Secondary battery and electronic apparatus

Abstract

The present invention provides a bendable secondary battery that is suited to foldable electronic apparatuses. The present invention also provides a secondary battery that is highly safe. According to the present invention, a guide part is provided to a packaging film so as to be capable of moving within an area in which folds or wrinkles do not occur. The guide part controls the bending of a secondary battery in an area for which the radius of curvature is 10–60 mm. Using a hinge part to control a bending part of the secondary battery to an area of 10–60 mm makes it possible to prevent reductions in reliability.

Description

Secondary batteries and electronic devices

[0001] One embodiment of the present invention relates to a semiconductor device, a portable information terminal, or an electronic device including a secondary battery.

[0002] One embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, an electronic device, or a manufacturing method thereof.

[0003] In this specification, the term "semiconductor device" refers to any device that can function by utilizing semiconductor characteristics, and electro-optical devices, semiconductor circuits, and electronic devices are all included in the category of semiconductor devices.

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

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

[0006] Patent Document 1 discloses a bendable secondary battery.

[0007] JP 2015-130650 A

[0008] 2. Description of the Related Art Electronic devices that are carried by or worn by users have been actively developed.

[0009] Electronic devices carried by users or worn by users operate using primary or secondary batteries, which are examples of power storage devices, as their power source. It is desirable for electronic devices carried by users to be used for long periods of time, and for this reason, large-capacity secondary batteries are used. However, incorporating a large-capacity secondary battery into an electronic device poses the problem of its large size and weight. Therefore, development is underway to develop small or thin, large-capacity secondary batteries that can be incorporated into portable electronic devices.

[0010] Furthermore, some portable electronic devices are foldable to reduce their size, and foldable electronic devices often have multiple housings separated by a folding region, typically a hinge portion.

[0011] Conventionally, secondary batteries cannot be placed in the folding area, such as the hinge, resulting in a difference in the capacity of the built-in secondary battery when comparing folding and non-folding electronic devices of the same size. Conventionally, in devices that fold in half, the folding area is the dividing line, and a non-folding secondary battery is built into one housing or multiple housings, each housing having multiple batteries. When only one non-folding secondary battery is placed in one housing, it is difficult to increase the battery capacity. Furthermore, when multiple batteries are built into multiple housings, the number of components increases, making it difficult to miniaturize the device when, for example, a control circuit or connection circuit for controlling the balance between multiple secondary batteries is built in.

[0012] Therefore, one of the objects is to provide a bendable secondary battery suitable for foldable electronic devices.

[0013] Another object of one embodiment of the present invention is to provide a novel substance, an active material, a power storage device, or a manufacturing method thereof.

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

[0015] When a secondary battery is formed by stacking a current collector provided with a positive electrode active material layer, a separator, and a current collector provided with a negative electrode active material layer in this order, and then stacking multiple such stacks to enclose an electrolyte solution in an exterior film, bending the secondary battery significantly will cause wrinkles, creases, or bending tendencies to form on the surface of the exterior film.

[0016] An electronic device that can be folded in half is used by a user to alternate between the unfolded state and the folded state.

[0017] The repetition of these two states causes the surface of the exterior film to be subjected to stress and repeated bending and stretching, and if folds or wrinkles form, the same areas are repeatedly subjected to stress, which can become the starting point for a decline in the reliability of the secondary battery.Because the exterior film is thin and soft, there is a risk of it breaking.

[0018] For example, the exterior film is laminated to seal the inside of the secondary battery, but it cannot follow the bending movement and there is a risk of holes forming along the creases. Therefore, the inventors have determined through experiments and experience that the rate-limiting point for a bendable battery is whether or not wrinkles or creases form in the exterior film.

[0019] Furthermore, secondary batteries using exterior film have multiple laminates, each including a positive electrode, a separator, and a negative electrode. Instead of using double-sided coated current collectors, the laminates use single-sided coated current collectors, with the uncoated surfaces of the current collectors in contact with each other, allowing the laminates to slide when bent. Therefore, folds or wrinkles in the exterior film, rather than defects in the stacked laminates, are the rate-limiting factor for reliability.

[0020] Therefore, a solution is to provide a structure that prevents folds or wrinkles from occurring in the exterior film.

[0021] The configuration disclosed in this specification is a secondary battery in which a laminate including a positive electrode, a separator, and a negative electrode is surrounded by an exterior film, and the secondary battery has a bent portion that can be bent, and the radius of curvature on the inner side of the bend of the bent portion is controlled within a range of 10 mm or more and 60 mm or less.

[0022] In the above configuration, the thickness of the laminate is set to 0.3 mm or more and 2 mm or less, preferably 0.5 mm or more and 1.5 mm or less.

[0023] Another configuration disclosed in this specification is an electronic device having a display unit, a hinge unit, and a secondary battery, in which the secondary battery is an electronic device in which a laminate including a positive electrode, a separator, and a negative electrode is surrounded by an exterior film, the secondary battery has a bending unit that overlaps with the hinge unit, and the hinge unit controls the radius of curvature on the inner side of the bending of the bending unit of the secondary battery to be within a range of 10 mm or more and 60 mm or less.

[0024] In the above configuration, the display unit at least partially overlaps with the bent portion of the secondary battery. The display unit is flexible.

[0025] For example, a guide portion is provided to allow movement within a range where no creases or wrinkles are formed in the exterior film. In a foldable electronic device, a member (a housing or a frame) that controls the displacement of the movable portion is called a guide portion, and one type of guide portion is called a hinge portion. The guide portion controls the bending of the secondary battery so that the radius of curvature at the bending portion of the secondary battery is 10 mm or more and 60 mm or less.

