secondary batteries

Abstract

The present invention provides a secondary battery which is provided with: an electrode assembly that is obtained by stacking at least one electrode constituent layer which comprises a positive electrode, a negative electrode and a separator; and an outer package that covers the electrode assembly. With respect to this secondary battery, the outer package is composed of two outer package sheets that are a first outer package sheet and a second outer package sheet; the electrode assembly is arranged between the first outer package sheet and the second outer package sheet; the thickness of the first outer package sheet is larger than the thickness of the second outer package sheet; and this secondary battery has a curved shape wherein the first outer package sheet is arranged on the inner side and the second outer package sheet is arranged on the outer side.

Description

[Technical Field]

[0001] The present disclosure relates to a secondary battery, and more particularly to a secondary battery having an electrode assembly including electrode constituent layers including a positive electrode, a negative electrode, and a separator. [Background technology]

[0002] Secondary batteries are so-called storage batteries that can be repeatedly charged and discharged, and are used in a variety of applications, including mobile devices such as mobile phones, smartphones, and laptops. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication (WO) No. 2018 / 037709 [Patent Document 2] Japanese Patent Application Publication No. 2020-145200 [Patent Document 3] JP 2017-33921 ​​A Summary of the Invention [Problem to be solved by the invention]

[0004] The inventors of the present invention have realized that conventional secondary batteries have problems that need to be overcome, and have found the need to take measures to address these problems. Specifically, the inventors have found the following problems:

[0005] For example, secondary batteries having a plate-like shape are disclosed in Patent Documents 1 to 3. Secondary batteries having a plate-like shape are generally designed to have a certain degree of flexibility so that they can bend inside electronic devices. For example, in the secondary battery disclosed in Patent Document 1, 9 Flexibility is ensured by constructing the exterior body using a resin layer with a Young's modulus of 100 Pa or more. In the secondary battery disclosed in Patent Document 2, a member having rubber elasticity is used as an exterior body, and flexibility is ensured by providing convex portions (or concave portions) on such a member. In the secondary battery disclosed in Patent Document 3, flexibility is ensured by specifying the coefficient of dynamic friction of the exterior member facing the battery body and by using an exterior member made of a laminate film.

[0006] When using a conventional secondary battery in a wearable device such as a smart watch or smart ring, it is necessary to curve the main body portion 101' of the battery into the desired shape, for example, by pressing the conventional secondary battery 100' against a rod 200' and winding it (see Figures 8A and 8B).

[0007] After bending, the secondary battery 100' has numerous wrinkles formed on the inner surface of the curved main body portion 101' (see Figure 8C), and it has been found that these wrinkles press on the inside of the battery, damaging the inside of the battery and potentially causing destruction of the inside of the battery.

[0008] Furthermore, while conventional secondary batteries have a certain degree of flexibility, this flexibility is reversible, making it difficult to maintain a curved shape, particularly when the battery body is bent into a ring shape.

[0009] The present disclosure has been made in view of the above-mentioned problems. That is, a main object of the present disclosure is to provide a secondary battery that can maintain a curved shape while suppressing the formation of wrinkles that occur when the battery is bent. [Means for solving the problem]

[0010] In order to achieve the above object, in one embodiment of the present disclosure, The battery includes an electrode assembly formed by laminating at least one electrode-constituting layer including a positive electrode, a negative electrode, and a separator, and an exterior body that covers the electrode assembly, the exterior body is composed of two exterior sheets, namely, a first exterior sheet and a second exterior sheet, the electrode assembly is disposed between the first exterior sheet and the second exterior sheet, The thickness of the first exterior sheet is greater than the thickness of the second exterior sheet, and A secondary battery having a curved shape is provided, with the first exterior sheet disposed on the inside and the second exterior sheet disposed on the outside. [Effects of the Invention]

[0011] The present disclosure provides a secondary battery that can maintain a curved shape while suppressing the formation of wrinkles that occur when bent. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view that schematically shows the configuration of an electrode assembly. [Figure 2] FIG. 2 is a schematic diagram illustrating a secondary battery according to an embodiment of the present disclosure. [Figure 3] FIG. 3 is a schematic diagram illustrating a cross section of a secondary battery according to an embodiment of the present disclosure. [Figure 4] FIG. 4 is a schematic view illustrating the production of a secondary battery according to an embodiment of the present disclosure. [Figure 5] FIG. 5 is a schematic view showing the production of a secondary battery according to another embodiment of the present disclosure. [Figure 6A] FIG. 6A is a schematic diagram showing a cross section (cross section of a portion where no leads are provided) of a secondary battery according to another embodiment of the present disclosure. [Figure 6B] FIG. 6B is a schematic diagram showing a cross section (cross section of a portion where a negative electrode lead is provided) of a secondary battery according to another embodiment of the present disclosure. [Figure 7A] FIG. 7A is a schematic view showing the secondary battery of the present disclosure before the start of a bending process. [Figure 7B] FIG. 7B is a schematic view illustrating a bending step for the secondary battery of the present disclosure. [Figure 7C] FIG. 7C is a schematic view illustrating a bending step for the secondary battery of the present disclosure. [Figure 7D] FIG. 7D is a schematic view illustrating a bending step for the secondary battery of the present disclosure. [Figure 7E] FIG. 7E is a schematic diagram illustrating the battery body (before the bending step) of the secondary battery of the present disclosure. [Figure 8A] FIG. 8A is a schematic diagram showing a conventional secondary battery in a state before being bent. [Figure 8B] FIG. 8B is a schematic view showing a conventional secondary battery during the bending step. [Figure 8C] FIG. 8C is a schematic diagram showing a conventional secondary battery in a bent state. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present disclosure will be described in more detail below with reference to a secondary battery according to an embodiment of the present disclosure. While the description will be made with reference to drawings as needed, the various elements in the drawings are merely shown schematically and illustratively to facilitate understanding of the present disclosure, and the appearance and / or dimensional ratios may differ from those of the actual objects.

[0014] The "cross-sectional view" directly or indirectly described in this specification is basically based on a virtual cross section of a secondary battery cut along the stacking direction or overlapping direction of the electrode assembly or electrode constituent layers that constitute the secondary battery (see Figure 1). Similarly, the "thickness" direction directly or indirectly described in this specification is basically based on the stacking direction of the electrode materials that constitute the secondary battery. For example, in the case of a "secondary battery having a plate-like thickness," the "thickness" direction corresponds to the plate thickness direction of such a secondary battery. The "planar view" or "planar view shape" used in this specification is based on a sketch of an object viewed from above or below along the thickness direction (i.e., the above-mentioned stacking direction).

[0015] Furthermore, the terms "upper-lower direction" and "left-right direction" used directly or indirectly in this specification correspond to the upper-lower direction and left-right direction in the drawings, respectively. Unless otherwise specified, the same reference numerals or symbols indicate the same members or parts or the same meanings. In a preferred embodiment, the stacking direction of the electrode assembly can correspond to the upper-lower direction, and the vertically downward direction (i.e., the direction in which gravity acts) can be considered to correspond to the "downward direction," and the opposite direction to that can be considered to correspond to the "upward direction."

[0016] [Basic structure of secondary batteries] As used herein, the term "secondary battery" refers to a battery that can be repeatedly charged and discharged. Therefore, the secondary battery of the present disclosure is not limited to its name, and may also include, for example, an energy storage device. Hereinafter, the above-described secondary battery may be referred to as the "secondary battery of the present disclosure" or simply as a "secondary battery."

