Cylindrical secondary battery

Abstract

To provide a high-safety cylindrical secondary battery capable of sufficiently preventing pop-out of the battery due to ejection of gas generated inside the battery when a battery abnormality occurs.SOLUTION: A cylindrical secondary battery includes: an electrode wound body having a structure in which a band-shaped positive electrode and a band-shaped negative electrode are stacked and wound with a separator interposed therebetween; a battery can having one end portion that is open, while accommodating the electrode wound body; and a battery lid provided at the one end portion of the battery can and having two or more opening portions. The two or more opening portions have a non-overlapping form during rotation that does not overlap the two or more opening portions before rotation when the two or more opening portions are rotated by more than 0° and less than 360° about an axis of a cylindrical shape of the secondary battery in top view, and the battery lid has a cleavage stamp at any one of joints between two adjacent opening portions out of the two or more opening portions.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] In recent years, with the demand for longer life and higher output in power tools and electrical appliances, there has been a demand for improved reliability in secondary batteries. Among secondary batteries, cylindrical secondary batteries in particular have a structure including an electrode winding, a battery can that houses the electrode winding and has one end open, and a battery lid that closes the one end of the battery can.

[0003] To improve the reliability of such cylindrical secondary batteries, a technique is known in which a battery lid is provided with multiple openings for venting gas generated inside the battery to the outside of the battery in the event of a battery abnormality (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-272085 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-161023 Summary of the Invention [Problem to be solved by the invention]

[0005] In the prior art, as shown in FIG. 11, the multiple openings 900a-900d provided in the battery lid have the same dimensions and shapes in a top view and are arranged at equal intervals around the cylindrical axis of the secondary battery. Furthermore, each of the multiple openings 900a-900d has a shape that is symmetrical about a line passing through the center C of the cylindrical axis in a top view. Therefore, if gas is generated inside the battery and ejects to the outside, the gas ejects evenly from each of the openings, which can cause the battery to fly like a bullet, creating a new safety issue. More specifically, as shown in FIG. 12, when a battery abnormality occurs, such as when an ignition point H is generated inside the battery due to the presence of a flame outside the battery, gas is generated inside the battery, causing an increase in internal pressure. When such an increase in internal pressure causes gas to be ejected to the outside, as shown in FIG. 13, the gas is ejected evenly from each of these openings 900a to 900d, which can cause the battery to fly out like a bullet, resulting in a new problem of a lower pass rate for combustion tests. FIG. 11 is a schematic top view showing an example of a battery lid for a secondary battery according to the prior art. FIG. 12 is a schematic cross-sectional view of a secondary battery showing the gas flow generated inside the secondary battery when a battery abnormality occurs. In FIG. 12, arrows indicate the direction of gas flow. FIG. 13 is a schematic top view of a battery lid for explaining the mechanism by which a battery's bullet-like ejection occurs due to the ejection of gas generated inside the secondary battery when a battery abnormality occurs.

[0006] On the other hand, the presence of such an opening in the battery lid raises concerns about the strength of the battery itself, and a new problem has arisen in that the pass rate in drop tests decreases.

[0007] An object of the present invention is to provide a cylindrical secondary battery with excellent safety, which can more fully prevent the battery from flying out like a bullet due to the release of gas generated inside the battery in the event of a battery abnormality.

[0008] Another object of the present invention is to provide a cylindrical secondary battery that has excellent safety and strength characteristics, while having sufficient strength and being able to more adequately prevent the battery from flying like a bullet due to the release of gas generated inside the battery in the event of a battery abnormality. [Means for solving the problem]

[0009] The present invention provides an electrode winding body having a structure in which a strip-shaped positive electrode and a strip-shaped negative electrode are stacked and wound with a separator interposed therebetween; a battery can containing the electrode winding body and having one open end; a battery cover provided at the one end of the battery can and having two or more openings; A cylindrical secondary battery having the two or more openings have a non-overlapping shape when rotated in a top view such that they do not overlap with the two or more openings before rotation, even when rotated by more than 0° and less than 360° around an axis of a cylindrical shape of the secondary battery; The battery cover relates to a cylindrical secondary battery, in which a cleavage mark is formed at one of the joints between two adjacent openings of the two or more openings. [Effects of the Invention]

[0010] The cylindrical secondary battery according to the present invention is excellent in safety because it can more fully prevent the battery from being ejected like a bullet due to the gas generated inside the battery being ejected in the event of a battery abnormality. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view showing one embodiment of a secondary battery according to the present invention. [Figure 2] FIG. 2 is a schematic top view (left side) showing one embodiment of a battery lid in a secondary battery according to the present invention, and a schematic cross-sectional view of the same taken along the line AA'. [Figure 3] FIG. 3 is a schematic top view (left side) showing one embodiment of a battery lid in a secondary battery according to the present invention, and a schematic cross-sectional view taken along the line BB' thereof. [Figure 4] FIG. 4 is a schematic top view showing one embodiment of a battery lid in a secondary battery according to the present invention. [Figure 5] FIG. 5 is a schematic top view showing one embodiment of a battery lid in a secondary battery according to the present invention. [Figure 6] FIG. 6 is a schematic top view of the battery lid for explaining the mechanism by which the secondary battery according to the present invention prevents bullets from flying out even when the battery is abnormal. [Figure 7] FIG. 7 is a connection diagram used to explain a battery pack as an application example of the present invention. [Figure 8] FIG. 8 is a connection diagram used to explain a power tool as an application example of the present invention. [Figure 9] FIG. 9 is a connection diagram used to explain an electric vehicle as an application example of the present invention. [Figure 10] FIG. 10 is a schematic top view showing an example of a battery lid in a secondary battery according to a comparative example. [Figure 11] FIG. 11 is a schematic top view showing an example of a battery lid in a secondary battery according to the prior art (or a comparative example). [Figure 12] FIG. 12 is a schematic cross-sectional view of a secondary battery showing the gas flow generated inside the secondary battery when an abnormality occurs in the battery. [Figure 13] FIG. 13 is a schematic top view of a battery lid for explaining the mechanism of bullet ejection of the battery due to the ejection of gas generated inside the secondary battery when an abnormality occurs in the battery. DETAILED DESCRIPTION OF THE INVENTION

[0012] <Cylindrical secondary battery> A cylindrical secondary battery (hereinafter sometimes simply referred to as a "secondary battery") according to the present invention will be described in detail below. While the description will be made with reference to the drawings as necessary, the various elements in the drawings are merely shown schematically and as examples to facilitate understanding of the present invention, and unless otherwise specified, the appearance and dimensional ratios may differ from those of the actual product.

[0013] The "cross-sectional view" directly or indirectly described in this specification is based on a virtual cross section (or cross-sectional view) of the secondary battery cut along the rotation axis direction (i.e., the winding axis direction) of the electrode winding body that constitutes the secondary battery. The "top view" used in this specification is based on a sketch (or plan view) of the object as seen from above along the rotation axis direction.