[0026] The inventors discovered that when the exterior film is embossed, bending the secondary battery at a bent portion with a curvature radius of less than 10 mm may result in reduced reliability. On the other hand, embossing the exterior film is preferable to reduce the bending stress of the secondary battery. Furthermore, reducing the bending stress of the secondary battery also depends on the thickness of the laminate housed in the exterior film, i.e., the number of laminate layers, with a thinner thickness being preferable. Furthermore, a larger surface area of ​​the secondary battery is preferable to increase the capacity of the secondary battery. The designer can appropriately design the planar size of the secondary battery to match the size of the electronic device in which it will be installed. Furthermore, if the bending stress of the secondary battery is high, the user must apply strong force to the electronic device, making it difficult to create an electronic device that can be easily folded with one hand. Furthermore, users should avoid applying sudden force when folding an electronic device to prevent damage to the hinge. Depending on the hinge, the hinge may not be folded completely, but rather the movable portion of the hinge may be configured to be 120° or more but less than 180°.

[0027] Furthermore, if the radius of curvature at the bent portion of the secondary battery is greater than 60 mm, the size of the hinge portion becomes large, making it difficult to make the electronic device thinner, and the purpose of bending the electronic device is lost.

[0028] The radius of curvature of a surface will be described with reference to FIG. 12 . In FIG. 12A , on a plane 3701 obtained by cutting a curved surface 3700, a portion of a curve 3702 included in the curved surface 3700 is approximated to an arc of a circle, and the radius of the circle is defined as radius of curvature 3703, and the center of the circle is defined as center of curvature 3704. FIG. 12B shows a top view of the curved surface 3700. FIG. 12C shows a cross-sectional view of the curved surface 3700 cut at plane 3701. When a curved surface is cut with a plane, the radius of curvature of the curve that appears in the cross section varies depending on the angle of the plane relative to the curved surface or the cutting position. In this specification, the smallest radius of curvature is defined as the radius of curvature of the surface. Note that when an embossed exterior film is used, this corresponds to the radius of curvature in a cross section obtained by cutting a curved surface connecting the ridge lines or the vertices of the convex portions with a plane.

[0029] The cross-sectional shape of the secondary battery is not limited to a simple arc shape, and can be a shape that includes a partial arc, such as a wave shape, an S-shape, an N-shape, or a W-shape.When the curved surface of the secondary battery has a shape with multiple centers of curvature, the secondary battery can be deformed so that the radius of curvature of the exterior body film that is closest to the center of curvature of the exterior body film of the two film surfaces is in the range of 10 mm to 60 mm, on the curved surface with the smallest radius of curvature among the radii of curvature at each of the multiple centers of curvature.

[0030] In other words, a bending restriction member (guide portion) that restricts bending at a radius of curvature smaller than the range of radius of curvature in a specified bending direction is provided around the bent portion of the secondary battery, thereby preventing a decrease in reliability due to bending of the secondary battery.

[0031] It is possible to provide an optimal secondary battery for foldable electronic devices. By controlling the bending portion of the secondary battery to a range of 10 mm to 60 mm using the hinge portion, it is possible to prevent a decrease in reliability.

[0032] Furthermore, by controlling the bent portion of the secondary battery to 10 mm or more and 60 mm or less, it is possible to prevent folds or wrinkles from occurring in the exterior film.

[0033] FIG. 1 is a cross-sectional view schematically illustrating one embodiment of the present invention. FIG. 2 is a cross-sectional view schematically illustrating one embodiment of the present invention. FIGS. 3A to 3D are views illustrating a bendable secondary battery. FIGS. 4A and 4B are views illustrating a bendable secondary battery. FIGS. 5A and 5B are views illustrating a film processing method. FIGS. 6A to 6E are views illustrating a method for manufacturing a secondary battery. FIG. 7A is an example of a perspective view of an electronic device, and FIG. 7B is a schematic view illustrating a portion of a cross section of the electronic device. FIG. 8A is an example of a perspective view of an electronic device, and FIG. 8B is a schematic view illustrating a portion of a cross section of the electronic device. FIG. 9A is an external view illustrating one embodiment of an electronic device according to the present invention, FIG. 9B is an external view seen from another direction, and FIG. 9C is a view illustrating one example of the external appearance of a secondary battery built into the electronic device. FIGS. 10A, 10B, and 10C are photographs illustrating experimental results of Example 1. FIGS. 11A and 11B are graphs illustrating experimental results of Example 2. 12A to 12C are diagrams illustrating the radius of curvature.

[0034] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be readily understood by those skilled in the art that various modifications can be made to the embodiments and details. Furthermore, the present invention should not be interpreted as being limited to the description of the embodiments shown below.

[0035] Embodiment 1 An example of a bendable secondary battery will be described with reference to FIGS. 1, 2, 3, and 4. FIG.

[0036] FIG. 1 is a schematic cross-sectional view of a secondary battery 200.

[0037] The secondary battery 200 includes an exterior film 251 and an electrode laminate 210 housed in the interior region of the exterior film 251. The electrode laminate 210 includes at least a positive electrode 211a and a negative electrode 211b. The positive electrode 211a and the negative electrode 211b together constitute the electrode laminate 210. Note that a separator disposed between the positive electrode 211a and the negative electrode 211b is not shown in FIG. 1 . The positive electrode 211a has a configuration in which a positive electrode active material layer is provided on a positive electrode current collector. The negative electrode 211b has a configuration in which a negative electrode active material layer is provided on a negative electrode current collector.

