Cylindrical secondary battery

Abstract

To provide a cylindrical secondary battery capable of attaining improvement of adhesiveness between a sheath part and a coating part.SOLUTION: A cylindrical secondary battery comprises: a cylindrical sheath part in which a battery element is included and which has both opposed ends and an outer peripheral surface disposed therebetween; and a coating part coating at least a portion of both the ends of the sheath part and the entire outer peripheral surface. The sheath part includes a cylindrical main body portion which includes an opening on one end side and includes a bottom on the other end side opposed to the one end side; and a lid portion which closes the opening. Arithmetic average roughness (Ra) of the cylindrical main body portion is 0.7 to 1.5 μm, and maximum height roughness (Rz) of an inner side face of the coating part in a radial direction of the bottom of the main body portion is equal to or less than 2.5 μm.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a cylindrical secondary battery. [Background technology]

[0002] Cylindrical secondary batteries have been used for some time. Known cylindrical secondary batteries include a cylindrical exterior housing containing a battery element and a covering (equivalent to a heat-shrinkable tube or film) that covers the surface of the exterior housing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-132865 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-171127 [Patent Document 3] Special Publication No. 2019-535100 Summary of the Invention [Problem to be solved by the invention]

[0004] The present inventors have found that conventional cylindrical secondary batteries need to be improved in the following respects.

[0005] Specifically, in conventional cylindrical secondary batteries, there are cases where the adhesion between the cylindrical exterior, which is a component of the battery, and the covering covering the surface of the exterior is insufficient. In such cases, moisture may penetrate between the exterior and the covering at the bottom of the exterior, causing a so-called tracking phenomenon, which may result in a short circuit in the battery.

[0006] Therefore, an object of the present disclosure is to provide a cylindrical secondary battery that can improve the adhesion between the exterior portion and the covering portion. [Means for solving the problem]

[0007] In order to achieve the above object, the present disclosure provides: a cylindrical exterior part having a battery element therein and having opposite end parts and an outer circumferential surface disposed therebetween; and a covering part covering at least a part of the end parts and the entire outer circumferential surface of the exterior part; the exterior part has a cylindrical main body part having an opening at one end side and a bottom part at the other end side opposite to the one end side, and a lid part closing the opening, The cylindrical secondary battery has a calculated average roughness (Ra) of the cylindrical main body of 0.7 to 1.5 μm, and a maximum height roughness (Rz) of the inner surface of the covering portion in the radial direction of the bottom of the main body of 2.5 μm or less. [Effects of the Invention]

[0008] According to the cylindrical secondary battery of the present disclosure, it is possible to improve the adhesion between the exterior part and the covering part. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic perspective view of a cylindrical secondary battery according to an embodiment of the present disclosure. [Figure 2] 2 is a schematic cross-sectional view of a cylindrical secondary battery according to an embodiment of the present disclosure taken along the longitudinal direction of the battery in FIG. 1. FIG. [Figure 3] FIG. 1 is a schematic perspective view of a cylindrical secondary battery of a comparative example. [Figure 4] 4 is a schematic cross-sectional view of a cylindrical secondary battery of a comparative example taken along the longitudinal direction of the battery in FIG. 3. FIG. [Figure 5] FIG. 2 is a schematic cross-sectional view of a cylindrical secondary battery subjected to a tracking short test. [Figure 6] FIG. 2 is a cross-sectional view schematically showing the structure of a positive electrode and a negative electrode. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, a cylindrical secondary battery according to an embodiment of the present disclosure will be specifically described with reference to the drawings. Although the description will be made with reference to the drawings as needed, the various elements in the drawings are merely shown schematically and as examples for the purpose of understanding the present disclosure, and the appearance, dimensional ratios, etc. may differ from the actual product.

[0011] The term "secondary battery" used in this specification refers to a battery that can be repeatedly charged and discharged. The term "secondary battery" is not limited to the name itself, and can also include, for example, "electricity storage devices."