[0017] The secondary battery of the present disclosure includes an electrode assembly formed by laminating at least one electrode configuration layer, for example, including a positive electrode, a negative electrode, and a separator. For example, FIG. 1 schematically illustrates an electrode assembly 10. As shown in the figure, a positive electrode 1 and a negative electrode 2 may be stacked with a separator 3 interposed therebetween to form an electrode configuration layer 5. The electrode assembly may be formed by laminating at least one or more such electrode configuration layers 5. FIG. 1 shows a planar laminated structure in which the electrode configuration layers 5 are laminated in a planar manner. In a secondary battery, such an electrode assembly may be covered with an outer casing together with an electrolyte (e.g., a non-aqueous electrolyte). The structure of the electrode assembly is not necessarily limited to a planar laminated structure. For example, the electrode assembly may have a wound laminated structure. Alternatively, the electrode assembly may have a so-called stack-and-folded structure in which a positive electrode, a separator, and a negative electrode are laminated on a long film and then folded.

[0018] The positive electrode may be composed of at least a positive electrode material layer and a positive electrode current collector. For example, the positive electrode may have a positive electrode material layer provided on at least one side of the positive electrode current collector. The positive electrode material layer contains a positive electrode active material as an electrode active material. For example, each of the multiple positive electrodes in the electrode assembly may have a positive electrode material layer provided on both sides of the positive electrode current collector, or may have a positive electrode material layer provided on only one side of the positive electrode current collector. The positive electrode current collector may have, for example, a foil form. In other words, the positive electrode current collector may be composed of a metal foil.

[0019] The negative electrode may be composed of at least a negative electrode material layer and a negative electrode current collector. For example, the negative electrode may have a negative electrode material layer provided on at least one side of the negative electrode current collector. The negative electrode material layer contains a negative electrode active material as an electrode active material. For example, each of the multiple negative electrodes in the electrode assembly may have a negative electrode material layer provided on both sides of the negative electrode current collector, or may have a negative electrode material layer provided on only one side of the negative electrode current collector. The negative electrode current collector may have, for example, a foil form. In other words, the negative electrode current collector may be composed of a metal foil.

[0020] The electrode active materials that can be contained in the positive electrode material layer and the negative electrode material layer, i.e., the positive electrode active material and the negative electrode active material, are substances that can directly participate in the transfer of electrons in a secondary battery, and are the main substances of the positive electrode and the negative electrode that are responsible for charging and discharging, i.e., the battery reaction.

[0021] More specifically, ions can be introduced into the electrolyte due to the "positive electrode active material that can be contained in the positive electrode material layer" and the "negative electrode active material that can be contained in the negative electrode material layer." These ions move between the positive electrode and the negative electrode, transferring electrons and enabling charging and discharging.

[0022] The positive electrode material layer and the negative electrode material layer may be layers capable of absorbing and releasing lithium ions, in particular. In other words, the secondary battery according to an embodiment of the present disclosure may be a non-aqueous electrolyte secondary battery in which lithium ions can move between the positive electrode and the negative electrode via the non-aqueous electrolyte to charge and discharge the battery.

[0023] When lithium ions are involved in charging and discharging, the secondary battery according to an embodiment of the present disclosure may correspond to a so-called “lithium ion battery.” In a lithium ion battery, the positive electrode and the negative electrode have layers capable of absorbing and releasing lithium ions.

[0024] The positive electrode active material of the positive electrode layer may be composed of, for example, granules, and the positive electrode layer may contain a binder to ensure better contact between the particles and to maintain the shape. The positive electrode layer may also contain a conductive additive to facilitate smoother transfer of electrons that promote the battery reaction.

[0025] The negative electrode active material of the negative electrode material layer may be composed of, for example, granules, and the negative electrode material layer may contain a binder to ensure better contact between the particles and to maintain the shape. The negative electrode material layer may also contain a conductive additive to facilitate smoother transfer of electrons that promote the battery reaction.

[0026] Because they contain a plurality of components, the positive electrode material layer and the negative electrode material layer can also be referred to as a "positive electrode composite layer" and a "negative electrode composite layer", respectively.

[0027] The positive electrode active material may be, for example, a material that contributes to the absorption and desorption of lithium ions. From this perspective, the positive electrode active material may be, for example, a lithium-containing composite oxide. More specifically, the positive electrode active material may be a lithium transition metal composite oxide containing lithium and at least one transition metal selected from the group consisting of cobalt, nickel, manganese, and iron.

[0028] In other words, the positive electrode layer of the secondary battery according to an embodiment of the present disclosure may contain such a lithium transition metal composite oxide as a positive electrode active material, for example, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium iron phosphate, or a material in which part of the transition metal in any of these materials is replaced with another metal.

[0029] Such positive electrode active materials may be contained as a single species, or may be contained in combination of two or more species.

[0030] The binder that can be contained in the positive electrode layer is not particularly limited, but examples thereof include polymer compounds, etc. Specific examples include at least one selected from the group consisting of styrene-butadiene rubber, polyacrylic acid, polyimide resin, polyamide-imide resin, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and polytetrafluoroethylene.

[0031] The conductive additive that can be contained in the positive electrode layer is not particularly limited, but may include at least one selected from the group consisting of carbon black such as thermal black, furnace black, channel black, ketjen black, and acetylene black; carbon fibers such as graphite, carbon nanotubes, and vapor-grown carbon fibers; metal powders such as copper, nickel, aluminum, and silver; and polyphenylene derivatives.

[0032] The thickness of the positive electrode layer is not particularly limited, but may be 1 μm or more and 300 μm or less, for example, 5 μm or more and 200 μm or less. The thickness of the positive electrode layer is the thickness inside the secondary battery, and may be the average value of measurements taken at any 10 points.

[0033] The negative electrode active material may be a material that contributes to the absorption and desorption of lithium ions, such as various carbon materials, oxides, and / or lithium alloys, metallic lithium, etc.

[0034] Examples of various carbon materials for the negative electrode active material include at least one selected from the group consisting of graphite (specifically, natural graphite and / or artificial graphite), hard carbon, soft carbon, and / or diamond-like carbon, etc. Graphite, in particular, has high electronic conductivity and excellent adhesion to, for example, the negative electrode current collector.

[0035] The oxide of the negative electrode active material may be at least one selected from the group consisting of silicon oxide, tin oxide, indium oxide, zinc oxide, and lithium oxide.

[0036] Such oxides may have an amorphous structure, since this makes them less susceptible to degradation due to inhomogeneities such as grain boundaries or defects.

[0037] The lithium alloy of the negative electrode active material may be any alloy of a metal that can form an alloy with lithium, and may be, for example, a binary, ternary, or higher alloy of lithium with a metal such as Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, or La.

[0038] Such alloys may have an amorphous structure, since this makes them less susceptible to degradation due to inhomogeneities such as grain boundaries or defects.

[0039] The binder that can be contained in the negative electrode material layer is not particularly limited, but examples thereof include polymer compounds, etc. Specific examples include at least one selected from the group consisting of styrene-butadiene rubber, polyacrylic acid, polyimide resin, polyamide-imide resin, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and polytetrafluoroethylene.

[0040] The conductive additive that can be contained in the negative electrode material layer is not particularly limited, but may include at least one selected from the group consisting of carbon black such as thermal black, furnace black, channel black, ketjen black, and acetylene black; carbon fibers such as graphite, carbon nanotubes, and vapor-grown carbon fibers; metal powders such as copper, nickel, aluminum, and silver; and polyphenylene derivatives.

[0041] The thickness of the negative electrode layer is not particularly limited, but may be 1 μm or more and 300 μm or less, for example, 5 μm or more and 200 μm or less. The thickness of the negative electrode layer is the thickness inside the secondary battery, and the average value of measurements taken at any 10 points may be used.

[0042] The positive electrode current collector and the negative electrode current collector that can be used for the positive electrode and the negative electrode are components that can collect and supply electrons generated in the electrode active material due to the battery reaction. Such electrode current collectors may be sheet-shaped metal components. Also, such electrode current collectors may be porous or perforated. For example, the current collectors may be plates, metal foils, punched metals, meshes, expanded metals, etc.

[0043] The positive electrode current collector that can be used for the positive electrode may be made of a metal foil containing at least one selected from the group consisting of aluminum, stainless steel (SUS), nickel, etc. The positive electrode current collector may be, for example, an aluminum foil.