[0038] In the electrode laminate 210, it is preferable to use a current collector that is coated on one side rather than a current collector that is coated on both sides, and to stack the uncoated side of the current collector so that it comes into contact with the uncoated side of the current collector, thereby enabling the laminate to slide when the secondary battery is bent.

[0039] The thinner the thickness d of the laminate, the smaller the bending stress, which is preferable, but if it is too thin, a large electrode area is required to ensure the required capacitance. In this embodiment, the thickness d of the laminate is 0.3 mm or more and 2 mm or less, preferably 0.5 mm or more and 1.5 mm or less.

[0040] It is also preferable to have a space 273 between the longitudinal ends of the positive electrode 211 a and the negative electrode 211 b and the exterior body film 251. Providing the space 273 provides a space in which the laminate can slide when the secondary battery is bent, and this is preferable because it provides a margin for expansion and contraction of the exterior body film 251.

[0041] The exterior film 251 has a three-layer structure in which a thin, flexible metal film, such as aluminum, stainless steel, copper, or nickel, is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film, such as polyamide resin or polyester resin, is provided on the thin metal film as the outer surface of the exterior. Alternatively, a thin metal film may be formed on a resin sheet by sputtering and sandwiched between resins.

[0042] With the above configuration, it is possible to realize a secondary battery 200 that can be bent without embossing the exterior film.

[0043] The secondary battery 200 can be bent in the direction of the arrow along a jig with a curvature radius R as shown in FIG. 1, and if the curvature radius is within the range of 10 mm or more and 60 mm or less, the occurrence of wrinkles or creases can be reduced.

[0044] 2 and 3 show examples of secondary batteries in which the exterior body film is embossed. The grooves formed in the exterior body film after embossing can be formed in one direction or in multiple directions, and the grooves can be parallel to each other or can intersect each other.

[0045] 2 shows an example of the cross-sectional structure of a secondary battery 240 having a plurality of parallel grooves in one direction and a corrugated cross section. The exterior film 251 of the secondary battery 240 has a corrugated shape with alternating ridge lines 271 and valley lines 272. As shown in FIG. 2, the secondary battery 240 can be bent in the direction of the arrow along a jig with a curvature radius R, and the occurrence of wrinkles or creases can be reduced if the curvature radius is within the range of 10 mm to 60 mm.

[0046] Furthermore, an exterior film having intersecting grooves (an exterior film embossed with a cross-shaped wave pattern) is preferable because it can be flexibly bent in multiple directions, not just in one specific direction, and an example of this is shown in Figure 3.

[0047] FIG. 3A is a schematic top view of a bendable secondary battery 250. FIGS. 3B and 3C are schematic cross-sectional views taken along the lines C1-C2 and A1-A2 in FIG. 3A , respectively. The secondary battery 250 includes an exterior film 251 and an electrode stack 210 housed within the interior region of the exterior film 251. The electrode stack 210 includes at least a positive electrode 211a and a negative electrode 211b. The positive electrode 211a and the negative electrode 211b together constitute the electrode stack 210. A lead 212a electrically connected to the positive electrode 211a and a lead 212b electrically connected to the negative electrode 211b extend outside the exterior film 251. In the electrode stack 210, a separator is preferably disposed between the positive electrode 211a and the negative electrode 211b. Alternatively, a solid electrolyte layer may be disposed between the positive electrode 211a and the negative electrode 211b. The solid electrolyte layer preferably has flexibility. The solid electrolyte layer preferably has flexibility. In addition to the positive electrode 211a and the negative electrode 211b, an electrolyte (not shown) is enclosed in the area surrounded by the exterior film 251. An electrolytic solution may be added to the solid electrolyte. A gel electrolyte may also be used as the electrolyte.

[0048] The positive electrode 211a and the negative electrode 211b of the secondary battery 250 will be described with reference to Fig. 4. Fig. 4A is a perspective view illustrating the stacking order of the positive electrode 211a, the negative electrode 211b, and the separator 214. Fig. 4B is a perspective view showing the lead 212a and the lead 212b in addition to the positive electrode 211a and the negative electrode 211b.

[0049] 4A , the secondary battery 250 includes a plurality of rectangular positive electrodes 211a, a plurality of rectangular negative electrodes 211b, and a plurality of separators 214. The positive electrodes 211a and the negative electrodes 211b each have a protruding tab portion and a portion other than the tab. A positive electrode active material layer is formed on one surface of the positive electrodes 211a in the portion other than the tab, and a negative electrode active material layer is formed on one surface of the negative electrodes 211b in the portion other than the tab.

[0050] The positive electrode 211a and the negative electrode 211b are stacked so that the surfaces of the positive electrode 211a on which the positive electrode active material layer is not formed and the surfaces of the negative electrode 211b on which the negative electrode active material layer is not formed are in contact with each other.

[0051] A separator 214 is provided between the surface of the positive electrode 211a on which the positive electrode active material is formed and the surface of the negative electrode 211b on which the negative electrode active material is formed. In Figures 4A and 4B, the separator 214 is shown by a dotted line for ease of viewing.

[0052] 4B, the positive electrodes 211a and the leads 212a are electrically connected to each other at joints 215a, and the negative electrodes 211b and the leads 212b are electrically connected to each other at joints 215b.

[0053] Next, the exterior film 251 will be described with reference to FIGS. 3B to 3D.

[0054] The exterior body film 251 has a film-like shape and is folded in two to sandwich the positive electrode 211a and the negative electrode 211b. The exterior body film 251 has a folded portion 261, a pair of sealing portions 262, and a sealing portion 263. The pair of sealing portions 262 are provided to sandwich the positive electrode 211a and the negative electrode 211b and can also be called side seals. The sealing portion 263 has a portion that overlaps with the lead 212a and the lead 212b and can also be called a top seal.

