Secondary battery and electric device

Abstract

The invention discloses a secondary battery and electric equipment. The secondary battery comprises a shell, an electrode assembly accommodated in the shell and a tab which is connected with the electrode assembly and extends out along a first direction, the shell is a metal shell and comprises an upper shell body and a lower shell body which are fixedly connected in the second direction, and the upper shell body is provided with a groove. The electrode assembly comprises an outermost layer negative plate closest to the groove in the second direction, the outermost layer negative plate comprises a first edge and a second edge which are sequentially arranged in the direction opposite to the first direction, and the surface, opposite to the upper shell, of the outermost layer negative plate comprises a first area and a second area in the thickness direction of the electrode assembly; the first area comprises a first edge and a second edge which are sequentially arranged in the direction opposite to the first direction, the distance between the first edge and the second edge is 1 mm, and the distance between the second edge and the first edge is 3 mm. In the second direction, the groove and the first area are at least partially overlapped. And the groove is formed in the upper shell, so that the lithium precipitation problem of the pole piece of the secondary battery can be improved.

Description

Technical Field

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

[0002] With the development of various electronic devices, secondary batteries have become an indispensable part of daily life. Mobile phones, tablets, laptops, and digital cameras, for example, all rely on secondary batteries to provide power for normal operation. Steel-cased batteries are a type of secondary battery. Their outer shell generally consists of an upper shell and a lower shell, which together form a cavity containing the electrode assembly. However, existing steel-cased batteries suffer from lithium deposition in the electrode assemblies before leaving the factory. Summary of the Invention

[0003] For the secondary batteries in the prior art, the inventors found that when the steel shell battery is subjected to a hot pressing formation process, the silicone pad used for the formation applies pressure to the electrode assembly through the upper shell along the thickness direction of the electrode assembly. Since the polarity of the electrode assembly is led out through the pole ear, there is a large gap between the protruding edge of the pole ear of the electrode assembly and the side wall of the shell opposite to it. Therefore, during the formation process, the side wall of the shell does not provide sufficient support for the silicone pad, resulting in severe stress concentration in the area near the pole ear of the electrode assembly, and excessive bonding strength at the interface between the positive electrode sheet, the negative electrode sheet and the diaphragm in the area near the pole ear. As a result, poor electrolyte infiltration leads to the problem of lithium plating on the pole sheet when the secondary battery leaves the factory.

[0004] In view of the above situation, it is necessary to provide a secondary battery that can improve the problem of lithium plating in the electrode.

[0005] In a first aspect, the present application provides a secondary battery comprising a housing, an electrode assembly, and a tab. The electrode assembly is housed within the housing, and the tab is connected to the electrode assembly and extends out of the electrode assembly in a first direction. The housing is a metal housing and includes an upper housing and a lower housing. The upper and lower housings are fixedly connected along a second direction, which is the thickness direction of the electrode assembly and perpendicular to the first direction. The upper housing has a first surface facing away from the electrode assembly in the second direction, and the first surface is provided with a groove. The electrode assembly includes an outermost negative electrode sheet closest to the groove in the second direction. The outermost negative electrode sheet includes a first side and a second side arranged in sequence in a direction opposite to the first direction. The surface of the outermost negative electrode sheet, which faces the upper housing in the second direction, includes a first region. The first region includes a first edge and a second edge arranged in sequence in a direction opposite to the first direction. The first edge is spaced 1 mm from the first edge, and the second edge is spaced 3 mm from the first edge. In a third direction, the dimensions of the first region are equal to those of the outermost negative electrode sheet, and the third direction is perpendicular to the first and second directions. In the second direction, the groove at least partially overlaps with the first region.

[0006] The inventors discovered through research that, during the formation process of existing secondary batteries, stress concentration typically occurs in the first region of the electrode assembly. The secondary battery of the present application provides a groove in the upper housing that at least partially overlaps the first region along a second direction. When the silicone pad applies pressure to the electrode assembly through the upper housing, at least a portion of the silicone pad elastically deforms under the pressure and fills the groove in the upper housing. This filling process can partially offset the pressure applied by the silicone pad to the electrode assembly through the upper housing, thereby alleviating stress concentration in the first region of the electrode assembly and improving lithium deposition in the electrode sheets of the secondary battery.

[0007] In one or more of the above embodiments, along the first direction, the size of the groove is W, 1 mm ≤ W. Along the third direction, the size of the first region is M, and the size of the groove is L, 0.6 M ≤ L. By setting 1 mm ≤ W and 0.6 M ≤ L, the sizes of the groove along the first and third directions are not too small, which can better alleviate stress concentration in the first region of the electrode assembly.

[0008] In one or more of the above embodiments, the groove is located within the first region along the second direction. Since the process of filling the groove will share some of the pressure applied by the silicone pad to the electrode assembly, locating the groove within the first region along the second direction helps reduce the possibility of undervoltage problems in areas of the electrode assembly outside the first region.

[0009] In one or more of the above embodiments, W≤3mm. By setting W≤3mm, the size of the groove along the first direction is not too large, which can better alleviate the stress concentration of the electrode assembly in the first region and reduce the possibility of undervoltage problems in the electrode assembly during the formation process.