[0044] The negative electrode current collector that can be used for the negative electrode may be made of a metal foil containing at least one selected from the group consisting of copper, stainless steel (SUS), nickel, etc. The negative electrode current collector may be, for example, a copper foil.

[0045] In the present disclosure, "stainless steel" (SUS) refers to, for example, stainless steel as defined in "JIS G 0203 Iron and Steel Terminology," and may be an alloy steel containing chromium or chromium and nickel.

[0046] The thickness of each of the positive electrode current collector and the negative electrode current collector is not particularly limited, but may be 1 μm or more and 100 μm or less, for example, 10 μm or more and 70 μm or less. The thickness of each of the positive electrode current collector and the negative electrode current collector is the thickness inside the secondary battery, and may be the average value of measurements taken at any 10 points.

[0047] The separator that can be used for the positive electrode and the negative electrode is a member that can be provided from the viewpoint of preventing a short circuit due to contact between the positive electrode and the negative electrode, retaining an electrolyte, etc. In other words, the separator can be said to be a member that prevents electronic contact between the positive electrode and the negative electrode while allowing ions to pass through.

[0048] For example, the separator may be a porous or microporous insulating member, and may have a membrane form due to its small thickness. By way of example only, a microporous membrane made of polyolefin may be used as the separator.

[0049] The microporous membrane that can be used as the separator may contain, for example, only polyethylene (PE) or only polypropylene (PP) as the polyolefin. Furthermore, the separator may be a laminate that can be composed of a "microporous membrane made of PE" and a "microporous membrane made of PP." The surface of the separator may be covered with an inorganic particle coating layer and / or an adhesive layer. The surface of the separator may have adhesive properties.

[0050] The thickness of the separator is not particularly limited, but may be 1 μm or more and 100 μm or less, for example, 2 μm or more and 30 μm or less. The thickness of the separator is the thickness inside the secondary battery (particularly the thickness between the positive electrode and the negative electrode), and the average value of measurements taken at any 10 points may be used.

[0051] In the present disclosure, the separator should not be limited to a particular name, and may be a solid electrolyte, a gel electrolyte, and / or insulating inorganic particles that can have a similar function.

[0052] In a secondary battery according to an embodiment of the present disclosure, for example, an electrode assembly including at least one stacked electrode component layer including a positive electrode, a negative electrode, and a separator may be covered with an outer casing together with an electrolyte. The electrolyte can assist the migration of metal ions released from the electrodes (positive electrode and / or negative electrode). The electrolyte may be, for example, a "non-aqueous" electrolyte containing a non-aqueous or organic electrolyte and / or solvent, or an "aqueous" electrolyte containing water.

[0053] For example, when the positive electrode and the negative electrode have layers capable of absorbing and releasing lithium ions, the electrolyte may be a lithium-ion-containing electrolyte or a "non-aqueous" electrolyte (hereinafter referred to as a "nonaqueous electrolyte") that includes a non-aqueous or organic electrolyte and / or a solvent. That is, the electrolyte may be a non-aqueous electrolyte. Metal ions released from the electrodes (positive electrode and / or negative electrode) are present in the electrolyte, and therefore, the electrolyte can assist the migration of metal ions in the battery reaction.

[0054] A secondary battery according to an embodiment of the present disclosure may be a non-aqueous electrolyte secondary battery that uses a non-aqueous electrolyte containing a non-aqueous solvent and a solute as the electrolyte. The electrolyte may be in a liquid or gel form (note that in this specification, a liquid non-aqueous electrolyte is also referred to as a "nonaqueous electrolyte solution").

[0055] The non-aqueous electrolyte may be an electrolyte containing a non-aqueous solvent and a solute. A specific solvent for the non-aqueous electrolyte may contain at least a carbonate. The carbonate may be a cyclic carbonate and / or a chain carbonate.

[0056] Although not particularly limited, examples of cyclic carbonates include at least one selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC) and vinylene carbonate (VC).

[0057] The chain carbonates may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and dipropyl carbonate (DPC).

[0058] For example, in one preferred embodiment of the present disclosure, the non-aqueous electrolyte may be a combination of cyclic carbonates and chain carbonates, such as a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC), a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC), etc. Specific examples of the solute of the non-aqueous electrolyte include Li salts such as LiPF6 and / or LiBF4.

[0059] In this disclosure, the "exterior body" of a secondary battery generally refers to a member capable of covering an electrode assembly in which at least one electrode component layer including a positive electrode, a negative electrode, and a separator is laminated. The exterior body may be made of an electrically conductive or electrically conductive exterior body. Alternatively, the exterior body may be made of a laminate film or the like.

[0060] In the present disclosure, "lead" means a conductive member that can be electrically connected to the positive electrode and / or negative electrode of an electrode assembly, and can protrude or extend from the electrode assembly. Such leads may extend from the "positive electrode current collector" and / or "negative electrode current collector" described above, and may be integrally formed from the same material as such current collectors.

[0061] In the present disclosure, the above-described configuration may be appropriately changed or modified as needed. Alternatively, other components may be separately manufactured.

[0062] [Features of the Secondary Battery Disclosed Herein] The inventors attempted to solve the above problems by taking a new approach rather than simply extending the conventional technology, and as a result, they have invented a secondary battery that achieves the above-mentioned main object.

[0063] For example, as shown in FIG. 1, by disposing two exterior sheets (22a, 22b) of different thicknesses as exterior bodies on the surface of a plate-shaped electrode assembly having a laminated structure in which at least one electrode constituent layer (5) including a positive electrode (1), a negative electrode (2), and a separator (3) is laminated (see FIG. 2), it was thought that the difference in thickness could suppress the formation of wrinkles even when the battery body is curved significantly.

[0064] As a result of extensive research, the inventors of the present invention have found that by making the thickness of the inner sheet greater than the thickness of the outer sheet, the formation of wrinkles in the inner sheet can be significantly suppressed.

[0065] The present disclosure provides a secondary battery including an electrode assembly formed by laminating at least one electrode component layer including a positive electrode, a negative electrode, and a separator, and an exterior body covering the electrode assembly. In the secondary battery, the exterior body is composed of two exterior sheets, namely, a first exterior sheet and a second exterior sheet, the electrode assembly is disposed between the first exterior sheet and the second exterior sheet, the thickness of the first exterior sheet is greater than the thickness of the second exterior sheet, and the secondary battery has a curved shape with the first exterior sheet disposed on the inside and the second exterior sheet disposed on the outside.

[0066] For example, as shown in Fig. 2, a secondary battery 20 according to an embodiment of the present disclosure has a battery body 21. The battery body 21 has an exterior body 22 for covering an electrode assembly (not shown). In the exemplary embodiment shown in Fig. 2, the exterior body 22 may be composed of two exterior sheets, a first exterior sheet 22a and a second exterior sheet 22b. The electrode assembly may be positioned between the first exterior sheet 22a and the second exterior sheet 22b (see Figs. 3 and 4).

[0067] 2, for example, a resin member 23 may be disposed between the first exterior sheet 22a and the second exterior sheet 22b so as to cover the peripheral edge of the electrode assembly. The resin member 23 may be divided into two or more layers, as will be described in detail below.

[0068] In the present disclosure, the "peripheral edge of the electrode assembly" generally refers to the part of the electrode assembly excluding the main surfaces. For example, if the electrode assembly has a plate-like shape with two main surfaces, it refers to the surface excluding these two main surfaces.

[0069] In the embodiment shown in FIG. 2 , two leads, specifically a first lead 24 and a second lead 25, may extend from the battery body 21, particularly from the resin member 23. With regard to the first lead 24 and the second lead 25, one may be a positive electrode lead and the other a negative electrode lead. For convenience of explanation, the first lead 24 will be described as a positive electrode lead and the second lead 25 will be described as a negative electrode lead, but either may be the positive electrode or the negative electrode. There are no particular limitations on the positions from which the first lead 24 and the second lead 25 extend, and only one of the first lead 24 and the second lead 25 may extend.