[0014] Furthermore, the terms "upward / downward" and "leftward / rightward" used directly or indirectly in this specification correspond to the upward / downward and leftward / rightward directions in the drawings, respectively. Unless otherwise specified, the same reference numerals or symbols indicate the same members and / or parts or the same meanings. In a preferred embodiment, the vertical downward direction (i.e., the direction in which gravity acts) can be considered to correspond to the "downward direction," and the opposite direction can be considered to correspond to the "upward direction." In this specification, terms indicating the relationship between elements (e.g., "parallel," "orthogonal," "vertical," "coincident," "completely overlapping," etc.) and terms indicating the shapes of elements not only refer to the literal, strict aspects, but also refer to a range that is substantially equivalent, for example, a range that includes a difference of about a few percent.

[0015] In this specification, the term "secondary battery" refers to a battery that can be repeatedly charged and discharged. Therefore, the secondary battery according to one embodiment of the present invention is not limited to its name, and may also include electrochemical devices such as power storage devices. In the following, a detailed description will be given of a lithium-ion battery in which charging and discharging are performed by the movement of lithium ions between a positive electrode and a negative electrode. However, the intermediate ions are not particularly limited as long as they can be charged and discharged, and may be, for example, sodium ions or magnesium ions.

[0016] The secondary battery of the present invention has a cylindrical structure, as shown in FIG. 1 . The secondary battery 1 of the present invention includes an electrode winding 20 having a structure in which a strip-shaped positive electrode 21 and a strip-shaped negative electrode 22 are stacked and wound with a separator 23 interposed therebetween; a battery can 11 that houses the electrode winding 20 and has one end open; and a battery lid 14 provided at the one end of the battery can 11. The secondary battery typically further includes insulators 12 and 13, a gasket 15, a positive electrode lead 25, a negative electrode lead 26, a safety valve mechanism 30, and an electrolyte (not shown). The axis of the cylindrical shape of the secondary battery may coincide with the winding axis or rotation axis of the electrode winding 20, and may be simply referred to as the “axis” in this specification. FIG. 1 is a schematic cross-sectional view showing one embodiment of a cylindrical secondary battery of the present invention.

[0017] [Battery can] The battery can 11 is a member that mainly houses the electrode winding body 20. The battery can 11 is a cylindrical container with one end open and the other end closed. That is, the battery can 11 has one end that is open (open end). The battery can 11 contains one or more types of metal materials such as iron, stainless steel, aluminum, and alloys thereof. However, the surface of the battery can 11 may be plated with one or more types of metal materials such as nickel.

[0018] A battery lid 14 and a safety valve mechanism 30 (described later) are crimped to the open end of the battery can 11 via a gasket 15, forming a crimp structure 11R. This keeps the battery can 11 tightly sealed when the electrode wound body 20 and other components are housed inside the battery can 11.

[0019] [Insulator] The insulators 12 and 13 are sheet-like members having surfaces that are approximately perpendicular to the winding axis direction of the electrode winding body 20 (the vertical direction in FIG. 1). The insulators 12 and 13 are arranged so as to sandwich the electrode winding body 20 between them. Materials that can be used for the insulators 12 and 13 include polyethylene terephthalate (PET), polypropylene (PP), and bakelite. Bakelite includes paper bakelite and cloth bakelite, which are made by applying phenolic resin to paper or cloth and then heating it.

[0020] [Battery cover] The battery lid 14 is a member that closes the open end of the battery can 11 when the electrode winding body 20 and other components are housed inside the battery can 11, and as shown in FIGS. 2 to 5 , it has two or more openings 200 (including 200a1 to 200d1, 200a2 to 200d2, 200a3 to 200b3, and 200a4 to 200c4). Because the battery lid 14 has the openings 200, it does not strictly close the open end of the battery can 11. However, even if the battery lid 14 did not have any openings, the battery lid 14 has a structure and installation form that contributes to sealing the battery can 11. Each of FIGS. 2 to 5 is a schematic top view showing one embodiment of a battery lid for a secondary battery according to the present invention. In particular, each of FIGS. 2 and 3 shows, on the right side, schematic cross-sectional views along the A-A' and B-B' cross sections of the schematic top view shown on the left.

[0021] The battery lid 14 may have a hat shape. When the battery lid 14 has this shape, as shown in FIG. 1 , the central region has a protrusion 141 that protrudes toward the side opposite the electrode winding body in the axial direction J of the cylindrical shape of the secondary battery, and an annular flange portion 142 that is disposed around the protrusion 141. The side opposite the electrode winding body in the axial direction J means the side opposite the side where the electrode winding body 20 is located (the upper side in FIG. 1 ) with respect to the battery lid 14 in the axial direction J of the cylindrical shape of the secondary battery. In this case, the battery lid 14 typically has two or more openings 200 in a side surface portion 1410 of the protrusion 141. In this case, the battery lid 14 has all of the two or more openings 200 in the side surface portion 1410. The protrusion 141 typically has a substantially circular shape when viewed from above.

[0022] Two or more openings 200 (specifically, all openings 200) of the battery lid 14 usually have a rotationally extending shape that extends in the rotational direction around the axis of the cylindrical shape of the secondary battery (for example, the winding axis or rotation axis of the electrode winding body 20). The rotationally extending shape means a shape formed to extend in the rotational direction. The rotational direction extending shape may be, for example, an outwardly curved rectangular shape, as in openings 200a1-200d1 in FIG. 2, openings 200a3-200b3 in FIG. 4, and openings 200a4-200b4 in FIG. 5; or may be an outwardly curved rectangular shape tapered at one end (or only one end) as in openings 200a2-200d2 in FIG. 3; or may be an outwardly curved rectangular shape tapered at both ends as in opening 200c4 in FIG. 5. From the viewpoints of further improving safety and improving battery strength, the shape of opening 200 is preferably an outwardly curved rectangular shape or a tapered shape, more preferably an outwardly curved rectangular shape. Two or more openings 200 may have different shapes, but from the viewpoints of further improving safety and improving battery strength, it is preferable that they have the same shape. If two or more openings extend radially around the cylindrical axis of the secondary battery, the ejection pressure of the gas fluid increases the closer to the center, making it impossible to adequately prevent the battery from flying out like a bullet.

[0023] In this specification, safety refers to the property of the battery being able to more effectively prevent projectile ejection. The higher the pass rate of the flammability test (UL 1642 projectile test), the better the safety. The strength characteristic refers to a characteristic of a battery having sufficiently high strength, and is a characteristic that electrolyte leakage is more sufficiently prevented even when the battery is dropped from a height of 10 mm. The higher the pass rate of the drop test, the better the strength characteristic. The strength characteristic is not necessarily a characteristic that the secondary battery of the present invention must have, but is positioned as a characteristic that the secondary battery of the present invention preferably has.

[0024] Two or more openings 200 (specifically, all openings 200) in battery lid 14 are preferably usually arranged in a concentric circular region centered on the axis, as shown in Figures 2 to 5. "Two or more openings 200 arranged in a concentric circular region" means that the two or more openings 200 have different diameters and are all arranged in a region between two concentric circles centered on the axis. In particular, when battery lid 14 has protrusion 141 and flange portion 142, and two or more openings 200 are provided on side surface portion 1410 of protrusion 141, the two or more openings 200 are usually arranged in a concentric circular region centered on the axis.

