Secondary batteries and electrical equipment

Abstract

This application discloses a secondary battery and an electrical device. The secondary battery includes a casing and an electrode assembly, with the electrode assembly housed within the casing. The casing is a metal shell, and its orthographic projection along a first direction has a notch, the first direction being the thickness direction of the secondary battery. The casing includes a first wall located on one side of the secondary battery along its thickness direction. The first wall includes a first portion, the orthographic projection of which is formed by a first arc segment, a second arc segment, a first straight segment, and a second straight segment. A groove is provided on the side of the first wall opposite to the electrode assembly. The groove includes at least a first groove segment and a second groove segment connected together, with at least a portion of the first groove segment located in the first portion. The orthographic projection of the first groove segment along the first direction is an arc segment. Viewed along the first direction, the line connecting the center of the first groove segment to the base point does not intersect the first groove segment, and the second groove segment extends in a direction away from the notch. This facilitates an increase in the pressure relief rate.

Description

Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to a secondary battery and electrical equipment. Background Technology

[0002] In existing technologies, steel-cased battery cells often have pressure relief grooves to ensure that the cell can burst open and release pressure promptly when the internal pressure exceeds the safe pressure. Steel-cased battery cells can be square or irregularly shaped. Some irregularly shaped steel-cased cells are formed by creating notches in square steel-cased cells, such as at corners. Currently, the pressure relief grooves in these irregularly shaped steel-cased cells have a problem where the pressure relief rate is too slow after bursting, making the cell prone to ignition. Summary of the Invention

[0003] Regarding existing secondary batteries, the inventors discovered that the pressure relief grooves of these irregularly shaped steel-cased cells are not located in the stress concentration area of ​​the outer shell when the internal pressure exceeds the safe pressure. Furthermore, the orientation of the pressure relief grooves toward the notch is not conducive to expanding the burst crack after the burst, resulting in a smaller pressure relief opening formed by the burst crack and a slower pressure relief rate when the pressure relief groove bursts.

[0004] In view of the above situation, it is necessary to provide a secondary battery that can improve the pressure relief rate.

[0005] This application provides a secondary battery, including a casing and an electrode assembly housed within the casing. The casing is a metal shell, and its orthographic projection along a first direction has a notch, the first direction being the thickness direction of the secondary battery. The orthographic projection of the casing along the first direction includes at least a first side, a second side, a third side, and a fourth side connected in sequence. The boundary of the notch includes the second side and the third side. The first included angle between the second side and the third side is α, and the second included angle between the second side and the third side is β. The first included angle and the second included angle are complementary angles, where 0° < α < 180° and 180° < β < 360°. The casing includes a first wall located on one side of the secondary battery along the thickness direction. The first wall includes a first portion, the orthographic projection of which along the first direction is formed by a first arc segment, a second arc segment, a first straight line segment, and a second straight line segment. Define the intersection of the extensions of the second and third sides as the base point. Define the angle bisector of the angle between the extensions of the second and third sides as the reference line. The reference line includes a first segment extending from the base point within the first angle. The distance between the base point and the first side along the extension direction of the second side is L1, and the distance between the base point and the fourth side along the extension direction of the third side is L2, where L2 ≥ L1. The center of the first arc segment is located on the first segment, the radius of the first arc segment is L2, and the distance between the center of the first arc segment and the base point is L2. The center of the second arc segment is located on the first segment, the radius of the second arc segment is L2, and the distance between the center of the second arc segment and the base point is L2 - L1. A first straight line segment connects the endpoints of the first and second arc segments located on one side of the reference line. A second straight line segment connects the endpoints of the first and second arc segments located on the other side of the reference line. The extension of the first straight line segment passes through the midpoint of the second side and is parallel to the reference line. The extension of the second straight line segment passes through the midpoint of the third side and is parallel to the reference line. A groove is provided on the side of the first wall away from the electrode assembly. The groove includes at least a first groove segment and a second groove segment connected together, with at least a portion of the first groove segment located in the first part. Along the first direction, the orthographic projection of the first groove segment is an arc segment. The second groove segment includes a first end and a second end, with the first end connecting to the first groove segment and the second end being the end of the groove. Viewed along the first direction, the line connecting the center of the first groove segment and the base point does not intersect the first groove segment. The second groove segment extends from the first end in a direction away from the notch.

[0006] For a secondary battery with a notch in the orthographic projection of its casing along a first direction, when the internal pressure exceeds the safe pressure, the stress is mainly concentrated in the first part of the first wall. By providing at least a portion of the first groove in the first part, the groove can be positioned in the stress concentration area of ​​the casing when the internal pressure exceeds the safe pressure. Furthermore, the line connecting the center of the first groove to the base point does not intersect the first groove, and the second groove extends from the first end in a direction away from the notch. The second groove helps to enlarge the burst crack, thereby making the pressure relief port formed by the burst crack larger. This helps to improve the pressure relief rate.

[0007] In one or more of the above embodiments, the orthographic projection of the second groove segment along the first direction is a straight line segment. In this case, when the groove bursts open, it can increase the rate at which the burst crack expands, which is beneficial to further increase the pressure relief rate.

