Secondary battery

Abstract

This secondary battery comprises a columnar outer packaging member, and a battery element that is housed in the interior of the outer packaging member and includes a first electrode and a second electrode. The first electrode and the second electrode are wound while facing one another, and the first electrode includes a tip end section that is located on the side close to the center of the battery element. On the side that is closer to the center of the battery element than the second electrode is, the tip end section is wound one or more times and has one or more bend sections. In said bend section or sections, the tip end section is bent so as to be partially depressed toward the center of the battery element.

Description

Technical Field

[0001] This technology relates to secondary batteries.

Background Art

[0002] Due to the widespread use of various electronic devices such as mobile phones, the development of secondary batteries is underway as a power source that is small and lightweight while achieving a high energy density. This secondary battery includes battery elements (a positive electrode, a negative electrode, and an electrolyte) inside an exterior member, and various studies have been conducted on the configuration of the secondary battery.

[0003] Specifically, a positive electrode plate and a negative electrode plate are wound with a separator interposed therebetween, and an adhesive tape is attached to the back surface of the negative electrode plate at a location facing the starting end portion on the inner circumferential surface side of the positive electrode mixture layer (see, for example, Patent Document 1).

[0004] The positive electrode and the negative electrode are wound with a separator interposed therebetween, and the separator is adhered to the positive electrode over a range of at least one turn length in the winding direction from the start side end of the positive electrode composite layer (see, for example, Patent Document 2).

[0005] The anode and the cathode are wound with a polymer separator interposed therebetween, and a core that causes uniform swelling of the cathode is disposed at the center around which the anode and the cathode are wound (see, for example, Patent Document 3).

[0006] The positive electrode plate and the negative electrode plate are wound with a separator interposed therebetween. At the innermost side, only the separator is wound around a plurality of turns, and the separator wound around the plurality of turns is solidified so as to be integrated (see, for example, Patent Document 4).

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

[0008] Although various studies have been made on the configuration of secondary batteries, the operation reliability of such secondary batteries is still not sufficient, so there is room for improvement.

[0009] Therefore, a secondary battery capable of obtaining excellent operation reliability is desired.

[0010] The secondary battery according to one embodiment of the present technology includes a columnar exterior member and a battery element housed inside the exterior member and including a first electrode and a second electrode. The first electrode and the second electrode are wound while facing each other, and the first electrode includes a tip portion located closer to the center of the battery element. The tip portion is wound one or more times closer to the center of the battery element than the second electrode and has one or two or more bent portions, and at the bent portions, the tip portion is bent so as to be partially recessed toward the center of the battery element.

[0011] According to the secondary battery of one embodiment of the present technology, a battery element including a first electrode and a second electrode is housed inside a columnar exterior member, the first electrode and the second electrode are wound while facing each other, the first electrode includes a tip portion located closer to the center of the battery element, the tip portion is wound one or more times closer to the center of the battery element than the second electrode and has one or two or more bent portions, and at the bent portions, the tip portion is bent so as to be partially recessed toward the center of the battery element, so that excellent operation reliability can be obtained.

[0012] Note that the effects of the present technology are not necessarily limited to the effects described here, and any of the series of effects related to the present technology described later may be applicable.

Brief Description of Drawings

[0013]

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Modes for Carrying Out the Invention

[0014] Hereinafter, with reference to the drawings, a detailed description will be given of an embodiment of the present technology. The order of description is as follows. 1. Secondary battery 1-1. Configuration 1-2. Detailed configuration of battery element 1-3. Operation 1-4. Manufacturing method 1-5. Action and effect 2. Modification example

[0015] <1. Secondary battery> First, a secondary battery according to an embodiment of the present technology will be described.

[0016] The secondary battery described here is a secondary battery having a columnar three-dimensional shape. As will be described later, this secondary battery has a pair of bottom portions facing each other and side wall portions connected to each of the pair of bottom portions, and thus has an outer diameter and a height. Note that the "outer diameter" is the diameter (maximum diameter) of each of the pair of bottom portions, and the "height" is the distance (maximum distance) from one bottom portion to the other bottom portion.

[0017] The charge and discharge principle of the secondary battery is not particularly limited. Hereinafter, a case where the battery capacity is obtained by utilizing the occlusion and release of electrode reactants will be described. This secondary battery includes an electrolyte together with a positive electrode and a negative electrode, and the charge capacity of the negative electrode is larger than the discharge capacity of the positive electrode. That is, the electrochemical capacity per unit area of the negative electrode is set to be larger than the electrochemical capacity per unit area of the positive electrode. This is to prevent the deposition of electrode reactants on the surface of the negative electrode during charging.

[0018] The type of the electrode reactant is not particularly limited, but specifically, it is a light metal such as an alkali metal and an alkaline earth metal. Specific examples of the alkali metal include lithium, sodium, and potassium, and specific examples of the alkaline earth metal include beryllium, magnesium, and calcium.

[0019] Hereinafter, the case where the electrode reactant is lithium will be taken as an example. A secondary battery that obtains battery capacity by utilizing the intercalation and deintercalation of lithium is a so-called lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is intercalated and deintercalated in an ionic state.

[0020] <1-1. Configuration> FIG. 1 shows a perspective configuration of a secondary battery. FIG. 2 shows an enlarged cross-sectional configuration of the secondary battery shown in FIG. 1. FIG. 3 shows an enlarged cross-sectional configuration of the battery element 40 shown in FIG. 2.

[0021] However, in FIG. 2, for the sake of simplifying the illustration, each of the positive electrode 41, negative electrode 42, separator 43, positive electrode lead 51, and negative electrode lead 52, which will be described later, is shown linearly. Further, in FIG. 3, only a part of the battery element 40 is shown.

[0022] In the following description, for convenience, the upper side, lower side, right side, and left side in FIG. 2 are respectively defined as the upper side, lower side, right side, and left side of the secondary battery.

[0023] As described above, the secondary battery shown in FIGS. 1 and 2 has a columnar three-dimensional shape and has an outer diameter D and a height H. Here, the secondary battery has a three-dimensional shape in which the height H is smaller than the outer diameter D, that is, a flat and columnar three-dimensional shape. For this reason, the secondary battery is a secondary battery called a so-called coin type or button type. More specifically, the three-dimensional shape of the secondary battery is flat and cylindrical (circular columnar), and the ratio D / H of the outer diameter D to the height H is greater than 1.

[0024] The specific dimensions of the secondary battery are not particularly limited. For example, the outer diameter D = 3 mm to 30 mm and the height H = 0.5 mm to 70 mm. Note that the ratio D / H is preferably 25 or less.

[0025] As shown in FIGS. 1 to 3, this secondary battery includes an outer can 10 and a battery element 40. Here, the secondary battery further includes an external terminal 20, a gasket 30, a positive electrode lead 51, and a negative electrode lead 52.

[0026] [Outer can] As shown in FIGS. 1 and 2, the outer can 10 is a hollow outer member that houses the battery element 40 and the like. Here, the outer can 10 has a through-hole 10K.

[0027] This outer can 10 has a columnar three-dimensional shape similar to the three-dimensional shape of the secondary battery, that is, it has a flat and columnar (circular columnar) three-dimensional shape. Accordingly, the outer can 10 has an upper bottom portion M1 and a lower bottom portion M2 that face each other, and a side wall portion M3. This side wall portion M3 is disposed between the upper bottom portion M1 and the lower bottom portion M2 and is connected to each of the upper bottom portion M1 and the lower bottom portion M2. Here, the planar shapes of the upper bottom portion M1 and the lower bottom portion M2 are circular, and the surface of the side wall portion M3 is a convex curved surface that bulges outward.

[0028] Here, the outer can 10 includes a storage portion 11 and a lid portion 12, and the storage portion 11 and the lid portion 12 are joined to each other. Accordingly, the storage portion 11 is sealed by the lid portion 12. Specifically, the storage portion 11 and the lid portion 12 are welded to each other as will be described later.

[0029] The storage portion 11 is a cylindrical approximately container-shaped member (lower bottom portion M2 and side wall portion M3) that houses the battery element 40 and the like inside. Here, the storage portion 11 has a structure in which the lower bottom portion M2 and the side wall portion M3 are integrated with each other. However, the storage portion 11 may have a structure in which the lower bottom portion M2 and the side wall portion M3 are separated from each other. Since this storage portion 11 has a hollow structure with an open upper end and a closed lower end, it has an opening 11K at its upper end.

[0030] The lid portion 12 is a substantially disk-shaped member (upper bottom portion M1) that closes the opening portion 11K and has the above-described through-hole 10K. As will be described later, this through-hole 10K is used as a connection path for electrically connecting the battery element 40 and the external terminal 20 to each other.

[0031] In the completed secondary battery, as described above, since the lid portion 12 has already been joined to the housing portion 11, the opening portion 11K is closed by the lid portion 12. Thus, it may be considered that it is impossible to retrospectively confirm whether the housing portion 11 had the opening portion 11K even by looking at the appearance of the secondary battery.

[0032] However, in the manufacturing process of the secondary battery, when the housing portion 11 and the lid portion 12 are welded to each other in order to join them to each other, a welding mark remains on the surface of the outer can 10, more specifically, at the boundary between the housing portion 11 and the lid portion 12. Therefore, based on the presence or absence of the welding mark, it is possible to retrospectively confirm whether the housing portion 11 had the opening portion 11K.

[0033] That is, when a welding mark remains on the surface of the outer can 10 (the welding mark can be visually recognized), it means that the housing portion 11 had the opening portion 11K. On the other hand, when no welding mark remains on the surface of the outer can 10 (the welding mark cannot be visually recognized), it means that the housing portion 11 did not have the opening portion 11K.

[0034] Here, the lid portion 12 has a recessed portion 12U, and the through-hole 10K is provided in the recessed portion 12U. In this recessed portion 12U, since the lid portion 12 is bent so as to partially recess toward the inside of the housing portion 11, a part of the lid portion 12 is bent so as to form a downward step.