[0025] Two or more openings 200 (specifically, all of the openings 200) of the battery lid 14 are usually arranged in a line along the rotation direction around the axis, as shown in Figures 2 to 5. Therefore, two or more openings 200 (specifically, all of the openings 200) of the battery lid 14 are usually arranged as a whole in a ring shape around the axis, as shown in Figures 2 to 5.

[0026] The two or more openings 200 (specifically, all of the openings 200) of the battery cover 14 have a non-overlapping configuration in which, when viewed from above, they do not overlap with the two or more openings before rotation, even when rotated by more than 0° but less than 360° around the axis of the cylindrical shape of the secondary battery. In the non-overlapping configuration, specifically, when all of the two or more openings 200 are rotated by more than 0° but less than 360° around the axis, the two or more openings after rotation do not completely overlap with the two or more openings before rotation. More specifically, as shown in each of FIGS. 2 to 5, even when all of the two or more openings are gradually rotated counterclockwise around the axis by an angle greater than 0° but less than 360°, there is no rotation angle at which all of the two or more openings after rotation completely overlap with all of the two or more openings before rotation. Completely overlapping ("complete overlap") means that when all of the two or more openings are viewed as overlapping before and after rotation, each of the two or more openings after rotation matches one of the two or more openings before rotation in terms of the size, shape, and arrangement of each opening.

[0027] By having two or more openings 200 (specifically, all openings 200) in the battery lid 14 have a non-overlapping configuration during rotation, even if gas generated inside the battery is released to the outside, the gas is released unevenly from each of the openings, as shown in FIG. 6, thereby more effectively preventing battery bullet ejection. For example, even if gas is released to the outside, the secondary battery of the present invention rotates around the axial direction as a diameter due to the uneven release, thereby more effectively preventing battery bullet ejection. If two or more openings in the battery lid do not have a non-overlapping configuration during rotation, when gas generated inside the battery is released to the outside, the gas is released evenly from each of the openings, resulting in battery bullet ejection. FIG. 6 is a schematic top view of a battery lid to explain the mechanism by which the secondary battery of the present invention prevents bullet ejection even in the event of a battery abnormality.

[0028] The rotational non-overlapping configuration of two or more openings 200 (specifically, all openings 200) in the battery lid 14 may be based on non-uniform division and / or asymmetric shapes of the openings.

[0029] When the non-overlapping form during rotation is based on the non-uniform division of the opening, it means that the non-overlapping form during rotation is achieved based on the difference in the opening dimensions (particularly, the difference in the opening dimensions of the two openings (the openings before and after rotation) that are the targets of overlapping / non-overlapping), as shown in FIG. 2. In this case, the opening 200 may include two or more (particularly two) types of openings with different opening dimensions from each other. The opening dimension is the maximum length in the rotation direction of the opening, and specifically, it is the maximum length of the opening in the rotation direction (circumferential direction) centered on the axis. When the opening 200 includes two types of openings with different opening dimensions from each other, and the opening dimensions of the two types of openings are p and q (where p < q), p and q may satisfy the relational expression: 1.5×p≦q≦4×p (particularly 2×p≦q≦3×p).

[0030] The battery cover 14 in FIG. 2 has two types of openings with different opening dimensions from each other (the openings 200a1, 200b1 with the opening dimension x1 and the openings 200c1, 200d1 with the opening dimension x2). Therefore, the openings 200a1 to 200d1 of the battery cover 14 in FIG. 2 have a non-overlapping form during rotation based on the non-uniform division of the opening. Incidentally, the battery cover 14 in FIG. 4 has two types of openings with different opening dimensions from each other (the opening 200a3 with the opening dimension x4 and the opening 200b3 with the opening dimension x5). Therefore, the openings 200a3 to 200b3 of the battery cover 14 in FIG. 4 have a non-overlapping form during rotation based on the non-uniform division of the opening. On the other hand, the battery cover 14 in FIG. 3 has only openings with equal opening dimensions (the openings 200a2 to 200d2 with the opening dimension x3). Therefore, the openings 200a2 to 200d2 of the battery cover 14 in FIG. 3 do not have a non-overlapping form during rotation based on the non-uniform division, but as will be described later, they have a non-overlapping form during rotation based on the asymmetric shape of the opening.

[0031] The non-overlapping pattern during rotation based on the asymmetric shape of the openings means that the non-overlapping pattern during rotation is achieved based on differences in the opening shapes (particularly, differences in the opening shapes of two openings (openings before and after rotation) to be overlapped / non-overlapped), as shown in FIG. 3 . The difference in opening shapes may be based on the presence or absence of asymmetry in the opening shapes. In this case, opening 200 may include two types of openings with different opening shapes (e.g., openings 200a2 and 200b2 having a tapered shape that tapers counterclockwise, and openings 200c2 and 200d2 having a tapered shape that tapers clockwise). The asymmetry in the opening shapes means that there is no line symmetry about any line passing through the center of the axis. For example, each of openings 200a2 to 200d2 in FIG. 3 has asymmetry because there is no line symmetry about any line passing through the center of the axis. On the other hand, for example, each of the openings 200a1 to 200d1 in FIG. 2, the openings 200a3 to 200b3 in FIG. 4, and the openings 200a4 to 200c4 in FIG. 5 has line symmetry about the axis and a straight line m passing through the center, and therefore does not have asymmetry.

[0032] The battery cover 14 of FIG. 3 has two types of openings with different opening shapes (openings 200a2 and 200b2 tapered counterclockwise and openings 200c2 and 200d2 tapered clockwise). Therefore, the openings 200a2 to 200d2 of the battery cover 14 of FIG. 3 have a non-overlapping shape during rotation due to the asymmetrical shapes of the openings. The battery cover 14 of FIG. 4 has two types of openings with different opening dimensions (opening 200a3 with opening dimension x4 and opening 200b3 with opening dimension x5). Therefore, the openings 200a3 to 200b3 of the battery cover 14 of FIG. 4 have a non-overlapping shape during rotation due to the uneven division of the openings.

[0033] The arrangement of the two or more openings 200 in the battery lid 14 is not particularly limited as long as the two or more openings 200 (specifically, all of the openings 200) have a non-overlapping shape when rotated. For example, if the battery lid 14 has n openings, the n openings may be arranged one at a time in each region defined by a central angle expressed as 360° / n around the axis. The region defined by the central angle expressed as 360° / n is indicated by a dashed line in Figures 2 to 5. For example, if the battery cover 14 has four openings, the four openings may be arranged one in each of the areas separated by a central angle of 90° (=360° / 4) around the axis, as shown in Figures 2 and 3. For example, if the battery cover 14 has two openings, the two openings may be arranged one in each of the areas separated by a central angle of 180° (=360° / 2) around the axis, as shown in FIG. For example, if the battery cover 14 has three openings, the three openings may be arranged one in each of the areas separated by a central angle of 120° (=360° / 3) around the axis, as shown in FIG. 5.