[0010] In one or more of the above embodiments, 1.5 mm ≤ W ≤ 2.5 mm. Since the size of the region where stress concentration occurs in the first region along the first direction is generally 1 mm to 2 mm, setting 1.5 mm ≤ W ≤ 2.5 mm is beneficial for alleviating stress concentration in the first region of the electrode assembly and reducing the possibility of undervoltage problems in the first region of the electrode assembly.

[0011] In one or more of the above embodiments, L≤0.9 M. By setting L≤0.9 M, the dimension of the groove along the third direction is not too large, which is conducive to reducing the possibility of undervoltage problem in the first area of the electrode assembly.

[0012] In one or more of the above embodiments, the groove is centrally arranged relative to the first surface in the third direction. Along the second direction, the groove can better correspond to the area where stress concentration occurs in the first region, which is beneficial to reducing the possibility of overvoltage and undervoltage problems in the electrode assembly in the first region.

[0013] In one or more of the above embodiments, along the second direction, the thickness of the upper shell is n1, the depth of the groove is n2, and 0.1n1≤n2≤0.4n1. By setting 0.1n1≤n2, the groove will not be too shallow, and the process of the silicone pad filling the groove can share the pressure applied by the silicone pad to the electrode assembly, thereby better alleviating the stress concentration of the electrode assembly in the first area, which is beneficial to better improve the problem of lithium plating on the electrode sheet of the secondary battery. By setting n2≤0.4n1, the groove will not be too deep, and the process of the silicone pad filling the groove can share the pressure applied by the silicone pad to the electrode assembly, which is beneficial to reduce the possibility of undervoltage in the electrode assembly.

[0014] In one or more of the above embodiments, 0.1n1≤n2≤0.3n1. Setting n2≤0.3n1 is beneficial to further reduce the possibility of undervoltage in the electrode assembly and further enhance the effect of improving lithium deposition in the electrode sheet through the groove.

[0015] In one or more of the above embodiments, 50 μm≤n1≤150 μm.

[0016] In one or more of the above embodiments, when viewed along the second direction, the secondary battery is rectangular in shape, with an aspect ratio of the rectangle greater than or equal to 3:1, and the first direction is the length direction of the rectangle. Since the spacing between the two side walls of the rectangular battery's outer shell that are arranged opposite to each other along its length direction is larger than the spacing between the two side walls of the outer shell that are arranged opposite to each other along its width direction, the upper shell of the rectangular battery is squeezed by the silicone pad during the formation process, resulting in greater deformation. Therefore, the rectangular battery is more prone to stress concentration in the first area, which in turn leads to lithium deposition on the electrode. Providing a groove in the upper shell is conducive to improving the problem of lithium deposition on the electrode of the rectangular battery.

[0017] In one or more of the above embodiments, when viewed along the second direction, the secondary battery is an arc-shaped battery, and the first direction is the arc length direction of the arc. Since the two radially opposite sidewalls of the outer shell of the arc-shaped battery are curved, the silicone pad deforms more unevenly during the formation process. The silicone pad tends to deform more toward the area of the upper shell near the tab, resulting in greater deformation of the silicone pad near the tab. Therefore, the arc-shaped battery is more prone to stress concentration in the first area, which in turn leads to lithium deposition on the pole piece. Providing a groove in the upper shell can help improve the problem of lithium deposition on the pole piece of the arc-shaped battery.

[0018] In one or more of the above embodiments, the groove is a rectangular groove. Since the stress concentration region in the first region is generally a rectangular region, making the groove a rectangular groove is beneficial for alleviating the stress concentration in the first region of the electrode assembly. The rectangular groove design is also more convenient for manufacturing the upper shell.

[0019] The second aspect of the present application provides an electrical device comprising the secondary battery of the first aspect of the present application. The secondary battery of the present application is less susceptible to the problem of lithium deposition on the electrode, can have a larger capacity, and is conducive to improving the endurance of the electrical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a front view of a secondary battery provided in one embodiment of the present application.

[0021] Figure 2 A top view of a secondary battery provided in accordance with an embodiment of the present application.

[0022] Figure 3 For the Figure 2 Cross-section along the midline AA.

[0023] Figure 4 For the Figure 2 Cross-section along the midline BB.

[0024] Figure 5 A schematic diagram of a groove projected onto the outermost negative electrode sheet along the second direction provided in an embodiment of the present application.

[0025] Figure 6 This is an overall schematic diagram of an electrical device provided in one embodiment of the present application.

[0026] Description of main component symbols 1000. Electrical equipment; 100. Secondary battery; 10. Casing; 101. Bottom wall; 102. Side wall; 11. Upper shell; 111. First side; 112. Groove; 12. Lower shell; 20. Electrode assembly; 201. Outermost negative electrode sheet; 2011. First side; 2012. Second side; 202. First region; 2021. First edge; 2022. Second edge; 21. Negative electrode sheet; 22. Positive electrode sheet; 23. Separator; 30. Tab; 31. Negative electrode tab; 311. Negative electrode tab bundle; 32. Positive electrode tab; 321. Positive electrode tab bundle; 40. Post; 50. Insulator; X, first direction; Y, second direction; Z, third direction. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments.

[0028] It should be noted that when an element is considered to be “connected” to another element, it may be directly connected to the other element or there may be a centrally disposed element. When an element is considered to be “disposed on” another element, it may be directly disposed on the other element or there may be a centrally disposed element.

