroquinone have a weaker reducing power than hydrazine or sodium borohydride, and therefore are safer and easier to use industrially.

[0123] Although it has been described that a polar solvent can be used as the solvent in the graphene oxide dispersion, the polar solvent is not particularly limited as long as it can dissolve the reducing agent.

[0124] The graphene oxide dispersion may contain a reducing agent. That is, the graphene oxide dispersion may contain a reducing solution containing a solvent and a reducing agent instead of a solvent. The reducing solution may be, for example, a mixture of ethanol and ascorbic acid, or a mixture of water, ascorbic acid, and lithium hydroxide.

[0125] In the graphene oxide dispersion, protons may be added to the graphene oxide by, for example, ascorbic acid, and then the H ２ O can be eliminated to reduce graphene oxide.

[0126] After the reduction treatment, washing may be performed. The washing may be performed using, for example, a solution listed as a solvent. The washing may be performed using a solution having the same solvent as the solvent contained in the reduction solution, or a solution having a solvent different from the solvent contained in the reduction solution. Furthermore, a drying step may be performed after the washing.

[0127] Next, thermal reduction will be described. The thermal reduction step may be carried out, for example, at a temperature of 50°C or higher but lower than 500°C, preferably 120°C or higher but 400°C or lower, for 1 hour or higher but 48 hours or lower, preferably 2 hours or higher but 20 hours or lower. The thermal reduction may be carried out under reduced pressure (vacuum) or in a reducing atmosphere, or may be carried out at atmospheric pressure. Furthermore, air, nitrogen, or other inert gases may be used as the reflux gas.

[0128] The graphene compound or graphene compound sheet thus prepared can exhibit electrical conductivity.

[0129] Fig. 8A shows a negative electrode 101 having carbon fibers 108 as the carbon-containing material 105 shown in Fig. 5A etc. Fig. 8B shows an enlarged view of the carbon fibers 108. The rest of the configuration is the same as Fig. 5A etc., so a description thereof will be omitted.

[0130] Furthermore, the carbon fiber 108 can have the property of being flexible and easily deformable, and can increase the mechanical strength of the negative electrode and the like.

[0131] Carbon fiber 108 has a specific surface area of ​​5 m ２ / g or more 60m ２ It is preferable to use a fibrous material having a fiber density of less than 1 / g. For example, mesophase pitch-based carbon fiber, isotropic pitch-based carbon fiber, or other carbon fiber can be used as the carbon fiber 108. Furthermore, carbon nanofibers or carbon nanotubes can be used as the carbon fiber 108. Carbon nanofibers or carbon nanotubes can be produced by, for example, vapor phase growth.

[0132] 8A , when the carbon fibers 108 wrap around the active material layer 103, the carbon fibers 108 are preferably provided so as to follow the shape of the active material 104 located on the surface of the active material layer 103. Because the carbon fibers 108 are highly flexible, they can be provided so as to follow the shape of the active material 104.

[0133] If the active material 104 expands and contracts significantly during charging and discharging of the battery, the active material 104 may fall off the current collector 102 with repeated charging and discharging. Furthermore, the active material 104 may fall off the current collector 102 when the battery is in operation. In the flexible battery 100 of one embodiment of the present invention, the carbon fibers 108 are positioned so as to wrap around the current collector 102 and the active material layer 103, and thus exert a force to hold down the active material 104, thereby preventing the active material 104 from falling off the current collector 102. When the carbon fibers 108 have a region in contact with the current collector 102, the force to hold down the active material 104 may be strengthened.

[0134] Although not shown in Figure 8A etc., the active material layer 103 contains a binder and an electrolyte. A liquid electrolyte is also referred to as an electrolyte solution. The carbon fibers 108 can be impregnated with the electrolyte solution, and it is preferable that the electrolyte be dispersed in the carbon fibers 108 so that carrier ions can pass through.

[0135] The carbon-containing material 105 shown in Fig. 5A and the like and the carbon fiber 108 shown in Fig. 8 and the like may be conductive. Graphene or the like can be selected as the carbon-containing material 105 having conductivity.

[0136] 5 and the like may have insulating properties. Graphene oxide, reduced graphene oxide, or the like may be selected as the conductive carbon-containing material 105. The carbon-containing material 105 may have insulating properties sufficient to prevent short-circuiting between the positive electrode and the negative electrode, in which case a separator may be unnecessary. The insulating carbon-containing material 105 may be selected from the materials described below, and a material with a high oxygen content is preferred.

[0137] The carbon-containing material 105 shown in FIG. 5 and the carbon fibers 108 shown in FIG. 8 may be mixed with a polymer material. The insulating properties can be determined by the proportion of the polymer material. Examples of the polymer material that can be used include polypropylene (PP), polyethylene (PE), polybutene, nylon, polyester, polysulfone, polyacrylonitrile, polyvinylidene fluoride, and tetrafluoroethylene. Polymer materials are preferred because they can provide insulating properties without impairing the flexibility of the carbon-containing material 105 and the carbon fibers 108.

[0138] 9A and 9B show details of the positive electrode 131. Fig. 9A shows a cross-sectional view of the positive electrode 131, and Fig. 9B shows a top view of the positive electrode 131. The cross-sectional view in Fig. 9A corresponds to the cross section at the position indicated by the dotted line in Fig. 9B.

[0139] The positive electrode 131 has a current collector 132 and an active material layer 133. As shown in FIG. 9A , the active material layer 133 may be formed on two surfaces (one surface and the other surface) of the current collector 132. Again, forming the active material layer 133 on two surfaces is referred to as a double-sided formed structure or a double-sided coated structure. Although not shown in FIG. 9A , the active material layer 133 may be formed on either one surface or the other surface of the current collector 132. Again, forming the active material layer 133 on one surface is referred to as a single-sided formed structure or a single-sided coated structure.

[0140] 1A to 3B and 9A and 9B , in the positive electrode 131, the current collector 132 and the active material layer 133 are wrapped with the carbon-containing material 105. In other words, the carbon-containing material 105 wraps the current collector 132 and the active material layer 133. With such a structure including the carbon-containing material 105, the flexible battery 100 of one embodiment of the present invention becomes more mobile when the states of FIGS. 1A and 1B are repeated because the carbon-containing material 105 serves as a buffer material that reduces friction.

[0141] Furthermore, the material 105 containing carbon can have the property of being flexible and easily deformable, and can increase the mechanical strength of the positive electrode and the like.

[0142] 5, the positive electrode 131 also includes an active material, a conductive material, a binder, an electrolyte solution, etc. Also, similar to the configuration shown in Fig. 8, the positive electrode 131 may use carbon fiber 108 instead of the carbon-containing material 105.

[0143] Furthermore, the carbon fiber 108 can have the property of being flexible and easily deformable, and can increase the mechanical strength of the positive electrode and the like.

[0144] [Configuration Example 2] As Configuration Example 2, a flexible battery 200 will be described in which the active material layer has a single-sided formed structure or a single-sided coated structure, and a carbon-containing material is provided between overlapping current collectors, unlike Configuration Example 1. The cross-sectional view shown in Figure 10 shows the flexible battery 200 in a straight state, and the flexible battery 200 of one embodiment of the present invention can alternate between the straight state shown in Figure 10 and a bent state.

[0145] The negative electrode 201 includes a current collector 102 and an active material layer 103, similar to the negative electrode 101 of Configuration Example 1 described above. The active material layer 103 has a single-sided structure or a single-sided coated structure, and is therefore formed on one surface of the current collector 102. Another current collector 102 and active material layer 103 are prepared, and a carbon-containing material 105 is provided between the two stacked current collectors 102. Such a negative electrode 201 is prepared.

[0146] The positive electrode 231 has a current collector 132 and an active material layer 133, similar to the positive electrode 131 of Configuration Example 1 described above. The active material layer 133 has a single-sided formed structure or a single-sided coated structure, and is therefore formed on one surface of the current collector 132. Another current collector 132 and active material layer 133 are prepared, and a carbon-containing material 105 is provided between the two stacked current collectors 132. Such a positive electrode 231 is prepared.

[0147] A separator 221 is disposed between the negative electrode 201 and the positive electrode 231 .

[0148] In the case of Configuration Example 2, the carbon-containing material 105 is positioned between two current collectors. With such a configuration including the carbon-containing material 105, the flexible battery 200 of one embodiment of the present invention becomes more mobile when repeatedly switching between the state shown in FIG. 10 and a bent state because the carbon-containing material 105 serves as a so-called buffer material that reduces friction. That is, the carbon-containing material 105 is sometimes referred to as a buffer layer. Furthermore, the carbon-containing material 105 positioned between the two current collectors may exhibit insulating properties, but preferably exhibits conductivity.

[0149] Fig. 11 shows details of the negative electrode 201, specifically the active material layer 103 and the like. The active material layer 103 in Fig. 11 is similar to the active material layer 103 and the like shown in Fig. 5, but in the negative electrode 201, a carbon-containing material 105 is located between two current collectors 102. Although not shown in Fig. 11, the active material layer 103 has a binder and an electrolyte, as in Fig. 5, and an electrolytic solution may be used as the electrolyte. The carbon-containing material 105 located between the two current collectors 102 does not need to be impregnated with an electrolytic solution, and does not need to have pores through which carrier ions can pass.

[0150] FIG. 12 shows a configuration of the negative electrode 101 having carbon fibers 108 instead of the carbon-containing material 105 shown in FIG. 11 and the like. The other configurations are similar to those in FIG. 11 , and therefore description thereof is omitted. With such a configuration including carbon fibers 108, when the flexible battery 200 of one embodiment of the present invention is repeatedly bent and reversibly shifted between the state shown in FIG. 12 and another bent state, the carbon fibers 108 act as a so-called buffer material that reduces friction, making the battery more mobile. In other words, the carbon fibers 108 are sometimes referred to as a buffer layer. Furthermore, the carbon fibers 108 located between the two current collectors may be insulating, but are preferably conductive.

[0151] A flexible battery including a graphene compound, carbon fiber, or the like as in this embodiment is preferable because of its high safety and durability.

[0152] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0153] Embodiment 2 In this embodiment, a flexible battery 300 of one embodiment of the present invention will be described.

[0154] The flexible battery 300 has a new current collector that can be applied to the flexible batteries shown in Configuration Example 1 and Configuration Example 2. As shown in FIG. 13 , when the flexible battery 300 is bent, the current collector 302 has a straight region and a curved region. In the current collector 302, the first current collector 302a located in the straight region and the second current collector 302b located in the curved region are preferably made of different materials. For example, the second current collector 302b is preferably formed using a material that is more flexible than the first current collector 302a, and the graphene compound shown in the above embodiment may be used.

[0155] 14A shows a straightened flexible battery 300. The flexible battery 300 has a structure in which a negative electrode 301 and a positive electrode 331 are stacked, similar to the above-described embodiment.

[0156] The negative electrode 301 includes a current collector 302. The current collector 302 includes a first current collector 302a and a second current collector 302b. The second current collector 302b is disposed so as to overlap with a curved region. For example, the graphene compound described in the above embodiment mode may be used for the second current collector 302b. The other configurations of the negative electrode 301 are similar to those of the above embodiment mode.

[0157] The positive electrode 331 includes a current collector 332. The current collector 332 includes a first current collector 322a and a second current collector 322b. The second current collector 322b is disposed so as to overlap with a curved region. For example, the graphene compound described in the above embodiment mode may be used for the second current collector 322b. The other configurations of the positive electrode 331 are similar to those of the above embodiment mode.

[0158] 14B shows a top view of the negative electrode 301. As described above, the negative electrode 301 has a current collector 302 and an active material layer 103, with the active material layer 103 located above the current collector 302. A second current collector 302b overlaps the bending region of the flexible battery 300, and the position of the second current collector 302b is indicated by a dashed line in FIG. 14B. The second current collector 302b overlapping the bending region may be selectively formed so as to extend in a direction parallel to the short side of the current collector 302.

[0159] Figure 14C shows a cross-sectional view of the negative electrode 301. The cross-sectional view of Figure 14C corresponds to the cross section taken along the X1-X2 line indicated by the dashed dotted line in Figure 14B. As described above, the negative electrode 301 has a current collector 302 and an active material layer 103, with the active material layer 103 located above the current collector 302. The current collector 302 has a second current collector 302b that overlaps the curved region of the flexible battery 300 and a first current collector 302a that overlaps the straight region. It is preferable that the first current collector 302a be made of a different current collector material from that of the second current collector 302b.

[0160] Next, a manufacturing process of the negative electrode 301 corresponding to the cross-sectional view of FIG. 14C will be described with reference to FIGS. 15A to 15D. As shown in FIG. 15A, an active material layer 103 is formed on a current collector 302. The active material layer 103 is obtained by applying a slurry containing an active material and the like onto the current collector 302 and drying it. Then, as shown in FIG. 15B, an opening 303 is formed in the current collector 302 corresponding to the bending region. Then, as shown in FIG. 15C, a new current collector to become the second current collector 302b is formed in the opening 303. It is preferable to align the surface of the second current collector 302b with the surface of the current collector 302. As shown in FIG. 15D, the new current collector in the unnecessary region is removed to obtain the current collector 302 having the first current collector 302a and the second current collector 302b.

[0161] 16A shows a straightened flexible battery 300. The flexible battery 300 has a structure in which a negative electrode 301 and a positive electrode 331 are stacked, similar to the above-described embodiment.

[0162] The negative electrode 301 has a current collector 302, and the current collector 302 has a third current collector 302c that overlaps the curved region. In this structure, unlike the above-described structure example 3, the third current collector 302c is formed in a region other than the opening. Since the third current collector 302c is formed from a highly flexible material, it can be formed in a region other than the opening. Furthermore, the third current collector 302c has a region that is in contact with the carbon-containing material 105, and the carbon-containing material 105 is preferable because it has high adhesion to the third current collector 302c.

[0163] The positive electrode 331 has a current collector 332, and the current collector 332 has a third current collector 332c located in a bending region. In this structure, unlike the above-described structure example 3, the third current collector 332c is formed in a region other than the opening. Because the third current collector 332c is formed from a highly flexible material, it can be formed in a region other than the opening. Furthermore, the third current collector 332c has a region in contact with the carbon-containing material 105, and the carbon-containing material 105 is preferable because it has high adhesion to the third current collector 332c.

[0164] 16B to 16D show the steps of fabricating a negative electrode 301. As shown in FIG. 16B, an active material layer 103 is formed on a current collector 302. The active material layer 103 is obtained by applying a slurry containing an active material and the like onto the current collector 302 and drying it. Thereafter, as shown in FIG. 16C, an opening 303 is formed in the current collector 302 corresponding to the bending region. Then, as shown in FIG. 16D, a new current collector to become a third current collector 302c is formed so as to overlap at least the opening 303. A portion of the current collector 302 remains, and this will be referred to as a first current collector 302a.

[0165] This process does not include the step of removing the current collector as shown in Fig. 15D, and therefore the number of steps can be reduced.

[0166] 17A shows a straightened flexible battery 300. The flexible battery 300 has a structure in which a negative electrode 301 and a positive electrode 331 are stacked, similar to the above-described embodiment.

[0167] The negative electrode 301 has a current collector 302, and a fourth current collector 302d is formed over the entire negative electrode 301, including the curved region. In the configuration example 5, unlike the configuration examples 3 and 4, a fourth current collector 302d is provided as the current collector 302.

[0168] The positive electrode 331 has a current collector 332, and like the negative electrode, a fourth current collector 332d is formed over the entire surface including the curved region. In Configuration Example 5, unlike Configuration Examples 3 and 4, a fourth current collector 332d is provided as the current collector 322.

[0169] 17B to 17D show the steps of fabricating a negative electrode 301. As shown in FIG. 17B, an active material layer 103 is formed on a current collector 302. The active material layer 103 is obtained by coating a slurry containing an active material and the like on the current collector 302 and drying it. Thereafter, as shown in FIG. 17C, the current collector 302 is removed so that the active material layer 103 is exposed. Then, as shown in FIG. 17D, a new current collector to become a fourth current collector 302d is formed so as to cover the exposed active material layer 103. A portion of the current collector 302 remains, and this is referred to as a first current collector 302a.