[0008] In one or more of the above embodiments, the length of the second groove segment is S1, and the orthographic projection length of the second groove segment on the reference line is S2, where 1≤S1 / S2≤1.5. When the internal pressure exceeds the safe pressure, the first wall bulges under pressure and deforms in the thickness direction. The reference line passes through the area with the largest thickness difference in a relatively short distance. By setting 1≤S1 / S2≤1.5, the deviation of the second groove segment from the reference line is kept within a suitable range, which facilitates the rapid formation of burst cracks in the second groove segment and helps to further improve the pressure relief rate.

[0009] In one or more of the above embodiments, 1≤S1 / S2≤1.2. By setting 1≤S1 / S2≤1.2, the deviation of the second groove segment from the reference line is kept within a smaller range, which facilitates the formation of burst cracks in the second groove segment more quickly, and is conducive to further improving the pressure relief rate.

[0010] In one or more of the above embodiments, 0.5mm ≤ S2 ≤ 0.5L1. By setting 0.5mm ≤ S2, the second groove segment is not too short, which facilitates the formation of a larger pressure relief port through bursting cracks, thus further improving the pressure relief rate. By setting S2 ≤ 0.5L1, while ensuring a certain pressure relief rate, the second groove segment is not too long, which helps to improve the processing efficiency of the groove and the structural strength of the first wall.

[0011] In one or more of the above embodiments, the distance between the midpoint of the first groove segment and the base point is D, where 0mm≤D≤5mm. When the internal pressure exceeds the safe pressure, the stress in the first part of the first wall becomes more concentrated closer to the base point. By setting 0mm≤D≤5mm, the first groove segment is closer to the base point, which allows the burst crack after the first groove segment bursts to form a larger pressure relief port, which is beneficial to further improve the pressure relief rate.

[0012] In one or more of the above embodiments, the entire first tank section is located in the first part. This is beneficial for further improving the pressure relief rate.

[0013] In one or more of the above embodiments, the first end is connected to the endpoint of the first slot segment. In this case, when the internal pressure exceeds the safe pressure, it is easier for the burst crack to extend from the first slot segment to the second slot segment, which is beneficial to further improve the pressure relief rate.

[0014] In one or more of the above embodiments, the two endpoints of the first groove segment are located on different sides of the straight line connecting the center of the first groove segment and the base point. In this case, when the internal pressure exceeds the safe pressure, it is convenient for both ends of the first groove segment to quickly form burst cracks, which is beneficial to further improve the depressurization rate.

[0015] In one or more of the above embodiments, there are two second groove segments. By setting two second groove segments, the burst cracks in the second groove segments can form larger pressure relief ports, which is beneficial to further improve the pressure relief rate.

[0016] A second aspect of this application provides an electrical device including the secondary battery of the first aspect of this application. The secondary battery of the first aspect of this application can increase the pressure relief rate when the groove bursts, thus improving the safety of the electrical device. Attached Figure Description

[0017] Figure 1 This is a front view of a secondary battery provided in an embodiment of this application.

[0018] Figure 2 This is a top view of a secondary battery provided in an embodiment of this application.

[0019] Figure 3 for Figure 2 A magnified view of the area where the gap is located.

[0020] Figure 4 This is a schematic diagram illustrating the determination of a first part according to an embodiment of this application.

[0021] Figure 5 A schematic diagram of a groove provided for another embodiment of this application.

[0022] Figure 6 This is a schematic diagram of a groove provided in yet another embodiment of this application.

[0023] Figure 7 This is a schematic diagram of an electrical device provided in an embodiment of this application.

[0024] Explanation of main component symbols 100. Secondary battery; 10. Outer casing; 101. First side; 102. Second side; 103. Third side; 104. Fourth side; 105. Reference line; 1051. First segment; 11. Cover; 12. Casing; 121. Bottom wall; 122. Side wall; 13. Notch; 14. First wall; 141. First part; 1411. First arc segment; 1412. Second arc segment; 1413. First straight segment; 1414. Second straight segment; 142. Groove; 1421. First groove segment; 1422. Second groove segment; 1422a. First end; 1422b. Second end; 15. Terminal post; 1000. Electrical equipment; X. First direction. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0026] It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or may also have a component that is centrally located. When a component is considered to be "set" on another component, it can be directly set on the other component or may also have a component that is centrally located.

[0027] Unless otherwise stated, the term "multiple" as used herein refers to two or more.

[0028] The terms “first”, “second”, etc., are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implying the quantity, specific order, or primary and secondary relationship of the indicated technical features.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0030] It should be understood that the "orthographic projection" used in this application is an orthographic projection of one or two components along a certain direction.