[0029] Unless otherwise specified, the term "plurality" as used herein means two or more than two.

[0030] The terms "first", "second", etc. are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implying the quantity, specific order or primary and secondary relationship of the technical features indicated.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0032] It should be understood that, considering the actual processing tolerance factors, in the technical solution of the present application, when the two elements are arranged parallel / vertically and in the same direction, there may be a certain angle between the two elements, and a tolerance of 0-±10% is allowed between the two elements. A tolerance of 0-±10% is allowed when the two elements are greater than, equal to or less than.

[0033] Embodiments of the present application provide a secondary battery comprising a housing, an electrode assembly, and a tab. The electrode assembly is housed within the housing, and the tab is connected to the electrode assembly and extends out of the electrode assembly in a first direction. The housing is a metal housing and includes an upper housing and a lower housing. The upper and lower housings are fixedly connected along a second direction, which is the thickness direction of the electrode assembly and perpendicular to the first direction. The upper housing has a first surface facing away from the electrode assembly in the second direction, and the first surface is provided with a groove. The electrode assembly includes an outermost negative electrode sheet closest to the groove in the second direction. The outermost negative electrode sheet includes a first side and a second side arranged in sequence in a direction opposite to the first direction. The surface of the outermost negative electrode sheet opposite the upper housing in the second direction includes a first region. The first region includes a first edge and a second edge arranged in sequence in a direction opposite to the first direction. The first edge is spaced 1 mm from the first edge, and the second edge is spaced 3 mm from the first edge. In a third direction, the dimensions of the first region are equal to those of the outermost negative electrode sheet, and the third direction is perpendicular to the first and second directions. In the second direction, the groove at least partially overlaps with the first region.

[0034] During the formation process of existing secondary batteries, stress concentration occurs primarily within the first region of the electrode assembly. The secondary battery of the present application provides a groove in the upper housing that at least partially overlaps the first region along the second direction. When the silicone pad applies pressure to the electrode assembly through the upper housing, at least a portion of the silicone pad elastically deforms under pressure and fills the groove in the upper housing. This filling process can relieve some of the pressure applied by the silicone pad to the electrode assembly through the upper housing, thereby alleviating stress concentration in the first region of the electrode assembly and improving the problem of lithium deposition in the electrode sheets of the secondary battery.

[0035] The following will describe some embodiments of the present application in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0036] See also Figures 1 to 4 An embodiment of the present application provides a secondary battery 100, comprising a housing 10, an electrode assembly 20, and a tab 30. The electrode assembly 20 is housed within the housing 10, and the tab 30 is connected to the electrode assembly 20 and extends out of the electrode assembly 20 along a first direction X. That is, the first direction X is the direction in which the tab 30 extends out of the electrode assembly 20.

[0037] The housing 10 is a metal shell and includes an upper shell 11 and a lower shell 12. The upper shell 11 and the lower shell 12 are fixedly connected along the second direction Y. The second direction Y is the thickness direction of the electrode assembly 20 and is perpendicular to the first direction X. The upper shell 11 has two surfaces arranged opposite to each other along the second direction Y, wherein the surface facing away from the electrode assembly 20 is a first surface 111. The first surface 111 is provided with a groove 112, and the concave direction of the groove 112 is parallel to the second direction Y. The so-called metal shell includes but is not limited to steel shells, copper shells, zinc shells and nickel shells, and the so-called fixed connection includes but is not limited to adhesive fixation, riveting fixation and welding fixation. For example, the upper shell 11 and the lower shell 12 are both steel shells, and the upper shell 11 and the lower shell 12 are welded and fixed. It should be noted that the "upper" and "lower" in the upper shell 11 and the lower shell 12 of this application are only for the convenience of description and cannot be understood as indicating or implying their relative positional relationship in three-dimensional space.

[0038] See also Figure 3 or Figure 4 In some embodiments, the upper housing 11 is a plate-like structure and serves as the cover of the secondary battery 100, while the lower housing 12 is a recessed structure and serves as the body of the secondary battery 100. In some embodiments, the upper housing 11 is a recessed structure and serves as a portion of the body of the secondary battery 100, while the lower housing 12 is a recessed structure and serves as another portion of the body of the secondary battery 100. The recessed structure includes a bottom wall 101 and side walls 102. The side walls 102 connect to the periphery of the bottom wall 101, forming a recess with the side walls 102 and the bottom wall 101. The recessed structure facilitates the housing 10 to accommodate the electrode assembly 20.

[0039] In some embodiments, the thickness of the upper shell 11 is n1, 50 μm ≤ n1 ≤ 150 μm. For example, n1 is 50 μm, 60 μm, 70 μm, 80 μm, 100 μm, 120 μm, 150 μm, or any value between the listed endpoints. In some embodiments, the thickness of the lower shell 12 is 50 μm to 150 μm. For example, the thickness of the lower shell 12 is 50 μm, 75 μm, 100 μm, 125 μm, 150 μm, or any value between the listed endpoints. It should be understood that the thickness ranges of the upper shell 11 and the lower shell 12 are merely illustrative examples and should not be construed as substantially limiting the thickness values of the upper shell 11 and the lower shell 12.