[0012] Various numerical ranges mentioned in this specification are intended to include the lower and upper limit numerical values themselves, unless otherwise specified, such as "less than" or "more than / greater than." For example, a numerical range such as 1 to 10 can be interpreted as including the lower limit of "1" and the upper limit of "10." Furthermore, terms such as "about" and "approximately" mean that the range may include a variation of a few percent, for example, ±10%.

[0013] In this specification, the term "cross-sectional view" refers to the state when the object (cylindrical secondary battery) is cut along the longitudinal direction. In this specification, the term "oblique view" refers to the state when the appearance (particularly the appearance of the bottom and side) of the object (cylindrical secondary battery) is viewed obliquely.

[0014] The overall configuration of a cylindrical secondary battery according to an embodiment of the present disclosure will be described below. Fig. 1 is a schematic perspective view of a cylindrical secondary battery according to an embodiment of the present disclosure. Fig. 2 is a schematic cross-sectional view of the cylindrical secondary battery according to an embodiment of the present disclosure taken along the longitudinal direction of the battery in Fig. 1.

[0015] As shown in FIGS. 1 and 2, a cylindrical secondary battery 100 according to an embodiment of the present disclosure includes a cylindrical exterior part 20 having a battery element therein, and a covering part 30 covering the surface of the exterior part 20.

[0016] The exterior casing 20 contains the above-described battery elements (corresponding to the electrode assembly) and encapsulates an electrolyte. The electrode assembly may include a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes. The electrode assembly may be a stacked electrode assembly or a wound (jelly roll) electrode assembly. A stacked electrode assembly is formed by stacking multiple electrode constituent layers, each including a positive electrode, a negative electrode, and a separator. A wound electrode assembly is formed by winding an electrode constituent layer, each including a positive electrode, a negative electrode, and a separator. Alternatively, for example, the electrode assembly may have a so-called stack-and-fold structure in which the positive electrode, separator, and negative electrode are stacked on a long film and then folded.

[0017] The positive electrode 10A is composed of at least a positive electrode current collector 11A and a positive electrode material layer 12A (see FIG. 6), with the positive electrode material layer 12A provided on at least one side of the positive electrode current collector 11A. A positive electrode-side lead-out tab is located at a portion of the positive electrode current collector 11A where the positive electrode material layer 12A is not provided, i.e., at an end of the positive electrode current collector 11A. The positive electrode material layer 12A contains a positive electrode active material as an electrode active material. The negative electrode 10B is composed of at least a negative electrode current collector 11B and a negative electrode material layer 12B (see FIG. 6), with the negative electrode material layer 12B provided on at least one side of the negative electrode current collector 11B. A negative electrode-side lead-out tab is located at a portion of the negative electrode current collector 11B where the negative electrode material layer 12B is not provided, i.e., at an end of the negative electrode current collector 11B. The negative electrode material layer 12B contains a negative electrode active material as an electrode active material.

[0018] The positive electrode active material contained in the positive electrode layer 12A and the negative electrode active material contained in the negative electrode layer 12B are materials directly involved in the transfer of electrons in the secondary battery and are the main materials of the positive and negative electrodes responsible for charge and discharge, i.e., the battery reaction. More specifically, the "positive electrode active material contained in the positive electrode layer 12A" and the "negative electrode active material contained in the negative electrode layer 12B" provide ions to the electrolyte, and these ions move between the positive electrode 10A and the negative electrode 10B, transferring electrons and causing charge and discharge. The positive electrode layer 12A and the negative electrode layer 12B are preferably layers capable of absorbing and releasing lithium ions. In other words, a secondary battery in which lithium ions move between the positive electrode 10A and the negative electrode 10B via the electrolyte to charge and discharge the battery is preferred. When lithium ions are involved in charge and discharge, the secondary battery corresponds to a so-called "lithium ion battery."

[0019] The positive electrode active material of the positive electrode layer 12A is, for example, granular, and preferably contains a binder to ensure sufficient contact between the particles and maintain their shape. Furthermore, the positive electrode layer 12A may contain a conductive additive to facilitate the transfer of electrons that drive the battery reaction. Similarly, the negative electrode active material of the negative electrode layer 12B is, for example, granular, and preferably contains a binder to ensure sufficient contact between the particles and maintain their shape. The negative electrode layer 12B may contain a conductive additive to facilitate the transfer of electrons that drive the battery reaction. Because they contain multiple components, the positive electrode layer 12A and the negative electrode layer 12B may also be referred to as a "positive electrode composite layer" and a "negative electrode composite layer," respectively.