[0055] The exterior body film 251 preferably has a cross-wave shape (also called a mesh shape or a chevron shape) in which ridge lines 271 and valley lines 272 intersect at the portions overlapping the positive electrode 211 a and the negative electrode 211 b. The angle of intersection is 20° or more and 160° or less. Furthermore, the seal portions 262 and 263 of the exterior body film 251 are preferably flat.

[0056] Fig. 3B is an example of a cross section, which corresponds to a cross section in the width direction of the secondary battery 250, the positive electrode 211a, and the negative electrode 211b.

[0057] Here, the distance La is the distance between the widthwise ends of the positive electrode 211a and the negative electrode 211b, i.e., the ends of the positive electrode 211a and the negative electrode 211b, and the seal portion 262. When the secondary battery 250 is bent, the positive electrode 211a and the negative electrode 211b deform so as to be displaced from each other in the longitudinal direction, as described below. In this case, if the distance La is too short, the exterior body film 251 may rub strongly against the positive electrode 211a and the negative electrode 211b, resulting in damage to the exterior body film 251. In particular, if the metal film of the exterior body film 251 is exposed, the metal film may be corroded by the electrolyte. Therefore, it is preferable to set the distance La as long as possible. On the other hand, if the distance La is too large, the volume of the secondary battery 250 increases.

[0058] Furthermore, it is preferable that the greater the total thickness t of the stacked positive electrode 211a and negative electrode 211b, the greater the distance La between the positive electrode 211a and negative electrode 211b and the seal portion 262.

[0059] Furthermore, when the distance between the pair of seal portions 262 is distance Lb, it is preferable to set distance Lb sufficiently larger than the width of the positive electrode 211 a and the negative electrode 211 b (here, width Wb of the negative electrode 211 b). This allows parts of the positive electrode 211 a and the negative electrode 211 b to shift in the width direction even if the positive electrode 211 a and the negative electrode 211 b come into contact with the exterior body film 251 when the secondary battery 250 is repeatedly bent and deformed, thereby effectively preventing the positive electrode 211 a and the negative electrode 211 b from rubbing against the exterior body film 251.

[0060] 3C is a cross section including lead 212a, and corresponds to a longitudinal cross section of secondary battery 250, positive electrode 211a, and negative electrode 211b. As shown in Figures 3C and 3D, it is preferable that a space 273 be formed between exterior body film 251 and the longitudinal ends of positive electrode 211a and negative electrode 211b at bent portion 261.

[0061] 3D is a schematic cross-sectional view of the secondary battery 250 when the battery is gently bent so as to form an arc at the center of the secondary battery 250. FIG. 3D corresponds to the cross section taken along the line B1-B2 in FIG. 3A.

[0062] When the secondary battery 250 is bent, a portion of the exterior body film 251 located on the outside of the bend stretches, while another portion located on the inside shrinks. More specifically, the portion located on the outside of the exterior body film 251 deforms so that the wave amplitude becomes smaller and the wave period becomes larger. On the other hand, the portion located on the inside of the exterior body film 251 deforms so that the wave amplitude becomes larger and the wave period becomes smaller. In this way, the deformation of the exterior body film 251 relieves the stress applied to the exterior body film 251 due to bending, so the material constituting the exterior body film 251 itself does not need to stretch. As a result, the exterior body film 251 does not break, and the secondary battery 250 can be bent with a small force.

[0063] 3D , when the secondary battery 250 is bent, the positive electrodes 211a and the negative electrodes 211b are displaced relative to each other. At this time, because the ends of the stacked positive electrodes 211a and negative electrodes 211b on the sealing portion 263 side are fixed by the fixing member 217, the positive electrodes 211a and negative electrodes 211b are displaced (slid) relative to each other such that the amount of displacement increases the closer they are to the bending portion 261. This relieves stress on the positive electrodes 211a and negative electrodes 211b, eliminating the need for the positive electrodes 211a and negative electrodes 211b themselves to expand and contract. As a result, the secondary battery 250 can be bent without damaging the positive electrodes 211a and negative electrodes 211b.

[0064] Furthermore, by providing a space 273 between the positive electrode 211a and the negative electrode 211b and the exterior body film 251, when the battery is bent, the positive electrode 211a and the negative electrode 211b located on the inside can shift relative to each other without coming into contact with the exterior body film 251.

[0065] The exterior film 251 may have an area that contacts the electrode stack 210 at the valley line 272 .

[0066] The secondary battery 250 illustrated in FIG. 3 is a battery that is resistant to breakage of the exterior film, the positive electrode 211a, and the negative electrode 211b, and deterioration of the battery characteristics, even when repeatedly bent.

[0067] 5A and 5B are perspective views showing an example of a cross wave shape obtained by performing embossing twice in different directions on the exterior body film.

[0068] Specifically, a film 61 having the embossed shape (which can be referred to as a cross-wave shape) shown in FIGS. 5A and 5B can be obtained by embossing the exterior film in a first direction and then embossing the exterior film in a second direction rotated 90 degrees from the first direction. The embossed shape shown in FIGS. 5A and 5B also corresponds to FIG. 3A . The film 61 having the cross-wave shape shown in FIG. 5A shows the shape used when a secondary battery is fabricated using a single film 61, and can be folded in half along the dashed line. The multiple films (films 62 and 63) having the cross-wave shape shown in FIG. 5B show the shape used when a secondary battery is fabricated using two films (films 62 and 63), and films 62 and 63 can be stacked together.

[0069] The exterior film shown in FIG. 2 is obtained by embossing the exterior film in a wave pattern in the first direction only once.