[0031] Embodiments of this application provide a secondary battery, including a casing and an electrode assembly housed within the casing. The casing is a metal shell, and its orthographic projection along a first direction has a notch, the first direction being the thickness direction of the secondary battery. The orthographic projection of the casing along the first direction includes at least a first side, a second side, a third side, and a fourth side connected in sequence. The boundary of the notch includes the second side and the third side. The first included angle between the second side and the third side is α, and the second included angle between the second side and the third side is β. The first included angle and the second included angle are complementary angles, where 0° < α < 180° and 180° < β < 360°. The casing includes a first wall located on one side of the secondary battery along the thickness direction. The first wall includes a first portion, the orthographic projection of which is formed by a first arc segment, a second arc segment, a first straight line segment, and a second straight line segment. Define the intersection of the extensions of the second and third sides as the base point. Define the angle bisector of the angle between the extensions of the second and third sides as the reference line. The reference line includes a first segment extending from the base point within the first angle. The distance between the base point and the first side along the extension direction of the second side is L1, and the distance between the base point and the fourth side along the extension direction of the third side is L2, where L2 ≥ L1. The center of the first arc segment is located on the first segment, the radius of the first arc segment is L2, and the distance between the center of the first arc segment and the base point is L2. The center of the second arc segment is located on the first segment, the radius of the second arc segment is L2, and the distance between the center of the second arc segment and the base point is L2 - L1. A first straight line segment connects the endpoints of the first and second arc segments located on one side of the reference line. A second straight line segment connects the endpoints of the first and second arc segments located on the other side of the reference line. The extension of the first straight line segment passes through the midpoint of the second side and is parallel to the reference line. The extension of the second straight line segment passes through the midpoint of the third side and is parallel to the reference line. A groove is provided on the side of the first wall away from the electrode assembly. The groove includes at least a first groove segment and a second groove segment connected together, with at least a portion of the first groove segment located in the first part. Along the first direction, the orthographic projection of the first groove segment is an arc segment. The second groove segment includes a first end and a second end, with the first end connecting to the first groove segment and the second end being the end of the groove. Viewed along the first direction, the line connecting the center of the first groove segment and the base point does not intersect the first groove segment. The second groove segment extends from the first end in a direction away from the notch.

[0032] This application addresses a secondary battery with a notch in the orthographic projection of its casing along a first direction. When the internal pressure exceeds the safe pressure and the casing expands and deforms, the stress is primarily concentrated in the first portion of the first wall. By providing at least a portion of the first groove in the first portion, the groove can be positioned in the stress concentration area of ​​the casing when the internal pressure exceeds the safe pressure. Furthermore, the line connecting the center of the first groove to the base point does not intersect the first groove, and the second groove extends from the first end in a direction away from the notch. The second groove facilitates the widening of the burst crack, thereby increasing the pressure relief opening formed by the burst crack. This, in turn, improves the pressure relief rate.

[0033] Some embodiments of this application will now be described with reference to the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0034] Please see Figure 1 This application provides a secondary battery 100, including a housing 10 and an electrode assembly (not shown), the electrode assembly being housed within the housing 10. The housing 10 has a receiving cavity for housing the electrode assembly within the housing 10. The receiving cavity is filled with an electrolyte, the electrolyte comprising an electrolyte salt. The electrolyte salt comprises at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the electrolyte salt includes, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium hexafluorocesium oxide (LiCsF6), lithium perchlorate (LiClO4), or lithium trifluoromethanesulfonate (LiCF3SO3).

[0035] The outer casing 10 is a metal casing, which includes, but is not limited to, steel, copper, and nickel casings. Please refer to [link / reference]. Figure 1 In some embodiments, the outer casing 10 includes a cover 11 and a housing 12, which are fixedly connected along a first direction X, where X is the thickness direction of the secondary battery 100. In this case, the metal materials of the cover 11 and the housing 12 may be the same or different, and the fixed connection between the cover 11 and the housing 12 includes, but is not limited to, welding, bonding, and riveting. This application does not impose any restrictions on these methods.

[0036] The cover 11 and the housing 12 together form a receiving cavity. In some embodiments, both the cover 11 and the housing 12 are recessed structures. The recessed structure includes a bottom wall 121 and a side wall 122, the side wall 122 connecting to the periphery of the bottom wall 121, and the side wall 122 and the bottom wall 121 enclosing each other to form a recess. See also... Figure 1 In some embodiments, the cover 11 is a plate-like structure, the housing 12 is a recessed structure, and the cover 11 covers the recess along the first direction X.

[0037] Please see Figure 2The outer casing 10 has a notch 13 in its orthographic projection along the first direction X. The orthographic projection of the outer casing 10 along the first direction X includes at least a first side 101, a second side 102, a third side 103, and a fourth side 104 connected in sequence. The boundary of the notch 13 includes the second side 102 and the third side 103. The first included angle between the second side 102 and the third side 103 is α, and the second included angle between the second side 102 and the third side 103 is β. The first and second included angles are complementary angles, where 0° < α < 180° and 180° < β < 360°. For example, α is 5°, 10°, 20°, 50°, 70°, 90°, 120°, 150°, 175°, or any value between the listed endpoints, and β corresponds to 355°, 350°, 340°, 310°, 290°, 270°, 240°, 210°, 185°, or any value between the listed endpoints. Along the extension direction of the second side 102, the first side 101 and the third side 103 are located on different sides of the extension line of the second side 102, and along the extension direction of the third side 103, the second side 102 and the fourth side 104 are located on different sides of the extension line of the third side 103. It should be understood that when the second side 102 and the third side 103 are directly connected, the first included angle is the angle between the second side 102 and the third side 103; when the second side 102 and the third side 103 are connected by a rounded transition, the first included angle is the angle between the extension lines of the second side 102 and the third side 103.

[0038] In this application, the number of notches 13 can be multiple. Correspondingly, the orthographic projection of the outer shell 10 along the first direction X can include multiple sets of structures in which the first side 101, the second side 102, the third side 103 and the fourth side 104 are connected in sequence.