[0020] The positive electrode active material is preferably a material that contributes to the absorption and desorption of lithium ions. From this perspective, the positive electrode active material is preferably, for example, a lithium-containing composite oxide. More specifically, the positive electrode active material is preferably a lithium transition metal composite oxide containing lithium and at least one transition metal selected from the group consisting of cobalt, nickel, manganese, and iron. That is, such a lithium transition metal composite oxide is preferably contained as the positive electrode active material in the positive electrode layer 12A of the secondary battery. For example, the positive electrode active material may be lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium iron phosphate, or a material in which part of the transition metal is replaced with another metal. Such positive electrode active materials may be contained alone or in combination of two or more types. In a more preferred embodiment, the positive electrode active material contained in the positive electrode layer 12A is lithium cobalt oxide.

[0021] The binder that can be contained in the positive electrode layer 12A is not particularly limited, but can include at least one selected from the group consisting of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and polytetrafluoroethylene. The conductive additive that can be contained in the positive electrode layer 12A is not particularly limited, but can include at least one selected from the group consisting of carbon black such as thermal black, furnace black, channel black, ketjen black, and acetylene black; carbon fibers such as graphite, carbon nanotubes, and vapor-grown carbon fibers; metal powders such as copper, nickel, aluminum, and silver; and polyphenylene derivatives. For example, the binder of the positive electrode layer 12A can be polyvinylidene fluoride. By way of example only, the conductive additive of the positive electrode layer 12A is carbon black. Furthermore, the binder and conductive additive of the positive electrode layer 12A may be a combination of polyvinylidene fluoride and carbon black.

[0022] The negative electrode active material is preferably a material that contributes to the absorption and desorption of lithium ions, and from this perspective, the negative electrode active material is preferably, for example, any of various carbon materials, oxides, or lithium alloys.

[0023] Examples of various carbon materials for the negative electrode active material include graphite (natural graphite, artificial graphite), soft carbon, hard carbon, and diamond-like carbon. Graphite is particularly preferred due to its high electronic conductivity and excellent adhesion to the negative electrode current collector 11B. Examples of oxides for the negative electrode active material include at least one selected from the group consisting of silicon oxide, tin oxide, indium oxide, zinc oxide, and lithium oxide. The lithium alloy for the negative electrode active material may be any metal capable of forming an alloy with lithium, such as a binary, ternary, or higher alloy of lithium with a metal such as Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, or La. Such oxides preferably have an amorphous structure, as this reduces degradation due to inhomogeneities such as grain boundaries or defects. By way of example only, the negative electrode active material for the negative electrode material layer 12B may be artificial graphite.

[0024] The binder that can be contained in the negative electrode material layer 12B is not particularly limited, but can include at least one selected from the group consisting of styrene-butadiene rubber, polyacrylic acid, polyvinylidene fluoride, polyimide resin, and polyamide-imide resin. For example, the binder contained in the negative electrode material layer 12B can be styrene-butadiene rubber. The conductive additive that can be contained in the negative electrode material layer 12B is not particularly limited, but can include at least one selected from carbon black such as thermal black, furnace black, channel black, ketjen black, and acetylene black; carbon fiber such as graphite, carbon nanotubes, and vapor-grown carbon fiber; metal powder such as copper, nickel, aluminum, and silver; and polyphenylene derivatives. The negative electrode material layer 12B may also include a component derived from a thickener component (e.g., carboxymethyl cellulose) used during battery production.

[0025] By way of example only, the negative electrode active material and binder in the negative electrode material layer 12B may be a combination of artificial graphite and styrene-butadiene rubber.