[0040] The housing 10 is filled with an electrolyte, which includes an electrolyte salt. In some embodiments, the electrolyte salt includes at least one of an organic lithium salt or an inorganic lithium salt. The electrolyte salt includes, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)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).

[0041] See also Figure 3 or Figure 4 The electrode assembly 20 includes a negative electrode sheet 21, a positive electrode sheet 22, and a separator 23. The negative electrode sheets 21 and the positive electrode sheets 22 are arranged alternately, and the separator 23 separates the negative electrode sheets 21 and the positive electrode sheets 22. In some embodiments, the electrode assembly 20 has a laminated structure, in which the negative electrode sheets 21 and the positive electrode sheets 22 are alternately stacked, and the separator 23 is arranged between adjacent negative electrode sheets 21 and positive electrode sheets 22. In some embodiments, the electrode assembly 20 has a wound structure, in which the negative electrode sheets 21 and the positive electrode sheets 22 are alternately wound, and the separator 23 is arranged between the negative electrode sheets 21 and the positive electrode sheets 22.

[0042] In some embodiments, the negative electrode sheet 21 includes a negative electrode current collector and a negative electrode active material layer, with the negative electrode active material layer being disposed on at least one surface of the negative electrode current collector along the thickness direction. The positive electrode sheet 22 includes a positive electrode current collector and a positive electrode active material layer, with the positive electrode active material layer being disposed on at least one surface of the positive electrode current collector along the thickness direction. Examples of negative electrode current collectors include, but are not limited to, copper foil, copper alloy foil, nickel foil, titanium foil, nickel foam, and copper foam; examples of positive electrode current collectors include, but are not limited to, aluminum foil and aluminum alloy foil. Examples of materials for the negative electrode active material layer include, but are not limited to, graphite, hard carbon, soft carbon, silicon, silicon-oxygen materials, and silicon-carbon materials. Examples of materials for the positive electrode active material layer include, but are not limited to, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, and lithium manganese oxide. The separator 23 is an insulating film material such as polyethylene film, polypropylene film, polyester film, or polyimide film.

[0043] See also Figure 5 The electrode assembly 20 includes an outermost negative electrode sheet 201 that is closest to the groove 112 along the second direction Y. When the electrode assembly 20 has a laminated structure, the outermost negative electrode sheet 201 is the negative electrode sheet 21 that is closest to the groove 112 along the second direction Y among the multiple negative electrode sheets 21 in the electrode assembly 20. When the electrode assembly 20 has a wound structure, the outermost negative electrode sheet 201 is the flat portion of the negative electrode sheet 21 that is located at the outermost layer of the wound layer and closest to the groove 112. The outermost negative electrode sheet 201 includes a first side 2011 and a second side 2012. The first side 2011 and the second side 2012 are arranged in sequence in a direction opposite to the first direction X. That is, the second side 2012 is farther away from the tab 30 than the first side 2011.

[0044] See also Figure 5 Along the second direction Y, the surface of the outermost negative electrode sheet 201, facing the upper housing 11, includes a first region 202. The first region 202 includes a first edge 2021 and a second edge 2022, which are arranged sequentially in a direction opposite to the first direction X. The distance between the first edge 2021 and the first side 2011 is 1 mm, and the distance between the second edge 2022 and the first edge 2021 is 3 mm. Along the third direction Z, the dimensions of the first region 202 are equal to those of the outermost negative electrode sheet 201. The third direction Z is perpendicular to the first and second directions X and Y.

[0045] Along the second direction Y, the groove 112 at least partially overlaps with the first region 202. By providing the groove 112 in the upper housing 11 that at least partially overlaps with the first region 202 along the second direction Y, when the silicone pad applies pressure to the electrode assembly 20 through the upper housing 11, at least a portion of the silicone pad elastically deforms under the pressure and fills the groove 112 of the upper housing 11. This filling process can relieve some of the pressure applied by the silicone pad to the electrode assembly 20 through the upper housing 11, thereby alleviating stress concentration in the first region 202 of the electrode assembly 20, and facilitating improvement of lithium deposition in the electrode sheet of the secondary battery 100.

[0046] See also Figure 5 In some embodiments, along the first direction X, the size of the groove 112 is W, 1 mm ≤ W. For example, W is 1 mm, 1.2 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 4 mm, or any value between the listed endpoint values. Along the third direction Z, the size of the first region 202 is M, and the size of the groove 112 is L, 0.6 M ≤ L. For example, L is 0.6 M, 0.65 M, 0.7 M, 0.75 M, 0.8 M, 0.85 M, 0.9 M, 0.95 M, or any value between the listed endpoint values. By setting 1 mm ≤ W and 0.6 M ≤ L, the size of the groove 112 along the first direction X and the third direction Z will not be too small, which can better alleviate the stress concentration of the electrode assembly 20 in the first region 202.

[0047] In some embodiments, 2 mm ≤ M ≤ 70 mm. For example, M is 2 mm, 5 mm, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, 70 mm, or any value between the listed endpoints. It should be understood that the range of M here is merely illustrative and should not be construed as a substantial limitation on the value of M.