[0070] The first lead 24 and / or the second lead 25 may be covered with an insulating sealant 26 and / or 27, respectively, as needed. It is preferable that the portion of the electrode lead that contacts the resin member 23 be covered with the sealant.

[0071] For convenience of explanation, the secondary battery 20, particularly the battery body 21, is shown in a plate-like, preferably strip-like, shape, but the shape of the battery body 21 is not limited to a plate-like or strip-like shape. By making the secondary battery 20, particularly the battery body 21, have a plate-like, preferably strip-like, shape, the battery body 21 can be curved more easily without wrinkles.

[0072] FIG. 3 is a schematic cross-sectional view of the battery body 21 taken along line III-III in FIG.

[0073] As shown schematically in the cross-sectional view of FIG. 3, the secondary battery 20 of the present disclosure is characterized in that the thickness (T1) of the first exterior sheet (22a) is greater than the thickness (T2) of the second exterior sheet (22b) (T1>T2). The thickness (T1) of the first exterior sheet (22a) and the thickness (T2) of the second exterior sheet (22b) generally refer to the largest thickness of the portion covering the electrode assembly (see FIG. 3).

[0074] For example, as shown schematically in Figures 7A to 7E, by applying force in the direction of the arrow as shown in Figure 7A to wind the battery body 21 (see Figure 7E) of the secondary battery 20 of the present disclosure around a rod 200, the battery body 21 can be bent into an approximately circular shape, preferably into a perfect circle (see Figures 7A to 7D).

[0075] As described above, the secondary battery 20 of the present disclosure has a curved shape with the first exterior sheet 22a having the above-described configuration disposed on the inside and the second exterior sheet 22b having the above-described configuration disposed on the outside. As a result, when the secondary battery 20, particularly the battery body 21, is bent so that the first exterior sheet 22a of the secondary battery 20 faces inside and the second exterior sheet 22b faces outside, the curved shape of the battery body 21 can be maintained and wrinkles that may occur in the first exterior sheet 22a can be significantly suppressed.

[0076] In the present disclosure, "wrinkles can be significantly suppressed" broadly means that the formation of wrinkles or distortions cannot be visually confirmed, and narrowly means that a flat or smooth surface is obtained without irregularities having a height of 0.01 μm to 30 μm, preferably 10 μm or less. The irregularities can be confirmed by means of, for example, a laser interference thickness meter.

[0077] Without being bound by any particular theory, in the secondary battery of the present disclosure, the thickness of the first exterior sheet is greater than the thickness of the second exterior sheet, which significantly reduces wrinkles that may occur on the first exterior sheet (inner surface). This is a unique and unprecedented effect. It is believed that this effect is obtained by shifting the neutral point of deformation toward the first exterior sheet when the battery body is bent and deformed. Furthermore, since it was previously believed that increasing thickness would increase wrinkles, the fact that increasing thickness reduces wrinkles is a completely unexpected, surprising, and remarkable effect.

[0078] For example, as shown schematically in Fig. 3, the ratio (T1 / T2) of the thickness (T1) of the first outer sheet 22a to the thickness (T2) of the second outer sheet 22b (i.e., the ratio of the thickness (T1) of the first outer sheet 22a to the thickness (T2) of the second outer sheet 22b) is, for example, 1.1 to 25, preferably 1.7 to 25, and more preferably 3.0 to 10. Within the above range, the curved shape can be maintained and wrinkles that may occur on the surface of the first outer sheet 22a can be significantly suppressed.

[0079] The difference (T1-T2) between the thickness (T1) of the first exterior sheet 22a and the thickness (T2) of the second exterior sheet 22b is, for example, 10 μm to 240 μm, preferably 20 μm to 90 μm. Within this range, the curved shape can be maintained and wrinkles that may occur on the surface of the first exterior sheet 22a can be significantly suppressed.

[0080] The thickness (T1) of the first exterior sheet 22a is generally 300 μm or less, for example, 25 μm or more and 250 μm or less. The thickness (T2) of the second exterior sheet 22b is generally 300 μm or less, for example, 10 μm or more and 240 μm or less.

[0081] The total thickness (T3) of the electrode assembly 30 is, for example, 0.100 mm or more and 2.50 mm or less. The total thickness (T3) of the electrode assembly 30 generally refers to the thickness of the thickest portion in the cross section of the electrode assembly 30 (see FIG. 3).

[0082] The thickness (T0) of the battery body is, for example, 0.150 mm or more and 3.000 mm or less. The thickness (T0) of the battery body generally means the thickness of the thickest part in the cross section of the battery body (see FIG. 3).

[0083] 7D, the radius of curvature when the secondary battery 20 according to the present disclosure, particularly the main body portion 21, is bent is, for example, 5 mm or more, preferably 5 mm to 20 mm, and more preferably 6.5 mm to 20 mm. Even with such a radius of curvature, the curved shape can be maintained and wrinkles that may occur on the surface of the first exterior sheet 22a can be significantly suppressed.

[0084] The "radius of curvature" of the secondary battery 20, particularly the battery body 21, can be determined from the radius of the rod 200 having a circular cross-sectional shape, for example (see FIG. 7D).

[0085] Thus, the secondary battery of the present disclosure has a curved shape, and can maintain that shape. A secondary battery having a curved shape may have a curved shape that forms at least a part of an imaginary circle, for example, in a cross section in the stacking direction, preferably in a cross section in the stacking direction along the longitudinal direction of the main body portion. In other words, the curved shape means a shape in which at least a part of the main body portion is bent, and may be, for example, a circle as shown in FIG. 7D or a part of a circle (e.g., a C-shape). Such a curved shape allows the secondary battery of the present disclosure to be more easily placed inside a ring-shaped structure such as a bracelet or a finger ring.

[0086] In the present disclosure, the term "imaginary circle" refers to a circle that can be formed by the cross section of rod 200, for example, as shown in FIGS. 7A to 7D.

[0087] The secondary battery of the present disclosure can maintain its curved shape and significantly reduce wrinkles that may occur on the surface of the curved main body, thereby preventing damage to the inside of the battery (electrode assembly). Therefore, it can be more appropriately used as a battery for wearable devices such as smart watches, smart rings, and smart glasses.

[0088] The configuration and manufacturing method of the secondary battery of the present disclosure will be described in detail below with reference to FIG. 4, but the secondary battery of the present disclosure is not limited to the configuration shown in the drawing.

[0089] For example, as shown in Fig. 4, the electrode assembly 30 may be an electrode assembly made up of electrode constituent layers including a positive electrode 31, a negative electrode 32, and a separator 33. The illustrated configuration is merely for illustrative purposes, and the numbers of positive electrodes, negative electrodes, and separators can be changed as needed. In addition, the positive electrode 31 may be changed to a negative electrode, and the negative electrode 32 may be changed to a positive electrode.

[0090] The positive electrode 31 includes a positive electrode material layer 31a and a positive electrode current collector 31b. The positive electrode material layer 31a may be disposed so as to face the separator 33. The configuration of the positive electrode is not limited to the form shown in the drawing, and the number and arrangement of the positive electrode material layers 31Aa and positive electrode current collectors 31Ab can be changed as needed (see FIG. 5).

[0091] Specifically, in the embodiments shown in FIGS. 4 and 5, the first leads 24, 24A may extend from positive electrode tabs 31b1, 31Ab1 located at the ends of the positive electrode current collectors 31b, 31Ab. The first leads 24, 24A may be formed from the same material as the positive electrode current collectors 31b, 31Ab, or from other conductive materials. If necessary, at least a portion of the first leads 24, 24A may be covered or protected with an insulating sealant 26, 26A. In particular, the periphery of the boundary of the first leads 24, 24A protruding from the battery body may be covered or protected with the sealant 26, 26A. Note that in FIG. 5, the capital letter A is added to the reference numerals of components corresponding to those shown in FIG. 4.