[0026] The positive electrode current collector 11A and the negative electrode current collector 11B used in the positive electrode 10A and the negative electrode 10B are members that contribute to collecting and supplying electrons generated in the active material due to the battery reaction. Such current collectors may be sheet-like metal members and may be porous or perforated. For example, the current collectors may be metal foil, punched metal, mesh, expanded metal, etc. The positive electrode current collector 11A used in the positive electrode 10A is preferably made of a metal foil containing at least one selected from the group consisting of aluminum, stainless steel, nickel, etc., and may be, for example, aluminum foil. On the other hand, the negative electrode current collector 11B used in the negative electrode 10B is preferably made of a metal foil containing at least one selected from the group consisting of copper, stainless steel, nickel, etc., and may be, for example, copper foil.

[0027] The separator is a component provided to prevent short circuits due to contact between the positive and negative electrodes and to maintain electrolyte integrity. In other words, the separator is a component that allows ions to pass through while preventing electronic contact between the positive electrode 10A and the negative electrode 10B. Preferably, the separator is a porous or microporous insulating component, and has a membrane shape due to its small thickness. By way of example only, a microporous membrane made of polyolefin may be used as the separator. In this regard, the microporous membrane used as the separator may contain, for example, only polyethylene (PE) or only polypropylene (PP) as the polyolefin. Furthermore, the separator may be a laminate composed of a "microporous membrane made of PE" and a "microporous membrane made of PP." The surface of the separator may be covered with an inorganic particle coating layer and / or an adhesive layer. The surface of the separator may have adhesive properties.

[0028] The separator is not particularly limited by its name, and may be a solid electrolyte, a gel electrolyte, insulating inorganic particles, or the like, which have similar functions. From the viewpoint of further improving the ease of handling of the electrodes, it is preferable that the separator and the electrode (positive electrode 10A / negative electrode 10B) are bonded together. Bonding between the separator and the electrode can be achieved by using an adhesive separator, applying an adhesive binder to the electrode material layer (positive electrode material layer 12A / negative electrode material layer 12B) and / or by thermocompression bonding. Examples of adhesive binder materials that provide adhesiveness to the separator or electrode material layer include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene polymer, and acrylic resin. The thickness of the adhesive layer formed by applying an adhesive binder or the like may be 0.5 μm or more and 5 μm or less.

[0029] When the positive electrode 10A and the negative electrode 10B have layers capable of absorbing and releasing lithium ions, the electrolyte is preferably a non-aqueous electrolyte such as an organic electrolyte and / or an organic solvent (i.e., the electrolyte is preferably a non-aqueous electrolyte). The electrolyte contains metal ions released from the electrodes (positive electrode 10A and negative electrode 10B), and therefore, the electrolyte assists the migration of metal ions in the battery reaction.

[0030] The nonaqueous electrolyte is an electrolyte containing a solvent and a solute. A specific solvent for the nonaqueous electrolyte preferably contains at least a carbonate. The carbonate may be a cyclic carbonate and / or a chain carbonate. Although not particularly limited, the cyclic carbonate may include at least one selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and vinylene carbonate (VC). The chain carbonate may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dipropyl carbonate (DPC). By way of example only, a combination of a cyclic carbonate and a chain carbonate may be used as the nonaqueous electrolyte, such as a mixture of ethylene carbonate and diethyl carbonate. As a specific solute of the non-aqueous electrolyte, a Li salt such as LiPF6, LiBF4, etc. is preferably used. As a specific solute of the non-aqueous electrolyte, a Li salt such as LiPF6 and / or LiBF4, etc. is preferably used.

[0031] Any current collecting leads used in the field of secondary batteries can be used as the positive electrode current collecting lead and the negative electrode current collecting lead. Such current collecting leads may be made of any material that allows electron transfer, such as conductive materials such as aluminum, nickel, iron, copper, and stainless steel. The positive electrode current collecting lead is preferably made of aluminum, and the negative electrode current collecting lead is preferably made of nickel. The shape of the positive electrode current collecting lead and the negative electrode current collecting lead is not particularly limited and may be, for example, wire-like or plate-like.

[0032] A cylindrical exterior with a bottom can be used as the exterior 20. Specifically, the exterior 20 is made up of a main body 21 and a lid 24.