[0048] See also Figure 5 In some embodiments, along the second direction Y, the groove 112 is located within the first region 202. Since the process of filling the groove 112 will share some of the pressure applied by the silicone pad to the electrode assembly 20, by locating the groove 112 within the first region 202 along the second direction Y, the possibility of undervoltage problems in areas of the electrode assembly 20 outside the first region 202 is reduced. It should be understood that when an undervoltage problem occurs in the electrode assembly 20, the negative electrode sheet 21 and the positive electrode sheet 22 have poor contact with the separator 23, which blocks the transmission path of ions serving as charge carriers (such as lithium ions in lithium-ion batteries and sodium ions in sodium-ion batteries, hereinafter referred to as charge carrier ions) within the electrode assembly 20. This results in an imbalance in the concentration of charge carrier ions in the local area of the electrode assembly 20, which may also cause lithium deposition in the electrode sheet of the secondary battery 100.

[0049] In some embodiments, W≤3mm. By setting W≤3mm, the size of the groove 112 along the first direction X is not too large, which can better alleviate the stress concentration of the electrode assembly 20 in the first region 202 and reduce the possibility of undervoltage problems in the electrode assembly 20 during the formation process.

[0050] In some embodiments, 1.5 mm ≤ W ≤ 2.5 mm. Since the size of the region where stress concentration occurs in the first region 202 along the first direction X is generally 1 mm to 2 mm, setting 1.5 mm ≤ W ≤ 2.5 mm can help alleviate stress concentration in the first region 202 of the electrode assembly 20 and reduce the possibility of undervoltage problems in the first region 202 of the electrode assembly 20.

[0051] See also Figure 5 In some embodiments, L≤0.9 M. By setting L≤0.9 M, the dimension of the groove 112 along the third direction Z is not too large, which helps to reduce the possibility of undervoltage problem in the first region 202 of the electrode assembly 20.

[0052] In some embodiments, the groove 112 is centered relative to the first surface 111 in the third direction Z. That is, along the third direction Z, the spacing between one side of the groove 112 and the side of the first surface 111 opposite to it, and the spacing between the other side of the groove 112 and the other side of the first surface 111 opposite to it, are approximately equal. Along the second direction Y, the groove 112 can better align with the stress concentration region within the first region 202, thereby reducing the likelihood of overvoltage and undervoltage issues within the first region 202 of the electrode assembly 20.

[0053] See also Figure 3 or Figure 4 In some embodiments, along the second direction Y, the depth of the groove 112 is n2, where 0.1n1≤n2≤0.4n1. For example, n2 is 0.1n1, 0.15n1, 0.2n1, 0.25n1, 0.3n1, 0.35n1, 0.4n1, or any value between the listed endpoints. By setting 0.1n1≤n2, the groove 112 is not too shallow, and the pressure applied by the silicone pad to the electrode assembly 20 during the process of filling the groove 112 is not too small, thereby better alleviating the stress concentration in the first region 202 of the electrode assembly 20, which is beneficial for better improving the lithium deposition problem of the electrode sheet of the secondary battery 100. By setting n2≤0.4n1, the groove 112 is not too deep, and the pressure applied by the silicone pad to the electrode assembly 20 during the process of filling the groove 112 is not too large, which is beneficial for reducing the possibility of undervoltage in the electrode assembly 20.

[0054] In some embodiments, 0.1n1≤n2≤0.3n1. Setting n2≤0.3n1 is beneficial to further reduce the possibility of undervoltage in the electrode assembly 20 and further enhance the effect of improving lithium deposition in the electrode sheet through the groove 112.

[0055] In some embodiments, when viewed along the second direction Y, the secondary battery 100 is in the shape of a rectangle, the aspect ratio of the rectangle is greater than or equal to 3:1, and the first direction X is the length direction of the rectangle. For example, the aspect ratio of the rectangle is 3:1, 4:1, 5:1, 6:1, or 7:1. Since the spacing between the two side walls of the rectangular battery's shell that are oppositely arranged along its length direction is larger than the spacing between the two side walls of the shell that are oppositely arranged along its width direction, the upper shell 11 of the rectangular battery is squeezed by the silicone pad during the formation process, resulting in greater deformation. Therefore, the rectangular battery is more prone to stress concentration in the first area 202, which in turn leads to lithium plating of the electrode. Providing a groove 112 in the upper shell 11 is beneficial to improving the problem of lithium plating of the electrode of the rectangular battery.

[0056] In some embodiments, when viewed along the second direction Y, the secondary battery 100 is a curved battery, and the first direction X is the length of the arc. Because the two radially opposed sidewalls of the curved battery's housing are curved, the silicone pad deforms more unevenly during the formation process. The silicone pad tends to deform more toward the area of the upper housing 11 near the tab 30, resulting in greater deformation of the silicone pad near the tab 30. As a result, curved batteries are more susceptible to stress concentration in the first region 202, leading to lithium deposition on the electrode sheet. Providing a groove 112 in the upper housing 11 can help alleviate the lithium deposition problem on the electrode sheet of curved batteries.

[0057] In some embodiments, the groove 112 is a rectangular groove. Since the area where stress concentration occurs in the first region 202 is generally a rectangular area, making the groove 112 a rectangular groove is beneficial for alleviating stress concentration in the first region 202 of the electrode assembly 20. The rectangular groove design is also more convenient for manufacturing the upper shell 11 during the process.