[0035] The shape of the recessed portion 12U, that is, the shape defined by the outer edge of the recessed portion 12U when the secondary battery is viewed from above, is not particularly limited. Here, the shape of the recessed portion 12U is circular. Note that the inner diameter and depth of the recessed portion 12U are not particularly limited and can be arbitrarily set.

[0036] As described above, the outer can 10 is a can in which two members (the storage portion 11 and the lid portion 12) that were physically separated from each other are joined together, that is, a so-called joined can. More specifically, the outer can 10 in which the storage portion 11 and the lid portion 12 are welded to each other is a so-called welded can. As a result, since the joined outer can 10 is physically one member as a whole, it is in a state where it cannot be separated into two members (the storage portion 11 and the lid portion 12) afterwards.

[0037] The outer can 10 which is a joined can is a different can from a crimp can formed using a crimping process, and is a so-called crimp less can. This is because the element space volume increases inside the outer can 10, so the volume energy density increases. This "element space volume" is the volume (effective volume) of the internal space of the outer can 10 that can be used to accommodate the battery element 40.

[0038] In addition, the outer can 10 which is a joined can does not have portions that overlap each other, nor does it have portions where two or more members overlap each other.

[0039] "Not having portions that overlap each other" means that a part of the outer can 10 is not processed (bent) so as to overlap each other. Also, "not having portions where two or more members overlap each other" means that since the outer can 10 is physically one member after the completion of the secondary battery, the outer can 10 cannot be separated into two or more members afterwards. That is, the state of the outer can 10 in the completed secondary battery is not a state where two or more members are combined while overlapping each other so as to be separable afterwards.

[0040] Here, since the exterior can 10 has conductivity, each of the storage part 11 and the lid part 12 has conductivity. As a result, since the exterior can 10 is connected to the battery element 40 (the negative electrode 42 described later) via the negative electrode lead 52, it is electrically connected to the negative electrode 42. Therefore, the exterior can 10 functions as an external connection terminal for the negative electrode 42. This is because even if the secondary battery does not separately include an external connection terminal for the negative electrode 42 from the exterior can 10, a decrease in the element space volume due to the presence of the external connection terminal for the negative electrode 42 is suppressed. Thereby, since the element space volume increases, the volume energy density increases.

[0041] Specifically, the exterior can 10 contains any one or two or more of conductive materials such as metal materials and alloy materials, and specific examples of the conductive materials are iron, copper, nickel, stainless steel, iron alloys, copper alloys, and nickel alloys. The type of stainless steel is not particularly limited, but specifically, it is SUS304, SUS316, etc. However, the material for forming the storage part 11 and the material for forming the lid part 12 may be the same as each other or different from each other.

[0042] Note that the lid part 12 is insulated from the external terminal 20, which functions as an external connection terminal for the positive electrode 41, via the gasket 30 as described later. This is to prevent contact (short circuit) between the exterior can 10 (the external connection terminal for the negative electrode 42) and the external terminal 20 (the external connection terminal for the positive electrode 41).

[0043] [External Terminal] As shown in FIGS. 1 and 2, the external terminal 20 is an electrode terminal that is connected to the electronic device when the secondary battery is mounted on the electronic device. This external terminal 20 is disposed outside the exterior can 10 and shields the through-hole 10K.

[0044] Note that the external terminal 20 is supported by the outer can 10 via the gasket 30. More specifically, as will be described later, the external terminal 20 is heat - welded to the lid portion 12 via the gasket 30. Thus, the external terminal 20 is fixed to the lid portion 12 via the gasket 30 while being insulated from the lid portion 12 via the gasket 30.

[0045] Since this external terminal 20 is connected to the battery element 40 (positive electrode 41) via the positive electrode lead 51, it is electrically connected to the positive electrode 41. Thus, the external terminal 20 functions as an external connection terminal for the positive electrode 41. When the secondary battery is in use, the secondary battery is connected to the electronic device via the external terminal 20 (external connection terminal for the positive electrode 41) and the outer can 10 (external connection terminal for the negative electrode 42), so that the electronic device can operate using the secondary battery as a power source.

[0046] This external terminal 20 is a substantially plate - shaped member. The three - dimensional shape of the external terminal 20 is not particularly limited, but specifically, it is a flat plate shape.

[0047] Here, the external terminal 20 is disposed inside the recessed portion 12U. That is, the external terminal 20 is housed inside the recessed portion 12U so as not to protrude outside (above) the recessed portion 12U. This is because, compared with the case where the external terminal 20 protrudes outside the recessed portion 12U, the height H of the secondary battery becomes smaller, so that the volume energy density increases.

[0048] Note that since the outer diameter of the external terminal 20 is smaller than the inner diameter of the recessed portion 12U, the external terminal 20 is separated from the lid portion 12 around it. Thus, the gasket 30 is disposed in part or all of the space between the lid portion 12 and the external terminal 20 inside the recessed portion 12U. More specifically, the gasket 30 is disposed at a place where the lid portion 12 and the external terminal 20 could come into contact with each other if the gasket 30 did not exist.

[0049] In addition, the external terminal 20 contains any one or two or more of conductive materials such as metal materials and alloy materials. Specific examples of the conductive materials include aluminum and aluminum alloys.

[0050] However, the external terminal 20 may contain a clad material. This clad material includes an aluminum layer and a nickel layer in order from the side closer to the gasket 30, and the aluminum layer and the nickel layer are roll-bonded to each other. Note that the clad material may include a nickel alloy layer instead of the nickel layer.

[0051] In particular, the external terminal 20 functions as an external connection terminal for the positive electrode 41. As will be described later, when the internal pressure of the outer can 10 rises excessively, it functions as a relief valve for releasing the internal pressure. The reasons for the increase in the internal pressure include the generation of gas due to the decomposition reaction of the electrolytic solution during charge and discharge, and the reasons for promoting the decomposition reaction of the electrolytic solution include internal short circuit of the secondary battery, heating of the secondary battery, and discharge of the secondary battery under high current conditions.

[0052] Details of the operation of the external terminal 20 functioning as a relief valve will be described later (see FIG. 6).

[0053] [Gasket] As shown in FIG. 2, the gasket 30 is an insulating sealing member disposed between the outer can 10 and the external terminal 20. Here, the gasket 30 is disposed between the lid portion 12 and the external terminal 20, and has a through hole 30K at a position overlapping the through hole 10K. Thereby, the gasket 30 is disposed so as not to shield the through hole 10K. Note that the inner diameter of the through hole 10K and the inner diameter of the through hole 30K may be the same as each other or different from each other.

[0054] Since this gasket 30 contains any one or more than two types of polymer compounds having insulation and heat fusibility, as described above, the external terminal 20 is heat welded to the lid portion 12 via the gasket 30. The types of polymer compounds are not particularly limited, but specifically, they are polypropylene, polyethylene, etc.

[0055] In addition, since the installation range of the gasket 30 is not particularly limited, it can be arbitrarily set. Here, the gasket 30 is disposed in the space between the upper surface of the lid portion 12 and the lower surface of the external terminal 20 inside the recessed portion 12U. However, the installation range of the gasket 30 may be extended to the outside of the space between the upper surface of the lid portion 12 and the lower surface of the external terminal 20.

[0056] [Battery element] As shown in FIGS. 1 to 3, the battery element 40 is a power generation element that allows a charge and discharge reaction to proceed, and is housed inside the exterior can 10. This battery element 40 includes a positive electrode 41 as a second electrode, a negative electrode 42 as a first electrode, a separator 43, and an electrolytic solution (not shown) that is a liquid electrolyte.

[0057] Since this battery element 40 is a so-called wound electrode body, the element structure of the battery element 40 is a so-called wound type. In this case, the positive electrode 41 and the negative electrode 42 are laminated on each other via the separator 43, and the positive electrode 41, the negative electrode 42, and the separator 43 are wound, so the battery element 40 has a winding center space 40K that is a winding core portion. Thereby, the positive electrode 41 and the negative electrode 42 are wound around the winding center space 40K located at the center C (see FIGS. 4 and 5) of the battery element 40 to be described later while facing each other.

[0058] In addition, since the battery element 40 has a columnar three-dimensional shape similar to the three-dimensional shape of the exterior can 10, it has a flat and columnar three-dimensional shape. Compared with the case where the battery element 40 has a three-dimensional shape different from the three-dimensional shape of the exterior can 10, when the battery element 40 is housed inside the exterior can 10, dead space (the surplus space between the exterior can 10 and the battery element 40) is less likely to occur, so the internal space of the exterior can 10 is effectively utilized. As a result, the element space volume increases, and the volume energy density increases.

[0059] (Positive electrode) As shown in FIGS. 2 and 3, the positive electrode 41 includes a positive electrode current collector 41A and a positive electrode active material layer 41B.

[0060] The positive electrode current collector 41A is a conductive support that supports the positive electrode active material layer 41B and has a pair of surfaces on which the positive electrode active material layer 41B is provided. This positive electrode current collector 41A contains a conductive material such as a metal material, and specific examples of the conductive material are aluminum and the like.

[0061] Here, the positive electrode active material layer 41B is provided on both surfaces of the positive electrode current collector 41A and contains any one or two or more kinds of positive electrode active materials capable of occluding and releasing lithium. However, the positive electrode active material layer 41B may be provided only on one side of the positive electrode current collector 41A on the side where the positive electrode 41 faces the negative electrode 42. Further, the positive electrode active material layer 41B may further contain any one or two or more kinds of materials such as a positive electrode binder and a positive electrode conductive agent. The method for forming the positive electrode active material layer 41B is not particularly limited, but specifically, it is a coating method or the like.

[0062] The positive electrode active material contains a lithium compound because a high energy density can be obtained. This lithium compound is a compound containing lithium as a constituent element, and more specifically, a compound containing one or more transition metal elements as constituent elements together with lithium. However, the lithium compound may further contain any one or more of other elements (elements other than lithium and transition metal elements respectively).