[0039] The outer casing 10 includes a first wall 14 located on one side of the secondary battery 100 in the thickness direction. The first wall 14 can be a plate-like casing 11 or a recessed bottom wall 121, and this application is not limited in this regard. The thickness of the first wall 14 can be from 75 μm to 200 μm. For example, the thickness of the first wall 14 is 75 μm, 80 μm, 90 μm, 100 μm, 120 μm, 150 μm, 200 μm, or any value between the listed endpoints.

[0040] Please refer to the following: Figure 2 and Figure 3 The first wall 14 includes a first portion 141, the orthographic projection of which along the first direction X is formed by a first arc segment 1411, a second arc segment 1412, a first straight line segment 1413, and a second straight line segment 1414. For example... Figure 3As shown, the intersection of the extensions of the second side 102 and the third side 103 is defined as the base point O0. The angle bisector of the angle between the extensions of the second side 102 and the third side 103 is defined as the reference line 105. The reference line 105 includes a first segment 1051 extending from the base point O0 within the first angle. The distance between the base point O0 along the extension direction of the second side 102 and the first side 101 is L1, and the distance between the base point O0 along the extension direction of the third side 103 and the fourth side 104 is L2, where L2 ≥ L1. The positions of the first arc segment 1411, the second arc segment 1412, the first straight line segment 1413, and the second straight line segment 1414 are determined by the following relationship: The center O1 of the first arc segment 1411 is located on the first segment 1051, the radius of the first arc segment 1411 is L2, and the distance between the center O1 of the first arc segment 1411 and the base point O0 is L2. The center O2 of the second arc segment 1412 is located on the first segment 1051, the radius of the second arc segment 1412 is L2, and the distance between the center O2 of the second arc segment 1412 and the base point O0 is L2-L1. It can be understood that when L2 = L1, the center O2 of the second arc segment 1412 is located on the base point O0. The first straight line segment 1413 connects the endpoints of the first arc segment 1411 and the second arc segment 1412 located on one side of the reference line 105. The second straight line segment 1414 connects the endpoints of the first arc segment 1411 and the second arc segment 1412 located on the other side of the reference line 105. The extension of the first straight line segment 1413 passes through the midpoint of the second side 102 and is parallel to the reference line 105. The extension of the second straight line segment 1414 passes through the midpoint of the third side 103 and is parallel to the reference line 105.

[0041] Please see Figure 4In some embodiments, the first arc segment 1411, the second arc segment 1412, the first straight line segment 1413, and the second straight line segment 1414 can be determined as follows: a first circle is drawn with a point on a portion of the reference line 105 located within the angle between the second side 102 and the third side 103, at a distance L2 from the base point O0, as the center and L2 as the radius; a second circle is drawn with a point on a portion of the reference line 105 located within the angle between the second side 102 and the third side 103, at a distance L2-L1 from the base point O0, as the center and L2 as the radius; a first straight line parallel to the reference line 105 is drawn through the midpoint of the second side 102, and a second straight line parallel to the reference line 105 is drawn through the midpoint of the third side 103. The first circle, the second circle, the first straight line, and the second straight line together form a closed region on the first wall 14. Specifically, the first arc segment 1411 is the portion of the first circle that forms the closed region, the second arc segment 1412 is the portion of the second circle that forms the closed region, the first straight line segment 1413 is the portion of the first straight line that forms the closed region, and the second straight line segment 1414 is the portion of the second straight line that forms the closed region. It should be understood that this application does not limit the manner in which the first arc segment 1411, the second arc segment 1412, the first straight line segment 1413, and the second straight line segment 1414 are determined, nor does it limit the order and manner in which the first circle, the second circle, the first straight line, and the second straight line are constructed; this is merely one example.

[0042] In some embodiments, 5mm ≤ L1 ≤ 50mm, and L1 ≤ L2 ≤ 100mm. For example, L1 is 5mm, 10mm, 15mm, 20mm, 25mm, 30mm, 40mm, 50mm, or any value between the listed endpoint values. As an example, when L1 is 50mm, 50mm ≤ L2 ≤ 100mm, for example, L2 is 50mm, 60mm, 70mm, 80mm, 90mm, 100mm, or any value between the listed endpoint values.

[0043] Please see Figure 3 and Figure 4A groove 142 is provided on the side of the first wall 14 facing away from the electrode assembly. The groove 142 has a depth of 30 μm to 120 μm, for example, a groove depth of 30 μm, 40 μm, 50 μm, 70 μm, 90 μm, 120 μm or any value between the listed endpoints. The groove 142 has a width of 0.05 mm to 0.2 mm, for example, a groove width of 0.05 mm, 0.06 mm, 0.08 mm, 0.1 mm, 0.12 mm, 0.15 mm, 0.2 mm or any value between the listed endpoints. The groove 142 includes at least a first groove segment 1421 and a second groove segment 1422 connected to each other, with at least a portion of the first groove segment 1421 located in the first portion 141. For a secondary battery 100 with a notch 13 in the orthographic projection of the outer casing 10 along the first direction X, when the internal pressure exceeds the safe pressure, the stress is mainly concentrated in the first part 141 of the first wall 14. By providing at least part of the first groove segment 1421 in the first part 141, the groove 142 can be set in the stress concentration area of ​​the outer casing 10 when the internal pressure exceeds the safe pressure, so that the groove 142 can burst open in time to release pressure.