[0170] [Configuration Example 6] The cross-sectional view shown in Figure 18A shows the flexible battery 300 in a straightened state. The flexible battery 300 has a structure in which a negative electrode 301 and a positive electrode 331 are stacked, as in the above-described embodiment. As in Configuration Example 3, second current collectors 302b are formed in the bending region, and the area of ​​the second current collectors 302b located on the outer side is larger than that of the second current collectors 302b located on the inner side in the bent state. In other words, the area of ​​the openings 303 located on the outer side is larger than that of the openings located on the inner side. The area may be expressed using the width in a cross-sectional view.

[0171] Although the above description has been given based on Configuration Example 3, in Configuration Example 4 as well, the area of ​​the openings 303 located on the outer side is made larger than that of the openings 303 located on the inner side. The area may be expressed using the width in a cross-sectional view.

[0172] 18B shows the flexible battery 300 in a straightened state. The flexible battery 300 has a structure in which the negative electrode 301 and the positive electrode 331 are stacked, as in the above-described embodiment. As in Configuration Example 3, a second current collector 302b is formed in the bending region, and the position of the opening 303 is shifted from the one located on the outside to the one located on the inside in the bent state.

[0173] Although the above description has been given based on the third configuration example, in the fourth configuration example as well, the positions of the openings 303 can be shifted from those positioned on the outside toward those positioned on the inside.

[0174] In the present embodiment, the new current collector is made of a different material from the other current collectors in the bending region. A flexible battery 300 having such a configuration is highly mobile and is therefore preferable.

[0175] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0176] (Embodiment 3) In this embodiment, a configuration example of an exterior body of a flexible battery will be described. The exterior body can be made of a metal material such as aluminum and / or a resin material. These materials may be laminated, for example, a three-layer exterior body may be formed by providing a thin metal film with excellent flexibility, such as aluminum, stainless steel, copper, or nickel, on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and then providing an insulating synthetic resin film, such as a polyamide-based resin or a polyester-based resin, on the thin metal film. The insulating synthetic resin film may be used on the outer surface of the exterior body.

[0177] The surface of the exterior body may be corrugated. A corrugated shape includes a shape with unevenness on the surface, and the protrusions may be continuous in one direction. It is more preferable that the intervals between successive protrusions are periodic, and it is even more preferable that the heights of the successive protrusions are uniform. When the flexible battery is bent, an exterior body having such a corrugated shape can deform so that the period and height of the protrusions change, thereby alleviating bending stress and preventing damage to the exterior body.

[0178] When the flexible battery is bent, it is preferable that one side of the exterior body to which the tab or the like is connected is fixed, and on the other side, specifically the side opposite to that side, the ends of the laminated electrodes are shifted. In other words, the laminated electrodes bend using the position of the tab or the like as a fixed point and fulcrum, and the corrugated exterior body can deform to follow this.

[0179] Furthermore, it is preferable to provide a space between the edge of the laminated electrode and the inner wall of the exterior body, specifically inside the exterior body, on one side of the exterior body corresponding to the position where the edge of the laminated electrode is shifted. This space allows the laminated battery to shift when the flexible battery is bent, preventing the edge of the laminated electrode from contacting the inner wall of the exterior body. This space prevents the edge of the laminated electrode from contacting the inner wall of the exterior body, even when the thickness of the laminated electrode is large, thereby preventing damage to the exterior body. For example, even when the thickness of the laminated electrode is greater than 400 μm, 500 μm or more, or 1 mm or more, the flexible battery can be safely bent and stretched. Furthermore, the space can prevent damage to the exterior and other components even when the thickness of the laminated electrode is extremely thin, from 1 μm to 400 μm.

[0180] In the flexible battery of one embodiment of the present invention, the thickness of the electrode having a stacked structure is not limited; however, the thickness may be determined according to the capacity required for an electronic device incorporating the flexible battery or the shape of the mounting area.

[0181] In the flexible battery of one embodiment of the present invention, the thickness of the negative electrode or positive electrode is, for example, 10 mm or less, preferably 5 mm or less, more preferably 4 mm or less, and still more preferably 3 mm or less.

[0182] Furthermore, in order to increase the space inside the exterior body, it is preferable that the positions of the convexities on the surface of the exterior body located above the laminated electrode and the back surface of the exterior body located below the laminated electrode are offset. Specifically, the positions of the convexities on the surface of the exterior body located above the laminated electrode and the convexities on the back surface of the exterior body located below the laminated electrode are formed so as not to overlap, i.e., to be offset. Note that the convexities on the back surface of the exterior body refer to the region protruding on the side opposite the laminated electrode. Because the convexities have periodicity, the above offset can be expressed as a 180-degree phase shift. Such a corrugated exterior body is preferable because it allows for the formation of a space at the position where the distance between the laminated electrode and the exterior body is longest.

[0183] In one aspect of the present invention, the laminated electrode can be sandwiched between two exterior bodies folded in half. When folding the exterior body in half, it is preferable to stagger the convex phases as described above. It is preferable for the convex phases to be shifted by 180 degrees. Pressure and heat can be applied to the folds of the exterior body to flatten them.

[0184] More specific configuration examples and manufacturing method examples will be described below with reference to the drawings.

[0185] [Configuration Example 8] Fig. 19A is a top view of the flexible battery 10 exemplified below. Fig. 19B is a view from the direction indicated by the outline arrow in Fig. 19A. Figs. 19C, 19D, and 19E are schematic cross-sectional views taken along the cutting lines A1-A2, B1-B2, and C1-C2 in Fig. 19A, respectively.

[0186] 19A to 19D, the flexible battery 10 has an exterior body 11 and a stacked battery 12 housed inside the exterior body 11. As shown in Fig. 19A, the flexible battery 10 has current collectors 13a and 13b that are electrically connected to the stacked battery 12 and extend outside the exterior body 11. In addition to the stacked battery 12, an electrolyte is sealed inside the exterior body 11.

[0187] As shown in Figures 19A, 19C, and 19D, the exterior body 11 has a corrugated shape and is folded in two to sandwich the stacked batteries 12. The exterior body 11 has a pair of portions 31 that overlap the stacked batteries 12, a folded portion 32, and a pair of joints 33 and 34. The pair of joints 33 are strip-shaped portions that extend approximately perpendicular to the folded portion 32 and are provided with the portion 31 in between. The joints 34 are strip-shaped portions located on the opposite side of the folded portion 32 with the portion 31 in between. The portion 31 can also be described as the area surrounded by the folded portion 32, the pair of joints 33, and the joints 34. Here, Figures 19A, 19C, etc. show an example in which the joints 34 sandwich portions of the current collectors 13a and 13b.

[0188] Portion 31 of exterior body 11 has a wave shape in which ridge lines 21 and valley lines 22 are alternately repeated. In Fig. 19A , ridge lines 21 connecting the peaks of convex portions are shown by dashed lines, and valley lines 22 connecting the bottoms of valley portions are shown by broken lines, and in Figs. 19C and 19D , some of ridge lines 21 are circled, and some of valley lines 22 are also circled. In other words, at least the surface of portion 31 has a wave shape in which concave and convex portions are repeated in the extension direction of a pair of joints 33.

[0189] In addition, in a plan view, the length of the joint 33 in the extension direction is longer than the length in the direction parallel to the extension direction of the joint 33. As shown in Fig. 19A, with respect to a line connecting the ends of the pair of joints 33 on the folding portion 32 side, the part of the folding portion 32 located closest to the joint 34 is located a distance L1 toward the joint 34.

[0190] The stacked battery 12 has a configuration in which at least positive electrodes and negative electrodes are alternately stacked. The stacked battery 12 may also be referred to as an electrode stack. A separator may be provided between the positive electrode and the negative electrode. Here, the greater the number of stacked layers in the stacked battery 12, the greater the capacity of the flexible battery 10. For details of the stacked battery 12, please refer to the above embodiment.

[0191] The thickness of the laminated battery 12 is, for example, 500 μm to 9 mm, preferably 400 μm to 3 mm, more preferably 200 μm to 2 mm, and typically about 1.5 mm.

[0192] 19A, 19C, and 19D, a space 25 is formed inside the exterior housing 11 between the end of the stacked battery 12 and the folded portion 32. Here, the length of the space 25 in a direction parallel to the extension direction of the joint 33 is defined as distance d0. Distance d0 can also be said to be the distance between the end of the stacked battery 12 and the inner surface of the exterior housing 11 located at the folded portion 32.

[0193] Furthermore, the joint 34 joins the exterior body 11 and the current collector 13a (and current collector 13b) extending inside and outside the exterior body 11. Therefore, the laminated battery 12 is fixed in a position relative to the exterior body 11. The current collector 13a is one of the negative electrode current collector and the positive electrode current collector of the laminated battery 12, and the current collector 13b is the other of the negative electrode current collector and the positive electrode current collector. Note that the one and the other are examples and may be interpreted differently. Furthermore, tabs made of metal foil or the like may be disposed instead of the current collectors 13a and 13b. The exterior body 11 and the tab are joined at the joint 34, and the laminated battery 12 is fixed to the exterior body 11.

[0194] 19A, 19C, and 19D, it is preferable that the portion 31 of the exterior body 11 has a region in which the period of the convexities becomes longer and the height of the convexities becomes smaller closer to the bent portion 32. The flexible battery 10 is manufactured to have such an exterior body, and a space 25 is formed inside the exterior body 11.

[0195] 19C and 19D, the pair of portions 31 that overlap the stacked battery 12 should be positioned so that the convex portions are 180 degrees out of phase with each other. In other words, the exterior body 11 should be folded so that the stacked battery 12 is sandwiched between the ridge lines 21 and the valley lines 22. This allows a large space 25 to be obtained.

[0196] [Regarding Spaces] Next, the shape of the battery having the spaces 25 formed therein when bent will be described.

[0197] FIG. 20A is a schematic cross-sectional view showing a simplified portion of the configuration of the flexible battery 10.

[0198] Here, the pair of portions 31 of the exterior body 11 are distinguished and denoted as portions 31a and 31b, respectively. Similarly, the ridge lines of each portion are distinguished and denoted as ridge lines 21a and 21b, and the valley lines of each portion are distinguished and denoted as valley lines 22a and 22b.

[0199] 20A , the stacked battery 12 has a configuration in which five electrodes 43 are stacked. The electrodes 43 correspond to the negative and positive electrodes in the above embodiment. The stacked battery 12 is fixed to the exterior body 11 at the joints 34.

[0200] A space 25 is provided inside the exterior body 11 near the bent portion 32. Here, the distance between one end of the electrode 43 and the inner wall of the exterior body 11 when the exterior body 11 is not bent is defined as a distance d0.

[0201] The neutral plane of the flexible battery 10 is defined as neutral plane C. Here, neutral plane C is assumed to coincide with the neutral plane of the central electrode 43 among the five electrodes 43 of the stacked battery 12.

[0202] 20B is a schematic cross-sectional view of the flexible battery 10 when it is bent into an arc shape around point O. Here, the flexible battery 10 is bent so that the portion 31a faces outward and the portion 31b faces inward.

[0203] As shown in Figure 20B, the outer portion 31a deforms so that the height of the convexities becomes smaller and the period of the convexities becomes longer. That is, the distance between the ridge lines 21a and the distance between the valley lines 22b of the outer portion 31a become wider. On the other hand, the inner portion 31b deforms so that the height of the convexities becomes larger and the period of the convexities becomes shorter. That is, the distance between the ridge lines 21b and the distance between the valley lines 22b of the inner portion 31b after bending become narrower. By deforming the portions 31a and 31b in this way, the stress applied to the exterior body 11 is alleviated, and the flexible battery 10 can be bent without damaging the exterior body 11.

[0204] As shown in Figure 20B, the multiple electrodes 43 deform so as to be misaligned relative to one another. This relieves the stress on the stacked battery 12, allowing the flexible battery 10 to bend without damaging the stacked battery 12. By making the thickness of the electrodes 43 sufficiently small relative to the radius of curvature of the bend, the stress on each electrode 43 itself can be reduced. Note that Figure 20B shows the electrodes 43 themselves as not stretching when bent.

[0205] Of the multiple electrodes 43, those located outside the neutral plane C have one end shifted toward the joint 34. On the other hand, those electrodes 43 located inside the neutral plane C have one end shifted toward the bent portion 32. Here, the distance between the end of the innermost electrode 43 on the bent portion 32 side and the inner wall of the exterior body 11 is reduced from distance d0 to distance d1 by bending. Here, the relative amount of shift between the electrode 43 located on the neutral plane C and the innermost electrode 43 is defined as distance d2. Distance d1 is equal to the value obtained by subtracting distance d2 from distance d0.

[0206] If the distance d0 before bending is smaller than the distance d2 after bending, the electrode 43 located inside the neutral plane C of the laminated battery 12 will come into contact with the inner wall of the exterior body 11. Therefore, the necessary distance d0 will be considered below.

[0207] The following explanation will be made using Figure 20C. In Figure 20C, a curve corresponding to the neutral plane C is shown by a dashed line, and a curve corresponding to the innermost surface of the stacked battery 12 is shown by a solid line as curve B. Furthermore, the arc angle of curve C is set to θ, and the arc angle of curve B is set to θ + Δθ.

[0208] Curve C has a radius r ０ The curve B is an arc of radius r １ It is an arc of radius r ０ and radius r １ The difference between these two is defined as t. Here, t is equal to half the thickness of the stacked battery 12. The arc lengths of curves C and B are equal.

[0209] From the above relationship, the distance d2, which is the deviation of the curve B from the end of the curve C, can be calculated as follows:

[0210]

[0211] In other words, the distance d2 can be estimated from the thickness of the stacked battery 12 and the bending angle, and is not dependent on the length of the stacked battery 12 or the radius of curvature of the bend.

[0212] As described above, by making the distance d0 in the space 25 greater than or equal to the distance d2, it is possible to prevent contact between the stacked battery 12 and the exterior body 11 when the flexible battery 10 is bent. Therefore, when a flexible battery 10 having a stacked battery 12 with a thickness of 2t is bent for use, if the maximum angle is angle θ, then the distance d0 between the stacked battery 12 and the inner wall of the exterior body 11 in the space 25 should be set to a value greater than or equal to t × θ.

[0213] For example, when the battery is bent at 30 degrees for use, the distance d0 of the space 25 should be set to πt / 6 or more. Similarly, when the battery is bent at 60 degrees for use, d0 should be set to πt / 3 or more. When the battery is bent at 90 degrees for use, d0 should be set to πt / 2 or more. When the battery is bent at 180 degrees for use, d0 should be set to πt or more.

[0214] For example, if the flexible battery 10 is not used for applications such as winding, the maximum expected bending angle of the flexible battery 10 can be 180 degrees. Therefore, in such applications, if the distance d0 is set to a length equal to or greater than πt, preferably greater than πt, the flexible battery 10 can be used in any device. For example, when the flexible battery 10 is used by bending it in two, the flexible battery 10 can be incorporated into various electronic devices that use the flexible battery 10 bent in a V-shape or U-shape.

[0215] Furthermore, for example, when the flexible battery 10 is wound around a cylindrical shape, the distance d0 of the space 25 may be set to 2πt or more to accommodate 360-degree bending. When the flexible battery 10 is wound around more than one circumference, the distance d0 of the space 25 may be set to an appropriate value accordingly. When the flexible battery 10 is deformed into an accordion-like shape, the distance d0 of the space 25 may be set to an appropriate value depending on the direction and angle of the bending portion of the flexible battery 10 and the number of bending portions.

[0216] The above is the description of the space 25.

[0217] [Example of Manufacturing Method] An example of a method for manufacturing the flexible battery 10 will be described below.

[0218] First, a flexible film that will become the exterior body 11 is prepared.

[0219] It is preferable to use a material with high water resistance and gas resistance for the film. It is also preferable to use a laminate film in which a metal film and an insulating film are laminated as the film used as the exterior body. Metals or alloys that can be used as metal foils, such as aluminum, stainless steel, nickel steel, gold, silver, copper, titanium, chromium, iron, tin, tantalum, niobium, molybdenum, zirconium, and zinc, can be used as the metal film. Furthermore, the insulating film can be a single-layer film selected from a plastic film made of an organic material, a hybrid material film containing an organic material (such as an organic resin or fiber) and an inorganic material (such as a ceramic), or a carbon-containing inorganic film (such as a carbon film or graphite film), or a laminate film made of a plurality of these. Metal films are easy to emboss, and forming protrusions by embossing increases the surface area of ​​the film exposed to the outside air, resulting in excellent heat dissipation.

[0220] Next, the flexible film is subjected to processing such as embossing to form the exterior body 11 having a corrugated shape.