[0063] The type of lithium compound is not particularly limited, but specifically, it is an oxide, a phosphate compound, a silicate compound, a borate compound, etc. Specific examples of the oxide are LiNiO2, LiCoO2, LiMn2O4, etc. Specific examples of the phosphate compound are LiFePO4, LiMnPO4, etc.

[0064] The positive electrode binder contains any one or more of synthetic rubber and polymer compounds, etc. Specific examples of the synthetic rubber are styrene-butadiene rubber, etc., and specific examples of the polymer compound are polyvinylidene fluoride, etc. The positive electrode conductive agent contains any one or more of conductive materials such as carbon materials, and specific examples of the conductive materials are graphite, carbon black, acetylene black, ketjen black, etc. However, the conductive material may also be a metal material, a polymer compound, etc.

[0065] (Negative electrode) As shown in FIGS. 2 and 3, the negative electrode 42 includes a negative electrode current collector 42A and a negative electrode active material layer 42B. This negative electrode current collector 42A is the current collector of the negative electrode 42 which is the first electrode, and the negative electrode active material layer 42B is the active material layer of the negative electrode 42 which is the first electrode.

[0066] The negative electrode current collector 42A is a conductive support for supporting the negative electrode active material layer 42B, and has a pair of surfaces on which the negative electrode active material layer 42B is provided. This negative electrode current collector 42A contains a conductive material such as a metal material, and specific examples of the conductive material are copper, etc.

[0067] The negative electrode active material layer 42B is provided on the negative electrode current collector 42A. Here, the negative electrode active material layer 42B is provided on both sides of the negative electrode current collector 42A and contains any one or more of negative electrode active materials capable of occluding and releasing lithium. However, the negative electrode active material layer 42B may be provided only on one side of the negative electrode current collector 42A on the side where the negative electrode 42 faces the positive electrode 41. Further, the negative electrode active material layer 42B may further contain any one or more of materials such as a negative electrode binder and a negative electrode conductive agent. Details regarding each of the negative electrode binder and the negative electrode conductive agent are the same as the details regarding each of the positive electrode binder and the positive electrode conductive agent. The method for forming the negative electrode active material layer 42B is not particularly limited, but specifically, it is any one or more of a coating method, a vapor phase method, a liquid phase method, a spraying method, and a firing method (sintering method).

[0068] The negative electrode active material contains any one or more of a carbon material and a metal-based material, etc. This is because a high energy density can be obtained. Specific examples of the carbon material are graphitizable carbon, non-graphitizable carbon, and graphite (natural graphite and artificial graphite), etc. The metal-based material is a material containing any one or more of metal elements and semi-metal elements capable of forming an alloy with lithium as constituent elements, and specific examples of the metal elements and semi-metal elements are silicon and tin, etc. However, the metal-based material may be a single substance, an alloy, a compound, a mixture of two or more of them, or a material containing two or more of those phases. Specific examples of the metal-based material are TiSi2 and SiO x (0 < x ≤ 2 or 0.2 < x < 1.4), etc.

[0069] Note that the negative electrode 42 is arranged on the inner side of the winding relative to the positive electrode 41 and has a bent portion 42M on the inner peripheral side. Details of the battery element 40 including this negative electrode 42 (bent portion 42M) will be described later (see FIGS. 4 and 5).

[0070] (Separator) As shown in FIGS. 2 and 3, the separator 43 is an insulating porous membrane interposed between the positive electrode 41 and the negative electrode 42, and allows lithium ions to pass through while preventing a short circuit between the positive electrode 41 and the negative electrode 42. This separator 43 contains a polymer compound such as polyethylene. (Electrolyte solution) The electrolyte solution is impregnated in each of the positive electrode 41, the negative electrode 42, and the separator 43, and contains a solvent and an electrolyte salt.

[0071] Here, the solvent contains any one or two or more of non-aqueous solvents (organic solvents), and the electrolyte solution containing the non-aqueous solvent is a so-called non-aqueous electrolyte solution. This non-aqueous solvent is esters, ethers, etc., and more specifically, carbonate-based compounds, carboxylic acid ester-based compounds, lactone-based compounds, etc.

[0072] The carbonate-based compounds are cyclic carbonates, chain carbonates, etc. Specific examples of cyclic carbonates are ethylene carbonate, propylene carbonate, etc., and specific examples of chain carbonates are dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc. The carboxylic acid ester-based compounds are chain carboxylic acid esters, etc. Specific examples of chain carboxylic acid esters are methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, ethyl trimethylacetate, methyl butyrate, ethyl butyrate, etc. The lactone-based compounds are lactones, etc. Specific examples of lactones are γ-butyrolactone, γ-valerolactone, etc. In addition to the above-mentioned lactone-based compounds, the ethers may also be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, etc.

[0073] The electrolyte salt is a light metal salt such as a lithium salt. Specific examples of the lithium salt include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(fluorosulfonyl)imide (LiN(FSO2)2), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), lithium tris(trifluoromethanesulfonyl)methide (LiC(CF3SO2)3), lithium bis(oxalato)borate (LiB(C2O4)2), and lithium difluoro(oxalato)borate (LiB(C2O4)F2).

[0074] The content of the electrolyte salt is not particularly limited, but specifically, it is 0.3 mol / kg to 3.0 mol / kg with respect to the solvent. This is because high ionic conductivity can be obtained.

[0075] [Positive electrode lead] As shown in FIG. 2, the positive electrode lead 51 is a wiring member for electrically connecting the positive electrode 41 to the external terminal 20 and is housed inside the exterior can 10. Since this positive electrode lead 51 is connected to the positive electrode current collector 41A and the external terminal 20 of the positive electrode 41 via the through-hole 10K, it is electrically connected to each of the positive electrode 41 and the external terminal 20. Note that the positive electrode lead 51 is connected to the positive electrode 41 on the side closer to the lid portion 12.

[0076] Here, the secondary battery includes one positive electrode lead 51. However, the secondary battery may include two or more positive electrode leads 51. When the number of positive electrode leads 51 increases, the electrical resistance of the battery element 40 decreases.

[0077] Details regarding the forming material of the positive electrode lead 51 are the same as those regarding the forming material of the positive electrode current collector 41A. However, the forming material of the positive electrode lead 51 and the forming material of the positive electrode current collector 41A may be the same as each other or different from each other.

[0078] Here, since the positive electrode lead 51 is physically separated from the positive electrode current collector 41A, it is separated from the positive electrode current collector 41A. However, since the positive electrode lead 51 is physically continuous with the positive electrode current collector 41A, it may be integrated with the positive electrode current collector 41A.

[0079] [Negative electrode lead] As shown in FIG. 2, the negative electrode lead 52 is a wiring member for electrically connecting the negative electrode 42 to the exterior can 10 and is housed inside the exterior can 10. Since this negative electrode lead 52 is connected to each of the negative electrode current collector 42A of the negative electrode 42 and the storage portion 11, it is electrically connected to each of the negative electrode 42 and the exterior can 10. Note that since the negative electrode lead 52 is connected to the negative electrode 42 on the side far from the lid portion 12, it is connected to the bottom portion M2.

[0080] Here, the secondary battery includes one negative electrode lead 52. However, the secondary battery may include two or more negative electrode leads 52. When the number of negative electrode leads 52 increases, the electrical resistance of the battery element 40 decreases.

[0081] Details regarding the formation material of the negative electrode lead 52 are the same as those regarding the formation material of the negative electrode current collector 42A. However, the formation material of the negative electrode lead 52 and the formation material of the negative electrode current collector 42A may be the same as each other or different from each other.

[0082] Since this negative electrode lead 52 is physically separated from the negative electrode current collector 42A, it is separated from the negative electrode current collector 42A. However, since the negative electrode lead 52 is physically continuous with the negative electrode current collector 42A, it may be integrated with the negative electrode current collector 42A.

[0083] [Others] Note that the secondary battery may further include any one or two or more of other components (not shown).

[0084] Specifically, another component is an insulating film disposed between the lid portion 12 and the battery element 40, and a part of the insulating film is disposed between the storage portion 11 and the positive electrode lead 51. Since this insulating film has a through-hole at a position overlapping with the through-hole 10K, it is arranged so as not to shield the through-hole 10K. Further, the insulating film contains any one or two or more of insulating materials such as insulating polymer compounds, and specific examples of the insulating material are polyimide and the like.

[0085] Also, another component is another insulating film disposed between the storage portion 11 (lower bottom portion M2) and the battery element 40. In this case, a part of the other insulating film is disposed between the storage portion 11 and the negative electrode lead 52. The configuration and forming material of the other insulating film are the same as those of the above-described insulating film.

[0086] Also, another component is a sealant (insulating coating member) that covers the surface of the positive electrode lead 51. Since this sealant has a tubular structure, it covers the periphery of the positive electrode lead 51. Thereby, the positive electrode lead 51 is insulated from each of the exterior can 10 and the negative electrode 42 via the sealant. The forming material of the sealant is the same as the forming material of the above-described insulating film.

[0087] <1-2. Detailed Configuration of Battery Element> Each of FIGS. 4 and 5 shows a detailed schematic configuration of the battery element 40 shown in FIG. 2.

[0088] However, each of FIGS. 4 and 5 shows only a part of the battery element 40 in the vicinity of the winding center space 40K. More specifically, it shows the winding states of the positive electrode 41 and the negative electrode 42 as viewed from the extending direction (upward) of the winding center space 40K. In this case, the illustration of the separator 43 is omitted.