[0092] The negative electrode 32 has a negative electrode material layer 32a and a negative electrode current collector 32b. The negative electrode material layer 32a may be disposed so as to face the separator 33. The configuration of the negative electrode is not limited to the form shown in the figure, and the number and arrangement of the negative electrode material layers 32Aa and negative electrode current collectors 32Ab can be changed as needed (see FIG. 5).

[0093] Specifically, in the embodiment shown in FIG. 4, the second lead 25 may extend from a tab 32b1 located at the end of the negative electrode current collector 32b. In the embodiment shown in FIG. 5, the second lead 25A may extend from a portion sandwiched between a negative electrode tab 32Ab1 located at the end of the negative electrode current collector 32Ab and a negative electrode tab 32Ab1 located at the end of the negative electrode current collector 32Ab. The second leads 25, 25A may be formed from the same material as the negative electrode current collectors 32b, 32Ab, or from another conductive material. If necessary, at least a portion of the second leads 25, 25A may be coated or protected with an insulating sealant 27, 27A. In particular, the periphery of the boundary of the second leads 25, 25A protruding from the battery body may be coated or protected with the sealant 27, 27A.

[0094] The electrode assembly 30 comprising the positive electrode 31, the negative electrode 32 and the separator 33 is preferably prepared in advance according to a conventionally known method.

[0095] Two exterior sheets (first exterior sheet 22a and second exterior sheet 22b) can be arranged on electrode assembly 30 as an exterior body. More specifically, the first exterior sheet 22a may be disposed so as to face the negative electrode current collector 32b, and the second exterior sheet 22b may be disposed so as to face the positive electrode current collector 31b (see FIGS. 3 and 4). With this configuration, the electrode assembly 30 can be positioned between the first exterior sheet 22a and the second exterior sheet 22b (FIG. 3).

[0096] Furthermore, a resin member made of, for example, two resin sheets (specifically, a first resin sheet 23a and a second resin sheet 23b) may be disposed around the peripheral edge of the electrode assembly 30 (see FIGS. 3 and 4). When such an arrangement is adopted, a resin member 23 made of two resin sheets 23a, 23b may be interposed between the exterior sheets, as shown in, for example, FIGS. 3 and 4. Note that when the exterior sheets are made of a laminate film, the innermost layer includes an adhesive layer having an adhesive function, as described below, and therefore the "resin sheet" is not an essential component in the present disclosure. Furthermore, the first resin sheet 23a and the second resin sheet 23b may each have an opening (preferably openings of the same shape and size), and the electrode assembly 30 can be positioned inside such an opening. However, such an opening is not essential.

[0097] The first resin sheet 23a and the second resin sheet 23b preferably have insulating properties and heat-sealing properties, and the first resin sheet 23a and the second resin sheet 23b may be bonded to each other by heat fusion. Furthermore, the first resin sheet 23a and the first exterior sheet 22a may be bonded to each other by heat fusion, and the second resin sheet 23b and the second exterior sheet 22b may be bonded to each other by heat fusion.

[0098] Such bonding by heat fusion can be achieved by arranging the electrode assembly 30, the resin member 23 (specifically, the first resin sheet 23a and the second resin sheet 23b), and the exterior body 22 (specifically, the first exterior sheet 22a and the second exterior sheet 22b) in appropriate positions relative to one another, and then applying heat and pressure to the peripheral edge of the battery body 21. Although such heat fusion may form steps (S1, S2) on the edge of the surface of the exterior body 22 (specifically, the first exterior sheet 22a and the first exterior sheet 22b) (see FIG. 3), such steps are not an essential configuration of the present invention and may or may not be present.

[0099] The secondary battery 20 of the present invention manufactured in this manner can be curved by bending the main body 21 and can then maintain the curved shape. In other words, the present invention can provide a curved cell or curved battery.

[0100] For example, as shown in FIG. 7A, by applying a force in the direction of the arrow, the battery body 21 can be wound around the rod 200, thereby bending the battery body 21 into a circular shape (see FIGS. 7A to 7D). Although not particularly limited, the longitudinal dimension of the battery body 21 wound around the rod 200 may be longer than the circumferential length of the rod 200. In this case, the battery body 21 can be wound around the rod 200 one or more times. Note that the longitudinal dimension of the battery body 21 wound around the rod 200 is preferably equal to or less than the circumferential length of the rod 200, and more preferably equal to or more than half the circumferential length of the rod 200 and less than the circumferential length of the rod 200.

[0101] Although there are no particular limitations on the force to be applied or the bending time, it is preferable to apply a force of 5 N to 300 N for, for example, 1 second to 30 seconds. Under these conditions, the curved shape of the battery body can be maintained and wrinkles that may occur on the inner surface of the exterior body can be significantly suppressed.

[0102] The pressure for curving the battery body 21 is, for example, 1.0 to 20.0 MPa, and preferably 1.0 to 10.0 MPa. As shown in FIGS. 7A to 7D, the speed at which the battery body 21 is wound around the rod 200 is, for example, 1 to 20 mm / sec, and preferably 1 to 10 mm / sec. These pressure and / or speed conditions allow the battery body to maintain its curved shape while significantly suppressing wrinkles that may occur on the inner surface of the exterior body. Note that if the effective battery width (the width of the battery that comes into contact with the rod) changes, the force and pressure applied during bending must also be changed.

[0103] The "exterior body," "resin member," "lead," and "sealant" will be described in detail below.

[0104] (exterior body) The exterior body is, for example, a part or member that can be arranged to face the two main surfaces of the electrode assembly, and generally has a plate-like, preferably sheet-like, shape.

[0105] 4, the exterior body may be composed of, for example, two exterior sheets, for example, a first exterior sheet 22a and a second exterior sheet 22b. For ease of explanation, the thicker one will be referred to as the "first exterior sheet" and the thinner one will be referred to as the "second exterior sheet." There are no particular limitations on the shape of the first exterior sheet and the second exterior sheet when viewed from above, and they may be rectangular as shown in the drawings, or any other geometric shape other than rectangular.

[0106] The first and second exterior sheets may each independently be made of a metal plate, a clad material, or a laminate film. The first and second exterior sheets may be made of the same material or different materials. Surprisingly, even when different materials are used, the curved shape of the battery body can be maintained, and by making the first exterior sheet thicker than the second exterior sheet, wrinkles that may occur on the inner surface of the exterior body can be significantly suppressed.

[0107] The "metal plate" can be any plate- or strip-shaped material made of aluminum, copper, stainless steel (SUS), nickel, or the like, without any particular limitations.

[0108] In the metal plate, "stainless steel" (SUS) refers to, for example, stainless steel as defined in "JIS G 0203 Iron and Steel Terminology," and may be an alloy steel containing chromium or chromium and nickel.

[0109] In the present disclosure, the term "plate-like" refers to a structure having two parallel or nearly parallel main surfaces. In the present disclosure, the term "strip-like" refers to a structure having two parallel or approximately parallel main surfaces, a longitudinal direction, and a width direction perpendicular to the longitudinal direction.

[0110] The metal plate can be electrically connected to either the positive or negative electrode of the electrode assembly. In this case, the metal plate can function as either the positive or negative terminal, eliminating the presence of the positive and / or negative leads described in more detail below. Either the positive or negative lead may be eliminated.

[0111] The thickness of the metal plate is generally 0.3 mm or less, for example, 0.01 mm or more and 0.250 mm or less.

[0112] In this disclosure, the term "clad material" refers to a member made by simultaneously rolling and bonding multiple metal materials.

[0113] The clad material may be made of at least two metal materials selected from the group consisting of aluminum, tin, copper, invar (alloy), stainless steel (SUS), and nickel. For example, clad materials such as tin / copper (two layers), nickel / copper (two layers), nickel / copper / nickel (three layers), and copper / invar / copper (three layers) can be used.