[0034] One opening does not necessarily have to be arranged strictly within the range of one region bounded by the central angle expressed as 360° / n, and may be arranged across two adjacent regions. For example, as long as more than 50% (particularly 70% or more) of the opening area of ​​one opening is arranged within a predetermined region, the one opening may be arranged across two of the regions bounded by the central angle expressed as 360° / n.

[0035] Specifically, as shown in FIG. 2, for example, one opening 200a1 located in region I may have the remaining area located in adjacent region IV, as long as more than 50% of its opening area is located within region I.

[0036] The opening ratio of the opening of the battery lid 14 is typically 5.0% or more and 12.0% or less, and from the viewpoint of further improving safety and improving battery strength, it is preferably 7.0% or more and 12.0% or less, more preferably 8.0% or more and 10.0% or less, and even more preferably 8.5% or more and 9.5% or less.

[0037] The aperture ratio of the openings is the total aperture ratio of two or more openings in the battery lid 14 in a plan view, and is the ratio to the radial area of ​​the battery. The radial area of ​​the battery means the area of ​​the battery in a plan view, and is the top view area E of the battery can 11 (see FIG. 1).

[0038] The distance (particularly the shortest distance) r1 (see Figures 2 and 3) of the opening of the battery lid 14 from the axis (center) is typically, independently, 0.3 × r (mm) or more and 0.8 × r (mm) or less, where r (mm) is the radius of the battery lid 14, and from the viewpoint of further improving safety and improving battery strength, it is preferably 0.4 × r (mm) or more and 0.7 × r (mm) or less, and more preferably 0.4 × r (mm) or more and 0.6 × r (mm) or less.

[0039] The width w1 (particularly the maximum width) w1 (see Figures 2 and 3) of the opening in the battery lid 14 in the radial direction from the axis (center) is usually, independently, 0.1 × r (mm) or more and 0.5 × r (mm) or less, where r (mm) is the radius of the battery lid 14, and from the viewpoint of further improving safety and improving battery strength, it is preferably 0.1 × r (mm) or more and 0.3 × r (mm) or less, and more preferably 0.1 × r (mm) or more and 0.2 × r (mm) or less.

[0040] The radius r of the battery lid 14 is not particularly limited and may be, for example, 7 mm or more and 11 mm or less. A value equivalent to twice the radius r of the battery lid 14 may correspond to the outer diameter (diameter of the battery can 11) of the secondary battery of the present invention.

[0041] The opening dimension x of the opening in battery lid 14 (e.g., x1 and x2 in FIG. 2, x3 in FIG. 3, x4 and x5 in FIG. 4, and x6 and x7 in FIG. 5) is typically an opening angle (e.g., α1 to α4 in FIG. 2, and β1 to β4 in FIG. 3) about the axis, which is independently 10° to 160°, and from the viewpoint of further improving safety and improving battery strength, is preferably 20° to 100°, more preferably 30° to 95°. The opening angle about the axis is based on the opening dimension x of the opening in battery lid 14.

[0042] The battery cover 14 has a cleavage mark 145 at one of the joints between two adjacent openings in the two or more openings 200. When the battery cover 14 has a cleavage mark, the safety of the secondary battery is significantly improved. If the battery cover 14 does not have a cleavage mark, safety will be reduced. The joint refers to the battery cover material between two adjacent openings. In particular, when the battery cover 14 has the above-mentioned protrusion 141 and flange-shaped portion 142, the joint refers to the side surface material between two adjacent openings on the side surface portion 1410 of the protrusion 141. The cleavage mark 45 is usually formed across the entire width of the joint.

[0043] The cleavage marking 145 promotes cleavage of the battery (particularly the battery lid) when gas generated inside the battery is released to the outside, and is formed thinner than the thickness of other parts of the battery lid. The thickness t1 (mm) of the cleavage marking 145 is typically 0.1 × t2 (mm) to 0.8 × t2 (mm), where t2 (mm) is the thickness of other parts of the battery lid 14 (e.g., protrusion 141). From the viewpoint of further improving safety and improving battery strength, the thickness t1 is preferably 0.1 × t2 (mm) to 0.6 × t2 (mm), and more preferably 0.1 × t2 (mm) to 0.4 × t2 (mm).

[0044] The thickness t2 of other parts of the battery cover 14 (for example, the protruding portion 141 and the flange portion 142) is not particularly limited, and may be, for example, 0.3 mm or more and 0.7 mm or less, particularly 0.4 mm or more and 0.6 mm or less.

[0045] The joint where the cleavage mark 145 is placed is usually the joint where the load (or stress) due to the gas ejection is greatest. For example, if gas is ejected from inside the secondary battery, the load (or stress) due to the ejection is greatest, and therefore the cleavage mark is placed at the joint that is most likely to cleave.

[0046] The seam at which the load due to the ejection is greatest is the seam between the two openings with the largest opening areas among two or more openings in the battery lid 14, and may also be the seam between the opening with the largest opening area and the opening with the second largest opening area, if all the seam dimensions are equal, as shown in Fig. 2. The seam dimension refers to the overall width dimension of the seam (particularly, the shortest distance between two adjacent openings).

[0047] As shown in Figure 3, when all joint dimensions are equal, all openings have equal opening areas, and the openings include openings 200a2 and 200b2 having a tapered end that tapers counterclockwise and openings 200c2 and 200d2 having a tapered end that tapers clockwise, the joint at which the load due to ejection is greatest is the joint between an opening having a tapered end that tapers counterclockwise and an opening having a tapered end that tapers clockwise, and the joint between the other ends of the tapered ends that do not have a tapered end.

[0048] The battery lid 14 contains one or more metal materials such as iron, stainless steel, aluminum, and alloys thereof. The surface of the battery lid 14 may be plated with one or more metal materials such as nickel.

[0049] [gasket] The gasket 15 is a member that is mainly interposed between the folded portion 11P (also referred to as the crimp portion) of the battery can 11 and the battery lid 14 and safety valve mechanism 30, thereby sealing the gap between the folded portion 11P and the battery lid 14 and safety valve mechanism 30. The surface of the gasket 15 may be coated with, for example, asphalt.

[0050] The gasket 15 contains an insulating material. The type of insulating material is not particularly limited, but is preferably a polymer material such as polybutylene terephthalate (PBT) or polypropylene (PP). This is because the battery can 11 and the battery lid 14 are electrically isolated from each other while the gaps between the bent portion 11P and the battery lid 14 and between the bent portion 11P and the safety valve mechanism 30 are sufficiently sealed.

[0051] [Safety valve mechanism] The safety valve mechanism 30 substantially maintains the sealed state of the battery can 11, and when the pressure inside the battery can 11 (internal pressure) increases, releases the internal pressure by releasing the sealed state of the battery can 11 as necessary. The increase in the internal pressure of the battery can 11 is caused by gas generated due to the decomposition reaction of the electrolyte solution during charging and discharging.