[0070] Embossing is a process performed using an embossing roll, which allows for the use of a smaller device. Furthermore, since the process can be performed without cutting the film, it is suitable for mass production. The process is not limited to the use of an embossing roll, and the film may be processed, for example, by pressing a pair of embossing plates with irregularities formed on the surface against the film. In this case, one of the embossing plates may be flat, and the process may be performed in multiple stages.

[0071] In the above-described configuration example of the secondary battery, the exterior body film on one side of the secondary battery and the exterior body film on the other side have the same embossed shape, but the configuration of the secondary battery of one embodiment of the present invention is not limited to this. For example, the secondary battery may have an embossed shape on the exterior body film on one side and an embossed shape on the exterior body film on the other side. Furthermore, the exterior body film on one side of the secondary battery may have different embossed shapes.

[0072] [Example of Method for Producing Secondary Battery] The following describes an example of a method for producing a secondary battery, in particular, when the battery 10 is a secondary battery. Note that explanations that overlap with those described above may be omitted.

[0073] Here, the method used is to fold the exterior film 11 having a cross-wave shape in the center, overlap the two edges, and seal the three sides with an adhesive layer. This is a so-called two-fold method, and although it can be folded in three for larger secondary batteries, it is preferable to fold it in one place because the fewer folding points the higher the reliability.

[0074] The exterior film 11 processed into a cross-wave shape is bent into the state shown in FIG. 6A.

[0075] 6B , a stack of a positive electrode current collector 72, a separator 73, and a negative electrode current collector 74 that constitute a secondary battery is prepared. Although not shown, a positive electrode active material layer is formed on a portion of the surface of the positive electrode current collector 72. Furthermore, a negative electrode active material layer is formed on a portion of the surface of the negative electrode current collector 74. For the sake of simplicity, an example has been shown in which a single stacked combination of the positive electrode current collector 72 on which a positive electrode active material layer is formed, the separator 73, and the negative electrode current collector 74 on which a negative electrode active material layer is formed is housed in a space formed by an exterior film. However, to increase the capacity of the secondary battery, multiple combinations can be stacked and housed in a space formed by an exterior film.

[0076] Then, two lead electrodes 76 having a sealing layer 75 shown in Fig. 6C are prepared. The lead electrodes 76 are also called lead terminals or tabs, and are provided to pull out the positive electrode or negative electrode of the secondary battery to the outside of the exterior film. For the lead electrodes 76, for example, aluminum is used for the positive electrode lead, and nickel-plated copper is used for the negative electrode lead.

[0077] Then, the positive electrode lead and the protruding portion of the positive electrode current collector 72 are electrically connected by ultrasonic welding, and the negative electrode lead and the protruding portion of the negative electrode current collector 74 are electrically connected by ultrasonic welding.

[0078] Then, to leave one side for containing the electrolyte, two sides of the exterior body film 11 are thermocompression bonded using the method described above, forming a joint 33. A desired amount of electrolyte is then dripped onto the inside of the bag-shaped exterior body film 11 under reduced pressure or an inert atmosphere. Finally, the remaining edge of the exterior body film that was not thermocompression bonded is thermocompression bonded to form a joint 34. During thermocompression bonding, the sealing layer 75 provided on the lead terminal also melts, fixing the lead terminal and the exterior body film 11. Finally, to fit the width of the bending tester, a portion whose width is a margin, for example, about 6 cm as seen from the portion containing the laminate, is thermocompression bonded, and then the margin portion, for example, a portion greater than 6 cm, is cut to adjust the size.

[0079] In this way, the secondary battery 10 shown in FIG. 6D can be fabricated.

[0080] The resulting exterior film 11, which serves as the exterior of the secondary battery 10, has a cross-wave pattern. The area between the dotted line and the end in Fig. 6D is the joint 33 or 34, and this area is processed to be flat.

[0081] FIG. 6E shows an example of a cross section taken along the dashed line D1-D2 in FIG. 6D.

[0082] 6E , a positive electrode current collector 72, a positive electrode active material layer 78, a separator 73, a negative electrode active material layer 79, and a negative electrode current collector 74 are laminated in this order, sandwiched between folded exterior film 11, and further sealed at the end portions with joints 34, with the remaining space filled with electrolyte 77. That is, the internal space surrounded by exterior film 11 is filled with electrolyte 77. Note that known positive electrode current collectors, positive electrode active material layers, separators, negative electrode active material layers, negative electrode current collectors, and electrolytes can be used as positive electrode current collector 72, positive electrode active material layer 78, separator 73, negative electrode active material layer 79, negative electrode current collector 74, and electrolyte 77.

[0083] A polypropylene layer is provided on the surface of the film to be bonded, and only the thermocompression bonded portion serves as an adhesive layer.

[0084] 6E shows an example in which the lower side of the exterior body film 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 laminated layers are provided between the folded exterior body film 11, the step becomes large, and there is a risk of excessive stress being applied to the upper exterior body film 11. This may also result in a large misalignment between the edge of the upper exterior body film and the edge of the lower exterior body film. In this case, a step may also be provided in the lower exterior body film to prevent misalignment at the edges, and the film may be crimped at the center to equalize the stress.

[0085] Furthermore, if a large misalignment occurs, there will be an area where part of the edge of one exterior body film does not overlap with the other exterior body film, and this area can be cut out to align the edge of the upper exterior body film with the edge of the lower exterior body film, thereby correcting the misalignment.

[0086] This embodiment mode can be freely combined with other embodiment modes.

[0087] Embodiment 2 In this embodiment, electronic devices of one embodiment of the present invention will be described with reference to FIGS.