[0033] The main body 21 is made up of a bottom portion 22 that forms the bottom surface of the exterior portion 20, and a side portion 23. That is, the main body 21 is a cylindrical member having one open end and the other opposing end being the bottom portion 22. The side portion 23 has an outer circumferential surface that is disposed between these opposing ends.

[0034] The covering portion 30 covers at least a portion of both end portions of the exterior portion 20 and the entire outer circumferential surface of the side portion 23. The lid portion 24 is configured to close the opening of the main body portion 21. The main body portion 21 and the lid portion 24 are sealed together after the battery element, electrolyte, current collecting leads, and external terminals are housed inside. With this configuration, the cylindrical secondary battery has positive and negative electrode terminals at the bottom 22 of the exterior portion 20, which are both end surfaces, and the electrodes provided on the lid portion 24.

[0035] The sealing method is not particularly limited, and examples thereof include laser irradiation. Any material that can be used to form a hard case-type exterior in the field of secondary batteries can be used as the material for the main body 21 and the lid 24. Such a material may be any material that can achieve electron transfer, and examples thereof include conductive materials such as aluminum, nickel, iron, copper, and stainless steel.

[0036] The dimensions of the main body 21 and the lid 24 are determined mainly according to the dimensions of the electrode assembly, and preferably have dimensions that, when the electrode assembly is housed, prevent the electrode assembly from moving or shifting within the exterior casing 20. Preventing movement of the electrode assembly prevents damage to the electrode assembly and improves the safety of the secondary battery.

[0037] As described above, the covering portion 30 is a component that covers the surface of the exterior portion 20. The area covered by the covering portion 30 may be the entire surface of the side portion 23 of the exterior portion 20, a portion of the bottom portion 22 of the exterior portion 20, and a portion of the lid portion 24 of the exterior portion 20 other than the portion where the electrode terminals are arranged. A heat-shrinkable tube may be used as the covering portion 30. For example, a polyester-based resin may be used as the heat-shrinkable tube. As an example, saturated crystalline polyethylene terephthalate (PET) may be used. The covering portion 30 may have a thickness of 30 μm or more and 150 μm or less.

[0038] (Characteristic parts of the present disclosure) With the above-described configuration as a premise, the cylindrical secondary battery 100 of the present disclosure is characterized by the interface between the exterior part 20 and the covering part 30. In particular, the present disclosure is characterized by the interface between the bottom part 22 of the exterior part 20 and the covering part 30. Specifically, the cylindrical secondary battery 100 of the present disclosure is characterized in that, when the calculated average roughness (Ra) of the cylindrical main body part 21 is 0.7 to 1.5 μm, the maximum height roughness (Rz) of the inner surface 21 of the covering part 30 in the radial direction of the battery is 2.5 μm or less.

[0039] The term "maximum height roughness (Rz)" as used herein refers to the numerical value of the highest peak within the reference length of a cross-sectional curve, based on the JIS standard for surface roughness (JIS B 0601:2001). In other words, the maximum height roughness (Rz) is the value obtained by taking the difference between the lowest concave portion and the highest convex portion within a specified length.

[0040] This maximum height roughness (Rz) is used to distinguish it from the calculated average roughness (Ra) and the ten-point average roughness (Rzjis), which are used as indicators of surface roughness.

[0041] In addition, the term "calculated average roughness (or average surface roughness) (Ra)" used in this specification refers to a numerical value obtained by averaging the difference between convex and concave surfaces over a specified length. The ten-point average roughness (Rzjis) is the average value of a total of 10 points over a specified length, from the lowest five concave points to the highest five convex points.

[0042] According to the features of the present disclosure, when the calculated average roughness (Ra) of the cylindrical main body 21 is 0.7 to 1.5 μm, the adhesion between the inner side surface 31 of the covering 30 and the surface 25 of the exterior part 20 in the radial direction of the battery can be improved compared to when this Rz exceeds 2.5 μm. Specifically, the adhesion between the inner side surface 31 of the covering 30 and the surface 25 of the bottom part 22 of the exterior part 20 in the radial direction of the battery can be improved.