[0044] Along the first direction X, the orthographic projection of the first groove segment 1421 is an arc segment. It should be understood that, since the groove 142 has a certain groove width, the statement that the orthographic projection of the first groove segment 1421 along the first direction X is an arc segment means that the orthographic projection of the side of the first groove segment 1421 near the notch 13 along the first direction X is an arc segment. The central angle of the first groove segment 1421 can be from 30° to 120°, for example, 30°, 40°, 50°, 60°, 70°, 80°, 90°, 100°, 110°, 120°, or any value between the listed endpoint values. The radius of the first groove segment 1421 can be from 3mm to 20mm, for example, 3mm, 4mm, 6mm, 8mm, 10mm, 12mm, 15mm, 20mm, or any value between the listed endpoint values.

[0045] Along the first direction X, the orthographic projection of the second groove segment 1422 can be a straight line segment or a curved segment. The second groove segment 1422 includes a first end 1422a and a second end 1422b. The first end 1422a connects to the first groove segment 1421, and the second end 1422b is the end of the groove 142. Viewed along the first direction X, the line connecting the center of the first groove segment 1421 and the base point O0 does not intersect the first groove segment 1421, and the second groove segment 1422 extends from the first end 1422a in a direction away from the notch 13. In this case, the second groove segment 1422 is beneficial for enlarging the burst crack, thereby enabling a larger pressure relief port formed by the burst crack. This is beneficial for improving the pressure relief rate. As an example, Figure 3The diagram schematically shows the second groove segment 1422 as a straight line segment projected along the first direction X. In this case, when the groove 142 bursts open, it can increase the rate at which the burst crack expands, which is beneficial to further increase the pressure relief rate.

[0046] It should be understood that the center of the first groove segment 1421 can be determined as follows: draw a straight line segment connecting the two endpoints of the arc segment of the first groove segment 1421, draw a perpendicular line from the midpoint of the straight line segment to the straight line segment, and determine a point on the perpendicular line. This point satisfies the condition that the distance between this point and the endpoint of the arc segment of the first groove segment 1421 is equal to the distance between this point and the midpoint of the arc segment of the first groove segment 1421. This point is the center of the first groove segment 1421.

[0047] It should be understood that the extension of the second groove segment 1422 from the first end 1422a in the direction away from the gap 13 means extending the second side 102 in the direction away from the first side 101 and extending the third side 103 in the direction away from the fourth side 104. The second groove segment 1422 extends from the first end 1422a between the extension of the second side 102 and the extension of the third side 103.

[0048] In some embodiments, the midpoint O3 of the first groove segment 1421 is located in the first portion 141. It should be understood that the midpoint of the first groove segment 1421 refers to the midpoint of the side of the first groove segment 1421 closest to the notch 13 in the groove width direction.

[0049] In some embodiments, the two endpoints of the first groove segment 1421 are located on different sides of the straight line connecting the center of the first groove segment 1421 and the base point O0. In this case, when the internal pressure exceeds the safe pressure, it is convenient for both ends of the first groove segment 1421 to quickly form burst cracks, which is beneficial to further improve the depressurization rate.

[0050] Please see Figure 5 In some embodiments, the distance between the midpoint O3 of the first groove segment 1421 and the base point O0 is D, where 0mm ≤ D ≤ 5mm. For example, D can be 0mm, 1mm, 2mm, 3mm, 4mm, 5mm, or any value between the listed endpoints. When the internal pressure exceeds the safe pressure, the stress in the first portion 141 of the first wall 14 becomes more concentrated closer to the base point O0. By setting 0mm ≤ D ≤ 5mm, the first groove segment 1421 is closer to the base point O0, which allows the burst crack of the first groove segment 1421 to form a larger pressure relief port, thus further improving the pressure relief rate.

[0051] In some embodiments, the shortest distance between the midpoint O3 of the first groove segment 1421 and the reference line 105 is 0 mm to 0.5L1. As an example, when L1 = 50 mm, the shortest distance between the midpoint O3 of the first groove segment 1421 and the reference line 105 is 0 mm to 25 mm, for example, 0 mm, 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, or any value between the listed endpoint values. It should be understood that the length of a line segment perpendicular to the reference line 105 drawn through the midpoint O3 of the first groove segment 1421 is the shortest distance referred to herein.

[0052] In some embodiments, the entire first groove segment 1421 is disposed in the first portion 141. For example, when the groove 142 is composed of the first groove segment 1421 and the second groove segment 1422, at least the entire first groove segment 1421 is disposed in the first portion 141, and the second groove segment 1422 may or may not be disposed in the first portion 141. This is beneficial for further improving the pressure relief rate.

[0053] Please see Figure 5 In some embodiments, the first end 1422a of the second groove segment 1422 is connected to the end point of the first groove segment 1421. In this case, when the internal pressure exceeds the safe pressure, it is easier for the burst crack to extend from the first groove segment 1421 to the second groove segment 1422, which is beneficial to further improve the depressurization rate.