[0058] In some embodiments, see Figure 3 or Figure 4 The tabs 30 include a negative tab 31 and a positive tab 32. The negative tab 31 is electrically connected to the negative electrode current collector, and the positive tab 32 is electrically connected to the positive electrode current collector. Connection methods for the negative tab 31 and the negative electrode current collector, and for the positive tab 32 and the positive electrode current collector, include, but are not limited to, integral cutting and forming and welding.

[0059] In some embodiments, the negative electrode tab 31 and the positive electrode tab 32 extend out of the electrode assembly 20 in the same direction, and the number of grooves 112 may be one, and one groove 112 is disposed near the negative electrode tab 31 and the positive electrode tab 32 along the first direction X. In some embodiments, the negative electrode tab 31 and the positive electrode tab 32 extend out of the electrode assembly 20 in different directions, and the number of grooves 112 may be two, and one groove 112 is disposed near the negative electrode tab 31 and the other groove 112 is disposed near the positive electrode tab 32 along the first direction X.

[0060] See also Figure 3 or Figure 4 In some embodiments, the number of negative tabs 31 and positive tabs 32 is multiple, and the multiple negative tabs 31 are stacked in sequence along the first direction X, and then welded together to form a negative tab bundle 311, and the negative tab bundle 311 is welded to the housing 10 (see Figure 3 ). A plurality of positive tabs 32 are stacked in sequence along the second direction Y, and are welded together to form a positive tab bundle 321. The positive tab bundle 321 is welded to the pole 40, and the pole 40 is insulated and arranged in the housing 10 (see Figure 4 In some embodiments, the positive electrode tab bundle 321 is electrically connected to the pole 40 via an adapter, and the material of the adapter includes but is not limited to conductive materials such as copper, aluminum, nickel, and nickel alloy.

[0061] In some embodiments, see Figure 5 The pole 40 is insulated from the housing 10 by an insulating member 50 . The insulating member 50 includes, but is not limited to, an insulating gasket and an insulating sleeve. When the insulating member 50 is an insulating gasket, it is positioned between the contact surface between the pole 40 and the housing 10. When the insulating member 50 is an insulating sleeve, the insulating sleeve wraps around the outer circumference of the pole 40. The insulating member 50 may be made of, but is not limited to, plastic and rubber.

[0062] See also Figure 6 One embodiment of the present application provides an electric device 1000, comprising the aforementioned secondary battery 100. Secondary battery 100 is less susceptible to lithium deposition in the electrode and can have a larger capacity, thereby improving the battery life of electric device 1000. Electric 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 televisions, tape recorders, radios, cameras, tablet computers, and laptop computers.

[0063] To verify the effect of the solution provided in this application on the secondary battery 100, the inventors of this application conducted the following experiment. The preparation process of the secondary battery 100 in Example 1 includes the following steps: Preparation of the positive electrode sheet 22: The positive electrode active material, lithium cobalt oxide, the conductive agent, conductive carbon black, and the binder, polyvinylidene fluoride (PVDF), were dissolved in an N-methylpyrrolidone (NMP) solution at a weight ratio of 97.5:1:1.5 to form a positive electrode slurry. Aluminum foil was used as the positive electrode current collector, and the positive electrode slurry was coated onto the positive electrode current collector. After drying, cold pressing, and slitting, the positive electrode sheet 22 with a size of 2.7 mm x 24.1 mm and the positive electrode tab 32 cut and formed integrally with the positive electrode sheet 22 were obtained.

[0064] Preparation of the negative electrode sheet 21: The negative electrode active material artificial graphite, the thickener sodium carboxymethyl cellulose (CMC), and the binder styrene-butadiene rubber (SBR) are mixed in a weight ratio of 96:1.5:2.5, deionized water is added, and the mixture is stirred evenly in a vacuum mixer to obtain a negative electrode slurry; copper foil is used as the negative electrode current collector, and the negative electrode slurry is evenly coated on the negative electrode current collector; after drying, cold pressing, cutting, and slitting, a negative electrode sheet 21 with a specification of 4 mm × 25.4 mm and a negative electrode ear 31 cut and formed integrally with the negative electrode sheet 21 are obtained.

[0065] Preparation of the diaphragm 23: The base material layer of the diaphragm 23 is polyethylene (PE), and an alumina ceramic layer is coated on both sides of the base material layer of the diaphragm 23. Finally, a binder polyvinylidene fluoride (PVDF) is coated on both sides of the ceramic layer and 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, an electrolyte was obtained, in which the mass concentration of LiPF6 was 12.5%.

[0067] Preparation of the housing 10: Using CCD positioning, a groove 112 is formed on one side of the surface of a rectangular metal sheet along its thickness direction. Groove 112 is 2 mm from the nearest width edge along the length of the rectangular sheet and is centered along the width of the rectangular sheet. This serves as the upper shell 11 of the housing 10. The rectangular metal sheet has a thickness of 100 μm (i.e., n1), a length of 28 mm, and a width of 5 mm. The dimension of groove 112 along the length of the rectangular sheet is 2 mm (i.e., W), the dimension of groove 112 along the width of the rectangular sheet is 3.2 mm (i.e., L), and the depth of groove 112 along the thickness of the rectangular sheet is 20 μm (i.e., n2). A recessed structure is punched out of another metal sheet to form the lower shell 12 of the housing 10. The wall thickness of lower shell 12 is 100 μm, and the projection of lower shell 12 along the depth of the recessed structure is rectangular.