[0043] Such improved adhesion can prevent moisture from penetrating between the exterior part 20 and the covering part 30 from the bottom part 22 of the exterior part 20. In other words, moisture can be prevented from creeping up from the bottom part 22 of the exterior part 20 through the gap between the exterior part 20 and the covering part 30.

[0044] As a result, the so-called tracking phenomenon is suppressed, and the occurrence of short circuits in the cylindrical secondary battery 100 can be suitably suppressed. Furthermore, the suppression of moisture penetration can suitably suppress the occurrence of rust on the exterior part 20. For these reasons, the covering part 30 on the inner surface 31 in which Rz is set to a predetermined value or less can suitably function as a moisture penetration suppression member.

[0045] In this respect, compared to previous embodiments that focused on the calculated average roughness (Ra) and / or the ten-point average roughness (Rzjis) in order to improve the insertability of the heat-shrinkable tube as the covering part into the exterior part and to suppress a decrease in the unwindability of the heat-shrinkable film used as the covering part, the present disclosure is fundamentally different in its technical approach in that it also focuses on Rz in order to suppress moisture penetration.

[0046] In the cylindrical secondary battery 100 of the present disclosure, a washer member 40 is disposed on the top or upper surface side thereof to cover the lid portion 24 of the exterior portion 20 except for the exposed portions of the electrode terminals, and a covering portion 30 may be disposed to cover this washer member 40. The washer member 40 reduces the exposed area of the lid portion 24 of the exterior portion 20, thereby suppressing short-circuiting between the main body portion 21 of the exterior portion 20 and the lid portion 24.

[0047] In addition, in the present disclosure, the roughness in maximum height (Rz) of the inner surface 31 of the covering portion 30 in the longitudinal direction of the battery is preferably 2.0 μm or less, which can improve the adhesion between the inner surface 31 of the covering portion 30 and the surface 25 of the exterior portion 20 in the longitudinal direction of the battery compared to when Rz exceeds 2.0 μm.

[0048] That is, it is possible to improve the adhesion between the inner surface 31 of the covering portion 30 and the surface 25 of the side surface portion 23 of the exterior portion 20 in the longitudinal direction of the battery. Such improved adhesion makes it possible to suitably suppress further moisture creeping up between the side surface portion 23 of the exterior portion 20 and the covering portion 30.

[0049] Furthermore, in the present disclosure, from the viewpoint of improving the adhesion between the inner surface 31 of the covering portion 30 and the surface 25 of the exterior portion 20, it is preferable that the roughness in maximum height (Rz) of not only the inner surface 31 of the covering portion 30 but also the surface of the exterior portion 20 be equal to or less than a predetermined value. For example, the Rz may be 1.5 μm or less. As described above, the covering portion 30 may be made of a heat-shrinkable resin material, while the exterior portion 20 may be made of a metal material. Therefore, the Rz is relatively low depending on the processing mode of the exterior portion 20 and / or the properties of the constituent materials.

[0050] The cylindrical secondary battery of the present disclosure can be finally obtained by inserting a heat-shrinkable tube as a covering into an exterior part having the above-mentioned battery elements and electrolyte solution inside, applying heat using a heater, and shrinking and adhering the tube to the surface of the exterior part.

[0051] Although one embodiment of the present invention has been described above, it is merely a typical example within the scope of application of the present invention. Therefore, it will be readily understood by those skilled in the art that the present invention is not limited to this embodiment and that various modifications can be made.

[0052] For example, from the viewpoint of suppressing moisture penetration, in addition to setting Rz to a predetermined value or less, the area covering the outline and peripheral portion of the bottom of the exterior part 20 may be relatively increased. In this case, for example, approximately 10% to approximately 20% of the bottom of the exterior part 20 may be covered by the covering part. [Example]

[0053] Examples will be described below.

[0054] [Example 1] First, a heat-shrinkable tube as a covering was inserted into an exterior part having the above-mentioned battery element and electrolyte solution inside, and the tube was shrunk and adhered to the surface of the exterior part by the heat of a heater, thereby producing a predetermined cylindrical secondary battery.