[0052] Of the safety valve mechanism 30, the safety cover 31 is a substantially circular plate-like member and is also called a valve body. The safety cover 31 is made of, for example, aluminum. As shown in FIG. 1, the center of the safety cover 31 may have a protrusion that protrudes toward the electrode winding body 20. The outer periphery of the safety cover 31 may be joined to the outer periphery of the battery lid 14 by welding. The welding method is not particularly limited, and may be, for example, ultrasonic welding. A portion of the joined area 32 between the safety cover 31 and the battery lid 14 is covered with a gasket 15 (FIG. 1) and is fixed to the battery can 11.

[0053] [Electrode winding body] In a cylindrical lithium ion battery, a strip-shaped positive electrode 21 and a strip-shaped negative electrode 22 are spirally wound with a separator 23 sandwiched between them, and are housed in a battery can 11 in a state where they are impregnated with an electrolyte solution.

[0054] (positive and negative electrodes) The positive electrode 21 and the negative electrode 22 are formed by forming a positive electrode active material layer and a negative electrode active material layer on one or both sides of a positive electrode current collector and a negative electrode current collector, respectively (not shown). The material of the positive electrode current collector is a metal foil containing aluminum or an aluminum alloy. The material of the negative electrode current collector is a metal foil containing nickel, a nickel alloy, copper, or a copper alloy. The separator 23 is a porous, insulating film that electrically insulates the positive electrode 21 and the negative electrode 22 while allowing lithium ions to move.

[0055] A space (central space 20C) is provided in the center of the electrode winding body 20 when the positive electrode 21, negative electrode 22, and separator 23 are wound, and a center pin 24 is inserted into the central space 20C (FIG. 1). However, the center pin 24 can be omitted.

[0056] A positive electrode lead 25 is connected to the positive electrode 21, and a negative electrode lead 26 is connected to the negative electrode 22 (FIG. 1). The positive electrode lead 25 contains a conductive material such as aluminum. The positive electrode lead 25 is electrically connected to the battery lid 14 via a safety valve mechanism 30. The negative electrode lead 26 contains a conductive material such as nickel. The negative electrode lead 26 is electrically connected to the battery can 11. The detailed configurations and materials of the positive electrode 21, negative electrode 22, separator 23, and electrolyte will be described later.

[0057] The positive electrode active material layer contains at least a positive electrode material (positive electrode active material) capable of absorbing and releasing lithium, and may further contain a positive electrode binder, a positive electrode conductive agent, etc. The positive electrode material is preferably a lithium-containing composite oxide or a lithium-containing phosphate compound. The lithium-containing composite oxide has, for example, a layered rock salt type or a spinel type crystal structure. The lithium-containing phosphate compound has, for example, an olivine type crystal structure.

[0058] The positive electrode binder contains a synthetic rubber or a polymer compound. The synthetic rubber includes styrene-butadiene rubber, fluorine-based rubber, ethylene propylene diene, etc. The polymer compound includes polyvinylidene fluoride (PVdF), polyimide, etc.

[0059] The positive electrode conductive agent is a carbon material such as graphite, carbon black, acetylene black or ketjen black. However, the positive electrode conductive agent may also be a metal material or a conductive polymer.

[0060] Preferably, the surface of the negative electrode current collector is roughened to improve the adhesion with the negative electrode active material layer. The negative electrode active material layer contains at least a negative electrode material (negative electrode active material) capable of occluding and releasing lithium, and may further contain a negative electrode binder, a negative electrode conductive agent, etc.

[0061] The negative electrode material includes, for example, a carbon material. The carbon material is graphitizable carbon, non-graphitizable carbon, graphite, low-crystalline carbon, or amorphous carbon. The shape of the carbon material has a fibrous, spherical, granular or flaky shape.

[0062] In addition, the negative electrode material includes, for example, a metal-based material. Examples of the metal-based material include Li (lithium), Si (silicon), Sn (tin), Al (aluminum), Zr (zinc), Ti (titanium). The metal-based element forms a compound, mixture or alloy with other elements, and examples thereof include silicon oxide (SiOx (0 < x ≦ 2)), silicon carbide (SiC) or an alloy of carbon and silicon, lithium titanate (LTO).

[0063] In the lithium-ion battery 1, when the open circuit voltage (i.e., the battery voltage) at full charge is 4.25 V or more, the amount of lithium released per unit mass is increased even when the same positive electrode active material is used as compared with the case where the open circuit voltage at full charge is low. Thereby, a high energy density can be obtained.

[0064] (Separator) The separator 23 is a porous film containing a resin, and may be a laminated film of two or more types of porous film. Examples of resins include polypropylene and polyethylene. The separator 23 may include a porous film as a base layer and a resin layer on one or both sides of the base layer. This is because the adhesiveness of the separator 23 to each of the positive electrode 21 and the negative electrode 22 is improved, thereby suppressing distortion of the electrode winding body 20.

[0065] The resin layer contains a resin such as PVdF. To form this resin layer, a solution in which the resin is dissolved in an organic solvent is applied to the substrate layer, and the substrate layer is then dried. Alternatively, the substrate layer may be immersed in the solution and then dried. It is preferable that the resin layer contains inorganic or organic particles from the viewpoint of improving heat resistance and battery safety. Examples of inorganic particles include aluminum oxide, aluminum nitride, aluminum hydroxide, magnesium hydroxide, boehmite, talc, silica, and mica. Alternatively, instead of the resin layer, a surface layer mainly composed of inorganic particles formed by a sputtering method, an ALD (atomic layer deposition) method, or the like may be used.

[0066] (electrolyte) The electrolyte solution contains a solvent and an electrolyte salt, and may further contain additives as necessary. The solvent is a non-aqueous solvent such as an organic solvent, or water. An electrolyte solution containing a non-aqueous solvent is called a non-aqueous electrolyte solution. The non-aqueous solvent is a cyclic carbonate ester, a chain carbonate ester, a lactone, a chain carboxylic acid ester, a nitrile (mononitrile), or the like.

[0067] A typical example of the electrolyte salt is a lithium salt, but salts other than lithium salts may also be included. Examples of lithium salts include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium methanesulfonate (LiCHSO), lithium trifluoromethanesulfonate (LiCFSO), and dilithium hexafluorosilicate (LiSF). Mixtures of these salts can also be used, and a mixture of LiPF and LiBF is particularly preferred from the perspective of improving battery performance. The content of the electrolyte salt is not particularly limited, but is preferably 0.3 mol / kg to 3 mol / kg relative to the solvent.

[0068] <Manufacturing method for cylindrical secondary batteries> Next, a method for manufacturing a secondary battery will be described. First, when manufacturing the positive electrode 21, a positive electrode mixture is prepared by mixing a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent. Next, the positive electrode mixture is dispersed in an organic solvent to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry is applied to both sides of a positive electrode current collector and then dried to form a positive electrode active material layer. Next, while the positive electrode active material layer is being pressed, the positive electrode active material layer is compression-molded using a roll press to obtain the positive electrode 21.