[0068] Preparation of secondary battery 100: The positive electrode sheet 22, separator 23, and negative electrode sheet 21 are stacked to form electrode assembly 20. The bottom and top electrodes are both positive electrode sheets 22. During stacking, the negative electrode tab 31 and the positive electrode tab 32 extend out of the electrode assembly 20 in the same direction. The electrode assembly 20 is placed in the lower shell 12, with the positive electrode tab 32 and the negative electrode tab 31 facing each other along the length of the lower shell 12 and the side wall 102 of the recessed structure. The positive electrode tab 32 and the negative electrode tab 31 are welded to the positive and negative electrode terminals on the lower shell 12, respectively. The upper shell 11 and the lower shell 12 are assembled, with the width edge of the upper shell 11 near the groove 112 aligned with the side wall 102 of the recessed structure of the lower shell 12 opposite the electrode tab 30. The upper shell 11 and the lower shell 12 are sealed by laser welding and then hot pressed to form the secondary battery 100.

[0069] The preparation process of the secondary battery 100 in Comparative Example 1 is substantially the same as that in Example 1, except that the upper shell 11 of the secondary battery 100 in Comparative Example 1 does not have the groove 112 .

[0070] The manufacturing process of the secondary battery 100 in Examples 2 to 7 is substantially the same as that in Example 1. The difference lies in that the size W of the groove 112 in Examples 2 to 7 is different from that in Example 1.

[0071] The manufacturing process of the secondary battery 100 in Examples 8 to 11 is substantially the same as that in Example 1. The difference lies in that the size L of the groove 112 in Examples 8 to 11 is different from that in Example 1.

[0072] The manufacturing process of the secondary battery 100 in Examples 12 to 16 is substantially the same as that in Example 1. The difference lies in that the size n2 of the groove 112 in Examples 12 to 16 is different from that in Example 1.

[0073] The preparation process of the secondary battery 100 in Example 17 is substantially the same as that in Example 1, except that the position of the groove 112 in Example 17 is different from that in Example 1. The groove 112 in Example 17 is not centered in the third direction Z relative to the first surface 111 .

[0074] The preparation process of the secondary battery 100 in Example 18 is basically the same as that in Example 1, except that the position of the groove 112 in Example 18 is different from that in Example 1. The groove 112 in Example 18 is not entirely located within the first region 202 along the second direction Y (when the groove 112 is provided on the rectangular metal plate, the distance between the groove 112 and the nearest width edge along the length direction of the rectangular plate is 2.5 mm).

[0075] After the secondary batteries 100 in the comparative examples and examples were prepared, a lithium deposition test was performed on 100 secondary batteries 100 in each comparative example and example to observe the lithium deposition of the secondary batteries 100. After the test, the experimental results were recorded in Table 1.

[0076] The specific process of lithium precipitation testing is as follows: (1) Maintain the test temperature at 25°C; (2) The secondary battery 100 was left to stand for 30 minutes; (3) 1.3C constant current charging to 4.1V, then constant voltage charging to 1C; (4) 1C constant current charging to 4.2V, then constant voltage charging to 0.7C; (5) 0.7C constant current charging to 4.3V, then constant voltage charging to 0.025C; (6) Let stand for 5 minutes; (7) 0.7C constant current discharge to 3V; (8) Let stand for 5 minutes; (9) Steps 3 to 8 are repeated 800 times; (10) Disassemble the secondary batteries 100 and observe whether lithium deposition occurs on the negative electrode sheets 21. Count the number of secondary batteries 100 with lithium deposition on the negative electrode sheets 21 in each group. Count the number of secondary batteries 100 with lithium deposition on the negative electrode sheets 21 in this group of experiments as N. Then, the lithium deposition rate of the secondary batteries 100 in this group of experiments is N / 100.

[0077] Table 1 Note: “ / ” in Table 1 indicates that there is no such data.

[0078] In Table 1, the lithium plating rate of the secondary battery 100 in Examples 1 to 18 is lower than that of the secondary battery 100 in Comparative Example 1. In other words, the present application improves the lithium plating problem of the electrode of the secondary battery 100 by providing the groove 112 in the upper housing 11.

[0079] In Table 1, according to Examples 1 to 7, the lithium plating rate of the secondary battery 100 in Example 1 and Example 3 to Example 6 is significantly lower than the lithium plating rate of the secondary battery 100 in Example 2 and Example 7, and the lithium plating rate of the secondary battery 100 in Example 1, Example 4 and Example 5 is significantly lower than the lithium plating rate of the secondary battery 100 in Example 3 and Example 6. That is to say, the present application is conducive to reducing the possibility of lithium plating on the pole piece of the secondary battery 100 due to overvoltage problems by setting 1mm≤W≤3mm, and is conducive to reducing the possibility of lithium plating on the pole piece of the secondary battery 100 due to undervoltage problems. Furthermore, the present application is conducive to further reducing the possibility of lithium plating on the pole piece of the secondary battery 100 due to overvoltage problems by setting 1.5mm≤W≤2.5mm, which is conducive to further reducing the possibility of lithium plating on the pole piece of the secondary battery 100 due to overvoltage problems, and is conducive to further reducing the possibility of lithium plating on the pole piece of the secondary battery 100 due to undervoltage problems.