[0089] In FIGS. 4 and 5, for the sake of simplifying the illustrated content, each of the positive electrode current collector 41A and the negative electrode current collector 42A is shown as a thin line, and each of the positive electrode active material layer 41B and the negative electrode active material layer 42B is shown as a thick line. In this case, in order to make it easier to distinguish the positive electrode current collector 41A from the positive electrode active material layer 41B, a slight gap is provided between the positive electrode current collector 41A and the positive electrode active material layer 41B. Similarly, in order to make it easier to distinguish the negative electrode current collector 42A from the negative electrode active material layer 42B, a slight gap is provided between the negative electrode current collector 42A and the negative electrode active material layer 42B.

[0090] In the following description, FIGS. 2 and 3 that have already been described will be referred to as needed together with FIGS. 4 and 5.

[0091] [Wound state of positive electrode and negative electrode] As shown in FIGS. 4 and 5, the positive electrode 41 and the negative electrode 42 are wound while facing each other around a winding center space 40K located at the center C of the battery element 40.

[0092] The positive electrode active material layer 41B includes an inner winding layer 41BX provided on the inner winding surface of the positive electrode current collector 41A and an outer winding layer 41BY provided on the outer winding surface of the positive electrode current collector 41A. The negative electrode active material layer 42B includes an inner winding layer 42BX provided on the inner winding surface of the negative electrode current collector 42A and an outer winding layer 42BY provided on the outer winding surface of the negative electrode current collector 42A.

[0093] This "inner winding side" means the inner side in the radial direction of the battery element 40 when the battery element 40, which is a wound electrode body, is viewed from the extending direction of the winding center space 40K (the direction intersecting the paper surface of FIGS. 4 and 5 respectively), and more specifically, the inner side (the side closer to the center C) along the straight line L1 described later. The outer side in the radial direction of the battery element 40, that is, the outer side (the side farther from the center C) along the straight line L1, is the "outer winding side".

[0094] The positive electrode 41 and the negative electrode 42 are wound such that the negative electrode 42 is disposed on the inner side of the winding relative to the positive electrode 41. Thus, in the manufacturing process of the battery element 40, as will be described later, after the positive electrode 41 and the negative electrode 42 are laminated on each other with the separator 43 interposed therebetween, the negative electrode 42 is disposed on the inner side of the winding and the positive electrode 41 is disposed on the outer side of the winding, and then the positive electrode 41, the negative electrode 42, and the separator 43 are wound.

[0095] The positive electrode 41 has a tip 41S on the inner peripheral side, and the negative electrode 42 has a tip 42S on the inner peripheral side. This tip 42S is located on the inner peripheral side relative to the tip 41S.

[0096] This "inner peripheral side" refers to the inner side (the side closer to the center C) in the winding direction (the direction of rotation in a spiral shape) of each of the positive electrode 41 and the negative electrode 42, and more specifically, the inner side in the longitudinal direction of each of the positive electrode 41 and the negative electrode 42. Note that the outer side in the winding direction (the side farther from the center C), that is, the outer side in the longitudinal direction of each of the positive electrode 41 and the negative electrode 42 is the "outer peripheral side".

[0097] Here, the negative electrode 42 disposed on the inner side of the winding relative to the positive electrode 41 includes a tip portion 42P wound on the side closer to the center C than the positive electrode 41 as an end portion located on the inner peripheral side. Here, in the tip portion 42P, the negative electrode active material layer 42B (the inner winding side layer 42BX and the outer winding side layer 42BY) is not provided on the negative electrode current collector 42A. That is, in the tip portion 42P, both surfaces of the negative electrode current collector 42A are not covered by the inner winding side layer 42BX and the outer winding side layer 42BY, so that the negative electrode current collector 42A is exposed. As a result, the tip portion 42P is wound in a state of not facing the positive electrode 41. This is because the weight of the negative electrode active material layer 42B that does not participate in the charge and discharge reaction is reduced at the tip portion 42P that does not face the positive electrode 41, increasing the weight energy density. However, in the tip portion 42P, one or both of the inner winding side layer 42BX and the outer winding side layer 42BY may be provided on the negative electrode current collector 42A.

[0098] The position of the inner - peripheral - side tip of the inner - layer 42BX and the position of the inner - peripheral - side tip of the outer - layer 42BY may coincide with each other or may be different from each other. Here, since the tip of the outer - layer 42BY is located more on the inner - peripheral side than the tip of the inner - layer 42BX, the positions of the tip of the inner - layer 42BX and the tip of the outer - layer 42BY are shifted from each other in the winding direction.

[0099] In addition, the positive electrode 41 disposed outside the negative electrode 42 may or may not include a portion where the positive - electrode active - material layer 41B (inner - layer 41BX and outer - layer 41BY) is not provided on the positive - electrode current collector 41A as an end portion located on the inner - peripheral side. Here, since the positive electrode 41 does not include a portion where the positive - electrode active - material layer 41B is not provided on the positive - electrode current collector 41A, the positive - electrode current collector 41A is not exposed, and the entire surfaces of both sides of the positive - electrode current collector 41A are covered by the inner - layer 41BX and the outer - layer 41BY.

[0100] The position of the inner - peripheral - side tip of the inner - layer 41BX and the position of the inner - peripheral - side tip of the outer - layer 41BY may coincide with each other or may be different from each other. Here, the positions of the tip of the inner - layer 41BX and the tip of the outer - layer 41BY coincide with each other. However, the tips of the inner - layer 41BX and the outer - layer 41BY are located more on the outer - peripheral side than the tips of the inner - layer 42BX and the outer - layer 42BY, respectively.

[0101] Since the positions of the tips 41S and 42S are not particularly limited, they can be set arbitrarily. In each of FIGS. 4 and 5, the case where the tips 41S and 42S are located at positions along the straight line L1 described later is shown.

[0102] The tip portion 42P is wound one or more times, and the tip 41S of the positive electrode 41 is located more on the outer - peripheral side than the tip portion 42P. Here, the tip portion 42P is wound approximately two times.

[0103] [Configuration of the bent portion] The tip portion 42P of the negative electrode 42 disposed on the inner side of the winding than the positive electrode 41 has a bent portion 42M, and the number of the bent portions 42M may be only one or two or more. In each of FIGS. 4 and 5, the case where the number of the bent portions 42M is one is shown.

[0104] In this bent portion 42M, the tip portion 42P is bent so as to be partially recessed toward the center C. Here, in the bent portion 42M, the negative electrode current collector 42A that is not covered by the negative electrode active material layer 42B (the inner winding layer 42BX and the outer winding layer 42BY) and is exposed is bent partway so as to approach the center C, and then is folded back so as to move away from the center C. Since the width W and the depth D of the bent portion 42M are not particularly limited, they can be arbitrarily set.

[0105] Note that in the bent portion 42M, if the tip portion 42P is bent so as to be partially recessed, the bending shape of the tip portion 42P is not particularly limited. That is, the tip portion 42P may be bent so as to form an acute concave corner, or may be bent so as to form a curved concave corner. FIG. 4 shows the case where the tip portion 42P is bent so as to form a curved concave corner.

[0106] The tip portion 42P has the bent portion 42M because when the secondary battery is charged and discharged, buckling is less likely to occur inside the battery element 40 by using the bent portion 42M, and thus the occurrence of a short circuit (contact between the positive electrode current collector 41A and the negative electrode current collector 42A) is suppressed in the battery element 40. Details regarding the reason why the occurrence of a short circuit is suppressed by using this bent portion 42M will be described later.

[0107] [Position of the bent portion] The position of the bent portion 42M, that is, the position where the bent portion 42M is provided in the tip portion 42P is not particularly limited. If the tip portion 42P has the bent portion 42M, compared with the case where the tip portion 42P does not have the bent portion 42M, a short circuit is less likely to occur during charge and discharge regardless of the position of the bent portion 42M.

[0108] Among them, the position of the bent portion 42M is preferably a predetermined position determined based on an angle θ described later.

[0109] Specifically, a straight line L1 which is a first straight line connecting the center C of the battery element 40 and the tip 41S of the positive electrode 41, and a straight line L2 which is a second straight line connecting the center C and the center of the bent portion 42M are defined. The center of the bent portion 42M is a position that bisects the width W of the bent portion 42M, and the straight line L2 is used to determine the position of the bent portion 42M with reference to the straight line L1. Thus, the position of the bent portion 42M is determined based on the angle θ defined by the straight lines L1 and L2 as described above.

[0110] The angle θ is preferably 15° to 345°, and more preferably 15° to 165° or 195° to 345°. This is because buckling is less likely to occur inside the battery element 40, and the occurrence of a short circuit is more suppressed.

[0111] More specifically, when the tip portion 42P has one bent portion 42M, the position of the bent portion 42M is preferably a position substantially orthogonal to the straight line L1. That is, as shown in FIG. 4, the angle θ is preferably 75° to 105°. Alternatively, as shown in FIG. 5, the angle θ is preferably 255° to 285°.

[0112] Also, the circumference where the bent portion 42M is provided at the tip portion 42P is not particularly limited. Specifically, as described above, when the tip portion 42P is wound approximately twice, the bent portion 42M may be provided at the tip portion 42P in the inner circumference (the first turn from the center C), or the bent portion 42M may be provided at the tip portion 42P in the outer circumference (the second turn from the center C). Of course, when the number of bent portions 42M is two or more, the bent portion 42M may be provided at the tip portion 42P in each of the inner circumference (the first turn) and the outer circumference (the second turn).

[0113] (Dimension Conditions) As shown in Fig. 2, the battery element 40 has an outer diameter D1 and a height H1. As described above, it has a flat and columnar three-dimensional shape with a height H1 smaller than the outer diameter D1. Since this battery element 40 has an upper bottom M4 and a lower bottom M5 which are a pair of bottoms facing each other, the height H1 is the distance between the upper bottom M4 and the lower bottom M5. Since neither the outer diameter D1 nor the height H1 is particularly limited, they can be arbitrarily set in relation to the dimensions (outer diameter D, height H, and ratio D / H) of the secondary battery described above.