[0054] Please see Figure 5 In some embodiments, the orthographic projection of the second groove segment 1422 along the first direction X is a straight line segment, the length of the second groove segment 1422 is S1, and the projection length of the second groove segment 1422 on the reference line 105 is S2, where 1 ≤ S1 / S2 ≤ 1.5. For example, the value of S1 / S2 is 1, 1.1, 1.2, 1.3, 1.4, 1.5, or any value between the listed endpoint values. When the internal pressure exceeds the safe pressure, the first wall 14 bulges under pressure and deforms in the thickness direction. The reference line 105 passes through the area with the largest thickness difference in a relatively short distance. By setting 1 ≤ S1 / S2 ≤ 1.5, the deviation of the second groove segment 1422 from the reference line 105 is kept within a suitable range, which facilitates the rapid formation of burst cracks in the second groove segment 1422 and is beneficial to further improve the depressurization rate.

[0055] In some embodiments, 1 ≤ S1 / S2 ≤ 1.2. By setting 1 ≤ S1 / S2 ≤ 1.2, the deviation of the second groove segment 1422 from the reference line 105 is kept within a smaller range, which facilitates the formation of burst cracks in the second groove segment 1422 more quickly, and is conducive to further improving the pressure relief rate.

[0056] In some embodiments, 0.5mm ≤ S2 ≤ 0.5L1. For example, when L1 = 50mm, 0.5mm ≤ S2 ≤ 25mm, where S2 is 0.5mm, 1mm, 2mm, 5mm, 10mm, 15mm, 20mm, 25mm, or any value between the listed endpoints. By setting 0.5mm ≤ S2, the second groove segment 1422 is not too short, facilitating the formation of a larger pressure relief port through bursting cracks, which is beneficial for further improving the pressure relief rate. By setting S2 ≤ 0.5L1, while ensuring a certain pressure relief rate, the second groove segment 1422 is not too long, which is beneficial for improving the processing efficiency of the groove 142 and the structural strength of the first wall 14.

[0057] Please see Figure 6 In some embodiments, there are two second slot segments 1422. By providing two second slot segments 1423, the burst cracks in the second slot segments 1422 can form larger pressure relief vents, which is beneficial to further improve the pressure relief rate. It should be understood that the structural configuration parameters of the two second slot segments 1422 can be the same or different.

[0058] In some embodiments, the two second groove segments 1422 are located on different sides of the axis of symmetry of the arc segment of the first groove segment 1421. In some embodiments, the two second groove segments 1422 are symmetrically arranged on the first groove segment 1421. For example, please refer to... Figure 6 If the first end 1422a of a second slot 1422 is connected to the end point of the first slot 1421, then the first end 1422a of another second slot 1422 is also connected to the end point of the first slot 1421.

[0059] In some embodiments, the entire groove 142 is disposed in the first portion 141. For example, when the groove 142 is composed of a first groove segment 1421 and two second groove segments 1422, both the first groove segment 1421 and the two second groove segments 1422 are disposed in the first portion 141.

[0060] In some embodiments, the electrode assembly includes a positive electrode, a negative electrode, and a separator separating the positive and negative electrode. The positive electrode, negative electrode, and separator can be stacked to form a laminated structure or wound to form a wound structure; this application does not limit this. The positive electrode may have a positive tab, and the negative electrode may have a negative tab, to facilitate the extraction of the positive polarity of the electrode assembly through the positive tab and the extraction of the negative polarity through the negative tab. When the cover 11 and the housing 12 are electrically connected, one of the positive and negative tabs is connected to either the cover 11 or the housing 12, and the other of the positive and negative tabs is connected to an insulated terminal post 15 (see [link to documentation]). Figure 1 and Figure 2When the cover 11 is insulated from the housing 12, one of the positive and negative tabs is connected to the cover 11, and the other of the positive and negative tabs is connected to the housing 12. It should be understood that the positive electrode may not have a positive tab and / or the negative electrode may not have a negative tab, and the polarity of the electrode assembly can be revealed by setting an empty foil area.

[0061] Please see Figure 7 This application also provides an electrical device 1000, which includes the secondary battery 100 involved in any of the foregoing embodiments. The secondary battery 100 of this application can improve the timeliness of pressure relief when the groove 142 bursts, thus improving the safety of the electrical device 1000. The electrical device 1000 includes, but is not limited to, electronic devices such as e-book players, mobile phones, fax machines, copiers, printers, headphones, video recorders, LCD TVs, recorders, radios, cameras, tablets, and laptops.

[0062] To verify the impact of the solution provided in this application on the secondary battery 100, the inventors of this application conducted the following experiment.

[0063] The preparation process of the secondary battery 100 in Example 1 includes the following steps: Preparation of the positive electrode sheet: Lithium cobalt oxide (positive electrode active material), conductive carbon black (conductive agent), and polyvinylidene fluoride (PVDF) (binder) are dissolved in an N-methylpyrrolidone (NMP) solution at a mass ratio of 97.5:1:1.5 to form a positive electrode slurry. Aluminum foil is used as the positive electrode current collector. The positive electrode slurry is coated onto the current collector, and after drying, cold pressing, and slitting, the positive electrode sheet is obtained.

[0064] Preparation of negative electrode sheet: The negative electrode active material artificial graphite, the thickener sodium carboxymethyl cellulose (CMC), and the binder styrene-butadiene rubber (SBR) are mixed in a mass ratio of 96:1.5:2.5, deionized water is added, and the mixture is stirred evenly under the action of a vacuum mixer to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil; after drying, it is then cold-pressed, cut, and slit to obtain the negative electrode sheet.