[0069] The negative electrode 22 is also produced in the same manner as the positive electrode 21 described above.

[0070] Next, a positive electrode lead 25 and a negative electrode lead 26 are connected to the positive electrode current collector and the negative electrode current collector, respectively, using a welding method. Subsequently, the positive electrode 21 and the negative electrode 22 are stacked with a separator 23 interposed therebetween, and then wound to form the wound electrode body 20. Subsequently, a center pin 24 is inserted into the central space 20C of the wound electrode body 20.

[0071] Next, the electrode wound body 20 is sandwiched between a pair of insulators and housed inside the battery can 11. Next, one end of the positive electrode lead 25 is connected to the safety valve mechanism 30 and one end of the negative electrode lead 26 is connected to the battery can 11 using a welding method.

[0072] Next, a beading machine (grooving machine) is used to process the battery can 11, thereby forming a recess in the battery can 11. Next, an electrolyte is injected into the battery can 11, and the electrode wound body 20 is impregnated with the electrolyte. Next, the outer periphery of the battery lid 14 and the outer periphery of the safety cover 31 of the safety valve mechanism 30 are joined by welding, and the battery lid 14 and the safety valve mechanism 30 are housed inside the battery can 11 together with the gasket 15. Note that the battery lid 14 may be manufactured by forming the opening in a metal plate by a punching method or the like, and then providing a protrusion by a press forming method or the like, if desired.

[0073] 1, the outer periphery of the battery lid 14 and the outer periphery of the safety cover 31 are welded to each other at the open end of the battery can 11, and then the battery lid 14 and the safety valve mechanism 30 are crimped together via a gasket 15 to form a crimped structure 11R. Finally, the battery can 11 is sealed with the battery lid 14 using a press, thereby completing the secondary battery.

[0074] <Application example> (1) Battery pack 7 is a block diagram showing an example of a circuit configuration when the secondary battery of the present invention is applied to a battery pack 300. The battery pack 300 includes a battery pack 301, a switch unit 304 including a charge control switch 302a and a discharge control switch 303a, a current detection resistor 307, a temperature detection element 308, and a control unit 310. The control unit 310 controls each device, and can also control charging and discharging in the event of abnormal heat generation, and calculate and correct the remaining capacity of the battery pack 300. A positive terminal 321 and a negative terminal 322 of the battery pack 300 are connected to a charger or electronic device for charging and discharging.

[0075] The battery pack 301 is made up of a plurality of secondary batteries 301a connected in series and / or parallel. In Fig. 7, six secondary batteries 301a are connected in two parallel and three series (2P3S) configuration.

[0076] The temperature detection unit 318 is connected to the temperature detection element 308 (e.g., a thermistor), measures the temperature of the battery assembly 301 or the battery pack 300, and supplies the measured temperature to the control unit 310. The voltage detection unit 311 measures the voltage of the battery assembly 301 and each secondary battery 301a that constitutes it, A / D converts the measured voltage, and supplies it to the control unit 310. The current measurement unit 313 measures the current using the current detection resistor 307, and supplies the measured current to the control unit 310.

[0077] The switch control unit 314 controls the charge control switch 302a and the discharge control switch 303a of the switch unit 304 based on the voltage and current input from the voltage detection unit 311 and the current measurement unit 313. When the voltage of the secondary battery 301a becomes equal to or higher than the overcharge detection voltage (for example, 4.20 V±0.05 V) or equal to or lower than the overdischarge detection voltage (2.4 V±0.1 V), the switch control unit 314 sends an OFF control signal to the switch unit 304, thereby preventing overcharging or overdischarging.

[0078] After the charge control switch 302a or the discharge control switch 303a is turned OFF, charging or discharging is possible only via the diode 302b or the diode 303b. These charge / discharge switches can be semiconductor switches such as MOSFETs. Although the switch unit 304 is provided on the positive side in FIG. 7, it may also be provided on the negative side.

[0079] The memory 317 is made up of RAM and ROM, and stores and rewrites values ​​of battery characteristics calculated by the control unit 310, full charge capacity, remaining capacity, and the like.

[0080] (2)Electronic equipment The secondary battery of the present invention described above can be mounted in devices such as electronic devices, electric transport devices, and power storage devices and used to supply electric power.

[0081] Examples of electronic devices include laptop computers, smartphones, tablet devices, PDAs (personal digital assistants), mobile phones, wearable devices, digital still cameras, e-books, music players, game consoles, hearing aids, power tools, televisions, lighting equipment, toys, medical equipment, and robots. Furthermore, electric transport equipment, power storage devices, power tools, and electric unmanned aerial vehicles, which will be described later, can also be included in the category of electronic devices in a broad sense.

[0082] Examples of electric transportation devices include electric vehicles (including hybrid vehicles), electric motorcycles, electrically assisted bicycles, electric buses, electric carts, automated guided vehicles (AGVs), and railroad cars. Electric passenger aircraft and unmanned electric aircraft for transportation are also included. The secondary battery according to the present invention can be used not only as a driving power source for these devices, but also as an auxiliary power source and a power source for energy regeneration.

[0083] Examples of the power storage device include commercial or home power storage modules, and power storage power sources for buildings such as homes, buildings, and offices, or for power generation facilities.

[0084] (3) Power tools An example of an electric screwdriver as a power tool to which the present invention can be applied will be described briefly with reference to Fig. 8. An electric screwdriver 431 is provided with a motor 433 that transmits rotational power to a shaft 434 and a trigger switch 432 that is operated by the user. A battery pack 430 and a motor control unit 435 according to the present invention are housed in a housing below the handle of the electric screwdriver 431. The battery pack 430 is either built into the electric screwdriver 431 or is detachable.

[0085] The battery pack 430 and the motor control unit 435 may each be provided with a microcomputer (not shown) so that they can communicate with each other regarding charging and discharging of the battery pack 430. The motor control unit 435 controls the operation of the motor 433 and can cut off the power supply to the motor 433 in the event of an abnormality such as over-discharge.

[0086] (4) Energy storage system for electric vehicles As an example of applying the present invention to a power storage system for an electrically powered vehicle, a configuration example of a hybrid vehicle (HV) employing a series hybrid system is shown schematically in Fig. 9. A series hybrid system is a vehicle that runs on an electric power driving force conversion device using electric power generated by a generator powered by an engine, or electric power that is temporarily stored in a battery.

[0087] This hybrid vehicle 600 is equipped with an engine 601, a generator 602, an electric power driving force conversion device 603 (a DC motor or an AC motor, hereinafter simply referred to as "motor 603"), driving wheels 604a, 604b, wheels 605a, 605b, a battery 608, a vehicle control device 609, various sensors 610, and a charging port 611. As the battery 608, the battery pack 300 of the present invention or a power storage module equipped with a plurality of secondary batteries of the present invention can be applied.