[0221] The convex and concave portions of the film can be formed by press processing (e.g., embossing). The convex and concave portions formed in the film by embossing form a closed space with a variable volume, with the film serving as part of the wall of the sealing structure. This closed space can also be said to be formed when the film has a bellows structure. Furthermore, a sealing structure using a film has waterproof and dustproof effects. Furthermore, the method is not limited to embossing, which is a type of press processing, but may also be a method of forming a relief on part of the film. Furthermore, a combination of these methods, for example, embossing and another press processing, may be performed on a single film. Furthermore, a single film may be embossed multiple times.

[0222] The convex portions of the film may be hollow semicircular, hollow semielliptical, hollow polygonal, or hollow irregular. In the case of a hollow polygonal shape, having more corners than a triangle is preferable because it is possible to reduce stress concentration at the corners.

[0223] 21A shows an example of a perspective schematic diagram of the exterior body 11 formed in this manner. The exterior body 11 has a wave shape with multiple ridge lines 21 and valley lines 22 arranged alternately on the surface that faces the outside of the flexible battery 10. Here, it is preferable that adjacent ridge lines 21 and adjacent valley lines 22 are arranged at equal intervals.

[0224] Next, a portion of the exterior body 11 is folded so as to sandwich the stacked batteries 12 prepared in advance ( FIG. 21B ). At this time, it is preferable to adjust the length of the exterior body 11 so that the current collectors 13 a and other parts connected to the stacked batteries 12 are exposed to the outside. In addition, the portions of the exterior body 11 that extend beyond the batteries 12 will later become the joints 33 and 34, so the protruding portions should be long enough to take into account the thickness of the stacked batteries 12.

[0225] 21B shows an example in which a pair of portions 31 sandwiching the stacked battery 12 are arranged so that the phases of their respective waves are shifted by 180 degrees. That is, the state in which the exterior body 11 is bent is shown so that the ridge lines 21 of the pair of portions 31 overlap each other and the valley lines 22 of the pair of portions 31 overlap each other.

[0226] Here, the position and shape of the bending portion of the exterior body 11 will be described. Fig. 22A is a diagram schematically illustrating a cross section of the exterior body 11. Figs. 22B to 22E respectively show the cross-sectional shape of the bending portion 32 when points P1 to P4 shown in Fig. 22A are the bending positions. Note that, in order to describe the case where the exterior body 11 is bent by being pushed in the direction of the arrow shown in Fig. 22A, the lower surface of the exterior body 11 in Fig. 22A corresponds to the outer surface of the flexible battery 10. Therefore, in Fig. 22A, the portion protruding upward is shown as a valley line 22, and the portion protruding downward is shown as a ridge line 21.

[0227] 22B to 22E, a hatched pattern is applied to the area surrounded by the bent portion 32. Here, two positions where the periodicity of the waves of the exterior body 11 is disrupted are taken as boundaries, and the area sandwiched between these boundaries is taken as the bent portion 32. Note that in Figures 22B to 22E, etc., the shape of the bent portion 32 is exaggerated, and therefore its perimeter may not be drawn correctly.

[0228] Point P1 coincides with valley line 22. As shown in Fig. 22B, bending at point P1 allows bent portion 32 to have a substantially arcuate shape. In addition, bending at point P1 allows the phases of opposing waves to be shifted by 180 degrees.

[0229] Point P2 coincides with ridge line 21. As shown in Fig. 22C, bending at point P2 also allows bent portion 32 to have a substantially arc-like shape. Bending at point P2 also allows the phases of the opposing waves to be shifted by 180 degrees.

[0230] Point P3 is between ridge line 21 and valley line 22 and is closer to ridge line 21 than their midpoint. As shown in Fig. 22D, by shifting from ridge line 21 or valley line 22, the shape of bent portion 32 becomes distorted and not symmetrical from above. Furthermore, by bending at point P3, it is possible to bend so that the ridge lines, the valley lines, and the ridge and valley lines of the opposing waves do not coincide with each other.

[0231] Point P4 coincides with the midpoint between ridge line 21 and valley line 22. As shown in Figure 22E, when the battery is bent at point P4, the shape of bent portion 32 becomes extremely irregular. Specifically, bent portion 32 tends to protrude upward or downward. This makes it difficult to ensure a large distance between one end of stacked battery 12 and the inner wall of exterior body 11.

[0232] 22B, 22C, and 22D have in common that they all have a ridge line 21 between the bent portion 32 and the valley line 22 of the portion 31 closest to the bent portion 32. In particular, FIG. 22B shows an example in which the boundary of the bent portion 32 coincides with the ridge line 21 of the wave. In this way, bending the exterior body 11 with the ridge line 21 or its vicinity as a boundary ensures a wide space in the thickness direction inside the bent portion 32 and its vicinity. As mentioned above, when bending the flexible battery 10, it is important to increase the distance between the outermost battery 12 and the inner wall of the exterior body 11. Therefore, by adopting such a shape, this distance can be increased.

[0233] 22E, on the underside, there is no ridge line 21 between the valley line 22 of the portion 31 that is closest to the bent portion 32 and the bent portion 32. Therefore, a wide space in the thickness direction is unlikely to be formed at the bent portion 32 and its vicinity.

[0234] Here, it is preferable that the portion of exterior body 11 that will become folded portion 32 has a flat shape without a corrugated shape. For example, as shown in Fig. 23A , a portion of exterior body 11 may be flattened by clamping it between molds 91 and 92, which have flat surfaces, and applying pressure or applying pressure while applying heat.

[0235] 23B is a schematic cross-sectional view of exterior body 11 that has been partially flattened in this manner. In this example, exterior body 11 is partially flattened so as to connect ridge lines 21 with each other.

[0236] 23C is a schematic cross-sectional view of exterior body 11 when it is pressed in the direction of the arrow at point P5 in the center of the formed flat portion and bent at point P5 as the bending position. As shown in FIG. 23C, by forming flattened exterior body 11 into bent portion 32, it is possible to form a larger space than that shown in FIG. 22B.

[0237] 23D and 23E show examples in which a wider area is flattened than in Fig. 23C. Here, as in Fig. 23B, a portion of the exterior body 11 is flattened so as to connect the ridge lines 21. In this way, flattening the exterior body 11 over an area wider than the thickness of the stacked battery 12 makes it possible to form a wide space that is uniform in the thickness direction.

[0238] The above is an explanation of the relationship between the position of the bent portion and the shape of the bent portion.

[0239] [Film Processing Method] Next, a method for processing a film that can be used for the exterior body 11 will be described.

[0240] First, a film made of a flexible substrate is prepared. The film is preferably a laminate, and one having a heat seal layer on one or both sides of a metal film is used. The adhesive layer is a heat-sealable resin film containing polypropylene or polyethylene. In this embodiment, the film used has nylon resin on the surface of an aluminum foil, and an acid-resistant polypropylene film and a laminate of polypropylene films on the back surface of the aluminum foil. This film is cut to the desired size.

[0241] Then, this film is embossed. As a result, a film having a concave-convex shape can be produced. The film has a plurality of concave-convex portions, and thus has a visible wavy pattern. Here, an example is shown in which the film is cut and then embossed, but the order is not particularly limited, and the film may be embossed before cutting and then cut. Alternatively, the film may be folded and thermocompressed before cutting.

[0242] Embossing, which is a type of press working, will be explained below.

[0243] Fig. 24 is a cross-sectional view showing an example of embossing. Embossing is a type of press processing, and refers to a process in which an embossing roll with an uneven surface is pressed against a film to form unevenness in the film corresponding to the unevenness of the embossing roll. The embossing roll is a roll with a pattern engraved on its surface.

[0244] 24 shows an example of embossing on both sides of a film, and an example of a process for producing a film having convex portions with peaks on one side of the film.

[0245] 24 shows a state in which a film 90 is sandwiched between an embossing roll 95 in contact with one side of the film and an embossing roll 96 in contact with the other side, and the film 90 is being fed in a film traveling direction 60. A pattern is formed on the film surface by pressure or heat. Alternatively, a pattern may be formed on the film surface by both pressure and heat.

[0246] As the embossing roll, a metal roll, a ceramic roll, a plastic roll, a rubber roll, an organic resin roll, a wooden roll, or the like can be used as appropriate.

[0247] In Figure 24, embossing is performed using an embossing roll 96, which is a male-pattern embossing roll, and a female-pattern embossing roll 95. The male-pattern embossing roll 96 has multiple convex portions 96a. These convex portions correspond to the convex portions to be formed on the film to be processed. The female-pattern embossing roll 95 has multiple convex portions 95a. Adjacent convex portions 95a form recesses in which the convex portions 96a on the male-pattern embossing roll 96 fit into the convex portions to be formed on the film.

[0248] By successively performing embossing to raise a portion of the film 90 and blank pressing to depress a portion of the film 90, it is possible to continuously form convex portions and flat portions. As a result, a pattern can be formed on the film 90.

[0249] Figures 25A and 25B are bird's-eye views showing the resulting shape when embossing is performed twice, changing the direction of film 90. Embossing does not have to be performed on the thermocompression-bonded area. Specifically, film 90 is embossed in a first direction, and then embossed in a second direction rotated 90 degrees from the first direction, resulting in films 61 to 63 having the embossed shape (which can be referred to as a cross-wave shape) shown in Figures 25A and 25B. Film 61 having the cross-wave shape shown in Figure 25A represents the outer shape used when fabricating a flexible battery using a single film 61, and can be folded in half along the dashed line. Multiple films (films 62 and 63) having the cross-wave shape shown in Figure 25B represent the outer shape used when fabricating a flexible battery using two films (films 62 and 63), and films 62 and 63 can be stacked together.

[0250] As described above, by performing processing using an embossing roll, it is possible to miniaturize the device. Furthermore, since processing can be performed without cutting the film, it is excellent in mass productivity. Note that processing is not limited to using an embossing roll, and for example, the film may be processed by pressing a pair of embossing plates with uneven surfaces against the film. In this case, one of the embossing plates may be flat, and processing may be performed in multiple steps.

[0251] In the above-described configuration example of the flexible battery, the exterior body on one side of the flexible battery and the exterior body on the other side have the same embossed shape, but the configuration of the flexible battery of one embodiment of the present invention is not limited to this. For example, the flexible battery may have an embossed shape on the exterior body on one side of the flexible battery and no embossed shape on the exterior body on the other side. Furthermore, the exterior body on one side of the flexible battery may have different embossed shapes.

[0252] 26 to 28, a flexible battery having an embossed shape on the exterior body on one side of the flexible battery and not having an embossed shape on the exterior body on the other side will be described.

[0253] First, a film made of a flexible substrate is prepared. The film has a laminated structure and has an adhesive layer (also called a heat seal layer) on one or both sides of the metal film. The adhesive layer is a heat-sealable resin film containing polypropylene or polyethylene. In this embodiment, the film is a metal film having nylon resin on the surface of an aluminum foil and an acid-resistant polypropylene film and a polypropylene film laminate on the back of the aluminum foil. This film is cut to prepare film 90 shown in FIG. 26A.

[0254] Then, a portion of this film 90 (film 90a) is embossed, while film 90b is not. The resulting film 61 shown in FIG. 26B is produced in this manner. As shown in FIG. 26B, a visible pattern is formed by forming projections and recesses on the surface of film 61a, but no projections and recesses are formed on the surface of film 61b. A boundary exists between film 61a, on which projections and recesses are formed, and film 61b, on which projections and recesses are not formed. In FIG. 26B, the embossed portion of film 61 is film 61a, and the unembossed portion is film 61b. The embossing of film 61a may form the same projections and recesses over the entire surface, or two or more different projections and recesses may be formed in different locations on film 61a. When two or more different projections and recesses are formed, a boundary exists between the different projections and recesses.

[0255] Alternatively, the entire surface of the film 90 in Fig. 26A may be embossed. The embossing of the film 61 may form the same unevenness over the entire surface, or may form two or more different unevennesses at different locations on the film 61. When two or more different unevennesses are formed, there is a boundary between the different unevennesses. Alternatively, as shown in Fig. 26C, a film 61a having unevenness on its surface and a film 61b having no unevenness on its surface may be prepared.

[0256] Although an example in which the embossing is performed after the film is cut is shown here, the order is not particularly limited, and the embossing may be performed before the film is cut, and then the film may be cut, resulting in the state shown in Fig. 26B. Alternatively, the film may be folded and thermocompressed before being cut.

[0257] In this embodiment, film 61 is fabricated by forming a pattern by providing projections and depressions on both sides of a portion of film 90 (film 90a), and film 61 is then folded in the center to overlap two edges, and three sides are sealed with adhesive layers. Here, film 61 is referred to as exterior body 11.

[0258] Next, the exterior body 11 is folded along the dotted line in Fig. 26B to obtain the state shown in Fig. 27A. Fig. 27B shows the positive electrode 12, separator 13, and negative electrode 14, and Fig. 27C shows the lead electrode 16 having the sealing layer 15. Fig. 27E shows an example of a cross section taken along the dashed dotted line A-B in Fig. 27D.

[0259] 27D and 27E , a stack of a positive electrode current collector 64 having a positive electrode active material layer 18 formed on a portion of its surface, a separator 65, and a negative electrode current collector 66 having a negative electrode active material layer 19 formed on a portion of its surface, which constitute a flexible battery, is prepared. Note that, for the sake of simplicity, an example is shown in which a single stacked combination of the positive electrode current collector 64 having the positive electrode active material layer 18 formed on it, the separator 65, and the negative electrode current collector 66 having the negative electrode active material layer 19 formed on it is housed in an exterior body, but multiple combinations may be stacked and housed in an exterior body to increase the capacity of the flexible battery.

[0260] Then, two lead electrodes 16 having a sealing layer 15 shown in Fig. 27C are prepared. The lead electrodes 16 are also called lead terminals and are provided to pull out the positive or negative electrodes of the flexible battery to the outside of the exterior body. For the lead electrodes, aluminum is used for the positive electrode lead and nickel-plated copper is used for the negative electrode lead.

[0261] The positive electrode lead electrode and the protruding portion of the positive electrode current collector 64 are then electrically connected by ultrasonic welding or the like. The negative electrode lead electrode and the protruding portion of the negative electrode current collector 66 are also electrically connected by ultrasonic welding or the like.

[0262] Then, two sides of the exterior body 11 are sealed by thermocompression bonding, leaving one side for the electrolyte to be placed in (hereinafter, the shape of the exterior body in this state will also be referred to as a bag-like shape). During thermocompression bonding, the sealing layer 15 provided on the lead terminal also melts, fixing the lead terminal and the exterior body 11 together. Then, under reduced pressure or in an inert atmosphere, a desired amount of electrolyte is dripped onto the inside of the bag-like exterior body 11. Finally, the remaining edge of the exterior body 11 that was not thermocompression bonded is sealed by thermocompression bonding.

[0263] In this way, the flexible battery 40 shown in FIG. 27D can be fabricated.

[0264] 27E, a positive electrode current collector 64, a positive electrode active material layer 18, a separator 65, a negative electrode active material layer 19, and a negative electrode current collector 66 are laminated in this order and sandwiched between folded exterior bodies 11, and further sealed at the ends with adhesive layers 30, with electrolyte solution 20 being contained in the remaining space inside the folded exterior body 11. It is preferable that the volume ratio of the battery portion to the entire flexible battery be 50% or more.

[0265] The exterior of the flexible battery 40 has a film 90 with a textured surface. The area between the dotted line and the edge in Figure 27D is the thermocompression bonded area 17, which also has a textured surface. The surface texture of the thermocompression bonded area 17 is smaller than that of the central area, but it can reduce stress when the flexible battery is bent. That is, the texture of the exterior 11a is different between the area overlapping with the positive electrode current collector 64 and the thermocompression bonded area 17.

[0266] 28A and 28B show cross-sectional views of the flexible battery of FIG. 27D taken along the dashed line C-D. FIG. 28A shows a battery 12 with a laminated structure inside the battery, an embossed film 61a covering the upper surface of the battery, and an unembossed film 61b covering the lower surface of the battery. To simplify the drawing, the laminated structure of the positive electrode current collector on which the positive electrode active material layer is formed, the separator, the negative electrode current collector on which the negative electrode active material layer is formed, and the electrolyte are collectively shown as the battery 12 with a laminated structure inside the battery. T is the thickness of the battery 12 with a laminated structure inside the battery, and t１ is the sum of the embossing depth and film thickness of the embossed film 61a covering the top surface of the battery, t ２ indicates the thickness of the unembossed film 61b covering the bottom surface of the battery and the sum of the embossing depth and film thickness of the embossed film 61b. In this case, the thickness of the entire flexible battery is T+t １ +t ２ T≧t １ +t ２ In this case, the volume ratio of the battery 12 portion of the laminated structure inside the battery to the entire flexible battery can be 50% or more.