[0065] Preparation of the diaphragm: The substrate layer of the diaphragm is polyethylene (PE). Alumina ceramic layers are coated on both sides of the substrate layer of the diaphragm. Finally, polyvinylidene fluoride (PVDF) adhesive is coated on both sides of the ceramic layer and then dried.

[0066] Preparation of electrolyte: In a dry argon atmosphere glove box, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of 3:5:2, and lithium salt LiPF6 was added. After mixing evenly, the electrolyte was obtained, wherein the mass percentage concentration of LiPF6 was 12.5%.

[0067] The etching process of groove 142: The shell cover 11 with notch 13 is fixed in a special fixture; the laser etching path is set according to the required etching shape and etching position; the laser energy is adjusted according to the required etching depth and the thickness of the shell cover 11, and the surface of the shell cover 11 is etched using a high-precision laser device. The shell cover 11 is prepared, and the inside of the shell 12 is clean and dust-free. The positive electrode tab is welded to the upper end of the shell 12, and the negative electrode tab is welded to the electrode post 15 insulated on the shell 12, ensuring a good electrical connection; the stacked electrode assembly is placed into the shell 12, ensuring a good fit between the electrode assembly and the shell 12; the shell cover 11 and the shell 12 are assembled and sealed by laser welding to ensure the airtightness of the secondary battery 100. The secondary battery 100 has a length of 70mm, a width of 55mm, and a height of 4.5mm. The second side 102 and the third side 103 are connected by a rounded corner with a radius of 2.5mm, and α is 90°. L1 is 14mm and L2 is 26mm. The shell cover 11 has a thickness of 100μm and a groove depth (i.e., the groove depth of the groove 142) of 66μm. The groove 142 includes a first groove segment 1421 and a second groove segment 1422. The midpoint O3 of the first groove segment 1421 is located on the reference line 105, and the distance D between the midpoint O3 of the first groove segment 1421 and the base point O0 is 0mm. The radius of the first groove segment 1421 is 5mm, and the central angle of the first groove segment 1421 is 90°. The second groove segment 1422 connects to the endpoint of the first groove segment 1421. The second groove segment 1422 is a straight line segment parallel to the reference line 105 and has a length S1 of 5mm.

[0068] The preparation process of the secondary battery 100 in Comparative Example 1 is basically the same as that in Example 1. The difference is that the groove 142 of the secondary battery 100 in Comparative Example 1 only includes the first groove segment 1421, and the first groove segment 1421 is located outside the first part 141. Accordingly, there is no data for S1, S2 and D.

[0069] The preparation process of the secondary battery 100 in Comparative Example 2 is basically the same as that in Example 1. The difference is that the groove 142 of the secondary battery 100 in Comparative Example 2 only includes the first groove segment 1421. Accordingly, there is no data for S1 and S2.

[0070] The preparation process of the secondary battery 100 in Comparative Example 3 is basically the same as that in Example 1. The difference is that the second groove segment 1422 of the secondary battery 100 in Comparative Example 3 does not extend from the first end 1422a in the direction away from the notch 13, and the first end 1422a is located outside the first part 141. Accordingly, there is no data for S1 and S2.

[0071] The preparation process of the secondary battery 100 in Comparative Example 4 is basically the same as that in Example 1. The difference is that the second groove segment 1422 of the secondary battery 100 in Comparative Example 4 does not extend from the first end 1422a in the direction away from the notch 13. Accordingly, there is no data for S1 and S2.

[0072] The preparation process of the secondary battery 100 in Comparative Example 5 is basically the same as that in Example 1. The difference is that the first end 1422a of the secondary battery 100 in Comparative Example 5 is located outside the first part 141.

[0073] The preparation process of the secondary battery 100 in Examples 2 to 4 is basically the same as that in Example 1. The difference is that the length of the second groove segment 1422 in Examples 2 to 4 is different from that in Example 1.

[0074] The preparation process of the secondary battery 100 in Examples 5 to 7 is basically the same as that in Example 1. The difference is that the degree to which the second groove segment 1422 deviates from the reference line 105 in Examples 5 to 7 is different from that in Example 1.

[0075] The preparation process of the secondary battery 100 in Examples 8 and 9 is basically the same as that in Example 1. The difference is that the value of D in Examples 8 and 9 is different from that in Example 1.

[0076] After the secondary batteries 100 in the comparative examples and embodiments were prepared, all secondary batteries 100 in each group were subjected to a hot box test to observe the bursting of the groove 142. The experimental results were recorded in Table 1 after the test. The specific process of the hot box test is as follows: 1) The secondary battery 100 to be tested was pretreated under the following conditions: after standing at a test temperature of 20℃ (±5℃) for 60 minutes, it was discharged to 3.0V with a constant current of 0.7C and then stood for 10 minutes; then it was charged to 4.25V with a constant current of 0.5C and then charged to 0.05C with a constant voltage of 4.25V.

[0077] 2) After pretreatment, the secondary battery 100 is placed vertically in a hot box for testing. The temperature in the hot box is increased to 130±2℃ at a rate of 5±2℃ / min and maintained for 60min. During the test, if the depressurization rate of the secondary battery 100 is greater than the gas production rate, the secondary battery 100 will not burn or explode, indicating that the hot box test is passed; otherwise, the hot box test is failed.

[0078] 3) If 100 secondary batteries are tested and the number of secondary batteries that pass the test is N, then the pass rate of the hot box test of the secondary batteries in this group of experiments is N / 100.