[0114] Among them, since the height H1 is smaller than the outer diameter D1, the battery element 40 preferably has a flat and columnar three-dimensional shape as described above. This is because even in a small secondary battery, the occurrence of short circuits in the battery element 40 is sufficiently suppressed.

[0115] Specifically, when the height H1 is larger than the outer diameter D1, the opposing area between the positive electrode 41 and the negative electrode 42 increases, so the frictional force generated between the positive electrode 41 and the negative electrode 42 increases. As a result, due to internal stress generated during charge and discharge, etc., the battery element 40 is likely to deform irregularly, so there is a possibility that the occurrence of short circuits in the battery element 40 is not sufficiently suppressed.

[0116] On the other hand, when the height H1 is smaller than the outer diameter D1, the opposing area between the positive electrode 41 and the negative electrode 42 decreases, so the frictional force generated between the positive electrode 41 and the negative electrode 42 decreases. As a result, the battery element 40 is less likely to deform irregularly, so the occurrence of short circuits in the battery element 40 is sufficiently suppressed. In this case, in particular, even if the battery element 40 deforms, the internal stress generated during the deformation is likely to concentrate on the center C. Therefore, as described above, buckling is less likely to occur effectively inside the battery element 40 by using the bent portion 42M.

[0117] <1-3. Operation> FIG. 6 shows a cross-sectional configuration corresponding to FIG. 2 for explaining the operation of the secondary battery. Below, after explaining the operation during charging and discharging, the operation during the occurrence of an abnormality will be explained.

[0118] [Operation during charging and discharging] During charging, in the battery element 40, lithium is released from the positive electrode 41 and is occluded in the negative electrode 42 through the electrolyte. On the other hand, during discharging, in the battery element 40, lithium is released from the negative electrode 42 and is occluded in the positive electrode 41 through the electrolyte. During these charging and discharging processes, lithium is occluded and released in an ionic state.

[0119] [Operation during the occurrence of an abnormality] As described above, the external terminal 20 is disposed outside the lid portion 12 and is thermally welded to the lid portion 12 via the gasket 30. Thus, during normal operation, as shown in FIG. 2, since the external terminal 20 is fixed to the lid portion 12 via the gasket 30, the through-hole 10K is shielded by the external terminal 20 and the outer can 10 is sealed, so that the battery element 40 is enclosed inside the outer can 10.

[0120] On the other hand, when an abnormality occurs, that is, when the internal pressure of the outer can 10 rises excessively, the external terminal 20 is pushed outward (upward) via the through-hole 10K in response to the rise in the internal pressure. In this case, if the intensity of the force pushing the external terminal 20 outward is greater than the intensity of the strength (so-called seal strength) by which the external terminal 20 is fixed to the lid portion 12 via the gasket 30, as shown in FIG. 6, the external terminal 20 is partially or entirely separated from the lid portion 12. As a result, a gap 20G (an internal pressure release path) is formed between the lid portion 12 and the external terminal 20, and the internal pressure is released using this gap 20G. FIG. 6 shows the case where the external terminal 20 is partially separated from the lid portion 12.

[0121] As described above, while the lid portion 12 is joined to the storage portion 11, the external terminal 20 is thermally welded to the lid portion 12 via the gasket 30. Therefore, the above-described sealing strength is smaller than the joining strength of the lid portion 12 to the storage portion 11. In this case, when the internal pressure of the outer can 10 rises excessively, the external terminal 20 separates from the lid portion 12 before the lid portion 12 separates from the storage portion 11, that is, before the outer can 10 is destroyed. As a result, since the external terminal 20 functions as an open valve before the outer can 10 ruptures, the rupture of the outer can 10 is prevented.

[0122] <1-4. Manufacturing method> FIG. 7 shows a perspective configuration corresponding to FIG. 1 in order to explain the manufacturing process of the secondary battery. FIG. 8 shows a schematic configuration corresponding to FIG. 4 in order to explain the manufacturing process of the battery element 40.

[0123] However, in FIG. 7, since the state before the lid portion 12 is joined to the storage portion 11 is shown, the lid portion 12 is separated from the storage portion 11. In FIG. 8, since the process of winding each of the positive electrode 41 and the negative electrode 42 is shown, the bent portion 42M is not yet formed at the tip portion 42P. In FIG. 8, in order to easily distinguish between the tip portion 42P and a jig 60 described later, a slight gap is provided between the tip portion 42P and the jig 60, and the jig 60 is mesh-covered.

[0124] When manufacturing a secondary battery, the positive electrode 41 and the negative electrode 42 are manufactured and an electrolytic solution is prepared according to the procedure exemplified below. Then, the secondary battery is assembled using the positive electrode 41, the negative electrode 42, and the electrolytic solution, and a stabilization process for the assembled secondary battery is performed.

[0125] In the following description, both FIGS. 7 and 8 refer to FIGS. 1 to 4 that have already been described as needed. That is, in the following, the manufacturing method of the secondary battery in the case where the tip portion 42P has one bent portion 42M (angle θ = 90°) (FIG. 4) will be described.

[0126] Here, as shown in FIG. 7, in order to form the outer can 10, a storage part 11 and a lid part 12 that are physically separated from each other are used. As described above, the storage part 11 has an opening 11K, and the lid part 12 has a recess 12U. Also, as described above, an external terminal 20 is preliminarily heat-sealed to the lid part 12 via a gasket 30.

[0127] As shown in FIG. 8, in order to form the battery element 40, a substantially cylindrical jig 60 is used. This jig 60 extends in a direction intersecting the plane of FIG. 8 and has a recess 60N extending in that direction. The shape of this recess 60N corresponds to the shape of the bent portion 42M.

[0128] [Fabrication of the positive electrode] First, a paste-like positive electrode mixture slurry is prepared by introducing a positive electrode mixture in which a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent are mixed with each other into a solvent. This solvent may be an aqueous solvent or an organic solvent. The details regarding the solvent described here are the same hereinafter. Subsequently, the positive electrode mixture slurry is applied to both sides of the positive electrode current collector 41A, whereby a positive electrode active material layer 41B (an inner wound layer 41BX and an outer wound layer 41BY) is formed on the positive electrode current collector 41A. Finally, the positive electrode active material layer 41B is compression-molded using a roll press or the like. In this case, the positive electrode active material layer 41B may be heated, and the compression molding may be repeated a plurality of times. As a result, since the positive electrode active material layer 41B is formed on both sides of the positive electrode current collector 41A, the positive electrode 41 is fabricated.

[0129] [Fabrication of the negative electrode] First, a negative electrode mixture in which a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent are mixed with each other is put into a solvent, thereby preparing a paste-like negative electrode mixture slurry. Subsequently, the negative electrode mixture slurry is applied to both surfaces of the negative electrode current collector 42A to form a negative electrode active material layer 42B (an inner layer 42BX and an outer layer 42BY in the winding). In this case, by adjusting the application range of the negative electrode mixture slurry, a tip portion 42P on which the negative electrode active material layer 42B is not provided is formed on the negative electrode current collector 42A. Finally, the negative electrode active material layer 42B is compression-molded using a roll press or the like. Details regarding the compression molding of the negative electrode active material layer 42B are the same as those regarding the compression molding of the positive electrode active material layer 41B. As a result, since the negative electrode active material layer 42B is formed on both surfaces of the negative electrode current collector 42A, the negative electrode 42 including the tip portion 42P is produced.

[0130] [Preparation of Electrolyte Solution] An electrolyte salt is put into a solvent. As a result, since the electrolyte salt is dispersed or dissolved in the solvent, the electrolyte solution is prepared.

[0131] [Assembly of Secondary Battery] First, a positive electrode lead 51 is connected to the positive electrode current collector 41A of the positive electrode 41 using a welding method or the like, and a negative electrode lead 52 is connected to the negative electrode current collector 42A of the negative electrode 42 using a welding method or the like.

[0132] Subsequently, the positive electrode 41 to which the positive electrode lead 51 is connected and the negative electrode 42 to which the negative electrode lead 52 is connected are laminated on each other via a separator 43 to form a laminate 40Z1 as shown in FIG. 8. Subsequently, after the laminate 40Z1 is wound around a jig 60, the jig 60 is removed.

[0133] In this case, the negative electrode 42 is disposed on the inner side in the winding than the positive electrode 41, and the tip 42S is positioned on the inner peripheral side than the tip 41S. Also, the tip portion 42P is wound one or more times, and the tip 41S is positioned on the outer peripheral side than the tip portion 42P. As a result, the tip portion 42P is disposed on the recess 60N provided in the jig 60.

[0134] Therefore, as shown in FIG. 7, a wound body 40Z2 having a winding center space 40K is formed. This wound body 40Z2 has the same configuration as that of the battery element 40, except that the positive electrode 41, the negative electrode 42, and the separator 43 are not impregnated with the electrolytic solution. In FIG. 7, the illustration of each of the positive electrode lead 51 and the negative electrode lead 52 is omitted.

[0135] When the negative electrode 42 is wound around the jig 60 in the forming process of this wound body 40Z2, a part of the tip portion 42P is pressed against the jig 60 by utilizing the tension when the negative electrode 42 is wound. Therefore, a part of the tip portion 42P is deformed so as to follow the inner wall surface of the recessed portion 60N. As a result, a part of the tip portion 42P is folded back along the inner wall surface of the recessed portion 60N, and thus a bent portion 42M is formed at the tip portion 42P.

[0136] Subsequently, the wound body 40Z2 is stored inside the storage portion 11 through the opening 11K. In this case, the extending direction of the winding center space 40K is made substantially parallel to the direction in which the wound body 40Z2 is stored inside the storage portion 11. Further, the negative electrode lead 52 is connected to the storage portion 11 by using a welding method or the like.

[0137] Subsequently, the positive electrode lead 51 is connected to the external terminal 20 of the lid portion 12 in which the external terminal 20 is thermally welded in advance via the gasket 30, through the through hole 10K by using a welding method or the like.