[0267] Although the adhesive layer 30 is only partially shown in FIG. 27E, a layer made of polypropylene is provided on the surface of the film to which the film is bonded, and only the thermocompression bonded portion becomes the adhesive layer 30.

[0268] 27E shows an example in which the lower side of the exterior body 11 is fixed and crimped. In this case, the upper side is bent significantly, forming a step. Therefore, if multiple, for example, eight or more, combinations of the above-described layers are provided between the folded exterior body 11, the step becomes large, and there is a risk of excessive stress being applied to the upper side of the exterior body 11a. This may also result in a large misalignment between the end of the upper film and the end of the lower film. In this case, a step may also be provided in the lower film to prevent misalignment at the ends, and the film may be crimped in the center to equalize the stress.

[0269] In addition, if a large misalignment occurs, there will be an area where part of the edge of one film does not overlap with the other film, and this area can be cut out to align the edge of the upper film with the edge of the lower film, thereby correcting the misalignment.

[0270] The content of this embodiment mode can be freely combined with the content of other embodiment modes.

[0271] Embodiment Mode 4 In this embodiment mode, a structure of a battery that can be applied to the above embodiment modes will be described.

[0272] [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 further have a conductive material and a binder.

[0273] The current collector can be, for example, a metal foil. The negative electrode can be formed by applying a slurry to a metal foil and drying it. Pressing may be performed after drying. The negative electrode is formed by forming an active material layer on a current collector.

[0274] The slurry is a material liquid used to form an active material layer on a current collector, and refers to a material containing an active material, a binder, and a solvent, preferably further mixed with a conductive material. The slurry is also called an electrode slurry or an active material slurry, and when forming a negative electrode active material layer, it is also called a negative electrode slurry.

[0275] <Negative Electrode Active Material> As the negative electrode active material, for example, a carbon material or an alloy-based material can be used.

[0276] Examples of carbon materials that can be used include graphite (natural graphite, artificial graphite), graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), carbon fiber (carbon nanotube), graphene, and carbon black.

[0277] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, and pitch-based artificial graphite. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape and is preferred. Furthermore, it is relatively easy to reduce the surface area of ​​MCMB, and this may be preferred. Examples of natural graphite include flake graphite and spherical natural graphite.

[0278] When lithium ions are inserted into graphite (when a lithium-graphite intercalation compound is formed), graphite exhibits a potential as low as that of metallic lithium (0.05 V to 0.3 V vs. Li / Li ＋This allows lithium-ion batteries using graphite to exhibit high operating voltages. Graphite is also preferred because it has advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and greater safety compared to lithium metal.

[0279] The non-graphitizable carbon can be obtained by calcining a synthetic resin such as a phenolic resin or a plant-derived organic material. The non-graphitizable carbon contained in the negative electrode active material of the lithium-ion battery according to one embodiment of the present invention preferably has a (002) plane spacing measured by X-ray diffraction (XRD) of 0.34 nm or more and 0.50 nm or less, and more preferably 0.35 nm or more and 0.42 nm or less.

[0280] In addition, the negative electrode active material can be an element capable of undergoing a charge-discharge reaction through alloying and dealloying reactions with lithium. For example, a material containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc. can be used. These elements have a larger capacity than carbon, and silicon in particular has a high theoretical capacity of 4200 mAh / g. For this reason, it is preferable to use silicon as the negative electrode active material. Alternatively, compounds containing these elements may be used. For example, SiO, Mg ２ Si, Mg ２ Ge, SnO, SnO ２ , Mg ２ Sn, SnS ２ , V ２ Sn ３ , FeSn ２ , CoSn ２ , Ni ３ Sn ２ , Cu ６ Sn ５ , Ag ３ Sn, Ag ３ Sb, Ni ２ MnSb, CeSb ３ , LaSn ３ , La ３ Co ２ Sn ７ , CoSb ３, InSb, SbSn, etc. Here, elements capable of undergoing charge-discharge reactions by alloying / dealloying reactions with lithium, and compounds containing such elements, are sometimes referred to as alloy-based materials.

[0281] In this specification, "SiO" refers to, for example, silicon monoxide. ｘ Here, x preferably has a value of 1 or close to 1. For example, x is preferably 0.2 or more and 1.5 or less, and more preferably 0.3 or more and 1.2 or less.

[0282] Titanium dioxide (TiO ２ ), lithium titanium oxide (Li ４ Ti ５ O １２ ), lithium-graphite intercalation compound (Li ｘ C ６ ), niobium pentoxide (Nb ２ O ５ ), tungsten dioxide (WO ２ ), molybdenum dioxide (MoO ２ ) and other oxides can be used.

[0283] In addition, as the negative electrode active material, a nitride of lithium and a transition metal, Li ３ Li with N-type structure ３−ｘ M ｘ N (M=Co, Ni, Cu) can be used. For example, Li ２．６ Co ０．４ N has a large discharge capacity (900 mAh / g, 1890 mAh / cm ３ ) and is preferred.

[0284] When a nitride of lithium and a transition metal is used, lithium ions are contained in the negative electrode active material, so V, which does not contain lithium ions, is used as the positive electrode active material. ２ O ５ , Cr ３ O ８ It is preferable that the material can be combined with a material such as the above. Even when a material containing lithium ions is used as the positive electrode active material, it is possible to use a nitride of lithium and a transition metal as the negative electrode active material by first desorbing the lithium ions contained in the positive electrode active material.

[0285] Furthermore, a material that undergoes a conversion reaction can also be used as the negative electrode active material. For example, a transition metal oxide that does not form an alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), or iron oxide (FeO), can be used as the negative electrode active material. Further examples of materials that undergo a conversion reaction include Fe ２ O ３ , CuO, Cu ２ O, RuO ２ , Cr ２ O ３ oxides such as CoS ０．８９ , sulfides such as NiS and CuS, Zn ３ N ２ , Cu ３ N, Ge ３ N ４ Nitrides such as NiP ２ , FeP ２ , CoP ３ Phosphides such as FeF ３ , BiF ３ This also occurs with fluorides such as

[0286] Although one type of anode active material from among the above-described anode active materials can be used, a combination of two or more types of anode active materials can also be used, for example, a combination of a carbon material and silicon, or a combination of a carbon material and silicon monoxide.

[0287] <Binder> 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. Furthermore, as the binder, fluororubber can be used.

[0288] Furthermore, it is preferable to use, for example, a water-soluble polymer as the binder. Examples of the water-soluble polymer that can be used include polysaccharides. Examples of the polysaccharide that can be used include cellulose derivatives such as carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and regenerated cellulose, as well as starch. It is even more preferable to use these water-soluble polymers in combination with the above-mentioned rubber material.

[0289] Alternatively, it is preferable to use, as the binder, 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.

[0290] The binder may be used in combination with two or more of the above.

[0291] For example, a material with a particularly excellent viscosity adjusting effect may be used in combination with another material. For example, while rubber materials have excellent adhesive strength and elasticity, it may be difficult to adjust the viscosity when mixed with a solvent. In such cases, it is preferable to mix them with a material with a particularly excellent viscosity adjusting effect. For example, a water-soluble polymer may be used as a material with a particularly excellent viscosity adjusting effect. Furthermore, as a water-soluble polymer with a particularly excellent viscosity adjusting effect, the above-mentioned polysaccharides, for example, carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, and diacetyl cellulose, cellulose derivatives such as regenerated cellulose, or starch may be used.

[0292] In addition, the solubility of cellulose derivatives such as carboxymethyl cellulose can be increased by converting them into salts such as sodium or ammonium salts of carboxymethyl cellulose, making them more effective as viscosity adjusters. Higher solubility can also improve dispersibility with active materials or other components when preparing electrode slurry. In this specification, cellulose and cellulose derivatives used as electrode binders also include their salts.

[0293] Water-soluble polymers stabilize viscosity by dissolving in water, allowing active materials and other materials combined as binders, such as styrene-butadiene rubber, to be stably dispersed in aqueous solutions. Furthermore, the presence of functional groups is expected to facilitate stable adsorption to the surface of active materials. Furthermore, many cellulose derivatives, such as carboxymethyl cellulose, contain functional groups such as hydroxyl or carboxyl groups, and the presence of these functional groups is expected to facilitate interactions between polymers, resulting in widespread coverage of the active material surface.

[0294] When the binder covers the surface of the active material or contacts the surface and forms a film, it is expected to function as a passive film and have the effect of suppressing decomposition of the electrolyte. Here, the "passive film" refers to a film with no electrical conductivity or a film with extremely low electrical conductivity. For example, when a passive film is formed on the surface of the active material, it can suppress decomposition of the electrolyte at the battery reaction potential. Furthermore, it is more desirable that the passive film suppresses electrical conductivity while still allowing lithium ions to conduct.

[0295] <Conductive Material> The conductive material is also called a conductivity imparting agent or a conductivity aid, and is made of a carbon material. By attaching the conductive material between multiple active materials, the multiple active materials are electrically connected to each other, thereby increasing the conductivity. Note that the term "attachment" does not only refer to physical adhesion between the active material and the conductive material, but also includes cases where a covalent bond is formed, bonding due to van der Waals forces, where the conductive material covers part of the surface of the active material, where the conductive material is embedded in the surface irregularities of the active material, and where the materials are electrically connected even when not in contact with each other.

[0296] The active material layers such as the positive electrode active material layer and the negative electrode active material layer preferably contain a conductive material.

[0297] As the conductive material, for example, carbon black such as acetylene black and furnace black can be used. As the conductive material, graphite such as artificial graphite and natural graphite can be used. As the conductive material, carbon fibers such as carbon nanofibers and carbon nanotubes can be used. As the conductive material, graphene or a graphene compound described in the above embodiment can be used. As the conductive material, one or a mixture of two or more of the above materials can be used.

[0298] Examples of the carbon fiber that can be used include mesophase pitch-based carbon fiber and isotropic pitch-based carbon fiber. Also, examples of the carbon fiber that can be used include carbon nanofibers and carbon nanotubes. Carbon nanofibers and carbon nanotubes can be produced by, for example, vapor deposition.

[0299] Furthermore, the conductive material may be a metal powder or metal fiber such as copper, nickel, aluminum, silver, or gold, or a conductive ceramic material.

[0300] 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.

[0301] Unlike granular conductive materials such as carbon black, which make point contact with the active material, graphene or a graphene compound enables surface contact with the active material with low contact resistance, and therefore can improve the electrical conductivity between the granular active material and graphene or a graphene compound with a smaller amount than that of a typical conductive material. This allows the ratio of the active material in the active material layer to be increased, thereby increasing the discharge capacity of the battery.

[0302] Carbon black or carbon fiber easily enters into minute spaces, such as the spaces between multiple active materials. By combining carbon black or carbon fiber, which easily enters into minute spaces, with graphene or a graphene compound, which allows for surface contact, the density of the electrode can be increased and an excellent conductive path can be formed.

[0303] <Current Collector> As the current collector, a material that has high conductivity and does not alloy with carrier ions such as lithium, such as metals such as stainless steel, gold, platinum, zinc, iron, copper, aluminum, and titanium, and alloys thereof, can be used. The current collector can be appropriately shaped, such as a sheet, mesh, punched metal, or expanded metal. It is preferable to use a current collector with a thickness of 5 μm or more and 30 μm or less.

[0304] The negative electrode current collector is preferably made of a material that does not alloy with carrier ions such as lithium.

[0305] [Positive electrode] The positive electrode has a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer contains a positive electrode active material and may further contain at least one of a conductive material and a binder. Note that the positive electrode current collector, conductive material, and binder may be those described in [Negative electrode].

[0306] The current collector can be, for example, a metal foil. The positive electrode can be formed by applying a slurry to a metal foil and drying it. Pressing may be performed after drying. The positive electrode is formed by forming an active material layer on a current collector.

[0307] The slurry is a material liquid used to form an active material layer on a current collector, and refers to a material containing an active material, a binder, and a solvent, preferably further mixed with a conductive material. The slurry is also called an electrode slurry or an active material slurry, and when forming a positive electrode active material layer, it is also called a positive electrode slurry.

[0308] <Positive Electrode Active Material> As the positive electrode active material, at least one of a composite oxide having a layered rock salt structure, a composite oxide having an olivine structure, and a composite oxide having a spinel structure can be used.

[0309] As the composite oxide having a layered rock salt structure, any one or more of lithium cobalt oxide, lithium nickel-cobalt-manganese oxide, lithium nickel-cobalt-aluminate, and lithium nickel-manganese-aluminate can be used. ２ (M1 is one or more selected from nickel, cobalt, manganese, and aluminum), but the coefficients of the composition formula are not limited to integers.

[0310] As the lithium cobalt oxide, for example, lithium cobalt oxide to which magnesium and fluorine are added can be used. It is also preferable to use lithium cobalt oxide to which magnesium, fluorine, aluminum and nickel are added.

[0311] As the lithium nickel-cobalt-manganese oxide, for example, lithium nickel-cobalt-manganese oxide having a ratio of nickel:cobalt:manganese = 1:1:1, nickel:cobalt:manganese = 6:2:2, nickel:cobalt:manganese = 8:1:1, nickel:cobalt:manganese = 9:0.5:0.5, etc. Furthermore, as the lithium nickel-cobalt-manganese oxide, it is preferable to use lithium nickel-cobalt-manganese oxide to which one or more of aluminum, calcium, barium, strontium, and gallium have been added.

[0312] As the composite oxide having an olivine structure, any one or more of lithium iron phosphate, lithium manganese phosphate, lithium cobalt phosphate, and lithium iron manganese phosphate can be used. ４ (M2 is one or more elements selected from iron, manganese, and cobalt), but the coefficients of the composition formula are not limited to integers.

[0313] Also, LiMn ２ O ４ The above-mentioned composite oxides having a spinel structure can be used.

[0314] [Electrolyte] Examples of electrolytes are described below. As one form of electrolyte, a liquid electrolyte (also referred to as an electrolyte solution) having an organic solvent and an electrolyte dissolved in the organic solvent can be used. The electrolyte is not limited to an electrolyte solution that is liquid at room temperature or room temperature (25°C), and a solid electrolyte can also be used. Alternatively, an electrolyte (semi-solid electrolyte) containing both an electrolyte solution that is liquid at room temperature and a solid electrolyte that is solid at room temperature can also be used. When a solid electrolyte or semi-solid electrolyte is used in a bendable battery, the flexibility of the battery can be maintained by having a structure in which the electrolyte is included in a part of the laminate inside the battery.

[0315] When an electrolyte solution is used in a flexible battery, the organic solvent may be one of, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc., or two or more of these may be used in any combination and ratio.

[0316] Furthermore, by using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as the solvent for the electrolyte, it is possible to prevent the flexible battery from exploding or catching fire even if the temperature of the internal region of the flexible battery rises due to short-circuiting or overcharging. The ionic liquid is 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, as well as 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.

[0317] A flexible battery according to one embodiment of the present invention has, as carrier ions, for example, alkali metal ions such as lithium ions, sodium ions, and potassium ions, and alkaline earth metal ions such as calcium ions, strontium ions, barium ions, beryllium ions, and magnesium ions.

[0318] When lithium ions are used as carrier ions, the electrolyte contains a lithium salt, for example, LiPF ６ , LiClO ４ , LiAsF ６ , LiBF ４ , LiAlCl ４ , LiSCN, LiBr, LiI, Li ２ SO ４ , Li ２ B １０ Cl １０ , Li ２ B １２ Cl １２ , LiCF ３ SO ３ , LiC ４ F ９ SO ３ , LiC(CF ３ SO２ ) ３ , LiC(C ２ F ５ SO ２ ) ３ , LiN(CF ３ SO ２ ) ２ , LiN(C ４ F ９ SO ２ ) (CF ３ SO ２ ), LiN(C ２ F ５ SO ２ ) ２ etc. can be used.