[0088] The electronic device 6500 shown in FIG. 7A is a portable information terminal that can be used as a smartphone.

[0089] The electronic device 6500 includes at least a housing 6501, a display portion 6502a, a power button 6503, a button 6504, a speaker 6505, and a microphone 6506. The display portion 6502a has a touch panel function.

[0090] Furthermore, the electronic device 6500 can be bent at the hinge portion 6519. Therefore, a part of the display portion 6502a (the dotted line portion shown in FIG. 7A ) becomes the bent portion of the display portion 6502a and overlaps with the bent portion of the first battery 6518a or the second battery 6518b that overlaps with the bent portion of the display portion 6502a. When both or one of the first battery 6518a and the second battery 6518b is a bendable battery, the hinge portion 6519 controls the bending of the secondary battery within a range of a curvature radius of 10 mm to 60 mm.

[0091] FIG. 7B is a schematic cross-sectional view including the end of the housing 6501 on the microphone 6506 side.

[0092] 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.

[0093] 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).

[0094] 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.

[0095] 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. As the light-emitting elements, it is preferable to use EL elements (also referred to as EL devices) typified by OLEDs (organic light-emitting diodes) and QLEDs (quantum-dot light-emitting diodes). Examples of light-emitting materials that EL elements have include fluorescent materials, phosphorescent materials, inorganic compounds (quantum dot materials), and materials that exhibit thermally activated delayed fluorescence (thermally activated delayed fluorescence (TADF) materials). Furthermore, LEDs, such as micro LEDs or mini LEDs, can also be used as light-emitting elements. There are no particular limitations on the LEDs, and for example, micro LEDs with quantum well junctions and LEDs using nanocolumns can be used. The area of ​​the light-emitting region of the LED is 1 mm ２ Preferably, it is less than 10,000 μm ２ More preferably, 3000 μm or less ２ More preferably, 700 μm or less ２ More preferably, the area of ​​the region is 1 μm or less. ２ More than 10 μm is preferable. ２ More than 100 μm is preferable. ２ In this specification, the area of ​​the light-emitting region is 10,000 μm ２ The following LEDs may be referred to as micro LEDs. ２Larger LEDs are sometimes referred to as mini-LEDs. For example, multiple light-emitting diode chips are arranged at equal intervals on a flexible substrate to form one pixel region. A separate optical film may also be provided. For example, if the light-emitting diode chip used in the display unit is an ultraviolet light-emitting element, a color conversion layer may be provided to achieve full-color display. A color conversion layer may be provided in the path of light in the light-emitting direction. When two light-emitting directions are used, two color conversion layers (or color conversion films) are provided to sandwich the light-emitting diode chip from above and below. Because alignment is important, a color conversion layer (or color conversion film), an example of the optical member 6512, is preferably provided between the touch sensor panel 6513 and the display panel 6511. A full-color display may also be achieved by using a white light-emitting diode chip and providing a color filter.

[0096] 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.

[0097] Furthermore, in order to use a large-capacity battery, the electronic device 6500 is configured to have a second battery 6518b inside the cover portion 6520, and although the connection portion is not shown, the first battery 6518a and the second battery 6518b are electrically connected.

[0098] 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.

[0099] By using a bendable secondary 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 bent to reduce its size and realize a highly portable electronic device 6500.

[0100] 8A is a perspective view showing a state in which the portion of the dotted line in FIG. 7A is folded. The electronic device 6500 can be folded in two, and the display portion 6502a and the second battery 6518b can be repeatedly folded at a certain folding position.

[0101] 8A shows a configuration in which the second display unit 6502b is located at the portion 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.

[0102] 8B 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.

[0103] 8B, 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 can bend the display portion 6502a and the second battery 6518b. Furthermore, the hinge portion 6519 determines the positions of the bending portions of the display portion 6502a and the second battery 6518b, which may cause a problem of reduced reliability in those portions. However, by applying the secondary battery described in Embodiment 1 to the second battery 6518b, the reduction in reliability can be prevented.

[0104] Although one second battery 6518b is shown inside the cover portion 6520, multiple second batteries 6518b may be included inside the cover portion 6520. Furthermore, the cover portion 6520 may also include a charging control circuit or a wireless charging circuit for the second battery 6518b.

[0105] 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.

[0106] 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.

[0107] 8A and 8B 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, the display unit 6502a may also be folded in half so that the display surface faces outward.

[0108] The secondary battery of one embodiment of the present invention has high reliability against repeated deformation and can therefore be suitably used in such foldable devices.

[0109] This embodiment mode can be implemented by appropriately combining at least a part thereof with other embodiment modes described in this specification.

[0110] Embodiment 3 Although an example of a smartphone is shown in Embodiment 2, the present invention is not limited to this. An electronic device of one embodiment of the present invention will be described with reference to FIGS.

[0111] FIG. 9A shows an example of the appearance of a foldable personal computer or a foldable tablet manufactured by mounting the secondary battery disclosed in this specification as at least one component.

[0112] 9A shows a first housing 3001a, a second housing 3001b, and a hinge 3006 provided between the first housing 3001a and the second housing 3001b, which can be folded along the dotted line in the figure to open and close. A peripheral portion 3002 is protected by a rubber member that surrounds the periphery of the display unit.

[0113] The rubber member of the peripheral portion 3002 has openings, including an opening for the display portion and an opening for the sensor portion 3005. The sensor portion 3005 is provided with an optical system including a lens and an imaging element, and can capture an image of the user. A CCD camera or a CMOS camera can be used as the imaging element. In addition to these cameras, an infrared camera may be used in combination. The infrared camera's output level increases as the temperature of the subject increases, so it can detect or extract the living body of a person or animal. A distance image sensor may be provided as the imaging element, and it can also capture an image of the user and be used as a biometric authentication sensor.