[0138] Subsequently, the electrolytic solution is injected into the storage portion 11 through the opening 11K. As a result, since the wound body 40Z2 (the positive electrode 41, the negative electrode 42, and the separator 43) is impregnated with the electrolytic solution, the battery element 40 which is a wound electrode body is manufactured. In this case, since a part of the electrolytic solution is supplied into the winding center space 40K, the winding center space 40K is utilized as a supply path of the electrolytic solution. Thereby, the wound body 40Z2 is easily impregnated with the electrolytic solution.

[0139] Subsequently, using a welding method or the like, the lid portion 12 is joined to the storage portion 11. As a result, the outer can 10 is formed, and since the battery element 40 and the like are stored inside the outer can 10, as shown in FIG. 2, the secondary battery is assembled.

[0140] [Stabilization of Secondary Battery] The assembled secondary battery is charged and discharged. Various conditions such as the environmental temperature, the number of charge and discharge cycles (cycle number), and the charge and discharge conditions can be arbitrarily set. As a result, a film is formed on the surfaces of the positive electrode 41 and the negative electrode 42 in the battery element 40, so that the state of the secondary battery is electrochemically stabilized.

[0141] Therefore, since the battery element 40 and the like are enclosed inside the outer can 10, the secondary battery is completed.

[0142] <1-5. Actions and Effects> According to this secondary battery, the battery element 40 including the positive electrode 41 and the negative electrode 42 is stored inside the columnar outer can 10, and the positive electrode 41 and the negative electrode 42 are wound while facing each other. Further, the negative electrode 42 includes a tip portion 42P located closer to the center C of the battery element 40, and the tip portion 42P is wound one or more times on the side closer to the center C than the positive electrode 41. Furthermore, the tip portion 42P has a bent portion 42M, and at the bent portion 42M, the tip portion 42P is bent so as to be partially recessed toward the center C. Therefore, excellent operation reliability can be obtained for the reasons described below.

[0143] FIG. 9 shows a schematic configuration of a secondary battery of a comparative example and corresponds to FIG. 4. FIG. 10 shows a schematic configuration corresponding to FIG. 8 for explaining the manufacturing process of the battery element 40 in the secondary battery of the comparative example. FIG. 11 shows a schematic configuration corresponding to FIG. 9 for explaining the problems of the secondary battery of the comparative example. FIG. 12 shows a schematic configuration corresponding to FIG. 4 for explaining the advantages of the secondary battery of the present embodiment.

[0144] As shown in Fig. 9, the secondary battery of the comparative example has the same configuration as that of the secondary battery of the present embodiment shown in Fig. 4, except that the tip portion 42P does not have the bent portion 42M. As shown in Fig. 10, the secondary battery of this comparative example is manufactured by the same procedure as the manufacturing method of the secondary battery of the present embodiment shown in Fig. 8, except that the battery element 40 is formed using the jig 160 instead of the jig 60. This jig 160 has the same configuration as the jig 60, except that it does not have the recessed portion 60N.

[0145] In the manufacturing process of the secondary battery of the comparative example, as shown in Fig. 10, since each of the positive electrode 41 and the negative electrode 42 is wound using the jig 160 that does not have the recessed portion 60N, as shown in Fig. 9, the bent portion 42M is not formed at the tip portion 42P.

[0146] In this secondary battery of the comparative example, when the battery element 40 expands during charging, since each of the positive electrode 41 and the negative electrode 42 tries to tighten tightly in the vicinity of the center C, an internal stress is generated that tries to shift each of the tips 41S, 42S toward the inner peripheral side. The expansion of this battery element 40 is mainly caused by the expansion of the negative electrode active material contained in the negative electrode active material layer 42B (the inner wound layer 42BX and the outer wound layer 42BY).

[0147] In this case, since the internal stress is not relaxed inside the battery element 40, as shown in Fig. 11, the tip portion of the positive electrode active material layer 41B (the inner wound layer 41BX and the outer wound layer 41BY) on the inner peripheral side is likely to buckle toward the center C according to the internal stress. As a result, since the tip portion of the positive electrode active material layer 41B locally presses the negative electrode 42 toward the center C, that negative electrode 42 is likely to partially buckle toward the winding center space 40K. Note that the tip portion of the tip portion 42P is bent toward the center C in response to the tip portion of the positive electrode active material layer 41B locally pressing the negative electrode 42 toward the center C.

[0148] When the tip portion of the positive electrode active material layer 41B buckles and the tip portion breaks through the outer winding layer 42BY, the positive electrode current collector 41A and the negative electrode current collector 42A come into contact with each other, making it easy for a short circuit to occur in the battery element 40. This tendency for a short circuit to occur becomes more prominent when charging and discharging are repeated. That is, even if a short circuit does not occur during initial charging, a short circuit is more likely to occur as charging and discharging are repeated.

[0149] From these facts, in the secondary battery of the comparative example, since a short circuit is likely to occur during charging and discharging, it is difficult to obtain excellent operational reliability.

[0150] On the other hand, in the secondary battery of the present embodiment, when internal stress is generated due to the expansion of the battery element 40 during charging, as shown in FIG. 12, the tip portion 42P deforms so that the width W narrows at the bent portion 42M according to the internal stress. That is, at the bent portion 42M, the tip portion 42P is folded so that a part of the tip portions 42P facing each other approach each other. In FIG. 12, the bent portion 42M before deformation is shown by a dashed line.

[0151] In this case, by utilizing the bent portion 42M, the tip portion 42P deforms so that the winding length of the negative electrode 42 is substantially shortened, thereby relaxing the internal stress. As a result, the tip portion of the positive electrode active material layer 41B is less likely to buckle toward the center C, and it is only necessary for the tip portion of the positive electrode active material layer 41B to shift slightly toward the center C in the winding direction. Therefore, the tip portion of the positive electrode active material layer 41B is less likely to locally press the negative electrode 42 toward the center C, making it less likely for the negative electrode 42 to buckle.

[0152] When the negative electrode 42 is less likely to buckle, the tip portion of the positive electrode active material layer 41B is less likely to break through the outer winding layer 42BY, making it less likely for a short circuit to occur in the battery element 40. This tendency for a short circuit to be less likely to occur remains the same even when charging and discharging are repeated.

[0153] Therefore, in the secondary battery of this embodiment, short circuits are less likely to occur during charging and discharging, so excellent operational reliability can be obtained. In this case, particularly in a small secondary battery equipped with the columnar exterior can 10, the occurrence of short circuits is sufficiently suppressed, so sufficient operational reliability can be obtained.

[0154] In the secondary battery of this embodiment, particularly, if the negative electrode current collector 42A is exposed at the tip portion 42P without the negative electrode active material layer 42B (the inner wound layer 42BX and the outer wound layer 42BY) being provided, a high weight energy density can be obtained while the occurrence of short circuits is suppressed, so a higher effect can be obtained.

[0155] Also, if the angle θ that determines the position of the bent portion 42M is 15° to 345°, preferably 15° to 165° or 195° to 345°, short circuits are less likely to occur in the battery element 40, so a higher effect can be obtained.

[0156] In this case, if the tip portion 42P has one bent portion 42M and the angle θ is 75° to 105° or 255° to 285°, short circuits are even less likely to occur in the battery element 40, so an even higher effect can be obtained.

[0157] Also, if the conductive exterior can 10 has a through-hole 10K, the external terminal 20 disposed outside the exterior can 10 shields the through-hole 10K, and an insulating gasket 30 is disposed between the exterior can 10 and the external terminal 20, then the external terminal 20 functions as an external connection terminal for the secondary battery. Therefore, it becomes easier to connect the secondary battery to an electronic device via the external terminal 20 that functions as an external connection terminal, so a higher effect can be obtained.

[0158] In this case, if the positive electrode 41 is electrically connected to the external terminal 20 and the negative electrode 42 is electrically connected to the exterior can 10, the external terminal 20 functions as an external connection terminal for the positive electrode 41, and the exterior can 10 functions as an external connection terminal for the negative electrode 42. Therefore, since the secondary battery can be easily connected to the electronic device via the exterior can 10 and the external terminal 20 that function as a pair of external connection terminals, a higher effect can be obtained. Also, since the volume energy density increases according to the fact that the secondary battery does not necessarily have to have an external connection terminal for the negative electrode 42 separately from the exterior can 10, a higher effect can be obtained.

[0159] Also, if the exterior can 10 includes a storage part 11 and a lid part 12 and the storage part 11 and the lid part 12 are joined to each other, the secondary battery is configured using the exterior can 10 which is a so-called crimp press joined can. Therefore, since the volume energy density increases, a higher effect can be obtained.

[0160] In this case, if the lid part 12 has a recessed part 12U and the external terminal 20 is arranged inside the recessed part 12U, the height H of the secondary battery becomes small. Therefore, since the volume energy density further increases, a higher effect can be obtained.

[0161] Also, if the height H1 of the battery element 40 is smaller than the outer diameter D1 in the battery element 40, the occurrence of a short circuit in the battery element 40 is sufficiently suppressed even in a small secondary battery, so a higher effect can be obtained.

[0162] Also, if the secondary battery is a lithium ion secondary battery, since a sufficient battery capacity can be stably obtained by utilizing the absorption and release of lithium, a higher effect can be obtained.

[0163] <2. Modification Example> The configuration of the secondary battery described above can be appropriately changed as described below. However, any two or more of the series of modification examples described below may be combined with each other.

[0164] [Modification Example 1] In each of FIGS. 4 and 5, the tip portion 42P has one bent portion 42M. However, as described above, the number of bent portions 42M is not particularly limited, and thus is not limited to one, and may be two or more.

[0165] Specifically, as shown in FIG. 13 corresponding to FIGS. 4 and 5, the tip portion 42P may have two bent portions 42M. The angle θ that determines the position of the first bent portion 42M is 75° to 105°, and the angle θ that determines the position of the second bent portion 42M is 255° to 285°.