[0055] Specifically, the following cylindrical secondary batteries were used. Covering part (heat shrinkable tube): Rz of the inner surface in the radial and longitudinal directions of the battery: 2.5 μm Material: PET, Thickness: 100 μm Exterior: Material: Ni-plated low-carbon aluminum-killed steel, thickness: 0.3 mm, cylinder diameter: φ18 mm, height: 65 mm Calculated average roughness Ra of the outer periphery of the side and bottom edge of the exterior body: 1.1 μm Upper terminal material: Steel plate Washer material: PPE (polyphenylene ether) ·Electrolyte: (EC+DMC+EMC+LiPF6+LiBF4+FEC) Positive electrode active material: nickel-based lithium cobalt oxide Negative electrode active material: graphite Current collecting foil: Positive electrode side: Al, thickness 12 μm, Negative electrode side: Cu, thickness 10 μm

[0056] After fabricating the cylindrical secondary batteries, a tracking short test was conducted on the prepared cylindrical secondary batteries. Specifically, the batteries were first charged at a constant voltage of 4.20 V and a constant current of 4.0 A for 5 hours in an atmosphere of 23±2°C to prepare standard batteries.

[0057] After preparing a battery in a standard state, in accordance with the Byreck method of JIS L 1907, the cylindrical secondary battery 100 was held in a holder 300, and the bottom surface of the cylindrical secondary battery 100 was immersed 20 mm deep into tank water 200 as shown in FIG. 5. The immersion time was 24 hours. The number of batteries evaluated in this tracking short test was set to 100.

[0058] After 24 hours of immersion, an OCV (Open Circuit Voltage) tester was used to determine how many of the 100 evaluated batteries met the specified open circuit voltage value (4.0 V) or higher. Specifically, if 95 or more batteries had an open circuit voltage value of 4.0 V or higher, the test was deemed to have passed. If there were fewer than 95 batteries with an open circuit voltage value of 4.0 V or higher, or if the open circuit voltage value of the battery was less than 4.0 V, the test was deemed to have failed. The OCV (Open Circuit Voltage) tester used was manufactured by HIOKI Corporation.

[0059] [Example 2] The present embodiment differs from Example 1 in the following respects, but the remaining respects are the same. (Point of difference) -The following covering (heat shrinkable tubing) is used Rz of the inner surface in the radial direction of the battery: 2.5 μm Rz of the inner surface in the longitudinal direction of the battery: 2.0 μm

[0060] [Comparative Example] The comparative example differs from Examples 1 and 2 in the following respects, but is otherwise the same. In Figures 3 and 4 corresponding to the comparative example, a prime (') is added to the symbols to facilitate comparison with Figures 1 and 2 corresponding to Examples 1 and 2. (Point of difference) -The following covering (heat shrinkable tubing) is used Rz of the inner surface in the radial direction of the battery: 3.0 μm Rz of the inner surface in the longitudinal direction of the battery: 2.5 μm

[0061] [Measurement results] Example 1: Of the 100 evaluated batteries, 95 met the standard of an open-circuit voltage of 4.0 V or more and were judged to have passed the test. Example 2: Of the 100 evaluated batteries, 99 met the standard of an open-circuit voltage of 4.0V or more and were judged to have passed the test. Comparative Example: Of the 100 evaluated batteries, only 90 met the standard of an open-circuit voltage of 4.0 V or more and were judged to have failed the test.