[0114] When a user changes the distance between the first housing 3001 a and the second housing 3001 b to open or close the display, the display bends along the dotted line in the figure. Therefore, when the display unit is used as a single display area, the display unit is preferably configured using multiple flexible films. Note that the films are not limited to organic materials, and may be, for example, a flexible thin glass substrate.

[0115] The display section is made up of a plurality of flexible films, and uses a plurality of light-emitting elements arranged in a matrix.

[0116] As the light-emitting element, it is preferable to use an EL element (also called an EL device) represented by an OLED or a QLED. Examples of light-emitting materials contained in the EL element include a fluorescent material (a fluorescent material), a phosphorescent material (a phosphorescent material), an inorganic compound (a quantum dot material), and a material exhibiting thermally activated delayed fluorescence (a thermally activated delayed fluorescence (TADF) material). In addition, an LED represented by a micro LED can also be used as the light-emitting element.

[0117] The display unit can be divided into three display areas: a display area 3003 a overlapping with the first housing 3001 a , a display area 3003 b overlapping with the second housing 3001 b , and a display area 3003 c overlapping with the hinge portion 3006 .

[0118] The display unit may also have a touch input function, and FIG. 9A shows an example in which a keyboard display button 3004 is displayed.

[0119] Furthermore, when the light receiving element is used as a touch sensor, the light receiving element can be used to detect a touch operation of an object.

[0120] Furthermore, the display unit may be provided with both a light-emitting element and a light-receiving element, and an image can be captured using the light-receiving element. For example, the light-receiving element can be used as an image sensor. Using the function as an image sensor, data related to biometric information, such as fingerprints and palm prints, can be acquired. In other words, a biometric authentication sensor can be built into the display unit. By building a biometric authentication sensor into the display unit, the number of components in the electronic device can be reduced compared to when a biometric authentication sensor is provided separately from the display unit, and the electronic device can be made smaller and lighter. When the display unit has a built-in biometric authentication sensor, the sensor unit 3005 shown in FIG. 9A does not need to be provided.

[0121] The light receiving element may be, for example, a pn-type or pin-type photodiode. The light receiving element functions as a photoelectric conversion element (also called a photoelectric conversion device) that detects light incident on the light receiving element and generates electric charge. The amount of electric charge generated by the light receiving element is determined based on the amount of light incident on the light receiving element.

[0122] In particular, it is preferable to use an organic photodiode having a layer containing an organic compound as the light-receiving element. Organic photodiodes can be easily made thin, lightweight, and large in area, and have a high degree of freedom in shape and design, making them applicable to a variety of devices.

[0123] 9A is an external view seen from the side where the display unit is provided, while FIG. 9B is an external view seen from a different viewpoint than that of FIG. 9A.

[0124] In FIG. 9B, secondary batteries 3007 built into first casing 3001a and second casing 3001b are indicated by dotted lines.

[0125] By incorporating the secondary battery 3007 in both the first housing 3001a and the second housing 3001b, a secondary battery with a larger capacity can be installed.

[0126] 9C shows an example of the external appearance of a built-in flexible secondary battery 3007. In this embodiment, the secondary battery 3007 is flexible and can be bent at least in part, specifically in the region indicated by the dotted line, as a bent portion. The bent portion of the secondary battery 3007 overlaps with a display region 3003b, which is part of the display unit.

[0127] The flexible secondary battery 3007 can be the bendable battery described in Embodiment 1. The flexible secondary battery 3007 is manufactured according to the manufacturing method of a laminated secondary battery shown in Fig. 6 and has tab portions 3008 and 3009 for electrically connecting to a control circuit portion of the secondary battery.

[0128] Furthermore, the flexible secondary battery is not limited to the foldable personal computer or foldable tablet described in this embodiment. It can also be used as a secondary battery for vehicles, such as hybrid vehicles (HVs), electric vehicles (EVs), and plug-in hybrid vehicles (PHVs). The secondary battery can also be installed in agricultural machinery, motorized bicycles including electrically assisted bicycles, motorcycles, electric wheelchairs, electric carts, ships, submarines, aircraft, rockets, artificial satellites, space probes, planetary probes, or spacecraft. The secondary battery of one embodiment of the present invention can be installed anywhere, and can be bent to fit the space within the battery. For example, when a solar cell panel is foldable inside an artificial satellite, the bendable battery described in Embodiment 1 can be used in the bending portion.

[0129] The content of this embodiment mode can be freely combined with the content of other embodiment modes.

[0130] In this example, an exterior film containing a laminate was bent to determine at what radius of curvature wrinkles would occur.

[0131] First, three types of laminates with different thicknesses were prepared, and each laminate was surrounded by an exterior film to prepare a sample: three types of laminates with thicknesses of 1.5 mm, 1 mm, and 0.5 mm.

[0132] The exterior film is a three-layer structure film, for example, made of polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, on which a highly flexible metal thin film of aluminum, stainless steel, copper, or nickel is applied, and on top of that metal thin film, an insulating synthetic resin film, typically a polyamide resin or polyester resin, is applied as the exterior surface of the exterior body. In this example, an exterior film with an aluminum metal thin film was used for the experiment. The exterior film was also embossed with a twill pattern.

[0133] The curvature radius conditions were varied to 60 mm, 40.5 mm, 35 mm, 30.3 mm, 13.5 mm, 9.5 mm, and 8 mm, and the exterior film containing the laminate was bent at each curvature radius. If wrinkles or creases were formed, they were evaluated with a cross. If wrinkles of 1 mm or more were formed, the wrinkle height was measured with a vernier caliper. A circle indicates that no wrinkles were visible.