[0114] The cladding material can be electrically connected to either the positive or negative electrode of the electrode assembly. In this case, the cladding material can function as the positive or negative terminal, eliminating the presence of the positive and / or negative leads described in more detail below. Either the positive or negative lead may be eliminated.

[0115] The overall thickness of the cladding material is generally 0.3 mm or less, for example, 0.01 mm to 0.250 mm.

[0116] The term "laminate film" generally refers to a laminated structure. The laminate film may include, from the innermost layer to the outermost layer, at least an adhesive layer (innermost layer), a barrier layer (metal foil), and a protective layer (outermost layer). An adhesive layer may be interposed between the adhesive layer (innermost layer) and the barrier layer (metal foil), and / or between the barrier layer (metal foil) and the protective layer (outermost layer). At least one of the adhesive layer (innermost layer) and the protective layer (outermost layer) may be made of a resin sheet (i.e., a resin layer). Alternatively, at least one of the adhesive layer (innermost layer) and the protective layer (outermost layer) may be made of a barrier layer (metal foil) coated with a solvent and solidified.

[0117] The total thickness of the laminate film is generally 0.3 mm or less, for example, 0.06 mm or more and 0.30 mm or less.

[0118] In the present disclosure, by using exterior sheets made of the above-mentioned materials, the curved shape of the battery body can be maintained, and by configuring the first exterior sheet to be thicker than the second exterior sheet, wrinkles that may occur on the inner surface of the exterior body can be significantly suppressed.

[0119] (Resin parts) In this disclosure, the term "resin member" broadly refers to a member that can be made of a resin material or an elastomer material, and in a narrow sense refers to a member that can be made of a resin material or an elastomer material that has "insulating properties." It is preferable that the resin member have not only "insulating properties" but also "thermal fusion properties" (or thermal adhesive properties).

[0120] In the present disclosure, "insulating" broadly means electrical insulating property, and narrowly means insulating property that can prevent electrical short circuit between the electrode assembly, particularly the positive electrode and the negative electrode.

[0121] In the present disclosure, "thermally adhesive" generally means the property of exhibiting adhesiveness when heated.

[0122] The resin member can be a thermoplastic resin, preferably a heat-sealable resin. Examples of the thermoplastic resin include polyolefin resins such as polyethylene and / or polypropylene, preferably polypropylene and its copolymers. Examples of the resin member can include a single-layer film of a thermoplastic resin and a multilayer film containing a thermoplastic resin. An example of a multilayer film is a multilayer heat-sealable film in which both sides of a high-melting-point resin layer serving as an intermediate layer are sandwiched between low-melting-point resin layers (thermoplastic resin layers). Furthermore, examples of the elastomer material include polyester-based thermoplastic elastomers.

[0123] From another perspective, the resin member may contain an adhesive component that exhibits insulating properties. Examples of such adhesives include acrylic adhesives such as acrylate copolymers, rubber adhesives such as natural rubber, silicone adhesives such as silicone rubber, urethane adhesives such as urethane resins, α-olefin adhesives, ether adhesives, ethylene-vinyl acetate resin adhesives, epoxy resin adhesives, vinyl chloride resin adhesives, chloroprene rubber adhesives, cyanoacrylate adhesives, aqueous polymer-isocyanate adhesives, styrene-butadiene rubber adhesives, nitrile rubber adhesives, nitrocellulose adhesives, reactive hot melt adhesives, phenolic resin adhesives, modified silicone adhesives, polyamide resin adhesives, polyimide adhesives, polyurethane resin adhesives, polyolefin resin adhesives, polyvinyl acetate resin adhesives, polystyrene resin solvent-based adhesives, polyvinyl alcohol adhesives, polyvinylpyrrolidone resin adhesives, polyvinyl butyral resin adhesives, polybenzimidazole adhesives, polymethacrylate resin adhesives, melamine resin adhesives, urea resin adhesives, and / or resorcinol adhesives.

[0124] The resin member may have the form of a film, that is, the resin member may have the form of a membrane, i.e., a thin plate.

[0125] For example, as shown in FIG. 2, a secondary battery 20 according to the present disclosure may have a resin member 23 that may be arranged along at least the peripheral edge of the electrode assembly. The resin member 23 may be positioned between the first exterior sheet 22a and the second exterior sheet 22b. The first exterior sheet 22a and the second exterior sheet 22b may be bonded to each other via the resin member 23. This configuration can further improve the sealing performance of the secondary battery. In particular, it can further improve the sealing performance of the electrode assembly.

[0126] For example, as shown in FIGS. 3 and 4, the resin member 23 may be made up of two or more resin sheets.

[0127] 3 and 4, for example, the resin member 23 may be composed of two resin sheets, a first resin sheet 23a and a second resin sheet 23b. The first resin sheet 23a and the second resin sheet 23b may be bonded to each other at least along the peripheral edge of the electrode assembly 30. The first resin sheet 23a may be bonded to the first exterior sheet 22a, and the second resin sheet 23b may be bonded to the second exterior sheet 22b.

[0128] For example, as shown in FIG. 4, the resin member 23 can be composed of two resin sheets, a first resin sheet 23a and a second resin sheet 23b, which simplifies the manufacture of the battery and provides insulation to the electrode leads described below while further protecting the electrode leads by sandwiching them from both sides.

[0129] For example, in the embodiment shown in FIG. 4, openings for positioning and arranging the electrode assembly are provided in the first resin sheet 23a and the second resin sheet 23b, but such openings may or may not be present.

[0130] (Lead) The secondary battery of the present disclosure may, as needed, have a positive electrode lead and / or a negative electrode lead electrically connected to the positive electrode and / or the negative electrode, respectively, which may be included in the electrode assembly.

[0131] In the present disclosure, the terms "positive electrode lead" and / or "negative electrode lead" refer to conductors that can be electrically connected to the positive electrode and / or negative electrode that can be included in the electrode assembly. There are no particular limitations on the material that constitutes such conductors, and they can be selected from the group consisting of aluminum, copper, stainless steel (SUS), nickel, etc. The positive electrode lead and / or the negative electrode lead may be an extension of the positive electrode current collector and / or the negative electrode current collector, or may be another member separately made from the above-mentioned material. The positive electrode lead and / or the negative electrode lead may or may not be present, and if present, there is no particular limitation on their location. Either the positive electrode lead or the negative electrode lead may be present. There are no particular limitations on the shape of the positive electrode lead and / or the negative electrode lead. From the viewpoint of forming a thin battery, the positive electrode lead and / or the negative electrode lead preferably have a strip-like or film-like shape.

[0132] The positive electrode lead and / or the negative electrode lead may be positioned between the first resin sheet and the second resin sheet (see FIGS. 3 and 4). For example, as shown schematically in FIG. 4, a first lead 24 may extend as a positive electrode lead from the positive electrode 31 (more specifically, the positive electrode current collector 31b) of the electrode assembly 30, and a second lead 25 may extend as a negative electrode lead from the negative electrode 32 (more specifically, the negative electrode current collector 32b) of the electrode assembly 30. For example, as shown in FIG. 4, the first lead 24 and the second lead 25 may be positioned between the first resin sheet 23a and the second resin sheet 23b. Such a sandwich structure makes it possible to support the first lead 24 and the second lead 25 between the first resin sheet 23a and the second resin sheet 23b and maintain airtightness.

[0133] (sealant) At least a portion of the positive electrode lead and / or the negative electrode lead may be coated with a sealant.

[0134] In this disclosure, the term "sealant" refers to a member that can be provided to cover at least a portion of the positive electrode lead and / or the negative electrode lead to prevent moisture such as water vapor from penetrating into the battery along the positive electrode lead and / or the negative electrode lead. Such a sealant can also physically reinforce the positive electrode lead and / or the negative electrode lead. From this viewpoint, it is preferable that at least a part of the sealant is positioned inside the resin member, particularly between the first resin sheet and the second resin sheet.