[0062] [Consideration] Comparing the measurement results of Example 1 and the comparative example, it was found that when the calculated average roughness (Ra) of the cylindrical main body portion is a predetermined value, if the maximum height roughness (Rz) of the inner surface 21 of the covering portion 30 in the radial direction of the battery is 2.5 μm or less, the penetration of moisture from the bottom of the exterior portion 20 into between the exterior portion 20 and the covering portion 30, i.e., the climbing up of moisture, is suppressed, and as a result, the tracking phenomenon is suppressed. Comparing the measurement results of Examples 1 and 2 and the comparative example, it was found that when the maximum height roughness (Rz) of the inner surface of the covering portion 30 in the longitudinal direction as well as the radial direction of the battery is 2.0 μm or less, further creeping up of moisture between the side portion of the exterior portion 20 and the covering portion 30 is suppressed, and as a result, the tracking phenomenon is further suppressed. On the other hand, in the comparative example, the maximum height roughness (Rz) of the inner surface of the covering portion 30' in the radial and longitudinal directions of the battery was greater than the above-mentioned specified value, and therefore moisture 200' was observed passing through between the bottom / side portion of the exterior portion 20' and the covering portion 30' (see Figure 3). From the above, it has been found that when the calculated average roughness (Ra) of the cylindrical main body portion is a predetermined value, by setting the maximum height roughness (Rz) of the inner surface of the covering portion 30 in at least the radial direction of the battery to a predetermined value (2.5 μm) or less, it is possible to improve the adhesion between the inner surface of the covering portion 30 in the radial direction of the battery and the surface of the exterior portion 20. Furthermore, it was found that by setting the maximum height roughness (Rz) of the inner surface of the covering portion 30 in the longitudinal direction of the battery as well as the radial direction of the battery to a predetermined value (2.0 μm) or less, it is possible to further improve the adhesion between the inner surface of the covering portion 30 and the surface of the exterior portion 20 for the entire cylindrical secondary battery 100.

[0063] The present disclosure may include the following aspects. a cylindrical exterior part having a battery element therein and having opposite end parts and an outer circumferential surface disposed therebetween; and a covering part covering at least a part of the end parts and the entire outer circumferential surface of the exterior part; the exterior part has a cylindrical main body part having an opening at one end side and a bottom part at the other end side opposite to the one end side, and a lid part closing the opening, A cylindrical secondary battery in which the calculated average roughness (Ra) of the cylindrical main body is 0.7 to 1.5 μm, and the maximum height roughness (Rz) of the inner surface of the covering portion in the radial direction of the bottom of the main body is 2.5 μm or less. <2> The maximum height roughness (Rz) of the inner surface of the covering portion in the longitudinal direction of the battery is 2.0 μm or less. <1> The cylindrical secondary battery according to claim 1. <3> The coating portion has a thickness of 30 μm or more and 150 μm or less. <1> or <2> The cylindrical secondary battery according to claim 1. <4> The coating portion contains a polyester-based resin. <1> ~ <3> 1. The cylindrical secondary battery according to claim 1, <5> The covering portion is a heat-shrinkable tube. <1> ~ <4> 1. The cylindrical secondary battery according to claim 1, [Industrial Applicability]

[0064] A cylindrical secondary battery according to an embodiment of the present disclosure is used, for example, as a power source for electrically powered devices. [Explanation of symbols]

[0065] 300 Cylindrical secondary battery holder 200 aquarium water 100, 100' cylindrical secondary battery 10A positive electrode 11A positive electrode current collector 12A Cathode material layer 10B negative electrode 11B Negative electrode current collector 12B Negative electrode material layer 20, 20' Exterior part 21 Main body 22 Bottom 23 Side part 24 Lid 25 Exterior surface 30, 30' Covering section 31 Inner surface of the covering part 40, 40' washer member 50, 50' electrode terminal

Claims

1. a cylindrical exterior part having a battery element therein and having opposite end parts and an outer circumferential surface disposed therebetween; and a covering part covering at least a part of the end parts and the entire outer circumferential surface of the exterior part; the exterior part has a cylindrical main body part having an opening at one end side and a bottom part at the other end side opposite to the one end side, and a lid part closing the opening, A cylindrical secondary battery, wherein the calculated average roughness (Ra) of the cylindrical main body is 0.7 to 1.5 μm, and the maximum height roughness (Rz) of the inner surface of the covering portion in the radial direction of the bottom of the main body is 2.5 μm or less.

2. 2. The cylindrical secondary battery according to claim 1, wherein the roughness in maximum height (Rz) of the inner surface of the covering portion in the longitudinal direction of the battery is 2.0 μm or less.

3. The cylindrical secondary battery according to claim 1 , wherein the covering portion has a thickness of 30 μm or more and 150 μm or less.

4. The cylindrical secondary battery according to claim 1 , wherein the coating portion includes a polyester-based resin.

5. The cylindrical secondary battery according to claim 1 , wherein the covering portion is a heat-shrinkable tube.

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