[0319] As an example, the organic solvent described in this embodiment contains ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), and when the total amount of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate is 100 vol%, the volume ratio of the ethylene carbonate, the ethyl methyl carbonate, and the dimethyl carbonate can be x:y:100-x-y (where 5≦x≦35 and 0<y<65). More specifically, an organic solvent containing EC, EMC, and DMC in a volume ratio of EC:EMC:DMC=30:35:35 can be used.

[0320] Furthermore, the electrolyte is preferably highly purified, with a low content of granular dust or elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities"). Specifically, the weight ratio of impurities to the electrolyte is preferably 1% or less, more preferably 0.1% or less, and even more preferably 0.01% or less.

[0321] Furthermore, for the purpose of improving safety, etc., an additive such as vinylene carbonate (VC), propane sultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate)borate (LiBOB), or a dinitrile compound such as succinonitrile or adiponitrile may be added to the electrolyte to form a coating (solid electrolyte interface) at the interface between the electrode (active material layer) and the electrolyte. The concentration of the additive may be, for example, 0.1 wt % to 5 wt % relative to the solvent.

[0322] Furthermore, if the electrolyte contains a polymeric material that can be gelled, safety against leakage, etc. Typical examples of polymeric materials that can be gelled include silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, and fluorine-based polymer gel.

[0323] 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.

[0324] [Separator] When the electrolyte contains an electrolytic solution, a separator is disposed between the positive electrode and the negative electrode. Examples of separators that can be used include those made of cellulose-containing fibers such as paper, nonwoven fabrics, glass fibers, ceramics, or synthetic fibers such as nylon (polyamide), polyimide, vinylon (polyvinyl alcohol-based fibers), polyester, acrylic, polyolefin, and polyurethane. The separator is preferably processed into a bag shape and disposed so as to encase either the positive electrode or the negative electrode.

[0325] The separator may have a multilayer structure. For example, an organic film such as polypropylene or polyethylene may be coated with a ceramic material, a fluorine-based material, a polyamide material, a polyimide material, or a mixture thereof. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine-based materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aramid (meta-aramid, para-aramid).

[0326] Coating with ceramic materials improves oxidation resistance, suppressing separator degradation during high-voltage charging and discharging and improving battery reliability. 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 battery safety.

[0327] 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.

[0328] By using a separator with a multilayer structure, the safety of the battery can be maintained even if the overall thickness of the separator is thin, and therefore the capacity per unit volume of the battery can be increased.

[0329] [Exterior Body] The exterior body of the battery is as described in the above embodiment. Furthermore, when a laminated structure is used, the thickness of the aluminum layer used in the exterior body is preferably 50 μm or less, more preferably 40 μm or less, more preferably 30 μm or less, and more preferably 20 μm or less. Note that if the aluminum layer is thinner than 10 μm, there is a concern that pinholes in the aluminum layer may reduce the gas barrier properties, so the thickness of the aluminum layer is preferably 10 μm or more.

[0330] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0331] Embodiment 5 In this embodiment, a manufacturing method 1 for a positive electrode active material that can be applied to the above-described embodiments will be described with reference to Fig. 29. Note that manufacturing method 1 uses a coprecipitation method, and specifically, is characterized in that a coprecipitated precursor containing Co, Ni, and Mn is prepared using a coprecipitation apparatus, a Li salt is mixed with the coprecipitated precursor, the mixture is heated, and then a calcium compound (calcium carbonate) is added and the mixture is further heated.

[0332] As shown in FIG. 29 , a cobalt source, a nickel source, and a manganese source are prepared, an alkaline aqueous solution is prepared as aqueous solution 893, and chelating agents are prepared as aqueous solutions 892 and 894. The cobalt source, nickel source, and manganese source are mixed to prepare aqueous solution 890. Aqueous solution 890 and aqueous solution 892 are mixed to prepare mixed solution 901. Mixed solution 901, aqueous solution 893, and aqueous solution 894 are reacted to produce a compound containing at least nickel, cobalt, and manganese. This reaction may be referred to as a neutralization reaction, an acid-base reaction, or a coprecipitation reaction, and the compound containing at least nickel, cobalt, and manganese (the nickel compound in FIG. 29 ) may be referred to as a precursor of a nickel-cobalt-manganese compound. The reaction occurring by performing the process surrounded by the dashed line in FIG. 29 may also be referred to as a coprecipitation reaction.

[0333] <Cobalt aqueous solution> An aqueous cobalt solution is prepared as a cobalt source. ４ ), cobalt chloride (e.g., CoCl ２ ) or cobalt nitrate (e.g., Co(NO ３ ) ２ ), cobalt acetate (e.g., C ４ H ６ CoO ４ ), cobalt alkoxide, or organic cobalt complex, or an aqueous solution containing a hydrate thereof. Organic acids of cobalt, such as cobalt acetate, or hydrates thereof, may also be used. In this specification, the organic acid includes citric acid, oxalic acid, formic acid, and butyric acid in addition to acetic acid.

[0334] For example, an aqueous solution of these compounds in pure water can be used. The cobalt aqueous solution is acidic, so it can be referred to as an acidic aqueous solution.

[0335] <Nickel aqueous solution> A nickel aqueous solution is prepared as a nickel source. As the nickel aqueous solution, an aqueous solution of nickel sulfate, nickel chloride, nickel nitrate, or a hydrate thereof can be used. Alternatively, an aqueous solution of an organic acid salt of nickel, such as nickel acetate, or a hydrate thereof can be used. Alternatively, an aqueous solution of nickel alkoxide or an organic nickel complex can be used.

[0336] <Manganese aqueous solution> A manganese aqueous solution is prepared as a manganese source. As the manganese aqueous solution, a manganese salt such as manganese sulfate, manganese chloride, manganese nitrate, or an aqueous solution of a hydrate thereof can be used. Alternatively, an aqueous solution of an organic acid salt of manganese, such as manganese acetate, or an aqueous solution of a hydrate thereof can be used. Alternatively, an aqueous solution of a manganese alkoxide or an organic manganese complex can be used.

[0337] The above-described cobalt aqueous solution, nickel aqueous solution, and manganese aqueous solution may be prepared and then mixed to prepare the aqueous solution 890, or nickel sulfate, cobalt sulfate, and manganese sulfate may be mixed and then mixed with water to prepare the aqueous solution 890. In the present embodiment, desired amounts of nickel sulfate, cobalt sulfate, and manganese sulfate are weighed out and mixed to prepare the aqueous solution 890 containing a mixture of nickel sulfate, cobalt sulfate, and manganese sulfate.

[0338] The aqueous solution 890 is mixed with the aqueous solution 892 to prepare a mixed solution 901. The aqueous solutions 892 and 894 are aqueous solutions that function as chelating agents, but are not particularly limited thereto, and the aqueous solutions 892 and 894 may be pure water.

[0339] <Alkaline aqueous solution> An alkaline solution is prepared as the aqueous solution 893. Examples of the alkaline aqueous solution include aqueous solutions containing sodium hydroxide, potassium hydroxide, lithium hydroxide, or ammonia. For example, an aqueous solution obtained by dissolving these in pure water can be used. An aqueous solution obtained by dissolving multiple types selected from sodium hydroxide, potassium hydroxide, and lithium hydroxide in pure water may also be used.

[0340] <Reaction Conditions> When reacting the mixed solution 901 and the aqueous solution 893 according to the coprecipitation method, the pH of the reaction system is adjusted to 9.0 or more and 12.0 or less, preferably 10.5 or more and 11.5 or less. For example, when the aqueous solution 894 is placed in a reaction tank and the mixed solution 901 and the aqueous solution 893 are added dropwise to the reaction tank (also referred to as a reaction vessel), the pH of the aqueous solution in the reaction tank is preferably maintained within the above-mentioned range. The same applies when the aqueous solution 893 is placed in a reaction tank and the aqueous solution 894 and the mixed solution 901 are added dropwise. The same applies when the mixed solution 901 is placed in a reaction tank and the aqueous solution 894 and the aqueous solution 893 are added dropwise. The drop rate of the aqueous solution 893, the aqueous solution 894, or the mixed solution 901 is preferably 0.1 mL / min or more and 0.8 mL / min or less, which is preferable because it makes it easier to control the pH conditions.

[0341] The aqueous solution in the reaction vessel is preferably stirred using a stirring means. The stirring means has a stirrer or stirring blades. Two to six stirring blades can be provided. For example, when four stirring blades are used, they are preferably arranged in a cross shape when viewed from above. The rotation speed of the stirring means is preferably 800 rpm to 1200 rpm.

[0342] The temperature of the reaction vessel is adjusted to be 50° C. or higher and 90° C. or lower. The dropping of the aqueous solution 893, the aqueous solution 894, or the mixed solution 901 may be started after the temperature has reached the appropriate temperature.

[0343] The inside of the reaction vessel is preferably kept in an inert atmosphere. For example, when a nitrogen atmosphere is used, nitrogen gas is preferably introduced at a flow rate of 0.5 L / min to 2 L / min.

[0344] The reactor may also be equipped with a reflux condenser, which allows nitrogen gas to escape from the reactor and water to return to the reactor.

[0345] After the above reaction, a compound containing at least nickel, cobalt, and manganese is precipitated in the reaction vessel. Filtration is performed to recover the compound containing nickel, cobalt, and manganese. It is preferable to wash the reaction product precipitated in the reaction vessel with pure water, add an organic solvent with a low boiling point (e.g., acetone), and then perform the above filtration.

[0346] The filtered compound containing at least nickel, cobalt, and manganese may be further dried. For example, it may be dried under vacuum or reduced pressure at 60°C to 120°C for 0.5 to 12 hours. In this manner, a compound containing nickel, cobalt, and manganese can be obtained. In Figure 29, the compound containing nickel, cobalt, and manganese is referred to as a nickel compound.

[0347] The compound containing at least nickel, cobalt, and manganese obtained by the above reaction is obtained as secondary particles formed by aggregation of primary particles. In this specification, the term "primary particle" refers to the smallest particle (clump) without grain boundaries when observed, for example, at 5000x magnification using a scanning electron microscope (SEM). In other words, the term "primary particle" refers to the smallest particle surrounded by grain boundaries. The term "secondary particle" refers to particles (particles independent from others) formed by aggregation of the primary particles so as to share part of the grain boundaries (peripheries of the primary particles) and which are not easily separated. In other words, the secondary particles may have grain boundaries.

[0348] In this embodiment, in the compound containing nickel, cobalt, and manganese obtained by the coprecipitation method, the atomic ratio of nickel, cobalt, and manganese is appropriately adjusted to Ni:Co:Mn=8:1:1 or approximately therein.

[0349] <Lithium Compound> Next, a lithium compound is prepared. As the lithium compound, lithium hydroxide (e.g., LiOH), lithium carbonate (e.g., Li ２ CO ３ (melting point 723°C)), or lithium nitrate (e.g., LiNO ３) are examples. In particular, among lithium compounds typified by lithium hydroxide (melting point 462°C), it is preferable to use a material with a low melting point. A positive electrode active material with a high proportion of nickel is more susceptible to cation mixing than lithium cobalt oxide, so the first heating must be performed at a low temperature. Therefore, it is preferable to use a material with a low melting point. The lithium concentration of the positive electrode active material 400, which will be described later, can be adjusted appropriately at this stage. In this embodiment, the molar ratio is adjusted appropriately to 1.01 with respect to the nickel compound (a compound containing nickel, cobalt, and manganese) which is the coprecipitated precursor.

[0350] In this embodiment, a compound containing nickel, cobalt, and manganese is mixed with a lithium compound to obtain the mixture 904. A mortar or a stirring mixer is used for mixing.

[0351] Next, the first heating is performed. As a firing device for performing the first heating, an electric furnace, for example, a rotary kiln furnace, can be used.

[0352] The first heating temperature is preferably higher than 400° C. and equal to or lower than 1050° C. The first heating time is preferably 1 hour or more and 20 hours or less.

[0353] The material is then crushed or pulverized in a mortar to achieve a uniform particle size, and then recovered. It may also be classified using a sieve. When recovering the material after heating, it is preferable to transfer it from the crucible to a mortar and then recover it, since this prevents impurities from being mixed into the material.

[0354] Next, the second heating is performed. As a firing device for performing the second heating, an electric furnace, for example, a rotary kiln furnace, can be used.

[0355] The second heating temperature is preferably higher than 400°C and not higher than 1050°C. The second heating time is preferably 1 hour or more and 20 hours or less. The second heating is preferably performed in an oxygen atmosphere, and it is particularly preferable to perform the second heating while supplying oxygen. For example, the flow rate is 10 L / min per 1 L of the furnace volume. Specifically, the mixture 904 is preferably heated with the container containing the mixture 904 covered.

[0356] The mixture is then crushed or pulverized in a mortar to make the particle size uniform, and then recovered.Furthermore, the mixture may be classified using a sieve.

[0357] <Calcium Compound> Then, the obtained mixture 905 is mixed with a compound 910. In this embodiment, a calcium compound is used as the compound 910. Examples of calcium compounds include calcium oxide, calcium carbonate (melting point 825°C), and calcium hydroxide. In this embodiment, calcium carbonate (CaCO ３ The amount of the compound 910 is preferably such that calcium is weighed and added in a range of 0.5 atm % to 3 atm % relative to the amount of the compound containing nickel, cobalt, and manganese.

[0358] Thereafter, a third heating step is performed. The third heating temperature is at least higher than the first heating temperature, and is preferably higher than 662°C and lower than 1050°C. The third heating time is shorter than that of the second heating, and is preferably 0.5 hours or longer and 20 hours or shorter. The third heating step is preferably performed in an oxygen atmosphere, and it is particularly preferable to perform the third heating step while supplying oxygen. For example, the flow rate is 10 L / min per 1 L of the furnace volume. Specifically, the heating step is preferably performed with the container containing the mixture 905 covered.

[0359] The mixture is then crushed or pulverized in a mortar to make the particle size uniform, and then recovered.Furthermore, the mixture may be classified using a sieve.

[0360] The above steps can produce the positive electrode active material 400. The positive electrode active material 400 obtained by the above steps is nickel-cobalt-lithium manganese oxide (NCM), and contains calcium in the coating of the primary particles or the coating of the secondary particles.

[0361] 29, a process may be used in which a lithium compound and a calcium compound are mixed with a nickel compound, which is a coprecipitated precursor, and then heated. In this case, the third heating step may be unnecessary.

[0362] In the above-described production flow, heating after adding the calcium compound (calcium carbonate) is performed at a temperature at which the primary particles do not melt and at which calcium does not diffuse into the primary particles. The lower limit temperature for heating after adding the calcium compound (calcium carbonate) is preferably set to the eutectic point of 662°C. By heating at 662°C or higher after adding the calcium compound (calcium carbonate), calcium carbonate and lithium carbonate melt, resulting in the formation of molten calcium carbonate and lithium carbonate between the primary particles, and calcium diffuses and becomes scattered inside the secondary particles. In this way, calcium-doped nickel-cobalt-manganese lithium oxide can be obtained. Calcium may be present inside the nickel-cobalt-manganese lithium oxide or may be present in a state of coating the nickel-cobalt-manganese lithium oxide. The term "coated" is sometimes referred to as "a coating of the nickel-cobalt-manganese lithium oxide containing calcium."

[0363] In the above-mentioned production flow, the procedure for adding a calcium compound has been described, but an aluminum compound may be added instead of the calcium compound. The aluminum compound may be added at the same time as the calcium compound, or may be added when producing the coprecipitated precursor. In this way, aluminum-added lithium nickel-cobalt-manganese oxide can be obtained. Aluminum may be present inside the lithium nickel-cobalt-manganese oxide, or may be present in a state that coats it. A coated state may be expressed as a state in which the coating of the lithium nickel-cobalt-manganese oxide contains aluminum.

[0364] In the above-described production flow, an aluminum compound may be added in addition to a calcium compound. The timing of adding the aluminum compound may be the same as or different from the timing of adding the calcium compound. In the case where the timing is different, for example, the aluminum compound may be added when producing the coprecipitated precursor.

[0365] This embodiment mode can be implemented in appropriate combination with other embodiment modes.

[0366] 30A to 30C, a method for manufacturing a positive electrode active material that can be applied to the above-described embodiments will be described. Note that the method for manufacturing a positive electrode active material uses a solid phase method, and specifically, is characterized by undergoing annealing and initial heating.

[0367] <Step S11> In step S11 shown in FIG. 30A, a lithium source (Li source) and a transition metal M source (M source) are prepared as starting materials for lithium and transition metal M, respectively.