[0135] The sealant can be made of, for example, a resin or an elastomer, and the material is not particularly limited. The shape of the sealant is also not particularly limited. From the viewpoint of forming a thin battery, the sealant is preferably in the form of a strip or film.

[0136] 4, for example, a first sealant 26 may be provided on a first lead 24, which is a positive electrode lead, and a second sealant 27 may be provided on a second lead 25, which is a negative electrode lead. At least a portion of the first sealant 26 and / or the second sealant 27 can be sandwiched between a first resin sheet 23a and a second resin sheet 23b to form a sealed structure or a sealed structure.

[0137] The above configurations can be appropriately modified or combined depending on the specifications of the secondary battery.

[0138] For example, as shown in FIGS. 5, 6A, and 6B, the configuration of the electrode assembly that can be included in the secondary battery may be changed as appropriate. The electrode assembly 30A shown in FIGS. 5, 6A, and 6B is basically similar to the electrode assembly 30 shown in FIG. 4, and includes an additional (or second) positive electrode material layer 31Aa, an additional (or second) separator 33A, and an additional (or second) negative electrode 32A (a negative electrode including an additional (or second) negative electrode material layer 32Aa and an additional (or second) negative electrode current collector 32Ab).

[0139] The additional (or second) positive electrode material layer 31Aa may be the same as or different from the positive electrode material layer 31a shown in FIG. The additional (or second) separator 33A may be the same as or different from the separator 33 shown in FIG. The additional (or second) negative electrode 32A may be the same as or different from the negative electrode 32 shown in Figure 4. The negative electrode 32A may or may not have a lead 25A and a sealant 27A similar to those shown in Figure 4.

[0140] In the secondary battery of the present disclosure, the positive electrode lead 24 may or may not have a sealant 26 . In the secondary battery of the present disclosure, the negative electrode lead 25 may or may not have a sealant 27 .

[0141] In the secondary battery of the present disclosure, the first resin sheet 23a and the second resin sheet 23b may or may not have openings.

[0142] The secondary battery of the present disclosure should not be construed as being limited to the above-described embodiments.

[0143] The present invention will be explained in more detail below by way of examples and comparative examples, but the present invention should not be construed as being limited to the following examples. [Example]

[0144] The following five types of materials were prepared as exterior sheets used in the examples and comparative examples. (a) Aluminum laminate film (including a protective layer (outermost layer), a barrier layer (Al foil), and an adhesive layer (innermost layer)) (b) Cu plate (c) Aluminum plate (d) SUS plate (e) Clad material (two or three layers)

[0145] As the electrode assembly used in the examples and comparative examples, an electrode assembly having the same configuration as that shown in FIGS. 5, 6A, and 6B (T: 0.3 mm×W: 6.0 mm×L: 45.0 mm) was prepared. Positive electrode layer 31Aa: lithium cobalt oxide (thickness: 50 μm) Positive electrode current collector 31Ab: aluminum foil (thickness: 15 μm) Positive electrode lead 24A: Aluminum (thickness: 80 μm) Separator 33A: Polypropylene / Polyethylene (Thickness: 30 μm) Negative electrode layer 32Aa: graphite (thickness: 48 μm) Negative electrode current collector 32Ab: Copper foil (thickness: 12μm) Negative electrode lead 25A: Nickel (thickness: 80 μm)

[0146] As the resin member used in the examples and comparative examples, a resin sheet having the shape shown in FIGS. 5, 6A, and 6B (T: 0.1 mm×W: 10.0 mm×L: 50.0 mm) was prepared. First resin sheet 23Aa: polyolefin resin (extending longitudinally along the negative electrode lead 25A) (no opening) Second resin sheet 23Ab: polyolefin resin (extending longitudinally along the positive electrode lead 24A)

[0147] The positive electrode sealant 26A and the negative electrode sealant 27A shown in FIG. 5 are omitted.

[0148] (Examples 1 to 16) The secondary battery shown in Table 1 below was produced using an exterior body in which the material of the exterior body was selected from (a) an Al laminate film and (b) a Cu plate, and the materials of the first exterior sheet 22Aa and the second exterior sheet 22Ab were the same, and the thickness of the first exterior sheet 22Aa was made greater than the thickness of the second exterior sheet 22Ab. Furthermore, the battery body 21 was curved (15 N, 5 seconds, radius of curvature: 10 mm) using a round bar (rod 200) with a radius of 10 mm (see FIGS. 7A to 7D). Note that the schematic diagram of FIG. 7A shows an embodiment in which the longitudinal dimension of the battery body and the circumferential length of the rod 200 are substantially the same, but in this example, specifically, the battery body 21 used had a longitudinal dimension that was approximately three-quarters the circumferential length of the rod 200.

[0149] After bending, wrinkles that may occur on the inner surface of the battery body were visually observed. [evaluation] ◎: No wrinkles ×: Wrinkles The results are shown in Table 1 below.

[0150] [Table 1]

[0151] Surprisingly, in the secondary batteries of Examples 1 to 16, the thickness of the first exterior sheet 22Aa (inner side) was greater than the thickness of the second exterior sheet 22Ab (outer side), which prevented wrinkles from forming, and no wrinkles were visible in any of the examples. Furthermore, the shape was maintained even when the radius of curvature was 10 mm.

[0152] (Comparative Examples 1 to 16) The secondary batteries of Comparative Examples 1 to 16 shown in Table 2 below were fabricated in the same manner as the above examples, except that the thickness of the first exterior sheet 22Aa and the thickness of the second exterior sheet 22Ab were made the same or the thickness of the first exterior sheet 22Aa was made smaller than the thickness of the second exterior sheet 22Ab. In addition, the wrinkles that may occur on the inner surface of the battery body after bending in the same manner as above were evaluated, and the results are shown in Table 2 below.

[0153] [Table 2]

[0154] Surprisingly, in the secondary batteries of Comparative Examples 1 to 16, the thickness of the first exterior sheet 22Aa (inner side) was smaller than or equal to the thickness of the second exterior sheet 22Ab (outer side), resulting in significant wrinkles, and wrinkles could be visually confirmed in all of the comparative examples. It is believed that the formation of such wrinkles damages the electrode assembly and reduces battery performance.

[0155] (Examples 17 to 36) The secondary batteries shown in Table 3 below were produced using exterior bodies in which the material of the exterior body was selected from (a) Al laminate film, (b) Cu plate, (c) Al plate, (d) SUS plate, and (e) clad material, and the materials of the first exterior sheet 22Aa and the second exterior sheet 22Ab were different, and the thickness of the first exterior sheet 22Aa was made greater than the thickness of the second exterior sheet 22Ab. In addition, the possibility of wrinkles occurring on the inner surface of the battery body after bending was evaluated in the same manner as above, and the results are shown in Table 3 below.

[0156] [Table 3]

[0157] Surprisingly, in the secondary batteries of Examples 17 to 36, even when the materials were different, in other words, regardless of the materials, the thickness of the first exterior sheet 22Aa (inner side) was greater than the thickness of the second exterior sheet 22Ab (outer side), which prevented wrinkles from forming, and no wrinkles were visible in any of the examples. Furthermore, the shape was maintained even when the radius of curvature was 10 mm.

[0158] (Comparative Examples 17 to 38) The secondary batteries of Comparative Examples 17 to 38 shown in Table 4 below were fabricated in the same manner as the above examples, except that the thickness of the first exterior sheet 22Aa and the thickness of the second exterior sheet 22Ab were made the same or the thickness of the first exterior sheet 22Aa was made smaller than the thickness of the second exterior sheet 22Ab. In addition, the wrinkles that may occur on the inner surface of the battery body after bending were evaluated in the same manner as above, and the results are shown in Table 4 below.