[0166] Also in this case, since short - circuit is less likely to occur during charge and discharge by using the two bent portions 42M, the same effect can be obtained. In this case, in particular, compared with the case where the tip portion 42P has only one bent portion 42M, the internal stress generated during charging is more easily relaxed, so that a higher effect can be obtained. Further, since the two angles θ that determine the positions of the two bent portions 42M satisfy the above - mentioned preferred conditions (= 75° to 105° and 255° to 285°), a higher effect can be obtained.

[0167] Of course, although not specifically illustrated here, the number of bent portions 42M is not limited to one or two, and may be three or more. The angle θ that determines the position of the bent portion 42M may be set to satisfy the above - mentioned preferred conditions, or may be set to satisfy other conditions.

[0168] [Modification Example 2] In each of FIGS. 4 and 5, the positive electrode 41 and the negative electrode 42 are wound such that the negative electrode 42 is arranged on the inner side of the winding than the positive electrode 41, so the tip portion 42P has a bent portion 42M.

[0169] However, although not specifically illustrated here, the positive electrode 41, which is the first electrode, and the negative electrode 42 are wound such that the positive electrode 41 is disposed on the inner side of the winding than the negative electrode 42, which is the second electrode. Since the positive electrode 41 includes a tip portion corresponding to the tip portion 42P, the tip portion may have a bent portion. As described above, this tip portion may be a portion where the positive electrode active material layer 41B (the inner winding layer 41BX and the outer winding layer 41BY) is not provided on the positive electrode current collector 41A. The configurations of the positive electrode 41 and the negative electrode 42 in this case are the same as those shown in FIGS. 4 and 5, except that the configuration of the positive electrode 41 and the configuration of the negative electrode 42 are reversed from each other.

[0170] Even in this case, by utilizing the bent portion provided at the tip of the positive electrode 41, it becomes difficult for a short circuit to occur, so the same effect can be obtained.

[0171] [Modification Example 3] In FIG. 2, the lid portion 12 has a recessed portion 12U, and the external terminal 20 is disposed inside the recessed portion 12U.

[0172] However, as shown in FIG. 14 corresponding to FIG. 2, the lid portion 12 may be substantially flat without having the recessed portion 12U, and the external terminal 20 may be disposed on the lid portion 12. Even in this case, the same effect as that shown in FIG. 2 can be obtained. However, it should be noted that when the height H of the secondary battery increases, the volume energy density may decrease.

[0173] [Modification Example 4] In FIG. 2, the positive electrode 41, which is the second electrode, is connected to the external terminal 20 via the positive electrode lead 51, and the negative electrode 42, which is the first electrode, is connected to the storage portion 11 via the negative electrode lead 52. Thereby, the external terminal 20 functions as an external connection terminal for the positive electrode 41, and the exterior can 10 functions as an external connection terminal for the negative electrode 42.

[0174] However, as shown in FIG. 15 corresponding to FIG. 2, the positive electrode 41, which is the first electrode, may be connected to the storage portion 11 via the positive electrode lead 51, and the negative electrode 42, which is the second electrode, may be connected to the external terminal 20 via the negative electrode lead 52. Thereby, the exterior can 10 may function as an external connection terminal for the positive electrode 41, and the external terminal 20 may function as an external connection terminal for the negative electrode 42.

[0175] In this case, in order for the external terminal 20 to function as an external connection terminal for the negative electrode 42, it contains any one or two or more of conductive materials of metal materials and alloy materials. Specific examples of the conductive materials are iron, copper, nickel, stainless steel, iron alloys, copper alloys, and nickel alloys. Each of the exterior can 10, that is, the storage portion 11 and the lid portion 12, contains any one or two or more of conductive materials of metal materials and alloy materials in order to function as an external connection terminal for the positive electrode 41. Specific examples of the conductive materials are aluminum, aluminum alloys, and stainless steel.

[0176] Also in this case, since the secondary battery can be connected to the electronic device via the external terminal 20 (external connection terminal for the negative electrode 42) and the exterior can 10 (external connection terminal for the positive electrode 41), the same effects as those in the case shown in FIG. 2 can be obtained.

[0177] [Modification 5] A separator 43 that is a porous membrane is used. However, although not specifically illustrated here, instead of the separator 43, a laminated separator including a polymer compound layer may be used.

[0178] Specifically, the laminated separator includes a porous membrane having a pair of surfaces and a polymer compound layer provided on one or both surfaces of the porous membrane. This is because the adhesion of the separator to each of the positive electrode 41 and the negative electrode 42 is improved, suppressing the displacement of the battery element 40. As a result, even if a decomposition reaction of the electrolytic solution occurs, the secondary battery is less likely to swell. The polymer compound layer contains a polymer compound such as polyvinylidene fluoride. This is because polyvinylidene fluoride and the like are excellent in physical strength and electrochemically stable.

[0179] Note that one or both of the porous membrane and the polymer compound layer may contain any one or two or more of a plurality of insulating particles. This is because when the secondary battery generates heat, the plurality of insulating particles promote heat dissipation, improving the safety (heat resistance) of the secondary battery. The insulating particles are one or both of inorganic particles and resin particles. Specific examples of the inorganic particles are particles such as aluminum oxide, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide, and zirconium oxide. Specific examples of the resin particles are particles such as acrylic resin and styrene resin.

[0180] When producing the laminated separator, a precursor solution containing a polymer compound, a solvent, etc. is prepared, and then the precursor solution is applied to one or both surfaces of the porous membrane. In this case, instead of applying the precursor solution to the porous membrane, the porous membrane may be immersed in the precursor solution. Also, a plurality of insulating particles may be added to the precursor solution.

[0181] Even when this laminated separator is used, since lithium ions can move between the positive electrode 41 and the negative electrode 42, the same effect can be obtained. In this case, in particular, as described above, since the safety of the secondary battery is improved, a higher effect can be obtained.

[0182] [Modification Example 6] An electrolyte solution, which is a liquid electrolyte, was used. However, although not specifically illustrated here, an electrolyte layer, which is a gel-like electrolyte, may be used instead of the electrolyte solution.

[0183] In the battery element 40 using the electrolyte layer, the positive electrode 41 and the negative electrode 42 are laminated with each other via the separator 43 and the electrolyte layer, and the positive electrode 41, the negative electrode 42, the separator 43, and the electrolyte layer are wound. This electrolyte layer is interposed between the positive electrode 41 and the separator 43 and is also interposed between the negative electrode 42 and the separator 43. However, the electrolyte layer may be interposed only between the positive electrode 41 and the separator 43, or may be interposed only between the negative electrode 42 and the separator 43.

[0184] Specifically, the electrolyte layer contains a polymer compound together with the electrolyte solution, and the electrolyte solution is held by the polymer compound. This is because leakage of the electrolyte solution is prevented. The composition of the electrolyte solution is as described above. The polymer compound includes polyvinylidene fluoride and the like. When forming the electrolyte layer, a precursor solution containing the electrolyte solution, the polymer compound, a solvent, etc. is prepared, and then the precursor solution is applied to one side or both sides of each of the positive electrode 41 and the negative electrode 42.

[0185] Even when this electrolyte layer is used, lithium ions can move between the positive electrode 41 and the negative electrode 42 via the electrolyte layer, so the same effect can be obtained. In this case, in particular, as described above, since leakage of the electrolyte solution is prevented, a higher effect can be obtained.

Example

[0186] The examples of the present technology will be described.

[0187] <Examples 1 to 10 and Comparative Example 1> After manufacturing a secondary battery, the characteristics of the secondary battery were evaluated.

[0188] [Manufacture of secondary battery] A button-type lithium-ion secondary battery was fabricated according to the procedure described below.

[0189] (Fabrication of the positive electrode) First, 91 parts by mass of a positive electrode active material (LiCoO₂), 3 parts by mass of a positive electrode binder (polyvinylidene fluoride), and 6 parts by mass of a positive electrode conductive agent (graphite) were mixed with each other to obtain a positive electrode mixture. Subsequently, after the positive electrode mixture was put into a solvent (N-methyl-2-pyrrolidone, an organic solvent), the solvent was stirred to prepare a paste-like positive electrode mixture slurry. Subsequently, the positive electrode mixture slurry was applied to both sides of a positive electrode current collector 41A (a strip-shaped aluminum foil, thickness = 15 μm) using a coating device, and then the positive electrode mixture slurry was dried to form a positive electrode active material layer 41B (an inner winding layer 41BX and an outer winding layer 41BY). Finally, the positive electrode active material layer 41B was compression-molded using a roll press machine. Thereby, the positive electrode 41 was fabricated.

[0190] (Fabrication of the negative electrode) First, 95 parts by mass of a negative electrode active material (artificial graphite) and 5 parts by mass of a negative electrode binder (styrene-butadiene rubber and carboxymethyl cellulose) were mixed with each other to obtain a negative electrode mixture. Subsequently, after the negative electrode mixture was put into a solvent (pure water, an aqueous solvent), the solvent was stirred to prepare a paste-like negative electrode mixture slurry. Subsequently, the negative electrode mixture slurry was applied to both sides of a negative electrode current collector 42A (a strip-shaped copper foil, thickness = 10 μm) using a coating device, and then the negative electrode mixture slurry was dried to form a negative electrode active material layer 42B (an inner winding layer 42BX and an outer winding layer 42BY). In this case, the tip portion 42P was formed by adjusting the coating range of the negative electrode mixture slurry. Finally, the negative electrode active material layer 42B was compression-molded using a roll press machine. Thereby, the negative electrode 42 was fabricated.

[0191] (Preparation of the electrolyte) After adding an electrolyte salt (LiPF6) to the solvent, the solvent was stirred. As the solvent, a mixture of ethylene carbonate and propylene carbonate, which are cyclic carbonates, was used. In this case, the content of the electrolyte salt was set to 1 mol / kg with respect to the solvent. Thereby, an electrolytic solution was prepared.