[0368] As the lithium source, it is preferable to use a compound containing lithium, such as lithium carbonate, lithium hydroxide, lithium nitrate, or lithium fluoride. It is preferable that the lithium source has high purity, and it is preferable to use a material with a purity of, for example, 99.99% or higher.

[0369] The transition metal M can be selected from elements in Groups 4 to 13 of the periodic table, and for example, at least one of manganese, cobalt, and nickel is used. As the transition metal M, only cobalt may be used, only nickel may be used, two elements of cobalt and manganese may be used, two elements of cobalt and nickel may be used, or three elements of cobalt, manganese, and nickel may be used. When only cobalt is used, the resulting positive electrode active material has lithium cobalt oxide (LCO), and when three elements of cobalt, manganese, and nickel are used, the resulting positive electrode active material has lithium nickel-cobalt-manganese oxide (NCM).

[0370] As the transition metal M source, it is preferable to use a compound containing the transition metal M, and for example, an oxide or hydroxide of a metal exemplified as the transition metal M can be used. As a cobalt source, cobalt oxide, cobalt hydroxide, etc. can be used. As a manganese source, manganese oxide, manganese hydroxide, etc. can be used. As a nickel source, nickel oxide, nickel hydroxide, etc. can be used. As an aluminum source, aluminum oxide, aluminum hydroxide, etc. can be used.

[0371] The transition metal M source preferably has a high purity, for example, a material with a purity of 3N (99.9%) or higher, preferably 4N (99.99%) or higher, more preferably 4N (99.995%) or higher, and even more preferably 5N (99.999%) or higher. By using a high-purity material, impurities in the positive electrode active material can be controlled.

[0372] In addition, the transition metal M source preferably has high crystallinity, for example, single crystal grains. The crystallinity of the transition metal M source can be evaluated using TEM images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope) images, ABF-STEM (annular bright-field scanning transmission electron microscope) images, etc., or by X-ray diffraction (XRD), electron diffraction, neutron diffraction, etc. Note that the above-mentioned methods for evaluating crystallinity can be applied not only to the evaluation of transition metal M sources, but also to the evaluation of the crystallinity of other sources.

[0373] When two or more transition metal M sources are used, the two or more transition metal M sources are preferably prepared in a ratio (mixing ratio) that allows the two or more transition metal M sources to form a layered rock salt type crystal structure.

[0374] <Step S12> Next, in step S12 shown in FIG. 30A , the lithium source and the transition metal M source are pulverized and mixed to prepare a mixed material. The pulverization and mixing can be performed by either a dry or wet method. The wet method is preferred because it allows for smaller pulverization. When performing the wet method, a solvent is prepared. Examples of solvents that can be used include ketones such as acetone, alcohols such as ethanol and isopropanol, ether, dioxane, acetonitrile, and N-methyl-2-pyrrolidone (NMP). It is more preferable to use an aprotic solvent that is less likely to react with lithium. In this embodiment, dehydrated acetone with a purity of 99.5% or higher is used. It is preferable to mix the lithium source and the transition metal M source in dehydrated acetone with a purity of 99.5% or higher, with a water content reduced to 10 ppm or less, and then pulverize and mix them. Using dehydrated acetone with the above purity can reduce potential impurities.

[0375] A ball mill, a bead mill, or the like can be used as a means for mixing, etc. When using a ball mill, aluminum oxide balls or zirconium oxide balls are preferably used as grinding media. Zirconium oxide balls are preferred because they emit less impurities. Furthermore, when using a ball mill, a bead mill, or the like, the peripheral speed is preferably set to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media. In this embodiment, the peripheral speed is set to 838 mm / s (rotation speed 400 rpm, ball mill diameter 40 mm).

[0376] <Step S13> Next, in step S13 shown in FIG. 30A , the mixed material is heated. The heating temperature is preferably 800°C or higher and 1100°C or lower, more preferably 900°C or higher and 1000°C or lower, and even more preferably about 950°C. If the temperature is too low, the decomposition and melting of the lithium source and the transition metal M source may be insufficient. On the other hand, if the temperature is too high, defects may occur due to lithium evaporation from the lithium source and / or excessive reduction of the metal used as the transition metal M source. For example, when cobalt is used as the transition metal M, excessive reduction can cause cobalt to change from trivalent to divalent, which can induce oxygen defects.

[0377] If the heating time is too short, LiMO ２ However, if the heating time is too long, productivity decreases. For example, the heating time is preferably 1 hour or more and 100 hours or less, and more preferably 2 hours or more and 20 hours or less.

[0378] The temperature rise rate depends on the heating temperature reached, but is preferably 80° C. / h to 250° C. / h. For example, when heating at 1000° C. for 10 hours, the temperature rise rate should be 200° C. / h.

[0379] The heating atmosphere is preferably an atmosphere with little water, such as dry air, and for example, an atmosphere with a dew point of -50°C or less, more preferably an atmosphere with a dew point of -80°C or less. In this embodiment, heating is performed in an atmosphere with a dew point of -93°C. In addition, in order to suppress impurities that may be mixed into the material, the CH ４ , CO, CO２ , and H ２ The impurity concentrations of the above should be set to 5 ppb (parts per billion) or less.

[0380] An oxygen-containing atmosphere is preferred as the heating atmosphere. For example, dry air can be continuously introduced into the reaction chamber. In this case, the flow rate of the dry air is preferably 10 L / min. The method of continuously introducing oxygen into the reaction chamber and allowing oxygen to flow through the reaction chamber is called flow.

[0381] When the heating atmosphere is an atmosphere containing oxygen, a method of not allowing the oxygen to flow may be used. For example, a method of reducing the pressure of the reaction chamber and then filling it with oxygen to prevent the oxygen from entering or leaving the reaction chamber may be used, which is called purging. For example, the reaction chamber may be reduced in pressure to -970 hPa and then filled with oxygen to 50 hPa.

[0382] After heating, the material may be cooled naturally, but it is preferable that the time required for the temperature to drop from the specified temperature to room temperature is within a range of 10 to 50 hours. However, cooling to room temperature is not necessarily required, as long as the material is cooled to a temperature acceptable for the next step.

[0383] The heating in this step may be carried out using a rotary kiln or a roller hearth kiln. Heating in a rotary kiln can be carried out while stirring, whether in a continuous or batch system.

[0384] The crucible or sheath used during heating is preferably made of a highly heat-resistant material such as alumina (aluminum oxide), mullite / cordierite, magnesia, or zirconia. Furthermore, since aluminum oxide is a material that is less susceptible to impurities, the purity of the alumina crucible or sheath is 99% or higher, preferably 99.5% or higher. In this embodiment, a crucible made of aluminum oxide with a purity of 99.9% is used. It is preferable to heat the crucible or sheath with a lid, which prevents the material from volatilizing.

[0385] After heating, the material may be crushed and sieved as necessary. When recovering the heated material, it may be transferred from the crucible to a mortar and then recovered. It is preferable to use an aluminum oxide mortar or a zirconium oxide mortar. An aluminum oxide mortar is a material that does not easily release impurities. Specifically, an aluminum oxide mortar with a purity of 90% or more, preferably 99% or more, is used. Heating conditions equivalent to those of step S13 can also be applied to heating steps other than step S13, which will be described later.

[0386] <Step S14> By the above steps, a composite oxide having a transition metal M (LiMO ２ The composite oxide can be obtained by ２ The composition is not strictly limited to Li:M:O=1:1:2, as long as it has a crystalline structure of a lithium composite oxide represented by the formula: ２ The composition is not strictly limited to Li:Co:O=1:1:2.

[0387] Although the example of producing the composite oxide by the solid phase method in steps S11 to S14 has been shown, the composite oxide may also be produced by a coprecipitation method or a hydrothermal method.

[0388] <Step S15> Next, in step S15 shown in Fig. 30A, the composite oxide is heated. Because this is the first heating of the composite oxide, the heating in step S15 may be called initial heating. Alternatively, because this heating is performed before step S20 described below, it may be called preheating or pretreatment.

[0389] As described above, the initial heating causes lithium to be desorbed from a portion of the surface layer of the composite oxide. It is also expected to have the effect of increasing the internal crystallinity. Furthermore, impurities may be mixed into the lithium source and / or transition metal M prepared in step S11, etc. The initial heating can reduce the amount of impurities in the composite oxide completed in step S14.

[0390] Furthermore, initial heating has the effect of smoothing the surface of the composite oxide. A smooth surface means that there are few irregularities, the composite oxide is rounded overall, and the corners are rounded. Furthermore, a smooth surface means that there is little foreign matter adhering to the surface. Foreign matter is thought to be a cause of irregularities, so it is preferable that it does not adhere to the surface.

[0391] For this initial heating, it is not necessary to prepare a lithium compound source, a source of the additional element A, or a material that functions as a flux.

[0392] If the heating time in this step is too short, sufficient effects will not be obtained, but if it is too long, productivity will decrease. For example, the heating conditions can be selected from those described in step S13. In addition to the heating conditions, the heating temperature in this step should be lower than the temperature in step S13 in order to maintain the crystalline structure of the complex oxide. Furthermore, the heating time in this step should be shorter than the time in step S13 in order to maintain the crystalline structure of the complex oxide. For example, heating at a temperature of 700°C or higher and 1000°C or lower for 2 hours or longer and 20 hours or shorter is recommended.

[0393] The effect of increasing the internal crystallinity is, for example, the effect of alleviating distortion, displacement, etc. resulting from differences in shrinkage, etc., of the composite oxide produced in step S13.

[0394] The heating in step S13 may cause a temperature difference between the surface and the interior of the composite oxide. The temperature difference may induce a contraction difference. It is also thought that the temperature difference causes a difference in fluidity between the surface and the interior, resulting in a contraction difference. The energy associated with the contraction difference causes a difference in internal stress in the composite oxide. The internal stress difference is also called strain, and this energy is sometimes called strain energy. The internal stress is removed by the initial heating in step S15; in other words, the strain energy is thought to be homogenized by the initial heating in step S15. When the strain energy is homogenized, the strain in the composite oxide is alleviated. Therefore, the surface of the composite oxide may become smoother after step S15. This is also called an improved surface. In other words, it is thought that the contraction difference that occurred in the composite oxide is alleviated after step S15, resulting in a smoother surface of the composite oxide.

[0395] Furthermore, the difference in shrinkage may cause microscopic deviations in the composite oxide, such as deviations in crystals. This step is preferably carried out in order to reduce such deviations. This step makes it possible to equalize the deviations in the composite oxide. When the deviations are equalized, the surface of the composite oxide may become smooth. This is also referred to as the alignment of crystal grains. In other words, it is believed that step S15 reduces the deviations of crystals and the like that have occurred in the composite oxide, resulting in a smooth surface of the composite oxide.

[0396] When a composite oxide with a smooth surface is used as a positive electrode active material, deterioration during charging and discharging of the flexible battery is reduced, and cracking of the positive electrode active material can be prevented.

[0397] The smooth surface of a composite oxide can be expressed as a surface roughness of at least 10 nm or less when surface irregularity information is quantified from measurement data at a cross section of the composite oxide. The cross section is, for example, a cross section obtained when observing with a scanning transmission electron microscope (STEM).

[0398] In step S14, a composite oxide containing lithium, a transition metal M, and oxygen that has been synthesized in advance may be used. In this case, steps S11 to S13 can be omitted. By performing step S15 on a composite oxide that has been synthesized in advance, a composite oxide with a smooth surface can be obtained.

[0399] It is possible that the lithium in the composite oxide is reduced by the initial heating, and the added element A, which will be explained in the next step S20, etc., may be more likely to enter the composite oxide due to the reduced lithium.

[0400] <Step S20> The additive element A may be added to a composite oxide having a smooth surface, as long as it can form a layered rock salt crystal structure. Adding the additive element A to a composite oxide having a smooth surface allows the additive element A to be added evenly. Therefore, it is preferable to add the additive element A after the initial heating. The step of adding the additive element A will be described with reference to FIGS. 30B and 30C.

[0401] 30B, a source of an additive element A (A source) to be added to the composite oxide is prepared. A lithium source may be prepared together with the additive element A source.

[0402] The additive element A can be one or more selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. The additive element A can be one or more selected from bromine and beryllium. However, since bromine and beryllium are toxic to living organisms, it is more preferable to use the additive elements described above.

[0403] When magnesium is selected as the additional element A, the source of the additional element A can be called a magnesium source. As the magnesium source, magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, or the like can be used. Furthermore, a plurality of the above-mentioned magnesium sources may be used.

[0404] When fluorine is selected as the additional element A, the source of the additional element A can be called a fluorine source. Examples of the fluorine source that can be used include lithium fluoride, magnesium fluoride, aluminum fluoride, titanium fluoride, cobalt fluoride, nickel fluoride, zirconium fluoride, vanadium fluoride, manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride, calcium fluoride, sodium fluoride, potassium fluoride, barium fluoride, cerium fluoride, lanthanum fluoride, and sodium aluminum hexafluoride. Among these, lithium fluoride is preferred because it has a relatively low melting point of 848°C and is easily melted in the heating step described below.

[0405] Magnesium fluoride can be used as both a fluorine source and a magnesium source, and lithium fluoride can be used as a lithium source. Another lithium source that can be used in step S21 is lithium carbonate.

[0406] The fluorine source may be a gas, such as fluorine, carbon fluoride, sulfur fluoride, or oxygen fluoride, which may be mixed into the atmosphere in the heating step described below. A plurality of the above-mentioned fluorine sources may also be used.

[0407] In this embodiment, lithium fluoride is prepared as the fluorine source, and magnesium fluoride is prepared as the fluorine source and magnesium source. Lithium fluoride and magnesium fluoride are prepared in the form of LiF:MgF ２ The effect of lowering the melting point is greatest when the molar ratio is about 65:35. On the other hand, if the amount of lithium fluoride is too high, there is a concern that the lithium will be excessive and the cycle characteristics will deteriorate. Therefore, the molar ratio of lithium fluoride to magnesium fluoride is set to LiF:MgF ２ =x:1 (0≦x≦1.9), and LiF:MgF ２ =x:1 (0.1≦x≦0.5) is more preferable, and LiF:MgF ２ = x:1 (x = 0.33 or its vicinity) is more preferable. In this specification, "or its vicinity" refers to a value that is greater than 0.9 times and smaller than 1.1 times the value.

[0408] At the same time, the amount of magnesium added is２ Based on the standard, the content is preferably more than 0.1 atomic % and not more than 3 atomic %, more preferably 0.5 atomic % to 2 atomic %, and even more preferably 0.5 atomic % to 1 atomic %. When the amount of magnesium added is 0.1 atomic % or less, the initial discharge capacity is high, but the discharge capacity drops rapidly when charging and discharging are repeated to increase the depth of charge. When the amount of magnesium added is more than 0.1 atomic % and not more than 3 atomic %, both the initial discharge characteristics and the charge-discharge cycle characteristics are good even when charging and discharging are repeated to increase the depth of charge. On the other hand, when the amount of magnesium added exceeds 3 atomic %, both the initial discharge capacity and the charge-discharge cycle characteristics tend to gradually deteriorate.

[0409] 30B, the magnesium source and the fluorine source are pulverized and mixed. This step can be performed under pulverization and mixing conditions selected from those described in step S12.

[0410] If necessary, a heating step may be performed after step S22. The heating step can be performed under heating conditions selected from those described in step S13. The heating time is preferably 2 hours or more, and the heating temperature is preferably 800°C or higher and 1100°C or lower.

[0411] 30B, the pulverized and mixed materials are collected to obtain a source of the additional element A. The source of the additional element A shown in step S23 includes a plurality of starting materials and can be called a mixture.

[0412] The particle size of the mixture is preferably such that the median diameter (D50) is 600 nm or more and 20 μm or less, more preferably 1 μm or more and 10 μm or less. Even when a single material is used as the source of the additional element A, the median diameter (D50) is preferably 600 nm or more and 20 μm or less, more preferably 1 μm or more and 10 μm or less.

[0413] Such a finely powdered mixture (including the case where only one type of additive element A is used) is likely to be uniformly adhered to the surface of the composite oxide when mixed with the composite oxide in a later step. Having the mixture uniformly adhered to the surface of the composite oxide is preferred because it facilitates uniform distribution or diffusion of fluorine and magnesium in the surface layer of the composite oxide after heating. The region where fluorine and magnesium are distributed can also be referred to as the surface layer. If there is a region in the surface layer that does not contain fluorine and magnesium, it may be difficult to obtain the O3'-type crystal structure described below in the charged state. Although fluorine has been used in the description, fluorine may also be chlorine, and chlorine can be read as including these and therefore halogen.