[0159] [Table 4]

[0160] Surprisingly, in the secondary batteries of Comparative Examples 17 to 38, the thickness of the first exterior sheet 22Aa (inner side) was smaller than or equal to the thickness of the second exterior sheet 22Ab (outer side), resulting in significant wrinkles, and wrinkles could be visually confirmed in all of the comparative examples. It is believed that the formation of such wrinkles damages the electrode assembly and reduces battery performance.

[0161] The present disclosure may take the following forms. <1> The battery includes an electrode assembly formed by laminating at least one electrode-constituting layer including a positive electrode, a negative electrode, and a separator, and an exterior body that covers the electrode assembly, the exterior body is composed of two exterior sheets, namely, a first exterior sheet and a second exterior sheet, the electrode assembly is disposed between the first exterior sheet and the second exterior sheet, The thickness of the first exterior sheet is greater than the thickness of the second exterior sheet, and The secondary battery has a curved shape, with the first exterior sheet disposed on the inside and the second exterior sheet disposed on the outside. <2> the ratio of the thickness of the first exterior sheet to the thickness of the second exterior sheet is 1.1 or more and 25 or less; <1> The secondary battery according to claim 1. <3> The difference in thickness between the first exterior sheet and the second exterior sheet is 10 μm or more and 240 μm or less. <1> or <2> Described in secondary battery. <4> The radius of curvature when the secondary battery is bent is 5 mm or more. <1> ~ <3> 10. The secondary battery according to claim 9, <5> The first exterior sheet and the second exterior sheet are each independently made of a metal plate, a clad material, or a laminate film. <1> ~ <4> 10. The secondary battery according to claim 9, <6> The electrode assembly further includes a resin member disposed along a peripheral edge thereof, the resin member being positioned between the first exterior sheet and the second exterior sheet, and the first exterior sheet and the second exterior sheet being bonded to each other via the resin member. <1> ~ <5> 10. The secondary battery according to claim 9, <7> the resin member is composed of two resin sheets, a first resin sheet and a second resin sheet, the first resin sheet and the second resin sheet are bonded to each other at least along the peripheral edge of the electrode assembly, the first resin sheet is bonded to the first exterior sheet, and the second resin sheet is bonded to the second exterior sheet; <6> The secondary battery according to claim 1. <8> The electrode assembly further includes a positive electrode lead and / or a negative electrode lead electrically connected to the positive electrode and / or the negative electrode, respectively; the positive electrode lead and / or the negative electrode lead is positioned between the first resin sheet and the second resin sheet; <7> The secondary battery according to claim 1. <9> At least a portion of the positive electrode lead and / or the negative electrode lead is coated with a sealant, and at least a portion of the sealant is positioned between the first resin sheet and the second resin sheet. <8> The secondary battery according to claim 1. <10> The secondary battery has a plate-like shape. <1> ~ <9> 10. The secondary battery according to claim 9, <11> The secondary battery has a strip shape. <1> ~ <10> 10. The secondary battery according to claim 9, <12> the curved secondary battery has a curved shape that forms at least a part of an imaginary circle in a cross-sectional view in the stacking direction; <11> The secondary battery according to claim 1. <13> The secondary battery is a battery for a wearable device. <1> ~ <12> 10. The secondary battery according to claim 9, <14> The wearable device is a smart ring. <13> The secondary battery according to claim 1. [Industrial Applicability]

[0162] The secondary battery of the present disclosure can be used in various fields where electricity storage is conceivable. By way of example only, the secondary battery of the present disclosure can be used in the electrical, information, and communications fields where electrical and electronic devices can be used (for example, electrical and electronic devices or mobile devices including mobile phones, smartphones, laptop computers, digital cameras, activity monitors, arm computers, electronic paper, wearable devices (smart watches, smart rings, smart glasses), and small electronic devices such as RFID tags and card-type electronic money), household and small industrial applications (for example, power tools, golf carts, and household, nursing care, and industrial robots), large industrial applications (for example, forklifts, elevators, and harbor cranes), transportation systems (for example, hybrid cars, electric cars, buses, trains, electrically assisted bicycles, and electric motorcycles), power system applications (for example, various power generation systems, road conditioners, smart grids, and general household installation-type power storage systems), medical applications (medical devices such as earphone hearing aids), pharmaceutical applications (for example, medication management systems), as well as the IoT field and space and deep-sea applications (for example, space probes, submersible research vessels, and the like). [Explanation of symbols]

[0163] 1, 31, 31A positive electrode 2, 32, 32A negative pole 3, 33, 33A separator 5 Electrode composition layer 10, 30, 30A electrode assembly 20 Secondary battery 21 Battery body 22 Exterior body 22a, 22Aa First exterior sheet 22b, 22Ab Second exterior sheet 23, 23A Resin parts 23a, 23Aa First resin sheet 23b, 23Ab Second resin sheet 24, 24A 1st lead 25, 25A 2nd lead 26, 26A First sealant 27, 27A Second sealant 31a, 31Aa Cathode material layer 31b, 31Ab Positive electrode current collector 31b1, 31Ab1 Positive electrode tab 32a, 32Aa negative electrode material layer 32b, 32Ab negative electrode current collector 32b1, 32Ab1 negative electrode tab 100' Conventional secondary battery 101' Main body part 102' Positive Lead 103' Negative lead 104' Positive Sealant 105' Negative electrode sealant 200, 200' rod

Claims

1. The battery includes an electrode assembly formed by laminating at least one electrode-constituting layer including a positive electrode, a negative electrode, and a separator, and an exterior body that covers the electrode assembly, the exterior body is composed of two exterior sheets, namely, a first exterior sheet and a second exterior sheet, the electrode assembly is disposed between the first exterior sheet and the second exterior sheet, The thickness of the first exterior sheet is greater than the thickness of the second exterior sheet; and a curved shape in which the first exterior sheet is disposed on the inside and the second exterior sheet is disposed on the outside, a ratio of the thickness of the first exterior sheet to the thickness of the second exterior sheet is 1.1 or more and 25 or less.

2. 2. The secondary battery according to claim 1, wherein the difference in thickness between the first exterior sheet and the second exterior sheet is 10 μm or more and 240 μm or less.

3. The secondary battery according to claim 1 , wherein the radius of curvature when the secondary battery is bent is 5 mm or more.

4. The secondary battery according to claim 1 , wherein the first exterior sheet and the second exterior sheet are each independently made of a metal plate, a clad material, or a laminate film.

5. 2. The secondary battery according to claim 1, further comprising a resin member disposed along a peripheral edge of the electrode assembly, the resin member being positioned between the first exterior sheet and the second exterior sheet, and the first exterior sheet and the second exterior sheet being bonded to each other via the resin member.

6. 6. The secondary battery according to claim 5, wherein the resin member is made up of two resin sheets, a first resin sheet and a second resin sheet, the first resin sheet and the second resin sheet being bonded to each other at least along the peripheral edge of the electrode assembly, the first resin sheet being bonded to the first exterior sheet, and the second resin sheet being bonded to the second exterior sheet.

7. The electrode assembly further includes a positive electrode lead and / or a negative electrode lead electrically connected to the positive electrode and / or the negative electrode, respectively, The secondary battery according to claim 6 , wherein the positive electrode lead and / or the negative electrode lead is positioned between the first resin sheet and the second resin sheet.

8. 8. The secondary battery according to claim 7, wherein at least a portion of the positive electrode lead and / or the negative electrode lead is covered with a sealant, and at least a portion of the sealant is positioned between the first resin sheet and the second resin sheet.

9. The secondary battery according to claim 1 , wherein the secondary battery has a plate shape.

10. The secondary battery according to claim 1 , wherein the secondary battery has a strip shape.

11. The secondary battery according to claim 10 , wherein the curved secondary battery has a curved shape that forms at least a part of an imaginary circle in a cross-sectional view in the stacking direction.

12. The secondary battery according to claim 1 , wherein the secondary battery is a battery for a wearable device.

13. The secondary battery according to claim 12 , wherein the wearable device is a smart ring.

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