[0079] Table 1 Note: " / " in Table 1 indicates that the data is not available.

[0080] According to Example 1 and Comparative Examples 1 to 5, the hot box test pass rate of the secondary battery 100 in Comparative Examples 1 to 4 is less than 80 / 100. The hot box test pass rate of the secondary battery 100 in Example 1 is greater than that in Comparative Examples 1 to 4. That is, by having at least a portion of the first groove segment 1421 disposed in the first part 141, the first end 1422a disposed in the first part 141, and the second groove segment 1422 extending from the first end 1422a in a direction away from the notch 13, this application is beneficial to improving the pressure relief rate.

[0081] According to Examples 1 to 4, the pass rate of the hot box test of the secondary battery 100 in Examples 1 to 4 is greater than 80 / 100. Therefore, it can be seen that by setting 0.5mm≤S2, this application is beneficial to further improve the pressure relief rate. By setting S2≤0.5L1, while ensuring a certain pressure relief rate, it is beneficial to improve the processing efficiency of the groove 142 and the structural strength of the first wall 14.

[0082] According to Examples 1 and 5 to 7, the pass rate of the hot box test of the secondary battery 100 in Examples 1 and 5 to 7 is greater than 80 / 100. Therefore, it can be seen that by setting 1≤S1 / S2≤1.5, this application is conducive to further improving the pressure relief rate.

[0083] According to Examples 1 and 8 to 9, the pass rate of the hot box test of the secondary battery 100 in Examples 1 and 8 to 9 is greater than 80 / 100. Therefore, it can be seen that by setting 0≤D≤0.5L1, this application is conducive to further improving the pressure relief rate.

[0084] Furthermore, those skilled in the art should recognize that the above embodiments are merely illustrative of this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the substantive scope of this application fall within the scope of this application.

Claims

1. A secondary battery, comprising a casing and an electrode assembly, wherein the electrode assembly is housed within the casing, characterized in that, The outer casing is a metal casing, and the orthographic projection of the outer casing along a first direction has a notch, the first direction being the thickness direction of the secondary battery; the orthographic projection of the outer casing along the first direction includes at least a first side, a second side, a third side, and a fourth side connected in sequence, the boundary of the notch includes the second side and the third side, the first included angle between the second side and the third side is α, the second included angle between the second side and the third side is β, the first included angle and the second included angle are complementary angles, 0° < α < 180°, 180° < β < 360°; The outer casing includes a first wall located on one side of the secondary battery along its thickness direction. The first wall includes a first portion, the orthographic projection of which is formed by a first circular arc segment, a second circular arc segment, a first straight line segment, and a second straight line segment. The intersection of the extensions of the second side and the third side is defined as a base point. The angle bisector of the angle between the extensions of the second and third sides is defined as a reference line. The reference line includes a first segment extending from the base point within the first angle. The distance between the base point and the first side along the extension direction of the second side is L1, and the distance between the base point and the fourth side along the extension direction of the third side is L2, where L2 ≥ L1. The center of the arc segment is located on the first segment, the radius of the first arc segment is L2, and the distance between the center of the first arc segment and the base point is L2; ​​the center of the second arc segment is located on the first segment, the radius of the second arc segment is L2, and the distance between the center of the second arc segment and the base point is L2-L1; the first straight line segment connects the endpoints of the first arc segment and the second arc segment located on one side of the reference line, the second straight line segment connects the endpoints of the first arc segment and the second arc segment located on the other side of the reference line, the extension of the first straight line segment passes through the midpoint of the second side and is parallel to the reference line, and the extension of the second straight line segment passes through the midpoint of the third side and is parallel to the reference line; A groove is provided on the side of the first wall away from the electrode assembly. The groove includes at least a first groove segment and a second groove segment connected to each other. The first groove segment is located in the first part. Along the first direction, the orthographic projection of the first groove segment is an arc segment. The second groove segment includes a first end and a second end. The first end is connected to the first groove segment and is located in the first part. The second end is the end of the groove. In the first direction, the line connecting the center of the first groove segment and the base point does not intersect the first groove segment. The second groove segment extends from the first end in a direction away from the notch.

2. The secondary battery according to claim 1, characterized in that, Along the first direction, the orthographic projection of the second groove segment is a straight line segment.

3. The secondary battery according to claim 2, characterized in that, The length of the second groove segment is S1, and the orthographic projection length of the second groove segment on the reference line is S2, where 1≤S1 / S2≤1.

5.

4. The secondary battery according to claim 3, characterized in that, 1≤S1 / S2≤1.

2.

5. The secondary battery according to claim 3, characterized in that, 0.5mm≤S2≤0.5L1.

6. The secondary battery according to claim 1, characterized in that, The distance between the midpoint of the first groove segment and the base point is D, where 0mm≤D≤5mm.

7. The secondary battery according to claim 1, characterized in that, The entire first groove segment is located in the first part.

8. The secondary battery according to claim 1, characterized in that, The first end is connected to the endpoint of the first slot segment.

9. The secondary battery according to claim 1, characterized in that, The two endpoints of the first groove segment are located on different sides of the straight line connecting the center of the first groove segment and the base point.

10. The secondary battery according to claim 1, characterized in that, The second slot has two sections.

11. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1 to 10.

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