[0414] <Step S21> A step different from that shown in FIG. 30B will be described with reference to FIG. 30C. In step S21 shown in FIG. 30C, four types of additive element A sources to be added to the composite oxide are prepared. That is, the types of additive element A sources in FIG. 30C are different from those in FIG. 30B. A lithium source may be prepared together with the additive element A sources.

[0415] As sources of four types of additive element A, a magnesium source (Mg source), a fluorine source (F source), a nickel source (Ni source), and an aluminum source (Al source) are prepared. The magnesium source and the fluorine source can be selected from the compounds described in FIG. 30B . Nickel oxide, nickel hydroxide, etc. can be used as the nickel source. Aluminum oxide, aluminum hydroxide, etc. can be used as the aluminum source.

[0416] <Step S22> and <Step S23> Next, step S22 and step S23 shown in FIG. 30C are the same as the steps described in FIG. 30B.

[0417] 30A , the composite oxide is mixed with a source of the additional element A. The ratio of the number of atoms M of the transition metal M in the composite oxide containing lithium, the transition metal M, and oxygen to the number of atoms Mg of magnesium in the additional element A is preferably M:Mg=100:y (0.1≦y≦6), and more preferably M:Mg=100:y (0.3≦y≦3).

[0418] The mixing conditions in step S31 are preferably milder than those in step S12 so as not to destroy the composite oxide. For example, the mixing conditions are preferably lower in rotation speed or shorter in time than those in step S12. It can also be said that the dry method provides milder conditions than the wet method. For example, a ball mill, a bead mill, or the like can be used for mixing. When using a ball mill, it is preferable to use zirconium oxide balls as the media.

[0419] In this embodiment, dry mixing is performed in a ball mill using zirconium oxide balls with a diameter of 1 mm at 150 rpm for 1 hour in a dry room with a dew point of −100° C. or higher and −10° C. or lower.

[0420] <Step S32> Next, in step S32 of Fig. 30A, the mixed materials are collected to obtain a mixture 903. When collecting the materials, they may be crushed and then sieved, if necessary.

[0421] In this embodiment, a method is described in which lithium fluoride as a fluorine source and magnesium fluoride as a magnesium source are added to the composite oxide after the initial heating. However, the present invention is not limited to the above method. In step S11, that is, in the stage of the starting materials for the composite oxide, a magnesium source, a fluorine source, etc. can be added to the lithium source and the transition metal M source. Then, in step S13, heating is performed to obtain LiMO with added magnesium and fluorine. ２ In this case, it is not necessary to separate the steps S11 to S14 from the steps S21 to S23. This method is simple and has high productivity.

[0422] Alternatively, a composite oxide to which magnesium and fluorine have been added in advance may be used. If a composite oxide to which magnesium and fluorine have been added is used, steps S11 to S32 and step S20 can be omitted. This method can be said to be simple and highly productive.

[0423] Alternatively, a magnesium source and a fluorine source, or a magnesium source, a fluorine source, a nickel source and an aluminum source may be further added to a composite oxide to which magnesium and fluorine have been added in advance in step S20.

[0424] 30A, the mixture 903 is heated. The heating conditions can be selected from those described in step S13. The heating time is preferably 2 hours or more.

[0425] Here, a supplementary note about the heating temperature will be given. The lower limit of the heating temperature in step S33 is ２ The temperature at which the reaction between the LiMO and the additive element A source proceeds must be equal to or higher than the temperature at which the reaction between the LiMO and the additive element A source proceeds. ２ The temperature may be lower than the melting point of these materials as long as it is a temperature at which mutual diffusion of elements contained in the source of the additive element A occurs. ｍ 0.757 times (Tammann temperature T ｄ ) solid-phase diffusion occurs. Therefore, the heating temperature in step S33 should be 500° C. or higher.

[0426] Of course, the reaction proceeds more easily when the temperature is equal to or higher than the temperature at which at least a part of the mixture 903 melts. ２ When LiF and MgF ２ Since the eutectic point of is around 742°C, the lower limit of the heating temperature in step S33 is preferably set to 742°C or higher.

[0427] Also, LiCoO ２ :LiF:MgF ２ A mixture 903 obtained by mixing the components so that the molar ratio was 100:0.33:1 exhibits an endothermic peak at around 830° C. in differential scanning calorimetry (DSC). Therefore, the lower limit of the heating temperature is more preferably 830° C. or higher.

[0428] A higher heating temperature is preferable because the reaction proceeds more easily, the heating time is shorter, and productivity is higher.

[0429] The upper limit of heating temperature is LiMO ２Decomposition temperature of LiCoO ２ The decomposition temperature of LiMO is less than 1130°C. At temperatures close to the decomposition temperature, a small amount of LiMO ２ Therefore, the temperature is more preferably 1000°C or lower, even more preferably 950°C or lower, and even more preferably 900°C or lower.

[0430] Taking these factors into consideration, the heating temperature in step S33 is preferably 500°C to 1130°C, more preferably 500°C to 1000°C, even more preferably 500°C to 950°C, and even more preferably 500°C to 900°C. Also, it is preferably 742°C to 1130°C, more preferably 742°C to 1000°C, even more preferably 742°C to 950°C, and even more preferably 742°C to 900°C. Also, it is preferably 800°C to 1100°C, or 830°C to 1130°C, more preferably 830°C to 1000°C, even more preferably 830°C to 950°C, and even more preferably 830°C to 900°C. The heating temperature in step S33 is preferably higher than that in step S13.

[0431] Furthermore, when the mixture 903 is heated, it is preferable to control the partial pressure of fluorine or fluoride resulting from the fluorine source or the like within an appropriate range.

[0432] In the manufacturing method described in this embodiment, some materials, for example, LiF, which is a fluorine source, may function as a flux. This function allows the heating temperature to be controlled to the temperature of the composite oxide (LiMO). ２ ) can be lowered to a temperature lower than the decomposition temperature, for example, 742°C or higher and 950°C or lower, and additive element A including magnesium can be distributed in the surface layer portion, thereby producing a positive electrode active material with good characteristics.

[0433] However, since LiF has a lower specific gravity in a gaseous state than oxygen, there is a possibility that LiF will volatilize when heated, and if it volatilizes, the amount of LiF in the mixture 903 will decrease. This will weaken its function as a flux. Therefore, it is necessary to heat while suppressing the volatilization of LiF. Even if LiF is not used as a fluorine source, etc., LiMO ２There is a possibility that Li on the surface reacts with F in the fluorine source to produce LiF, which may then volatilize. Therefore, even if a fluoride with a higher melting point than LiF is used, it is still necessary to suppress volatilization.

[0434] Therefore, it is preferable to heat the mixture 903 in an atmosphere containing LiF, that is, to heat the mixture 903 in a state where the partial pressure of LiF is high in the heating furnace. By heating in this manner, it is possible to suppress the volatilization of LiF in the mixture 903.

[0435] The heating in this step is preferably performed so as not to stick together the mixture 903. If the mixture 903 sticks together during heating, the contact area with oxygen in the atmosphere decreases, and the route along which the additional element A (for example, fluorine) diffuses is blocked, which may result in a poor distribution of the additional element A (for example, magnesium and fluorine) in the surface layer portion.

[0436] Furthermore, it is believed that a smooth cathode active material with minimal irregularities can be obtained when the additive element A (e.g., fluorine) is uniformly distributed in the surface layer portion. Therefore, in order to maintain or further smooth the surface after the heating in step S15 in this process, it is preferable that the mixture 903 does not stick to itself.

[0437] Furthermore, when heating in a rotary kiln, it is preferable to control the flow rate of the oxygen-containing atmosphere in the kiln during heating. For example, it is preferable to reduce the flow rate of the oxygen-containing atmosphere, or to first purge the atmosphere and then not flow the atmosphere after introducing the oxygen atmosphere into the kiln. Flowing oxygen may cause the fluorine source to evaporate, which is undesirable in terms of maintaining surface smoothness.

[0438] When heating is performed using a roller hearth kiln, the mixture 903 can be heated in an atmosphere containing LiF by, for example, placing a lid on a container containing the mixture 903 .

[0439] The heating time is determined by the heating temperature, the LiMO ２ It changes depending on the size and composition of LiMO. ２ When is small, a lower temperature or shorter time may be more preferable than when is large.

[0440] The composite oxide (LiMO) in step S14 of FIG. ２ When the median diameter (D50) of the powder is about 12 μm, the heating temperature is preferably, for example, 600° C. or higher and 950° C. or lower. The heating time is, for example, preferably 3 hours or higher, more preferably 10 hours or higher, and even more preferably 60 hours or higher. The cooling time after heating is preferably, for example, 10 hours or higher and 50 hours or lower.

[0441] On the other hand, the composite oxide (LiMO) ２ When the median diameter (D50) of the powder is about 5 μm, the heating temperature is preferably, for example, 600° C. or higher and 950° C. or lower. The heating time is preferably, for example, 1 hour or higher and 10 hours or lower, and more preferably about 2 hours. The cooling time after heating is preferably, for example, 10 hours or higher and 50 hours or lower.

[0442] <Step S34> Next, in step S34 shown in Fig. 30A, the heated material is recovered and crushed as necessary to obtain positive electrode active material 500. At this time, it is preferable to further sieve recovered positive electrode active material 500. Through the above steps, positive electrode active material 500 according to one embodiment of the present invention can be produced. The positive electrode active material according to one embodiment of the present invention has a smooth surface.

[0443] This embodiment can be used in combination with other embodiments.

[0444] Embodiment 7 In this embodiment, electronic devices of one embodiment of the present invention will be described with reference to FIGS.

[0445] The electronic device 6500 shown in FIG. 31A is a portable information terminal that can be used as a smartphone.

[0446] The electronic device 6500 includes at least a housing 6501, a display portion 6502, a power button 6503, a button 6504, a speaker 6505, and a microphone 6506. The display portion 6502a has a touch panel function.

[0447] In addition, the electronic device 6500 can be folded at the hinge portion 6519.

[0448] FIG. 31B is a schematic cross-sectional view including the end of the housing 6501 on the microphone 6506 side.

[0449] A light-transmitting protective member 6510 is provided on the display surface side of the housing 6501, and a display panel 6511, an optical member 6512, a touch sensor panel 6513, a printed circuit board 6517, and a first battery 6518a are arranged in the space surrounded by the housing 6501 and the protective member 6510.

[0450] A display panel 6511, an optical member 6512, and a touch sensor panel 6513 are fixed to the protective member 6510 by adhesive layers (not shown).

[0451] In a region outside the display portion 6502a, a part of the display panel 6511 is folded back, and the folded back part is connected to an FPC 6515. An IC 6516 is mounted on the FPC 6515. The FPC 6515 is connected to a terminal provided on a printed circuit board 6517.

[0452] A flexible display can be applied to the display panel 6511. The flexible display is configured using a plurality of flexible films and uses a plurality of light-emitting elements arranged in a matrix. It is preferable to use an EL element (also referred to as an EL device) such as an OLED or a QLED as the light-emitting element. Examples of light-emitting materials included in the EL element include a fluorescent material (a fluorescent material), a phosphorescent material (a phosphorescent material), and a thermally activated delayed fluorescence (TADF) material. Light-emitting materials included in the EL element include not only organic compounds but also inorganic compounds (such as quantum dot materials). Furthermore, LEDs such as microLEDs can also be used as the light-emitting elements.

[0453] By using a flexible display, an extremely lightweight electronic device can be realized by effectively utilizing the internal space of the housing 6501. In addition, since the display panel 6511 is extremely thin, the thickness of the electronic device can be reduced and a large-capacity first battery 6518a can be mounted thereon.

[0454] Furthermore, in order to use a large-capacity battery, the electronic device 6500 is configured to include a second battery 6518b inside the cover portion 6520. Although a connection portion is not shown, the first battery 6518a and the second battery 6518b are electrically connected to each other. The flexible battery of one embodiment of the present invention can be used as the second battery 6518b.

[0455] In addition, by folding back a part of the display panel 6511 and arranging a connection portion with the FPC 6515 on the back side of the pixel portion, an electronic device with a narrow frame can be realized.

[0456] By using the flexible battery of one embodiment of the present invention as one or both of the first battery 6518a and the second battery 6518b, part of the electronic device 6500 can be folded to make it smaller, thereby realizing a highly portable electronic device 6500.

[0457] 32A is a perspective view showing a state in which the dotted line portion in FIG. 31A is folded. The electronic device 6500 can be folded in two, and the display portion 6502a and the second battery 6518b can be folded repeatedly.

[0458] 32A shows a configuration in which the second display unit 6502b is provided in the area where the cover unit 6520 slides when folded. Even when folded in two, the user can visually check the second display unit 6502b to see a simple time display or a notification display of incoming email.

[0459] 32B is a schematic diagram showing a cross section of the cover when the electronic device 6500 is folded. For simplicity, the inside of the housing 6501 is not shown in FIG.

[0460] 32B, the hinge portion 6519 can also be called a connecting portion, and is not limited to the example of a structure in which a plurality of pillars are connected, and can have various forms. In particular, it is preferable to have a mechanism that allows the display portion 6502a and the second battery 6518b to be bent without expanding or contracting.

[0461] Although the second battery 6518b is illustrated inside the cover portion 6520, a plurality of second batteries may be included. The cover portion 6520 may also include a charging control circuit or a wireless charging circuit for the second battery 6518b inside.

[0462] The cover portion 6520 is partially fixed to the housing 6501, and a portion overlapping with a hinge portion 6519 and a portion overlapping with the second display portion 6502b after being bent and slid are not fixed.

[0463] Furthermore, the cover unit 6520 does not need to be fixed to the housing 6501 and may be detachable. When a large capacity is not required, the electronic device 6500 can be used by detaching the cover unit 6520 and using the first battery 6518a. Furthermore, if the detached second battery 6518b is charged, the first battery 6518a can be replenished when the second battery 6518b is reconnected to the first battery 6518a. Therefore, the cover unit 6520 can also be used as a mobile battery.

[0464] 32A and 32B show an example in which the display unit 6502a is folded in half so that the display surface thereof faces inward, but this is not particularly limited thereto, and depending on the configuration of the hinge portion 6519, it may also be possible to fold the display unit 6502a in half so that the display surface faces outward.

[0465] The flexible battery of one embodiment of the present invention has high reliability against repeated deformation and can therefore be suitably used in such foldable devices.

[0466] This embodiment mode can be implemented by appropriately combining at least a part of it with other embodiment modes described in this specification.

[0467] (Embodiment 8) In this embodiment, an example in which a flexible battery according to one embodiment of the present invention is mounted in an electronic device will be described. Examples of electronic devices in which a flexible battery is mounted include television sets (also referred to as televisions or television receivers), computer monitors, digital cameras, digital video cameras, digital photo frames, mobile phones (also referred to as mobile phones or mobile phone devices), portable game consoles, personal digital assistants, sound players, and large game consoles such as pachinko machines. Examples of personal digital assistants include notebook personal computers, tablet terminals, e-book readers, and mobile phones.

[0468] 33A shows an example of a mobile phone. The mobile phone 2100 includes a display portion 2102 built into a housing 2101, operation buttons 2103, an external connection port 2104, a speaker 2105, a microphone 2106, and the like. Note that the mobile phone 2100 includes a flexible battery 2107 which is one embodiment of the present invention. The flexible battery 2107 can be bent, and therefore can be mounted in a bendable region of the mobile phone 2100.

[0469] The mobile phone 2100 can execute various applications such as mobile phone calls, e-mail, document browsing and creation, music playback, internet communication, and computer games.

[0470] The operation button 2103 can be provided with various functions such as time setting, power on / off operation, wireless communication on / off operation, silent mode activation / deactivation, power saving mode activation / deactivation, etc. For example, the functions of the operation button 2103 can be freely set by an operating system incorporated in the mobile phone 2100.

[0471] The mobile phone 2100 is also capable of performing standardized short-range wireless communication, and can also make hands-free calls by communicating with a wirelessly enabled headset, for example.

[0472] The mobile phone 2100 also includes an external connection port 2104, and can directly exchange data with other information terminals via a connector. Charging can also be performed via the external connection port 2104. Note that charging may be performed by wireless power supply without using the external connection port 2104.