[0080] In Table 1, according to Examples 1, 8, and 11, the lithium plating rate of the secondary battery 100 in Examples 1, 9, and 10 is significantly lower than the lithium plating rate of the secondary battery 100 in Examples 8 and 11. In other words, by setting 0.6M≤L≤0.9M, the present application is conducive to reducing the possibility of lithium plating on the electrode of the secondary battery 100 due to overvoltage problems and is conducive to reducing the possibility of lithium plating on the electrode of the secondary battery 100 due to undervoltage problems.

[0081] In Table 1, according to Examples 1 and 12 to 16, the lithium plating rate of the secondary battery 100 in Examples 1 and 13 to 15 is significantly lower than the lithium plating rate of the secondary battery 100 in Examples 12 and 16, and the lithium plating rate of the secondary battery 100 in Examples 1, 13 and 14 is significantly lower than the lithium plating rate of the secondary battery 100 in Example 15. That is, the present application is conducive to reducing the possibility of lithium plating on the electrode of the secondary battery 100 due to overvoltage problems by setting 0.1n1≤n2≤0.4n1, and is conducive to reducing the possibility of lithium plating on the electrode of the secondary battery 100 due to undervoltage problems. Furthermore, the present application is conducive to further reducing the possibility of lithium plating on the electrode of the secondary battery 100 due to undervoltage problems by setting n2≤0.3n1.

[0082] In Table 1, according to Example 1 and Example 17, the lithium plating rate of the secondary battery 100 in Example 1 is significantly lower than the lithium plating rate of the secondary battery 100 in Example 17. In other words, the present application reduces the possibility of lithium plating in the electrode of the secondary battery 100 due to overvoltage and undervoltage problems by locating the groove 112 centered relative to the first surface 111 in the third direction Z.

[0083] In Table 1, according to Example 1 and Example 18, the lithium plating rate of the secondary battery 100 in Example 1 is significantly lower than the lithium plating rate of the secondary battery 100 in Example 18. In other words, the present application reduces the possibility of lithium plating in the electrode of the secondary battery 100 due to undervoltage by locating the groove 112 in the first region 202 along the second direction Y.

[0084] In addition, those skilled in the art should recognize that the above embodiments are merely intended to illustrate the present application and are not intended to limit the present application. As long as they are within the substantive scope of the present application, appropriate changes and modifications to the above embodiments are within the scope disclosed in the present application.

Claims

1. A secondary battery comprising a housing, an electrode assembly, and a tab, wherein the electrode assembly is accommodated in the housing, the tab is connected to the electrode assembly and extends out of the electrode assembly along a first direction, wherein: The shell is a metal shell and includes an upper shell and a lower shell, the upper shell and the lower shell are fixedly connected along a second direction, the second direction is the thickness direction of the electrode assembly and is perpendicular to the first direction, the upper shell has a first surface facing away from the electrode assembly along the second direction, and the first surface is provided with a groove; the electrode assembly includes an outermost negative electrode sheet closest to the groove along the second direction, the outermost negative electrode sheet includes a first edge and a second edge arranged in sequence in a direction opposite to the first direction, the surface of the outermost negative electrode sheet arranged opposite to the upper shell along the second direction includes a first area, the first area includes a first edge and a second edge arranged in sequence in a direction opposite to the first direction, the spacing between the first edge and the first edge is 1 mm, and the spacing between the second edge and the first edge is 3 mm; along the third direction, the size of the first area is equal to the size of the outermost negative electrode sheet, and the third direction is perpendicular to the first direction and the second direction; along the second direction, the groove at least partially overlaps with the first area.

2. The secondary battery according to claim 1, wherein Along the first direction, the size of the groove is W, 1 mm ≤ W; along the third direction, the size of the first area is M, the size of the groove is L, 0.6M ≤ L.

3. The secondary battery according to claim 2, wherein Along the second direction, the groove is located within the first area.

4. The secondary battery according to claim 2, wherein: W≤3mm.

5. The secondary battery according to claim 3 or 4, characterized in that: 1.5mm≤W≤2.5mm.

6. The secondary battery according to claim 2, wherein: L≤0.9M.

7. The secondary battery according to claim 2, characterized in that The groove is centrally arranged relative to the first surface in the third direction.

8. The secondary battery according to claim 2, wherein Along the second direction, the thickness of the upper shell is n1, the depth of the groove is n2, and 0.1n1≤n2≤0.4n1.

9. The secondary battery according to claim 8, characterized in that 0.1n1≤n2≤0.3n1.

10. The secondary battery according to claim 8, wherein 50μm≤n1≤150μm.

11. The secondary battery according to claim 1, wherein When viewed along the second direction, the secondary battery is in a rectangular shape, the aspect ratio of the rectangle is greater than or equal to 3:1, and the first direction is the length direction of the rectangle.

12. The secondary battery according to claim 1, wherein The secondary battery is an arc-shaped battery, and the first direction is the arc length direction of the arc.

13. The secondary battery according to claim 1, wherein The groove is a rectangular groove.

14. An electrical device, characterized in that: The secondary battery according to any one of claims 1 to 13 is included.

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