[0192] (Assembly of secondary battery) First, a positive electrode lead 51 (aluminum foil) was welded to a positive electrode current collector 41A of the positive electrode 41 using a resistance welding method, and a negative electrode lead 52 (nickel foil) was welded to a negative electrode current collector 42A of the negative electrode 42 using a resistance welding method.

[0193] Subsequently, the positive electrode 41 and the negative electrode 42 were laminated on each other via a separator 43 (polyethylene film, thickness = 9.5 μm) to form a laminate 40Z1. Subsequently, using a jig 60 having a recessed portion 60N, the laminate 40Z1 was wound around the jig 60, and then the jig 60 was removed to form a wound body 40Z2 having a wound center space 40K. In this case, the negative electrode 42 was disposed on the inner side of the winding with respect to the positive electrode 41, and the tip 42S was positioned on the inner side of the winding with respect to the tip 41S. Also, the tip portion 42P was wound about two turns, and the tip 41S was positioned on the outer side of the winding with respect to the tip portion 42P. Thereby, a bent portion 42M was formed at the tip portion 42P.

[0194] The number and position of the bent portion 42M (the angle θ (°) that determines the position of the bent portion 42M) are as shown in Table 1. In this case, the number of the bent portions 42M was adjusted by changing the number of the recessed portions 60N provided in the jig 60. Also, the position (angle θ) of the bent portion 42M was adjusted by changing the position where the recessed portion 60N is provided in the jig 60.

[0195] Subsequently, the wound body 40Z2 was housed inside the housing portion 11 (SUS316) from the opening portion 11K. In this case, a welding electrode was inserted into the wound center space 40K, and the negative electrode lead 52 was welded to the housing portion 11 using a resistance welding method.

[0196] Subsequently, after injecting the electrolytic solution into the interior of the storage part 11 through the opening 11K, the lid part 12 (SUS316) was welded to the storage part 11 using the laser welding method. An external terminal 20 (SUS316) is thermally welded to this lid part 12 via a gasket 30 (polypropylene). In this case, the positive electrode lead 51 was welded to the external terminal 20 via the through-hole 10K using the resistance welding method.

[0197] As a result, since the wound body 40Z2 (positive electrode 41, negative electrode 42, and separator 43) was impregnated with the electrolytic solution, the battery element 40 was fabricated, and since the lid part 12 was welded to the storage part 11, the outer can 10 was formed. Thus, since the battery element 40 and the like were enclosed inside the outer can 10, the secondary battery was assembled.

[0198] Note that, for comparison, a secondary battery was assembled by the same procedure except that the laminate 40Z1 was wound using a jig 160 in which the recessed part 60N was not provided. In this case, the bent part 42M was not formed at the tip part 42P.

[0199] (Stabilization of the secondary battery) In a normal temperature environment (temperature = 23°C), the assembled secondary battery was charged and discharged for one cycle. During charging, it was charged at a constant current with a current of 0.5C until the voltage reached 4.4V, and then charged at a constant voltage with that 4.4V voltage until the current reached 0.05C. During discharging, it was discharged at a constant current with a current of 0.2C until the voltage reached 3.0V. 0.5C is the current value at which the battery capacity (theoretical capacity) can be completely discharged in 2 hours, 0.05C is the current value at which the battery capacity can be completely discharged in 20 hours, and 0.2C is the current value at which the battery capacity can be completely discharged in 5 hours.

[0200] As a result, since a film was formed on the surfaces of the positive electrode 41 and the negative electrode 42 respectively, the state of the secondary battery was electrochemically stabilized. Thus, the secondary battery was completed.

[0201] [Characteristic evaluation of the secondary battery] When the characteristics (operation reliability) of the secondary battery were evaluated, the results shown in Table 1 were obtained.

[0202] When evaluating the operation reliability, first, the position of the tip 41S of the positive electrode 41 (the position before charge and discharge) was specified by observing the secondary battery (the winding state of the positive electrode 41 and the negative electrode 42) using the X-ray radiography method.

[0203] Subsequently, the secondary battery was charged and discharged 500 cycles in a normal temperature environment (temperature = 23°C). The charge and discharge conditions were the same as those during the stabilization of the secondary battery described above.

[0204] Subsequently, the secondary battery was observed again using the X-ray radiography method to specify the position of the tip 41S (the position after charge and discharge). Finally, based on the position of the tip 41S before charge and discharge and the position of the tip 41S after charge and discharge, the buckling distance Q (μm), which is an index for evaluating the operation reliability, was measured. As shown in FIG. 11, this buckling distance Q is the distance between the position of the tip 41S before charge and discharge and the position of the tip 41S after charge and discharge. In FIG. 11, the tip portion of the positive electrode 41 before charge and discharge is shown by a broken line.

[0205] When measuring this buckling distance Q, the above-described evaluation procedure was repeated using 10 secondary batteries to measure 10 buckling distances Q. As a result, as shown in Table 1, the 10 buckling distances Q were classified into four types of ranges (Q ≤ 50 μm, 50 μm < Q ≤ 100 μm, 100 μm < Q ≤ 200 μm, Q > 200 μm) according to the values.

[0206] Note that the larger the buckling distance Q, the easier it is for the negative electrode 42 to buckle significantly, indicating that a short circuit is more likely to occur. On the other hand, the smaller the buckling distance Q, the more difficult it is for the negative electrode 42 to buckle significantly, indicating that a short circuit is less likely to occur.

[0207]

Table 1

[0208] [Investigation] As shown in Table 1, the buckling distance Q varied depending on the presence and configuration (number and angle θ) of the bent portion 42M.

[0209] Specifically, when the bent portion 42M was not provided at the tip portion 42P (Comparative Example 1), the buckling distance Q increased. Specifically, in all secondary batteries, the buckling distance Q became larger than 200 μm.

[0210] On the other hand, when the bent portion 42M was provided at the tip portion 42P (Examples 1 to 10), the buckling distance Q became smaller compared to the case where the bent portion 42M was not provided at the tip portion 42P (Comparative Example 1) described above. Specifically, in only some of the secondary batteries, the buckling distance Q became larger than 200 μm.

[0211] In particular, when the bent portion 42M was provided at the tip portion 42P, the following tendencies were obtained. First, when the angle θ was 90° (= 15° to 165°, more specifically 75° to 105°) or 270° (= 195° to 345°, more specifically 255° to 285°) (Examples 3, 7), the buckling distance Q was 200 μm or less in all secondary batteries. Second, when the number of the bent portions 42M was two or more (Examples 9, 10), the buckling distance Q became smaller. Third, when the number of the bent portions 42M was two and the angle θ was 90° and 270° (Example 9), the buckling distance Q became remarkably small.

[0212] [Summary] From the results shown in Table 1, when the tip portion 42P of the negative electrode 42 had the bent portion 42M, the buckling distance Q became smaller, so that the negative electrode 42 was less likely to buckle. Therefore, since a short circuit was less likely to occur during charge and discharge, excellent operational reliability was obtained in the secondary battery.

[0213] As described above, the present technology has been described by giving one embodiment and one example. However, the configuration of the present technology is not limited to the configuration described in one embodiment and one example, and thus can be variously modified.

[0214] Specifically, the case where the electrode reactant is lithium has been described, but the electrode reactant is not particularly limited. Therefore, the electrode reactant may be other alkali metals such as sodium and potassium as described above, or alkaline earth metals such as beryllium, magnesium, and calcium. In addition, the electrode reactant may be other light metals such as aluminum.

[0215] The effects described in this specification are merely examples, and thus the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present technology.

Claims

1. A columnar exterior member, and a battery element housed inside the exterior member and including a first electrode and a second electrode are provided, wherein the first electrode and the second electrode are wound while facing each other, the first electrode includes a current collector and an active material layer provided on the current collector, is located on the inner peripheral side in the winding direction from the second electrode, and has a tip portion where the current collector is exposed, the tip portion is wound one or more times, extends along the extending direction of the winding center space of the battery element, and has one or more bent portions that are recessed toward the winding center space, a secondary battery.

2. The angle defined by a first straight line connecting the center of the battery element and the tip of the second electrode on the side closer to the center of the battery element, and a second straight line connecting the center of the battery element and the center of the bent portion is 15° or more and 345° or less, The secondary battery according to Claim 1.

3. The angle is 15° or more and 165° or less or 195° or more and 345° or less, The secondary battery according to Claim 2.

4. The tip portion has one of the bent portions, the angle is 75° or more and 105° or less or 255° or more and 285° or less, The secondary battery according to Claim 2.

5. The tip portion has two of the bent portions, the angle related to the first bent portion is 75° or more and 105° or less, the angle related to the second bent portion is 255° or more and 285° or less, The secondary battery according to Claim 2.

6. The exterior member has a through-hole, furthermore, an electrode terminal disposed outside the exterior member and shielding the through-hole, and an insulating sealing member disposed between the exterior member and the electrode terminal are provided. The secondary battery according to Claim 1.

7. The exterior member has conductivity, one of the first electrode and the second electrode is electrically connected to the electrode terminal, the other of the first electrode and the second electrode is electrically connected to the exterior member, The secondary battery according to Claim 6.

8. The exterior member has a storage portion having an opening and housing the battery element inside, and a lid portion having the through-hole and closing the opening are included, the storage portion and the lid portion are joined to each other, The secondary battery according to Claim 6.

9. The lid portion has a recessed portion provided with the through-hole, In the recessed portion, the lid portion is bent so as to be partially recessed toward the inside of the storage portion. The electrode terminal is disposed inside the recessed portion. The secondary battery according to claim 8.

10. The battery element is columnar and has a pair of bottom portions facing each other. The height of the battery element, which is the distance between the pair of bottom portions, is smaller than the outer diameter of the battery element. The secondary battery according to claim 1.

11. It is a lithium ion secondary battery. The secondary battery according to any one of claims 1 to 10.

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