[0473] Furthermore, the mobile phone 2100 preferably has a sensor. As the sensor, for example, a fingerprint sensor, a pulse sensor, a body temperature sensor or other human body sensor, a touch sensor, a pressure sensor, an acceleration sensor, or the like is preferably mounted.

[0474] 33B shows an unmanned aerial vehicle 2300 having multiple rotors 2302. The unmanned aerial vehicle 2300 is sometimes called a drone. The unmanned aerial vehicle 2300 has a flexible battery 2301 according to one embodiment of the present invention, a camera 2303, and an antenna (not shown). The unmanned aerial vehicle 2300 can be remotely controlled via the antenna. The flexible battery 2301 is bendable and can be mounted in a bendable area of ​​the unmanned aerial vehicle 2300.

[0475] 33C illustrates an example of a robot. The robot 6400 illustrated in FIG. 33C includes a flexible battery 6409 according to one embodiment of the present invention, an illuminance sensor 6401, a microphone 6402, an upper camera 6403, a speaker 6404, a display unit 6405, a lower camera 6406, an obstacle sensor 6407, a moving mechanism 6408, a computing device, and the like. The flexible battery 6409 is bendable and can be mounted in a bending region of the robot 6400.

[0476] The microphone 6402 has a function of detecting the user's speaking voice, environmental sounds, etc. The speaker 6404 has a function of emitting sound. The robot 6400 can communicate with the user using the microphone 6402 and the speaker 6404.

[0477] The display unit 6405 has a function of displaying various information. The robot 6400 can display information desired by the user on the display unit 6405. The display unit 6405 may be equipped with a touch panel. The display unit 6405 may also be a detachable information terminal, which can be installed in a fixed position on the robot 6400 to enable charging and data transfer.

[0478] The upper camera 6403 and the lower camera 6406 have the function of capturing images of the surroundings of the robot 6400. In addition, the obstacle sensor 6407 can detect the presence or absence of obstacles in the direction of travel when the robot 6400 moves forward using the movement mechanism 6408. The robot 6400 can recognize the surrounding environment and move safely using the upper camera 6403, the lower camera 6406, and the obstacle sensor 6407.

[0479] The robot 6400 includes a flexible battery 6409 according to one embodiment of the present invention and a semiconductor device or electronic component in its internal area.

[0480] 33D illustrates an example of a cleaning robot. The cleaning robot 6300 includes a display unit 6302 disposed on the top surface of a housing 6301, a plurality of cameras 6303 disposed on the side surface, a brush 6304, an operation button 6305, a flexible battery 6306 which is one embodiment of the present invention, various sensors, and the like. Although not shown, the cleaning robot 6300 includes tires, a suction port, and the like. The cleaning robot 6300 can move by itself, detect dust 6310, and suck the dust from the suction port disposed on the bottom surface. The flexible battery 6306 is bendable and can be mounted in a bending area of ​​the cleaning robot 6300.

[0481] The cleaning robot 6300 can analyze an image captured by the camera 6303 and determine whether or not there is an obstacle such as a wall, furniture, or a step. Furthermore, when an object that may become entangled in the brush 6304, such as a wire, is detected by image analysis, the cleaning robot 6300 can stop rotation of the brush 6304. The cleaning robot 6300 includes a flexible battery 6306 according to one embodiment of the present invention and a semiconductor device or an electronic component in its internal area.

[0482] 34A shows an example of a wearable device. The wearable device uses a flexible battery as a power source. Furthermore, in order to improve splash-proof, water-resistant, or dust-proof performance when used at home or outdoors, there is a demand for a wearable device that can be charged wirelessly as well as via a wired connection with an exposed connector.

[0483] For example, a flexible battery according to one embodiment of the present invention can be mounted on a glasses-type device 4000 as shown in FIG. 34A . The glasses-type device 4000 includes a frame 4000a and a display unit 4000b. Mounting a flexible battery on the temples of the curved frame 4000a makes it possible to provide a glasses-type device 4000 that is lightweight, has a good weight balance, and can be used for a long time. The flexible battery can be bent, and can be mounted on curved parts.

[0484] Furthermore, a flexible battery according to one embodiment of the present invention can be mounted on a headset device 4001. The headset device 4001 includes at least a microphone unit 4001a, a flexible pipe 4001b, and an earphone unit 4001c. A flexible battery can be provided in the flexible pipe 4001b or the earphone unit 4001c. The flexible battery can be bent and can be mounted on a curved portion.

[0485] Furthermore, a flexible battery according to one embodiment of the present invention can be mounted on a device 4002 that can be directly attached to the body. A flexible battery 4002b can be provided in a thin housing 4002a of the device 4002. The flexible battery can be bent and can be mounted on a curved portion.

[0486] Furthermore, the flexible battery according to one embodiment of the present invention can be mounted on a device 4003 that can be attached to clothing. A flexible battery 4003b can be provided in a thin housing 4003a of the device 4003. The flexible battery can be bent and can be mounted on a curved portion.

[0487] Furthermore, the flexible battery according to one embodiment of the present invention can be mounted on the belt-type device 4006. The belt-type device 4006 includes a belt portion 4006a and a wireless power receiving portion 4006b, and the flexible battery can be mounted in an internal region of the belt portion 4006a. The flexible battery can be bent and can be mounted on a curved portion.

[0488] Furthermore, the flexible battery according to one embodiment of the present invention can be mounted on the wristwatch device 4005. The wristwatch device 4005 has a display portion 4005a and a belt portion 4005b, and a flexible battery can be provided on the display portion 4005a or the belt portion 4005b. The flexible battery can be bent and can be mounted on a curved portion.

[0489] The display unit 4005a can display not only the time but also various other information such as incoming emails or phone calls.

[0490] Furthermore, since the wristwatch device 4005 is a wearable device that is worn directly on the wrist, it may be equipped with sensors that measure the user's pulse, blood pressure, etc. Data on the user's exercise volume and health can be accumulated to manage the user's health.

[0491] FIG. 34B shows a perspective view of the wristwatch-type device 4005 removed from the wrist.

[0492] 34C shows a side view of the display device 4005. Fig. 34C illustrates a state in which a flexible battery 913 according to one embodiment of the present invention is built into the internal region. The flexible battery 913 is provided in a position overlapping with the display portion 4005a, and can have high density, high capacity, and is small and lightweight. The flexible battery 913 can be bent and can be mounted on a curved portion.

[0493] 34D shows an example of a wireless earphone. Here, the wireless earphone is shown having a pair of main bodies 4100a and 4100b, but this does not necessarily have to be a pair.

[0494] The main bodies 4100a and 4100b each include a driver unit 4101, an antenna 4102, and a flexible battery 4103 which is one embodiment of the present invention. A display portion 4104 may also be included. Furthermore, a substrate on which a circuit such as a wireless IC is mounted, a charging terminal, or the like is preferably included. A microphone may also be included. The flexible battery 4103 can be bent and can be mounted on a curved portion.

[0495] The case 4110 includes a flexible battery 4111 according to one embodiment of the present invention. The case 4110 preferably includes a substrate on which circuits such as a wireless IC and a charging control IC are mounted, and a charging terminal. The case 4110 may also include a display unit, a button, and the like. The flexible battery 4111 can be bent and can be mounted on a curved portion.

[0496] The main units 4100a and 4100b can wirelessly communicate with other electronic devices such as smartphones. This allows sound data and the like sent from other electronic devices to be played back on the main units 4100a and 4100b. If the main units 4100a and 4100b have microphones, the sound picked up by the microphones can be sent to the other electronic device, and the sound data after processing by the electronic device can be sent back to the main units 4100a and 4100b for playback. This allows the main units 4100a and 4100b to be used as, for example, a translation device.

[0497] The flexible battery 4103 of the main body 4100a can be charged from the flexible battery 4111 of the case 4110. The flexible battery 4111 and the flexible battery 4103 can be bent and can be mounted on a curved portion.

[0498] 35A to 35C show examples of eyeglass-type devices different from those described above. Fig. 35A is a perspective view of an eyeglass-type device 5000.

[0499] The glasses-type device 5000 has a function as a so-called mobile information terminal, and can execute various programs and play various contents by connecting to the Internet. For example, the glasses-type device 5000 has a function to display augmented reality content in AR mode. The glasses-type device 5000 may also have a function to display virtual reality content in VR mode. Note that the glasses-type device 5000 may also have a function to display substitutional reality (SR) or mixed reality (MR) content in addition to AR and VR.

[0500] The eyeglass-type device 5000 includes a housing 5001, an optical member 5004, a wearing device 5005, a light-shielding portion 5007, and the like. The housing 5001 preferably has a cylindrical shape. The eyeglass-type device 5000 is preferably configured to be wearable on the user's head. It is more preferable that the housing 5001 of the eyeglass-type device 5000 is worn on the user's head above the outer circumferential line of the head that passes through the eyebrows and ears. By making the housing 5001 into a cylindrical shape that curves along the user's head, the wearability of the eyeglass-type device 5000 can be improved. The housing 5001 is fixed to the optical member 5004. The optical member 5004 is fixed to the wearing device 5005 via the light-shielding portion 5007 or via the housing 5001.

[0501] The glasses-type device 5000 includes a display device 5021, a reflector 5022, a flexible battery 5024 according to one embodiment of the present invention, and a system unit. The display device 5021, the reflector 5022, the flexible battery 5024, and the system unit are preferably provided inside a housing 5001. The system unit may include a control unit, a storage unit, a communication unit, a sensor, and the like that are included in the glasses-type device 5000. The system unit is also preferably provided with a charging circuit, a power supply circuit, and the like. The flexible battery 5024 is bendable and can be mounted on a curved portion.

[0502] Fig. 35B shows the components of the glasses-type device 5000 in Fig. 35A. Fig. 35B is a schematic diagram for explaining the details of the components of the glasses-type device 5000 shown in Fig. 35A.

[0503] 35B , a flexible battery 5024 according to one embodiment of the present invention, a system unit 5026, and a system unit 5027 are provided along a cylindrical housing 5001. A system unit 5025 is also provided along the flexible battery 5024 and the like.

[0504] The housing 5001 preferably has a curved cylindrical shape. By providing the flexible battery 5024 along the curved cylinder, the flexible battery 5024 can be efficiently arranged in the housing 5001, the space inside the housing 5001 can be used efficiently, and the volume of the flexible battery 5024 can be increased in some cases.

[0505] The housing 5001 has, for example, a cylindrical shape, and the axis of the cylinder is, for example, along a part of an approximately ellipse. Furthermore, it is preferable that the cross section of the cylinder is, for example, approximately ellipse. Alternatively, it is preferable that the cross section of the cylinder has, for example, a part of an ellipse. In particular, when the eyeglass-type device 5000 is worn on the head, it is preferable that the part of the cross section having an ellipse shape is located on the side facing the head when worn. However, one aspect of the present invention is not limited to this. For example, the cross section of the cylinder may have a part that is polygonal (triangle, square, pentagon, etc.).

[0506] The housing 5001 is formed, for example, to be curved along the forehead of the user. The housing 5001 is also placed, for example, along the forehead.

[0507] The housing 5001 may be configured by combining two or more cases. For example, it may be configured by combining an upper case and a lower case. It may also be configured by combining an inner case (the side worn by the user) and an outer case. It may also be configured by combining three or more cases.

[0508] An electrode may be provided on the housing 5001 in a portion that touches the forehead, and brain waves may be measured by the electrode. Alternatively, an electrode may be provided on the portion that touches the forehead, and information such as the user's sweat may be measured by the electrode.

[0509] A plurality of flexible batteries 5024 may be arranged inside the housing 5001 .

[0510] Furthermore, the flexible battery 5024 is preferable because it can be shaped to fit the curved tube. Furthermore, the flexibility of the flexible battery allows for greater freedom in placement inside the housing. The flexible battery 5024, a system unit, and the like are placed inside the cylindrical housing. The system unit is configured, for example, on multiple circuit boards. The multiple circuit boards and the flexible battery are connected using connectors, wiring, and the like. The flexibility of the flexible battery allows for placement that avoids connectors, wiring, and the like.

[0511] The flexible battery 5024 may be provided inside the housing 5001 as well as inside the wearing device 5005, for example.

[0512] 36A to 36C show examples of head-mounted devices. Figures 36A and 36B show a head-mounted device 5100 having a band-shaped attachment 5105, and the head-mounted device 5100 is connected to a terminal 5150 shown in Figure 36C via a cable 5120.

[0513] 36A shows the first portion 5102 in a closed state, and FIG. 36B shows the first portion 5102 in an open state. When closed, the first portion 5102 has a shape that covers not only the front but also the sides of the face. This can shield the user's field of vision from external light, thereby enhancing the sense of realism and immersion. For example, depending on the content displayed, this can also enhance the sense of fear felt by the user.

[0514] 36A and 36B has a band-shaped wearing device 5105. This makes it less likely to slip off than the configuration shown in Fig. 36A etc., and is therefore suitable for enjoying content that requires a relatively large amount of physical activity, such as an attraction.

[0515] A flexible battery 5107 according to one embodiment of the present invention may be built into the back of the head side of the wearing equipment 5105. By balancing the weight of the housing 5101 on the front of the head side and the weight of the flexible battery 5107 on the back of the head side, the center of gravity of the head-worn device 5100 can be adjusted, and the wearing comfort can be improved.

[0516] Furthermore, a flexible battery 5108 according to one embodiment of the present invention may be placed inside a band-shaped attachment 5105. In the example shown in Fig. 36A, two flexible batteries 5108 are placed inside the attachment 5105. The use of a flexible battery having flexibility is preferable because it can be shaped to fit the curved band shape.

[0517] The wearing device 5105 also has a part 5106 that covers the forehead or forehead of the user. By including the part 5106, it is possible to make it less likely to slip off. Furthermore, an electrode can be provided on the part 5106 or on the part of the housing 5101 that touches the forehead, and brain waves can be measured using the electrode.

[0518] This embodiment can be implemented in appropriate combination with other embodiments. [Explanation of Symbols] 100 Flexible battery 101: negative electrode 102: current collector 103: active material layer 105: carbon-containing material 131: positive electrode 132: current collector 133: active material layer

Claims

1. having a negative electrode and a positive electrode, The negative electrode is a first current collector; a second current collector located in the opening of the first current collector; a negative electrode active material formed on the first current collector and the second current collector; a first carbon-containing material that encases the first current collector, the second current collector, and the negative electrode active material; The positive electrode is a third current collector; and a fourth current collector located in the opening of the third current collector; a positive electrode active material formed on the third current collector and the fourth current collector; a second carbon-containing material that encases the third current collector, the fourth current collector, and the positive electrode active material; Flexible battery.

2. 2. The method according to claim 1, wherein the second current collector and the fourth current collector are provided so as to overlap a bending region. Flexible battery.

3. 2. The method according to claim 1, wherein the first carbon-containing material and the second carbon-containing material each have a bag-like or cylindrical shape. Flexible battery.

4. 2. The method according to claim 1, wherein the first carbon-containing material and the second carbon-containing material each include a graphene compound. Flexible battery.

5. 5. The graphene compound according to claim 4, wherein the graphene compound is graphene oxide. Flexible battery.

6. 6. The graphene compound according to claim 5, wherein the graphene compound is reduced graphene oxide. Flexible battery.

7. 2. The method according to claim 1, wherein the first carbon-containing material and the second carbon-containing material each include graphene. Flexible battery.

8. 2. The method according to claim 1, wherein the first carbon-containing material and the second carbon-containing material each include carbon fibers. Flexible battery.

9. 9. The battery according to claim 1, further comprising a separator between the negative electrode and the positive electrode. Flexible battery.

10. According to claim 9, the separator has a bag-like or cylindrical shape. Flexible battery.

11. 9. The battery according to claim 1, wherein there is no separator between the negative electrode and the positive electrode. Flexible battery.

12. 12. The battery according to claim 1, wherein the area of ​​the positive electrode is smaller than the area of ​​the negative electrode. Flexible battery.

13. 13. The negative electrode active material according to claim 1, wherein the negative electrode active material or the positive electrode active material has a median diameter (D50) of 10 nm or more and 30 μm or less. Flexible battery.

14. 13. The positive electrode active material according to claim 1, wherein the positive electrode active material has secondary particles, and the median diameter (D50) of primary particles constituting the secondary particles is 10 nm or more and 1 μm or less. Flexible battery.

15. An electronic device equipped with the flexible battery according to any one of claims 1 to 14.