[0088] The motor 603 is operated by power from the battery 608, and the rotational force of the motor 603 is transmitted to the drive wheels 604a and 604b. The rotational force produced by the engine 601 can be used to generate power in the generator 602, which can be stored in the battery 608. Various sensors 610 control the engine speed via the vehicle control device 609 and the opening of a throttle valve (not shown).

[0089] When hybrid vehicle 600 is decelerated by a braking mechanism (not shown), the resistance force generated during deceleration is applied to motor 603 as a rotational force, and regenerative power generated by this rotational force is stored in battery 608. Battery 608 can be charged by connecting to an external power source via a charging port 611 of hybrid vehicle 600. Such an HV vehicle is called a plug-in hybrid vehicle (PHV or PHEV).

[0090] The secondary battery according to the present invention can also be applied to a miniaturized primary battery and used as a power source for a tire pressure monitoring system (TPMS) built into the wheels 604 and 605.

[0091] Although the above description has been given using a series hybrid vehicle as an example, the present invention can also be applied to a parallel hybrid vehicle that uses both an engine and a motor, or a hybrid vehicle that combines a series and parallel hybrid system. Furthermore, the present invention can also be applied to electric vehicles (EVs or BEVs) that run only on a drive motor without an engine, and fuel cell vehicles (FCVs).

[0092] The present invention includes the following preferred embodiments. <1> an electrode winding body having a structure in which a strip-shaped positive electrode and a strip-shaped negative electrode are stacked and wound with a separator interposed therebetween; a battery can containing the electrode winding body and having one open end; a battery cover provided at the one end of the battery can and having two or more openings; A cylindrical secondary battery having the two or more openings have a non-overlapping shape when rotated in a top view such that they do not overlap with the two or more openings before rotation, even when rotated by more than 0° and less than 360° around an axis of a cylindrical shape of the secondary battery; The battery lid has a cleavage mark at one of the joints between two adjacent openings of the two or more openings. <2> the two or more openings extend in a rotational direction about the axis; <1> The cylindrical secondary battery according to claim 1. <3> The two or more openings are arranged in concentric circular regions. <1> or <2> The cylindrical secondary battery according to claim 1. <4> The two or more openings are arranged along a rotational direction about the axis. <1> ~ <3> 1. The cylindrical secondary battery according to claim 1, <5> the battery lid has a central region including a protruding portion protruding toward the opposite side of the electrode winding body in the axial direction and an annular flange portion disposed around the protruding portion, and the two or more openings are formed in a side surface of the protruding portion. <1> ~ <4> 1. The cylindrical secondary battery according to claim 1, <6> The non-overlapping form during rotation is based on non-uniform division of the openings, and the openings include two or more types of openings having different opening dimensions. <1> ~ <5> 1. The cylindrical secondary battery according to claim 1, <7> The non-overlapping configuration during rotation is based on the asymmetric shapes of the openings, and the openings include an opening having a tapered shape at one end that tapers in a counterclockwise direction and an opening having a tapered shape at one end that tapers in a clockwise direction. <1> ~ <6> 1. The cylindrical secondary battery according to claim 1, <8> The one joint where the cleavage mark is arranged is the joint that will be subjected to the greatest load due to gas being ejected from inside the cylindrical secondary battery. <1> ~ <7> 1. The cylindrical secondary battery according to claim 1, <9> The aperture ratio of the two openings is 5.0% or more and 12.0% or less with respect to the radial area of ​​the battery. <1> ~ <8> 1. The cylindrical secondary battery according to claim 1, <10> The battery lid is made of a metal material selected from the group consisting of iron, stainless steel, aluminum, and alloys thereof. <1> ~ <9> 1. The cylindrical secondary battery according to claim 1, <11> <1> ~ <10> 10. An electronic device having the cylindrical secondary battery according to any one of claims 1 to 9. <12> <1> ~ <10> An electric power tool having the cylindrical secondary battery according to any one of the preceding claims. [Example]

[0093] [Examples 1 to 8 and Comparative Examples 1 to 6] In each of the examples and comparative examples, cylindrical secondary batteries were manufactured using common materials in accordance with the above-mentioned "Manufacturing method for cylindrical secondary battery", except that a battery lid having the configuration and structure shown in Table 1 was used.

[0094] In each of the examples and comparative examples, the detailed dimensions, shapes and arrangements of the openings in the battery lids are as follows: The radius r of the battery lid 14 was 8.1 mm, and the thickness t2 of the protruding portion 141 of the battery lid 14 was 0.4 mm.

[0095] Example 1 The battery cover 14 shown in FIG. 2 was used. The opening angle α1 of the opening 200a1 relative to the opening dimension x1 is 90°. Distance r1 from the axis (center) of the opening 200a1 = 0.5 × r The radial width of the opening 200a1 is w1=0.133×r The opening angle α2 of the opening 200b1 relative to the opening dimension x1 is 90°. Distance r1 (not shown) from the axis (center) of opening 200b1 = 0.5 × r The radial width w1 (not shown) of the opening 200b1 = 0.133 × r The opening angle α3 of the opening 200c1 relative to the opening dimension x2 is 40°. Distance r1 (not shown) from the axis (center) of the opening 200c1 = 0.5 × r The radial width w1 (not shown) of the opening 200c1 = 0.133 × r The opening angle α4 of the opening 200d1 relative to the opening dimension x2 is 40°. Distance r1 (not shown) from the axis (center) of the opening 200d1 = 0.5 × r The radial width w1 (not shown) of the opening 200d1 = 0.133 × r Thickness of cleavage mark 145 t1 = 0.2 × t2

[0096] Example 2 The battery cover 14 shown in FIG. 3 was used. The opening angle β1 of the opening 200a2 with respect to the opening dimension x3 is 60°. Distance r1 from the axis (center) of the opening 200a2 = 0.5 × r The radial width of the opening 200a2 is w1=0.133×r The opening angle β2 of the opening 200b2 with respect to the opening dimension x3 is 60°. Distance r1 (not shown) from the axis (center) of the opening 200b2 = 0.5 × r The radial width w1 (not shown) of the opening 200b2 = 0.133 × r The opening angle β3 of the opening 200c2 with respect to the opening dimension x3 is 60°. Distance r1 (not shown) from the axis (center) of the opening 200c2 = 0.5 × r The radial width w1 (not shown) of the opening 200c2 = 0.133 × r The opening angle β4 of the opening 200d2 with respect to the opening dimension x3 is 60°. Distance r1 (not shown) from the axis (center) of the opening 200d2 = 0.5 × r The radial width w1 (not shown) of the opening 200d2 = 0.133 × r Thickness of cleavage mark 145 t1 = 0.2 × t2

[0097] Example 3 A battery cover similar to that of Example 1 was used, except that the dimension W1=0.133×r was changed to the dimension W1=0.148×r.

[0098] Example 4 A battery cover similar to that of Example 1 was used, except that the dimension W1=0.133×r was changed to the dimension W1=0.160×r.

[0099] Example 5 A battery cover similar to that of Example 2 was used, except that the dimension W1=0.133×r was changed to the dimension W1=0.148×r.