[0134] The experimental results are shown in Table 1.

[0135]

[0136] FIG. 10A is a photograph of a laminate with a thickness of 0.5 mm, taken immediately after being manually wound around a jig with a curvature radius of 60 mm and then returned to a flat state. No particular wrinkles are observed, indicating a good condition. Meanwhile, FIG. 10B shows a photograph of a laminate with a thickness of 1 mm, taken immediately after being manually wound around a jig with a curvature radius of 9.5 mm and then returned to a flat state. FIG. 10C shows a photograph of a laminate with a thickness of 1.5 mm, taken immediately after being manually wound around a jig with a curvature radius of 9.5 mm and then returned to a flat state. As shown in the boxes in FIGS. 10B and 10C, wrinkles were observed in two places in each.

[0137] It was found that even though the laminate was embossed, wrinkles or creases occurred after just one bend at a curvature radius of less than 10 mm. The experimental results also showed that the thickness of the laminate also contributed to the occurrence of wrinkles or creases.

[0138] The number of times before bending was set to 0, and the sample was bent for 2 seconds using a jig to a curvature radius of 10 mm and 40 mm, and then the discharge capacity was measured.

[0139] The thickness of the laminate was 1.5 mm.

[0140] The term "embossed" refers to a secondary battery using an exterior film embossed with a twill pattern of intersecting grooves, and corresponds to the configuration in Fig. 3. The term "standard exterior" refers to a secondary battery using an exterior film without embossing, and corresponds to the configuration in Fig. 1. The same material is used for the exterior film, and a material containing aluminum foil is used.

[0141] The experimental results are shown in FIG.

[0142] In FIG. 11, the vertical axis indicates the discharge capacity, and the horizontal axis indicates the number of cycles after bending.

[0143] When the radius of curvature is 40 mm (sometimes referred to as R40), the discharge capacity is almost the same, so it has been confirmed that bending and straightening can be performed without any problems if the radius of curvature is 40 mm.

[0144] On the other hand, when the radius of curvature is 10 mm (sometimes referred to as R10), the discharge capacity varies before and after bending and straightening, and there is a difference depending on whether the film is embossed or not, so the use of an embossed exterior film can provide higher reliability.

[0145] The experimental results of Examples 1 and 2 indicate that it is preferable to bend the secondary battery to control the radius of curvature of the exterior body film to between 10 mm and 60 mm, and to emboss the exterior body film. It was also found that if the thickness of the laminate is between 0.5 mm and 1 mm, wrinkles are unlikely to form even when bent to a radius of curvature of about 10 mm. Furthermore, when the thickness of the laminate is 1 mm or more, it is preferable to bend the secondary battery to control the radius of curvature of the exterior body film to between 40 mm and 60 mm.

[0146] 10: Battery, 11: Exterior film, 33: Joint, 34: Joint, 61: Film, 62: Film, 63: Film, 72: Positive electrode current collector, 73: Separator, 74: Negative electrode current collector, 75: Sealing layer, 76: Lead electrode, 77: Electrolyte, 78: Positive electrode active material layer, 79: Negative electrode active material layer, 200: Secondary battery, 210: Electrode laminate, 211a: Positive electrode, 211b: Negative electrode, 21 2a: lead, 212b: lead, 214: separator, 215a: joint, 215b: joint, 217: fixing member, 240: secondary battery, 250: secondary battery, 251: exterior film, 261: folded portion, 262: seal portion, 263: seal portion, 271: ridge line, 272: valley line, 273: space, 3001a: housing, 3001b: housing, 3002: peripheral portion, 3003 a: display area, 3003b: display area, 3003c: display area, 3004: display button, 3005: sensor unit, 3006: hinge unit, 3007: secondary battery, 3008: tab unit, 3009: tab unit, 3700: curved surface, 3701: flat surface, 3702: curve, 3703: radius of curvature, 3704: center of curvature, 6500: electronic device, 6501: housing, 6502a: display unit, 65 02b: display unit, 6503: power button, 6504: button, 6505: speaker, 6506: microphone, 6510: protective member, 6511: display panel, 6512: optical member, 6513: touch sensor panel, 6515: FPC, 6516: IC, 6517: printed circuit board, 6518a: battery, 6518b: battery, 6519: hinge portion, 6520: cover portion

Claims

1. An electronic device having a display unit, a hinge unit, and a secondary battery, The secondary battery includes a laminate including a positive electrode, a separator, and a negative electrode, and the laminate is surrounded by an exterior film; the display unit and the secondary battery have bent portions, the bent portion of the display unit at least partially overlaps with the bent portion of the secondary battery, the hinge portion controls the bending portion of the display portion and the secondary battery, The electronic device wherein the radius of curvature on the inner side of the bent portion of the secondary battery is within a range of 10 mm or more and 60 mm or less.

2. An electronic device having a display unit, a hinge unit, a first secondary battery, and a second secondary battery, the first secondary battery includes a laminate including a positive electrode, a separator, and a negative electrode, and the laminate is surrounded by an exterior film; the display unit and the first secondary battery have a bent portion, the bent portion of the display unit at least partially overlaps with the bent portion of the first secondary battery, the hinge portion controls the display portion and the bending portion of the first secondary battery, The electronic device, wherein the radius of curvature on the inner side of the bent portion of the first secondary battery is within a range of 10 mm or more and 60 mm or less.

3. 3. The electronic device according to claim 1, wherein the exterior film has a groove where a ridge line and a valley line intersect, and the angle at which the ridge line and the valley line intersect is between 20 degrees and 160 degrees.