[0100] Example 6 A battery cover similar to that of Example 2 was used, except that the dimension W1=0.133×r was changed to the dimension W1=0.160×r.

[0101] Example 7 A battery cover similar to that in Example 1 was used, except that the constituent material was changed to stainless steel.

[0102] Example 8 A battery cover similar to that in Example 1 was used, except that the constituent material was changed to aluminum.

[0103] Comparative Example 1 The battery cover used was shown in Fig. 10. In Fig. 10, openings 800a to 800c had the same dimensions and shape, and were arranged at equal intervals in the circumferential direction around the axis of the cylindrical shape of the secondary battery. The opening angle α11 of the opening dimensions of the openings 800a to 800c = 80° Distance r11 from the axis (center) of the openings 800a to 800c = 0.5 × r The radial width w11 of the openings 800a to 800c = 0.133 × r

[0104] Comparative Example 2 The battery cover used was shown in Fig. 11. In Fig. 11, openings 900a to 900d had the same dimensions and shape, and were arranged at equal intervals in the circumferential direction around the axis of the cylindrical shape of the secondary battery. The opening angle α12 of the openings 900a to 900d is 60°. Distance r12 from the axis (center) of the openings 900a to 900d = 0.5 × r The radial width w12 of the openings 900a to 900d = 0.133 × r

[0105] Comparative Example 3 A battery cover similar to that of Comparative Example 1 was used, except that a cleavage mark having a thickness of 0.2×t2 was provided at the joint between the opening 800a and the opening 800b.

[0106] Comparative Example 4 A battery cover similar to that of Comparative Example 2 was used, except that a cleavage mark having a thickness of 0.2×t2 was provided at the joint between opening 900a and opening 900b.

[0107] Comparative Example 5 A battery cover similar to that of Example 1 was used, except that no tear mark was provided.

[0108] Comparative Example 6 A battery cover similar to that of Example 2 was used, except that no tear mark was provided.

[0109] [evaluation] The above examples and comparative examples were subjected to a combustion test and a drop test.

[0110] Flammability test: The flammability test was based on the UL 1642 projectile test. The flammability test was designed to evaluate the projectile ejection of batteries, and if a projectile ejection occurred, the battery was deemed to have failed. A passing rate of 90% or more in the flammability test was deemed "no problem for practical use (△)," and a passing rate of less than 90% in the flammability test was deemed "problem for practical use (×)." In particular, a passing rate of 92% or more was deemed "good (○)," and a passing rate of 95% or more was deemed "excellent (◎)." 100 batteries were tested.

[0111] Drop test: The passing condition was that a battery with a battery voltage of 4.4V was dropped 100 times from a height of 10m without even a slight leakage of the electrolyte inside the battery. The number of tests was 100. The evaluation criteria were as follows: a passing rate of 80% or more was deemed "no problem in practical use (△)", and a passing rate of less than 80% was deemed "problem in practical use (×)". In particular, a passing rate of 90% or more was deemed "good (○)", and a passing rate of 95% or more was deemed "excellent (◎)".

[0112] [Table 1]

[0113] Comparison of Examples 1 to 8 with Comparative Examples 1 to 6 revealed the following points. The battery cover has a gas vent opening that is non-overlapping when rotated (non-equally divided or asymmetrical) and is stamped with a cleavage mark, which prevents the battery from bursting out in the event of a battery abnormality, improving the pass rate of the combustion test and enhancing safety.

[0114] Comparison of Examples 1 to 3, 5 and 7 with Examples 4, 6 and 8 revealed the following points. By keeping the opening ratio between 8.0% and 10.0% and using iron or stainless steel as the material for the battery cover, we have improved safety while maintaining strength characteristics. [Industrial Applicability]

[0115] The secondary battery according to the present invention can be used in various fields where power storage is expected. For example, the secondary battery according to the present invention, particularly the nonaqueous electrolyte secondary battery, can be used in the electrical, information, and communications fields where mobile devices are used (e.g., mobile devices such as mobile phones, smartphones, smart watches, laptops, digital cameras, activity monitors, arm computers, and electronic paper), household and small industrial applications (e.g., power tools, golf carts, and household, nursing care, and industrial robots), large industrial applications (e.g., forklifts, elevators, and harbor cranes), transportation systems (e.g., hybrid cars, electric cars, buses, trains, electrically assisted bicycles, and electric motorcycles), power system applications (e.g., various power generation systems, road conditioners, smart grids, and general-purpose household power storage systems), medical applications (e.g., medical devices such as earphones and hearing aids), pharmaceutical applications (e.g., medication management systems), IoT, and space and deep-sea applications (e.g., space probes and submersible research vessels).

Claims

1. an electrode winding body having a structure in which a strip-shaped positive electrode and a strip-shaped negative electrode are stacked and wound with a separator interposed therebetween; a battery can containing the electrode winding body and having one open end; a battery cover provided at the one end of the battery can and having two or more openings; A cylindrical secondary battery having the two or more openings have a non-overlapping shape when rotated in a top view such that they do not overlap with the two or more openings before rotation, even when rotated by more than 0° and less than 360° around an axis of a cylindrical shape of the secondary battery; The battery lid has a cleavage mark at one of the joints between two adjacent openings of the two or more openings.

2. The cylindrical secondary battery according to claim 1 , wherein the two or more openings extend in a rotational direction around the axis.

3. The cylindrical secondary battery according to claim 1 , wherein the two or more openings are arranged in concentric circular regions.

4. The cylindrical secondary battery according to claim 1 , wherein the two or more openings are arranged along a rotational direction around the axis.

5. 2. The cylindrical secondary battery according to claim 1, wherein the battery lid has a central region including a protruding portion that protrudes toward the opposite side of the electrode winding body in the axial direction and an annular flange portion that is disposed around the protruding portion, and the two or more openings are provided in a side surface of the protruding portion.

6. The cylindrical secondary battery according to claim 1 , wherein the non-overlapping configuration during rotation is based on non-uniform division of the openings, and the openings include two or more types of openings having different opening dimensions.

7. 2. The cylindrical secondary battery according to claim 1, wherein the non-overlapping configuration during rotation is based on the asymmetric shapes of the openings, and the openings include an opening having a tapered shape at one end that tapers in a counterclockwise direction and an opening having a tapered shape at one end that tapers in a clockwise direction.

8. 2. The cylindrical secondary battery according to claim 1, wherein the one joint where the cleavage mark is located is the joint that receives the greatest load due to gas being ejected from inside the cylindrical secondary battery.

9. 2. The cylindrical secondary battery according to claim 1, wherein an opening ratio of the two openings is 5.0% to 12.0% of the area of ​​the battery in the radial direction.

10. 2. The cylindrical secondary battery according to claim 1, wherein the battery lid is made of a metal material selected from the group consisting of iron, stainless steel, aluminum, and alloys thereof.

11. An electronic device comprising the cylindrical secondary battery according to any one of claims 1 to 10.

12. An electric power tool comprising the cylindrical secondary battery according to any one of claims 1 to 10.

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